Mining Industry Safety Leadership Group
POWERED ROOF SUPPORT
Guidance document
1.9.3.795. – 5 June 2015
STATUS OF THIS DOCUMENT
This information and guidance was prepared by a working group
representative of sectors of the coal mining industry. It reflects
current good practice.
Members of the working group on the Design, Operation, Testing
and Maintenance of Powered Roof Supports in mines
Mr
Mr
Mr
Mr
Mr
Mr
Mr
Mr
Mr
Mr
Mr
Mr
P Hetherington UK Coal Mining Ltd
K Shaw UK Coal Mining Ltd
D Williams Maltby Colliery Ltd
G Parker Hatfield Colliery
P Yates Joy Mining Machinery Ltd
M Hole Joy Mining Machinery Ltd
N Cheesmond Eickhoff GB
N P Hill HSE
V Fowler HSE
P G Bradley HSE
T Lowe HSE
J R Leeming HSE
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2
CONTENTS
1
Introduction
2
What this guide is about
3
Primary legislation
3.1
Provisions relating to worker protection
3.2
Provisions relating to the supply of products
3.3
List of legislative provisions
4
PRS System Design
4.1
Introduction
4.2
Safety considerations
4.3
Assessment of ground conditions
4.4
How a powered roof support works
4.5
Structures
4.6
Yield loads
4.7
Modifications
4.8
Hydraulic system layout
4.9
Supply fluid
4.10 Connections to pumping stations and/or remote power
packs
4.11 Hose assemblies and adaptors
4.12 High pressure injuries
5 Safety Critical Components
6 Maintenance schemes & Commissioning
6.1
Classification of defects
6.2
Maintenance management
6.3
Frequency of maintenance
6.4
Maintenance log
6.5
Commissioning
7 Function Testing
7.1
System performance and individual tests
7.2
Pressure and performance monitoring
7.3
Acoustic vibration threshold levels
8 Working on pressurised PRS systems
9 PRS operations
9.1
Operating modes
9.2
Cleanliness
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10 Management of PRS system hydraulic fluid
10.1 Fire resistant fluids
10.2 ISO coding of fluids
10.3 Fluid cleanliness – target setting
10.4 Filtration
10.5 Underground sampling at a pumping station and/or
power pack
10.6 Pressure test and storage fluids for PRS
11 Electrical Systems and data logging
11.1 System construction
11.2 Lighting
11.3 PLC and data logging
11.4 Data logging system
11.5 System connection integrity
11.6 Hydraulic flow/pressure monitoring
11.7 Filtration and electronic monitoring
11.8 Oil mixture and electronic monitoring
11.9 Installation
11.10 Commissioning
11.11 Salvage
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1 INTRODUCTION
This guidance has been prepared to capture current best practice
and is intended to supplement Original Equipment Manufacturer’s
(OEM) technical information and operating rules. Future
technological advances will supplement this guidance.
2 WHAT THIS GUIDE IS ABOUT
This guidance sets out the key elements for the safe use of powered
roof support systems (PRS). It is aimed at:
• mine operators
• managers
• operators
• others, whose duties include the assessment, design,
operation, maintenance, supervision or monitoring of
powered roof support systems
• individuals whose duties include the installation or salvage
of powered roof supports systems
• safety representatives.
3 SAFETY MANAGEMENT SYSTEM (SMS) FOR PRS
Controlling and reducing the risks and hazards associated with PRS
operations must be an integral part of the required organisational
health and SMS.
The structure of any SMS should consider HSG65 “Successful Health
and Safety Management”, and the principles therein, to reduce the
likelihood of low frequency, high impact catastrophic incidents
associated with PRS.
Mine operators need to introduce and implement an effective health
and safety policy that meets legal requirements, controls health and
safety risks and is reactively revised to address additional hazards.
Operators must also maintain an effective health and safety
management system that is proportionate to the risks and ensures
communication of health and safety duties throughout the
organisation.
3.1 Plan, Do, Check, Act
The principles follow the “Plan, Do, Check, Act” sequence:
Plan
Determine your policy and plan for implementation
Do
Profile risks, organise for health and safety, implement
your plan
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Check
Measure performance, (using
Performance Indicators (SPI’s))
appropriate
Act
Review performance and act on lessons learned.
Safety
3.2 Safety performance indicators
Safety Performance Indicators (SPIs) provide information,
which can be used to identify, understand, and control major
hazard risks at PRS.
There are two types of SPI:
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Leading indicators are proactive monitors focussed on
critical risk control systems to ensure their continued
effectiveness.
They are factual precursors to
weaknesses in the risk control system and can be
identified during routine auditing (pre event) and
prevent significant events and include:
failure modes and effects analysis (FMEA)
o threats to barriers and control measures
o inspections, testing and maintenance completed on
time
o prioritised resolution of defects according to severity
o training and competence of operatives
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o staff turnover
o compliance with operational procedures
o correct
calibration,
use
and
operation
of
instrumentation,
alarms
and
environmental
monitoring
o provision of adequate communication systems
o PRS system design
o quality assurance
o routine condition monitoring techniques
o complaints are routinely investigated
o over inspections and audits
Lagging indicators identify weaknesses discovered
following an incident or near miss (post event) and
could be a precursor event to an undesirable outcome
(fire), including:
o inadequately trained operatives
o inadequate communication
o failure of components
o contamination and debris
o repeated alarms
o inadequate maintenance of installation standards
o supervisors inspections
o non compliance with recognised standards
o near miss/incidents
Analysis of SPIs for root cause failure of incidents and trend
analysis of leading and lagging indicators may provide
precursors to accidents and major hazards.
3.3 Risk assessment and risk ranking
A suitable and sufficient assessment of the risks to health and
safety to which employees at work are exposed must be
undertaken.
The risk assessment structure may include a generic
assessment reflecting the core hazards and risks associated
with PRS. This may be adapted to address the specific
hazards of each installation.
Hierarchical categorisation of control measures and tasks
should reflect inherent risks and ensure a safe system of work
and inspection.
Dynamic, on-site risk assessments should be undertaken and
identify hazards, and subsequent control measures, resulting
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from changing circumstances, for example breakdown and
maintenance.
4 PRS SYSTEM DESIGN
4.1 Introduction
Powered roof support systems are a range of assemblies; these can
be from a range of manufacturers or comprise a variety of different,
compatible components combined to form an integral system.
4.2 Safety considerations
Careful consideration must be given to complete system design to
ensure the compatibility and suitability of all elements. Assessment
of specific risks may inform the use of functional features to control
hazards associated with particular geotechnical conditions, typically,
anti-topple systems, base alignments, cusp supports.
The system contains a number of safety critical assemblies that are
essential to the safe control of the functions and operations
associated with roof stability and coal face production activities.
4.3 Assessment of Ground Conditions
This assessment is required by law and is a formal document
detailing the design process undertaken and the equipment to be
used should be compiled, maintained and reviewed following any
significant change to the system and/or conditions.
4.4 How a powered roof support works
Powered Roof Supports (PRS) are self advancing structures
(machines) which are interconnected along the length of the
longwall face. Each support along the line is also connected to each
pan of the Armoured Flexible Conveyor (AFC).
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The functions of the powered supports are:•
•
to control strata deformation, fracture and movement
around the coal face,
to maintain a safe working environment,
Each support structure consists of a roof canopy connected to a
base via a shield and rear linkages. Side shields mounted to the
canopy prevent excessive debris falling into the work space during
support advancement.
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Powered Roof Support at Test Facility
4.5 Structures
PRS structures must have the capability and strength to withstand
the external forces applied to them from the surrounding
underground strata. The duty cycle and loading configurations
imposed on them will vary depending on the local underground
conditions. Factors such as local geological faults, caving
characteristics and a corrosive environment will ultimately affect the
performance and longevity of the structures.
The specific roof and floor strength of the mine can also have an
influence on the performance of the structures due to local load
intensity effects.
Industry accepted design codes should be used to ensure that a
minimum design standard is adopted to determine the strength
requirements of the structures.
The European standard BSEN1804 -1 is the minimum specification
for the requirements of PRS; it contains the minimum design
requirements and specifies the acceptable design stress levels for
materials and welds used in the construction of the PRS. It also
specifies the minimum cyclic test requirements of design and the
recommended specific cyclic test regime, however, the in service
life can vary depending on the frequency of yielding experienced
and the roof and floor conditions.
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Structural examinations required during service life will be
stipulated by the OEM and may be stipulated to establish or limit
continued use beyond the number of design cycles or following
repair or modification.
The presence of sulphides and chlorides in the mine environment
create highly corrosive conditions that accelerate any deterioration
and consequent reduction in operational life.
Surveys on sample PRS at various positions during the operating life
of the equipment may determine any inherent damage or fatigue
experienced.
Inspection sites identified by the OEM should include load input
points such as leg pocket areas and other areas susceptible to
fatigue stress.
NDT methods, that may involve removing a whole PRS or specific
components from underground, should be considered for detailed
inspection procedures and thorough examination.
Scheduled inspection intervals reflect the number of operation
cycles conducted and record information to assist in the fatigue
management of the PRS structures and may typically be conducted
during interface transfer. Investigation of the effects of extraneous
loads must be determined by additional testing.
4.6 Yield loads
Yield loads are controlled by releasing pressure in the PRS legs at a
predetermined set value. The yield valves are fitted directly to the
leg cylinders and are designed to release pressure to avoid damage
to the PRS whilst maintaining roof support.
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The following drawing shows a simplified cross section of a PRS two
stage leg cylinder:
LOAD (W)
Roof
Roof Support
Canopy
Leg
Closing
Under
Load W
Internal transfer
valve
Cylinder
Mounted
Check
Valve
(POCV)
P2
Pressure
relief valve
(Yield
valve)
P1
Floor
As PRS system pressure is introduced into the leg circuit (via the
pilot operated check valve - POCV) major stage chamber P1 is filled.
Fluid then continues through the internal transfer valve and into the
minor stage chamber P2 until it is filled.
The PRS leg cylinder extends and the pressure equalises in both
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chambers, they remain equal until external resistance is met such
as contacting the roof.
On contact, when there is sufficient resistance, the internal transfer
valve closes and the pressure in both chambers increases. The
pressure in the major stage will continue up to the system pressure
(typically 320 Bar) and the PRS is set to the roof. Since the cross
sectional areas of the two chambers differ (P1 typically double P2),
the pressure in the minor stage can be twice that of the major
stage.
When mineral is extracted, the surrounding roof and floor exert
natural forces, load, deformation and movement. These forces can
typically occur during operations or during periods of inactivity and
result in convergence (closing); PRS inherent design resists these
forces.
To prevent damage and keep the PRS within their safe design
parameters, hydraulic leg cylinders are designed to converge in a
controlled manner under increasing forces and from the roof load
(W).
These external forces can cause the pressures in both the major
and minor stage chambers to increase. Eventually the pressure in
the major stage chamber equals the pressure relief valve (yield
valve) setting. If the roof continues to converge then the major
stage will continue to close (lower/yield) until the pressure relief
valve vents fluid at the predetermined “Yield Pressure”.
The internal transfer valve opens via a plunger when the major
stage is almost fully closed, releasing the minor stage pressure into
the major stage chamber. This pressure vents via the yield valve
upon further loading.
This process is capable of repetition, until undesirable full closure of
both the major and minor stages is achieved. This will result in
catastrophic degradation of support control and potential PRS
structural damage.
The yield capacity of a PRS will vary during its operating range due
to the leg angle variations. OEMs provide this information within
technical specifications.
Calculation of the yield load capacity of the PRS is determined by
information from geotechnical studies and relevant historical
knowledge of the mine environment and local conditions.
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The required roof support density is determined from geotechnical
assessment.
Equipment manufacturers determine the
suitable support
configuration from information contained in the geotechnical
assessment studies.
Yield capacity of the PRS is calculated to provide this density, over
the specified roof area. Typically, these values are stipulated in
tonnes per metre². Depending on the location along the face, a
minimum of 10 to 15 times the extracted height or 10-15 t/m² is
the recognised minimum parameter.
Roof support density loading and maximum pressure settings must
be maintained as the set to yield ratio of the leg operation can have
major effects on roof control. Designed setting resistance should be
at least 75% of the designed yield resistance based on a minimum
available setting pressure of at least 276 Bar (4,000psi). The
system pressure should be appropriate to meet the requirements of
the geotechnical assessment.
Positive leg setting can be achieved by using:
• guaranteed leg set circuits – addition of specialised valves
that sense leg pressure and initiate a leg set function.
• active set controls – electronic monitoring/correction of leg
pressure along the face.
• increased set to yield ratios – incorporation of a dedicated
high pressure set circuit.
PRS typically employ the Immediate Forward Support configuration
(IFS). This method of working allows the roof support to be fully
advanced and set immediately after the shearer has passed,
providing immediate support to the newly exposed roof.
To ensure roof control PRS must be correctly set with full system
pressure when advanced.
To engender roof break-off points behind the legs toward the
canopy cave line PRS must be correctly set.
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LLO
OA
AD
D ((W
W))
LLO
OA
AD
D ((W
W))
BREAK OFF POINT
The diagram illustrates PRS canopy loading changes as the break off
point of the detached block of roof moves. The desirable break off
point is behind the PRS, providing optimum tip and support load.
Examples of Tip and Cave Loads at 320 Bar Break off point over legs
and behind the canopy
420 Tonnes
100 Tonnes
310 Tonnes
-10 Tonnes
Tip Load
Cave Load
Tip Load
Cave Load
X
The tip loads that are designed into PRS structures diminish
proportionally as the loading point moves forwards away from the
rear of the canopy. This can lead to poor roof control and cavities
(broken roof voids) on the face side. Inevitably, zero tip load
causes the canopy to tip forwards and the rear of the PRS to push
upwards into the void behind the canopy as shown in the illustration
below.
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4.7 Modifications
Strength and fatigue properties are implicit in PRS design. Any
modification may have a detrimental effect on other features
designed to counteract fatigue.
Fatigue damage typically propagates from a weld feature or
inherent stress concentration present in the design. Repairing
fatigue damaged structures, to the original design, will never
exceed the performance of the original structure.
Repaired welds will generally perform as original with the exception
of critical stop/start weld locations. Parent plate repairs do not
always perform as well as the original plate.
The OEM, or a suitably qualified design authority, (notified body)
should be consulted to assess, verify and certify any proposed
significant repair or modification in accordance with the
requirements of Annex IV of the Machinery Directive.
The specification, content and quality of any modification should be
undertaken in accordance with OEM or approved supplier standards
to ensure that only the correct materials, welding procedures,
appropriate pre heat and welding consumables are used.
Maintenance procedures and requirements should be reviewed
following any repair or modification.
4.8 Hydraulic system layout
PRS hydraulic fluid systems typically comprise of:
• a surface mixing plant
• underground distribution ranges
• underground pumping stations either at the coal face or
remotely situated.
4.8.1 Surface mixing stations
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Hydraulic fluid is usually mixed on the surface to form a clean,
invert oil emulsion of typically 5% soluble oil to 95% water.
The synthetic, refined fluid is mixed with water, of the correct
properties and quality, at the pre-determined level. It is
stored in the mixing station and piped to the point of use
underground and fed into the system on demand.
Continuous monitoring techniques should be deployed to
ensure the effectiveness of the mixing station and quality and
cleanliness of the fluid.
Biocides inherent in hydraulic fluid invert oil emulsions may be
supplemented to control and prevent the growth of bacterial
organisms.
Surface mixing station
4.8.2 Underground distribution ranges
Distribution ranges should be of sufficient capacity to deliver
adequate quantity of clean mixed hydraulic fluid to the
pumping stations. They should be appropriately routed and
supported to avoid damage and leakage.
4.8.3 Pumping stations deliver the hydraulic fluid to PRS and
comprise:
• electrical and mechanical control equipment
• several pumps available on system demand
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•
•
•
•
a storage reservoir
a filtration system
a distribution system
an accumulator system to reduce pressure transients
A suitable underground location should be selected and
prepared for the pumping station and/or power pack (self
contained, typically temporary, localised pump unit) to
facilitate reliable, effective delivery of hydraulic fluid on
demand.
Pumping stations can be located either remotely to a coalface
or as a part of the pantechnicon unit; an example of a remote
pumping station is shown.
450kW Variable speed 5 piston pump and unloading unit
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Filtration unit and accumulators
Main supply tank 4500 litres capacity
Fluid is typically supplied and returned to and from the
pumping station via pipe ranges that should be adequately
routed, supported and clearly marked.
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4.8.4 Flexible hose supply
At their furthest point inbye, the rigid system ranges convert
to a flexible hose supply and return system to facilitate
retreating production activities.
The flexible supply system is typically managed by hose and
cable handling arrangements prior to connection to the inbye
distribution and control system.
4.8.5 Inbye distribution and control system
The inbye distribution and control system is typically mounted
on a series of ancillary platforms (pantechnicon) and
comprises the:
• electrical control system
• electro-hydraulic safety (dump) valve assemblies
• filtration system
• hydraulic distribution system
• high pressure boost facilities
• ancillary supplies
The electrical and hydraulic supply is routed from the
pantechnicon, via cable and hose handling arrangements into
the beam stage loader and onto the face.
A number of hydraulic supplies are configured to form an ring
main to supply the face equipment, including the powered
roof supports, to ensure all parts of the system are equally
served with adequate fluid flow and pressure.
The ring main is an essential design requirement of powered
roof support systems. A typical layout is shown in the
example of a coal face pumping station below.
4.9 Supply fluid
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4.9.1 Pressure Lines
For PRS to work effectively an adequate supply of fluid at the
correct quantity, quality and pressure is essential.
Operational demand determines the volume of supply fluid
required; typically up to 6,000 litres (280 gallons) per minute.
Filtration of the system fluid is of paramount importance to
maintain the cleanliness of the PRS system.
Fluid is typically supplied at a pressure of 320 bar (4,500 psi).
This pressure has the potential to cause serious injury or
death and careful selection and management of the hose
system is essential.
4.9.2 Return Lines
Fluid used at the face is returned to pumping stations by
means of the return lines. Flow resistance generates return
line pressure however excessive return line pressure should
be avoided to prevent deterioration of the effective operating
pressure and malfunction of PRS.
Typically this can be achieved by installing larger bore return
lines than pressure lines to minimise the effects of back
pressure.
4.9.3 Tidal flow – negative head
PRS operations remove fluid from reservoirs at a rapid rate.
Surges of return fluid can disrupt PRS sequences and typically
occur when operations cease and the face is higher than the
pumping station. Hydraulic fluid returns under gravity, until
the range is emptied to the reservoirs, potentially causing
overflow.
Limited capacity of surface mixing plants delays refill, and
adequate time is required to replenish reserves lost during
overflow. This undesirable fluid surge and range depletion is
mitigated by the installation of tidal flow control valves.
Tidal flow valves are adjustable return pressure regulators
typically located at pumping stations.
Face elevations determine the amount of tidal flow valve
adjustment required to control the pressure and flow of return
line fluid to reservoirs.
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The head of pressure developed and identified at incremental
points along elevations determines valve settings to maintain
charge and prevent surge.
The pressure head may decrease as the face retreats and
valves should be periodically regulated accordingly.
4.9.4 Tidal flow – positive head
An increase in return line pressure will occur when the face is
lower than the pumping station (positive head) and the fluid
returns to the reservoirs against gravity, increasing
approximately 1 bar per 10m of elevation. Positive head
effects should be considered at initial face design.
4.9.5 Minimum Standards of Installation for Protection of Powered
Supports Return Lines from over pressure.
The volume of the fluid flowing in the return line correlates to
the number of operations taking place.
The return lines are protected by a system of pressure relief
valves, typically set at a maximum pressure of 40 bar (600
psi).
Relief valves are located at points throughout the PRS system
determined by technical assessment, design engineering and
OEM recommendations.
Any section of a bank of PRS that can be isolated should have
its own return line relief valve to prevent inadvertent
operation caused by hydraulic back pressure.
Installation of relief valves in the return line system, at predetermined points determined by the technical assessment,
will protect against over pressurisation when isolation valves
are closed and hydraulic operations continue.
4.9.6 Safety Point
Return system pressure should be checked regularly,
preferably every working shift. A gauge with the facility to
retain the maximum recorded pressure value, or an electrical
transducer giving permanent outputs, should be positioned at
the furthest point from the pumping station.
4.10 Connections to pumping stations and/or remote power
packs
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The requirements for connection of the coal face powered roof
supports to the pumping stations and/or power pack systems are as
follows.
4.10.1 Temporary systems for installation purposes
Temporary systems must be fully commissioned prior to use
and have filtration capable of maintaining the required fluid
cleanliness.
Fluid composition should be sampled weekly to ensure it
meets the specified standard.
All hoses, fittings and staples should be of an approved
standard and in good condition.
Feed and return hoses should be routed safely to avoid
increased risk from equipment movement.
Inspections of flexible (wander) hoses and attachments
should reflect the environmental conditions, duty and the
number of operations.
Safety devices must be fitted to pumping stations and/or
power packs to stop and isolate the system hydraulic supply
in an emergency or to facilitate maintenance.
Risk assessment, documentation of isolation procedures and
Permit to Work systems must be provided and used.
Operations to attach and detach flexible hoses must only be
carried out by competent persons in accordance with safe
systems of work.
Pressures delivered by pumping stations and/or power packs
during installation procedures should typically not exceed 200
bar (3000 psi) max.
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•
during installation, reduced pressures should be used
initially and PRS canopies set to the roof protected by
wooden packing, to avoid puncture by roof bolts.
•
system pressures should be incrementally increased
following initial tests that have ratified the integrity of
the individual PRS’ operation and functionality.
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•
during installation, reduced pressures should be used on
the associated pulling equipment to provide adequate
factors of safety.
Isolation valves should be identifiable, easily operated,
incapable of being accidentally operated and lockable when
necessary.
4.10.2 Pre-operational requirements
Temporary systems must be fully commissioned prior to use
and have filtration capable of maintaining the required fluid
cleanliness.
Fluid composition should be sampled weekly to ensure it
meets the specified standard.
4.10.3 Connection to permanent pumping stations and/or power
packs
The risk assessment should be supported by method
statements detailing the process for connecting the supports
from a temporary system to the permanent system.
Pressure and return systems should be connected from power
packs to the face with hoses/pipes of sufficient size, relevant
to the number of pumps used and the most onerous
demands, to avoid turbulent flow or excessive fluid velocities
and to minimise the effects of back pressure.
Pump systems must have a suitable isolation, distribution and
pressure dissipation system.
During installation and production, a diagram should be
produced and maintained detailing the layout, sizing and
route of each of the feed and return systems.
This diagram should include positions of isolation valves, relief
valves, crossover links and monitoring equipment.
Construction of the feed and return systems throughout the
main distribution network should, where practicable, deploy
hoses of the same length.
Hoses should be routed in compliance with hose specifications
for minimum bend radii to prevent damage and premature
failure.
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Risk assessment and documentation of isolation procedures
should be undertaken and Permit to Work systems used.
4.11 Hose assemblies and adaptors
Hoses used on PRS systems must be designed to provide:
• flexible connections between equipment
• hose cover protection from abrasion
• hose crush protection
• leakage prevention
• hydraulic injection protection
Supplementary hose covers protect hoses from external damage
but can mask internal abrasion and/or damage and require
additional inspection.
4.11.1 Hose selection
Hose selection should take account of environmental
conditions, pressures and duty. The construction of the hose
determines its capabilities and use. The two main types of
hose used on PRS have two wire braiding or four wire spiral
wound construction around an inner core tube.
2 Wire Braid (2WB)
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Polyethylene
outer cover
Insulation rubber
The core tube
The reinforcement
4 wire spiral bound (4WS)
The reinforcement
The cover
The core tube
6 wire spiral bound (6WS)
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Core tube
Outer cover
Insulation
layer
Wire
reinforcement
Two wire braid hoses having a bore not exceeding 12.5mm
(½”) may be used up to a system pressure of 320 bar (4500
psi). Where system pressure and supply demands a hose
having a larger bore then four wire spiral bound hose should
be used. See comparison table below for selection.
Working pressure specifications
2-Wire Braid British Coal spec 174
Nominal Bore
Min Bend Radius
Working Pressure
Burst Pressure
mm
Inch
mm
BAR
PSI
BAR
PSI
6
10
12
20
25
32
40
50
1/4”
3/8”
1/2”
3/4”
1”
1.1/4”
1.1/2”
2”
100
130
150
230
300
380
450
600
450
379
362
276
214
172
145
112
6525
5500
5250
4000
3110
2500
2100
1625
1800
1517
1448
1103
858
690
579
448
26100
22000
21000
16000
12440
10000
8400
6500
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4-Wire Spiral British Coal Approved
Nominal Bore
Min Bend Radius
Working Pressure
Burst Pressure
mm
Inch
mm
BAR
PSI
BAR
PSI
10
3/8”
180
450
6500
1800
26000
12
1/2”
230
415
6000
1660
24000
20
3/4”
280
434
6250
1724
25000
25
1”
340
403
5800
1600
23200
32
1.1/4”
460
354
5100
1407
20400
40
1.1/2”
560
313
4500
1241
18000
50
2”
700
281
4050
1117
16200
Where excessive pressures/flow rates or adverse conditions exist six
wire spiral hoses are available for selection.
6-Wire Spiral British Coal Approved
Nominal Bore
Min Bend Radius
Working Pressure
Burst Pressure
mm
40
Inch
1.1/2”
mm
510
BAR
352
PSI
5100
BAR
1407
PSI
20400
50
2”
635
352
5100
1407
20400
4.11.2 Hose identification
Each length of hose should be embossed at intervals of not
more than 0.6m with the following information.
• hose manufacturer’s name
• number of the specification number
• British Coal approval number
• month and year of manufacture
• design working pressure
• longitudinal double line parallel to the axis to denote
construction
• Hoses are typically marked with both DN and imperial
nominal bore sizes as below.
DN 6 = 6.3 mm ¼”
DN 10 = 10 mm ⅜”
DN 12 = 12.5 mm ½”
DN 20 = 19 mm ¾”
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DN
DN
DN
DN
25
32
40
50
=
=
=
=
25 mm 1”
31.5 mm 1¼”
38 mm 1½”
51 mm 2”
Any other markings should be separate to avoid confusion.
Additional system identification information should be used
appropriately to differentiate between duties.
Where embossed details are not readily visible, e.g. beneath
inter support protective covers, hose identification should be
displayed by alternative means at one end of the hose using a
water/oil proof label of a fire resistant material as illustrated.
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4.11.3 Routing and Retention
All hoses should be routed correctly and retained to ensure
smooth radii and avoid stresses that may contribute to early
failure. The following are comparisons between good and
poor practice.
Swivel connectors can be used to prevent hoses becoming
twisted, weakened and applying torque to, and damaging, the
hose fittings.
Hose construction and connector damage,
resulting from seizure, should be prevented by ensuring the
swivel can operate freely.
Hose installed in twisted position
Ample bend radius should be provided to avoid bore collapse
and restrictions of flow. Excessive bend at hose ends results
in strain on the ferrule and reduced hose life.
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Careful selection of hose lengths, suitable adaptors and
manifolds will avoid exceeding minimum bend radii and strain
on the hose and hose connections.
Adaptors and manifolds should be used to:
• eliminate excess hose length
• minimise the number of connections
• ensure optimum installation and hose management
• facilitate maintenance
Clamps or fixings should secure hoses in position. Flexing hoses
should not be restricted or damaged by incorrect positioning and
should be clear of hot or abrasive areas.
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4.12 High pressure injuries
Hydraulic fluid released under pressure can puncture and penetrate
skin and body tissues. Pressure injection injuries are caused by
fluid at high velocities and can be attributable to high or low
pressure hydraulic systems.
A leak in a hydraulic hose under pressure can release fluid at a
speed in excess of 183m/s (600 feet per second). The illustration
below shows hydraulic burst damage to the external cover and the
exposed internal braiding which could result in high pressure injury.
Hose protection to avoid external damage
Injected fluid enters the fatty body tissue and tendons and deep
spaces of hand and body, the higher the system pressure the more
serious the injury.
Some personal protective equipment may not prevent high
pressure, high velocity, injection injuries and appropriate remedial
action must immediately follow any potential injection/velocity
injury.
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The illustration below shows the barely detectable point of entry of
hydraulic fluid under pressure.
The illustration below indicates the extent of surgery that may be
required to remove all traces of injected hydraulic fluid from fatty
body tissue.
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5 SAFETY CRITICAL COMPONENTS
Safety critical components include single-line components or
assemblies, which, if they were to become defective or fail in
service, may result in high risk of injury.
Investigation of component and/or system defects should have OEM
input to ensure cognisance of relevant technical and design aspects.
Reporting, recording, logging and investigation of near miss
incidents, inadvertent operation and/or unplanned events must be
undertaken thoroughly by competent persons to ensure that the
root cause of any incident is determined and adequate control
measures are introduced to minimise the risk of re-occurrence.
6 MAINTENANCE SCHEMES & COMMISSIONING
6.1 Classification of defects
Based on the requirements of the former National Coal Board
Manager’s Scheme for the Mine, defects can be categorised into
three types - Level 5, 6 and 7.
A Level 5 defect is that which if an action or repair is not
undertaken and by doing so it is unlikely that the equipment would
deteriorate to affect its safe operation.
A Level 6 defect is that which is deemed still safe to operate at the
time of examination, but has the potential to become a dangerous
fault affecting safe operation if not repaired within a specific time
frame.
A Level 7 defect is where a potentially dangerous fault affects safe
operation or is liable to quickly lead to an unacceptable risk to
persons.
PUWER 1998:- Regulation 5 describes that work equipment must be
maintained in an efficient state, in efficient working order and in
good repair and that where maintenance log is kept, it must be up
to date.
It is important that equipment is maintained so that its performance
does not deteriorate to the extent that it puts people at risk. In
regulation 5, ‘efficient’ relates to how the condition of the
equipment might affect health and safety. It is not concerned with
productivity.
Equipment, and ancillary components, should be maintained to
ensure that they are safe to use at all times, including:
• guards
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•
•
•
•
•
•
•
•
•
•
•
emergency shutdown systems
pressure relief devices
bearings
filters
valve gear
cylinders
connectors
hoses assemblies
cables
control equipment
hydraulic fluid
6.2 Maintenance management
The extent and complexity of maintenance can vary substantially
from simple checks on basic equipment to integrated programmes
for complex plant.
Maintenance management techniques may typically include:
• planned preventive (pro-active) - involves replacing parts
and consumables or making necessary adjustments at
preset intervals so that risks do not occur as a result of the
deterioration or failure of the equipment
• condition-based - involves monitoring the condition of
safety-critical parts that could fail and cause the
equipment, guards or other protection devices to fail and
lead to immediate or hidden potential risks.
• reactive maintenance - involves carrying out maintenance
only after faults or failures have occurred. It is appropriate
only if the failure does not present an immediate risk and
can be corrected before risk occurs, for example through
effective fault reporting and maintenance schemes.
PRS are complex powered equipment addressed by OEM
maintenance manuals and instructions that specify routine
recommended maintenance frequencies and requirements.
6.3 Frequency of maintenance
PRS must be maintained to ensure that they are functioning
correctly and safely. Any fault which affects production is typically
obvious, whereas more rigorous testing may be required to detect
faults in safety critical systems. This programme of testing should
be included in maintenance schemes and take account of:
• intensity of use – frequency and maximum working limits
• operating environment
• variety of operations
• risk to health and safety from malfunction or failure
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6.4 Maintenance log
A detailed maintenance log should be provided and kept up to date.
The log should record previous action taken and inform future
planning of maintenance activities.
Supplementary or additional maintenance may be required and
reviewed/revised, particularly when abnormal operating conditions
are foreseen or experienced or prior to transfer to a new coal face.
6.5 Commissioning
All PRS are subject to conformity and function tests by OEM prior to
delivery, to ratify system and individual performance.
During first
conformity,
accordance
engineers.
installation.
installation on a coal face, PRS are subject to further
function and commissioning tests by the operator in
with OEM instructions and typically with OEM service
PRS should be re-commissioned on each subsequent
6.5.1 Tasks prior to salvage from previous coalface
Identification of PRS overhaul, repair or any other remedial
requirements, prior to salvage or transfer to a successive coal
face is essential to ensure they are suitable for continued use.
PRS should be assessed, utilising previous examination
results, history, known defects and cycles completed since the
last overhaul, to determine if comprehensive works such as
major overhaul or full replacement are required.
The assessment should comprise a full physical external over
inspection of PRS and ancillaries pumps, pumping stations,
filter stations, dump valves assemblies etc., to determine
their suitability for continued, safe use/re-use.
Random samples should be compared with PPM history to
ensure they were not previously sampled or changed, and
include representative samples of:
• spool valves
• solenoid valves
• leg and stabiliser ram Pilot Operated Control Valves
(POCV)
• leg and stabiliser ram yield valves
The sampling process should be carried out by competent
persons to ensure:
• careful removal of components
• ancillary damage is avoided
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•
•
•
•
contamination is avoided
correct identification/labelling
location and orientation identification
a sampling audit trail
Operation of PRS leg circuits after the last cut on a salvage
face, before the supports are removed, can engender roof
disturbance that may prove difficult to rectify. It is imperative
that any diagnostic work associated with PRS leg circuits
should be carried out before this stage.
To determine leg seal/yield circuit condition it is
recommended that supports are set to the roof and a standing
test carried out for 24 hours following the last cut.
To complement the comprehensive assessment a full acoustic
survey should be carried out in the pre salvage inspection to
detect any bypassing defects on:
• spool valves
• solenoid valves
• gaskets
• pilot operated check valves
Defects identified during the acoustic survey should be
categorised, prioritised and addressed in accordance with the
PPM defect scheme.
All PRS hoses should be examined for external damage and
changed when assessment of their condition dictates further
use will increase risks of failure and injury.
Open hose ends or valves/connector parts should be capped
off to prevent contamination of PRS during salvage or storage.
The integrity of the individual support isolation and non-return
valves should be assessed, results recorded and suitable
action taken.
To remove any inherent contamination from the bottom of the
legs pressure should be defused and the legs completely
lowered.
To avoid contamination from entering into the
system return line hoses should be disconnected for this
operation.
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6.5.2 Tasks during transfer
Before PRS are transferred onto a new coal face any known
defects should be resolved.
Known defective equipment should be identified as such in
order to prevent reuse and must be removed as soon as
practicable. The identification of component parts by serial
number will aid identification and traceability of faulty items.
Examples of tasks and checks/changes during transfer:
• all cables and hoses between PRS
• all internal cables and hoses within PRS
• all linkages, pins and retainers for integrity and security
• all leg top and bottom housings and retainers
• side shield condition
• face sprags and beam extension facility
• security and condition of base lift facility and advance
cylinders
• valves, solenoids, spools, POCV, stabiliser and shield
control valves are operational and fit for continued use
(by OEM assessment)
• all isolation valves
• ensure all connecting bolts and fasteners are secure
6.5.3 Tasks during installation post-transfer
PRS must not be installed on a new coal face until known
safety critical defects have been rectified.
Where any safety critical defects become apparent during PRS
installation it is inadvisable to install subsequent supports
until the defects have been rectified.
Once a PRS being installed is hydraulically connected to the
system it should be operated by use of a remote control unit,
from a position of safety, until it is in place and set.
6.5.4 Tasks post installation
PRS are typically installed and pressurised at 140bar
(2000 psi) and set to the roof. For protection against canopy
puncture and roof deformation timber should be placed
between the canopy and the roof.
The PRS electrical controls must be fitted, checked and
commissioned in accordance with OEM installation procedures.
Until the pressure release or dump valve system from each
support is commissioned, a means to remove the electricity
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supply to the pumping station and/or power pack must be
provided throughout the face.
Commissioning of the pressure release or dump valve facility
must be undertaken prior to introducing the main system
hydraulic supply. Integration of the temporary and main
supply emergency dump systems should be avoided so that
control is from one system only.
6.5.5 Dynamic commissioning post installation
During initial face cutting operations the PRS will be
systematically advanced into the production section of the
coal face to support the newly exposed roof.
The system pressure to the PRS should be increased to 320
bar (4500/5000 psi) when the roof conditions are deemed
competent.
A full system pressure check must be carried out to identify
any leakage or other defect utilising diagnostic methods such
as acoustic or instrumented testing.
A post installation condition test report should be prepared to
record any leakage or other defects at full system pressure.
Faults should be resolved appropriately, reported and
recorded.
6.5.6 The hydraulic system
PRS may be installed, set and commissioned using either a
temporary or permanent pumping station and/or power pack.
The pumping station and/or power pack and its associated
connections to the face PRS should be installed,
commissioned and maintained to deliver the hydraulic fluid to
the PRS in accordance with ISO 4406 17/13.
Flushing and filtration of all lines to and from the temporary
or permanent pumping station and/or power pack should be
undertaken prior to connection of PRS to ensure removal of
contamination. Progressively graded filter changes may be
required to remove contamination following installation.
Individual PRS filters including “last chance” should be
changed as soon as possible after installation.
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7 FUNCTION TESTING
7.1 System performance and individual tests
PRS and systems function tests should reflect OEM commissioning
processes and be supported by periodic testing in accordance with a
suitable maintenance scheme.
Examples of individual and system tests:
• controls perform their intended designated function
correctly and safely and stop on command/release
• PRS maintain their set pressures
• operating functions perform correctly and safely
• sensory
and
instrumented
checks
for
hydraulic
bypasses/leakage
• electrical and electronic adequacy and stability
• fluid cleanliness
• filtration system cleanliness
• flow and pressure measurement
• electro-hydraulic (dump) valve operation
• emergency stop facilities
7.2 Pressure and performance monitoring
Individual and system pressure monitors and gauges and electronic
performance monitors should be provided at strategic points of the
systems.
Examples of individual and system pressure monitors:
• leg (set pressures)
• pumping stations
• distribution points
• isolation points
• return line indication
Examples of individual and system electronic performance monitors:
• system diagnostic facility
• audible/visual alarm monitors
• event fault logs
• plc diagnostic information
• individual display facility
• power stability testing
• transducers
7.3 Acoustic vibration threshold levels
The use of instrumented acoustic vibration equipment will detect
any increase in background noise level in any hydraulic valve; this
may be an indication of bypassing fluid. The root cause of any
bypass should be established and cognisance should be taken of
OEMs specifications for continued use.
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8 WORKING ON PRESSURISED PRS SYSTEMS
All hazards associated with pressurised systems must be assessed
and mitigated prior to any work commencing.
Control measures may be stipulated in a permit to work system and
craftsmen must be fully instructed prior to commencing work.
Control measures should take cognisance of the recommended
procedures in the OEM maintenance manuals.
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An example of a permit to work on PRS systems
Location
Date
Activity
Name of Supervisor issuing permit
Names of persons undertaking task
Date:………………………..
From: ……………………
HAZARD CONTROL MEASURES
YES
NO
To: ………………………..
COMMENT
Signature
Identification of circuit to be worked
on
Training of persons undertaking task
Identification of isolation points
Do you need electrical isolation
Have the isolating valves been locked
off
Test for decay of pressure
Provision of suitable eye protection
(goggles)
Provision of suitable gloves
Identification
of
hazards
to
other
persons
Warning notices posted
On site risk assessment completed
I hereby declare that being a Mechanical Supervisor/ Command Supervisor/Inspector possessing the
authority to issue a permit to work for the work specified above, it is safe to carry out the work on the
pressure system, and that the above detailed safety measures have been carried out.
Time:………………………..
Date: …………………
Signature: ………………………………………..
I hereby declare that I understand the control measures detailed on this permit
Time:………………………..
Date: …………………
Signature: ………………………………………..
I hereby declare as a Mechanical Supervisor/Command Supervisor/Inspector in charge that the work for
which this permit was issued is now SUSPENDED/COMPLETED/CANCELLED and that the pressure system
has been left safe to operate.
Time: ……………………………Date: ………………………
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42
9 PRS OPERATIONS
PRS have several modes of control and operation. These control
systems range from simple manual operation of the hydraulic
functions from within the PRS to fully programmable automation
sequences that are interactive with the shearer operation and
position.
The working areas around the PRS can be divided into three distinct
zones depending on whether the machine is being operated or
maintenance work is being carried out:
•
•
•
Prohibited Zones - No access allowed.
Restricted Zones - Limited access to these areas for
maintenance and repair work, Machines should not be
operating and equipment must be isolated prior to entering.
Walkway Zones – Machines may be operating within zone.
PRS designated zones
1. Prohibited Zone
2. Restricted Zone
3. Walkway Zone
9.1 Operation modes
The electro hydraulic control system of a PRS offers many modes of
operation to suit particular mining activities. For example:
• Manual control
• Adjacent control
• Remote Control
• Remote Adjacent Control
• Bank Control
• Face Primes (free running)
• Shearer initiated primes
Automated facilities of control systems should be used for the
normal mode of operation.
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9.2 Cleanliness
The operation of a coal face and mineral extraction inevitably
produces debris resulting from mineral loading operations,
accumulations on the floor, roof spoil and AFC blockages.
The presence of debris and obstacles should be minimised within
the designated pedestrian travelling route to permit the safe
passage of persons.
The extent of abrasion, wear and damage to external and/or
exposed hydraulic hoses, cylinders and associated valve gear is
typically attributable to the amount of debris situated between and
within all PRS.
External hose damage should be minimised by maintaining levels of
cleanliness, protective routing, shielding and management to
prevent contamination internally. Ingress of debris can produce
potentially significant defects within safety critical components.
In adverse geological conditions the application of phenolic foams
and/or resin injection to consolidate the roof will reduce the amount
of debris.
The chemically aggressive composition of phenolic foams and resins
has a damaging and detrimental effect on hose covers/cables,
resulting in degradation and separation of the protective cover.
10 MANAGEMENT OF PRS SYSTEM HYDRAULIC FLUID
10.1 Fire resistant fluids
Fire resistant fluid used in PRS systems, generally referred to as
soluble or emulsifying oils, have been specially developed for use in
hydraulic systems which operate in highly hazardous environments.
Soluble oil is emulsified in water and should be mixed in proportions
recommended by the equipment supplier and in accordance with
the OEM Fluid Approval List.
Emulsifying oils used in the mining industry for powered support
systems are classified as type HFA, mineral oil and type HFS,
synthetic oil.
The mining industry in the UK uses type HFA as classified in ISO
6742-4 and ISO 7745 emulsion oils in PRS systems as this has been
proven to have better corrosion inhibiting properties than synthetic
emulsifying oil.
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Chemical or physical changes in the fluid could produce impaired
fire resistance. Such situations could arise through persistent high
temperatures, fluid spillage where evaporation or separation could
occur or breakdown of fluid chemical properties during use. These
issues should be addressed through regular fluid condition
monitoring and maintenance.
HFA fluid used in PRS should meet British Coal Specification No
463/1981 Emulsifying Oils for Dilute Emulsions for Hydraulic
Purposes, or an equivalent, that contains the test procedures to
ascertain the ability of the emulsifying oil to form emulsions that do
not cause rusting on immersed ferrous surfaces.
10.2 Water quality
The consistency of the quality of water mixed with emulsifying oils
to form HFA fluids is critical to maintain the PRS hydraulic systems.
It is unlikely that an “ideal” water quality will be achievable or
available in sufficient quantities and it is imperative that
consultation takes place with a representative of the emulsifying oil
supplier to ensure that the specification of the emulsifying oil is
tailored to suit the available water quality.
In compliance with BC Spec No 463/1981, additives to the
emulsifying oil and the water may be required to achieve the ideal
HFA solution.
Critical water characteristics should be considered:
• hardness due to presence of salts of calcium and
magnesium (low water hardness can promote foaming,
inclusion of yellow metal passivators and antifoam agents
can combat these effects).
• air entrainment promotes attacks on none ferrous metals
• organic feeds promote bacterial growths which lead to
emulsion breakdown, filter blocking and increased corrosion
(biocides can be added to the emulsifying oils to control
such potential growths).
• high chloride levels above 200 mg/litre and sulphate above
400mg/litre promote corrosion (ionic emulsifying and
coupling agents give rust preventing characteristics).
Regular samples of both the raw water used and the emulsified oils
should be available to the supplier for conformity checks.
Variables in water supply should be monitored and managed by the
operator to allow adequate control by the oil supplier.
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10.3 Fluid cleanliness
Fluid condition monitoring regimes should include regular checks
with a correctly calibrated refractometer; using fluid outside the
specified mix proportions may lead to degradation of the hydraulic
components and spurious operations. Regular checks should also be
made for the presence of bacterial and fungicidal contaminants.
Solid particles of contaminant are always present due to component
wear and ingress. The distribution of particles within the hydraulic
fluid, and where they accumulate, is critical and may result in
damage; the abrasiveness of individual particles and their hardness
enhance their ability to become entrained in softer materials such
as valve seats and non metallic seals. The amount of contaminant
and its particle size should be managed to minimise system failure
including un-commanded operation. Typical modes of wear are:
•
•
•
•
1.9.3.795.
Abrasive wear - caused when hard contaminants larger
than the fluid film thickness become trapped and are forced
into contact with components’ inner surfaces. This causes
abrasion of the internal surfaces of components.
Adhesive wear - occurs when the dynamic fluid film breaks
down and component surfaces typically micro weld and
shear.
Fatigue wear - caused when contaminant particles become
trapped between component surfaces and successive
operations cause surface cracking and metallurgical failure
exacerbating particle release.
Erosive wear - occurs when contaminants impinge on the
component surface, particularly at an interface or seal, and
increased fluid velocity engenders removal of material.
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The following pictures of PRS valves show the results of damage
due to contaminants.
Erosive wear at interface between seal and spool valve caused by
contamination, exacerbated by increased fluid velocity.
Erosive and abrasive wear on a valve seat caused by trapped
contaminants.
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Erosive wear of a valve operating pin caused by constant leakage of
fluid.
Erosive and abrasive wear on a valve ball.
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Invasive maintenance typically occurs during PRS operational life
and can introduce contaminants.
Contamination can typically be
introduced whenever hoses are disconnected and/or components
changed. All free hose ends, open valve ports and components
should be capped/sealed to prevent the ingress of contaminants
when PRS are subject to invasive activities, transported or stored.
To avoid injury high pressure hydraulic systems must not be purged
to atmosphere to remove contaminants; individual PRS filters
should be inspected regularly for contamination and changed in
accordance with OEM instructions.
10.4 Filtration
Strainers and filters are contained within individual PRS to prevent
large particle contamination that may typically lead to adhesive
wear, valve seat separation and fluid bypass.
Filtration of the pressure and return circuit fluid to the pumping
stations/power pack is critical to capture finer contaminants which
evade the coarse filtration at PRS.
Fluid should be sampled after the filtration system, before the tank,
to ensure fluid cleanliness to an acceptable ISO code and avoid
return line contamination being delivered to the pumps and PRS.
Suction strainers will be required in the system, between the pump
and the tank, or within the tank, to avoid unacceptable pressure
drop which may lead to cavitation and accelerated wear
mechanisms.
The fluid supply to the tank should be adequately filtered before it
enters the storage tank. A typical system depicting the minimum
standards of filtration is illustrated.
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There are two types of filters:
• Nominal filters have an arbitrary value based on the particle
weight percentage removed and are not suitable for PRS.
•
Absolute filters are rated based on the diameter of the
largest hard spherical particle that will pass through the
filter media under specified test conditions.
Examples of the effects of contamination:
• A hydraulic pump continuously delivering ISO code 21/18
oil, at a rate of 250 litres/hr, equates to 4375kg of
contaminate being pumped during the period of one year
and the pump could typically have a life expectancy of
approximately 2 years.
•
A hydraulic pump continuously delivering ISO code of 14/11
oil, at a rate of 250 litres/hr, equates to 25kg of
contaminate being pumped during the period of one year.
This could potentially increase the life expectancy of the
pump to 14 years.
10.5 Underground sampling at a pumping station and/or
power pack
Fluid samples should be taken from the supply at the pumping
station and/or power pack storage tank between the return line
filters, before the storage tank, from the designated sampling point
and not be contaminated. Samples should be analysed for both
quality of water/oil mix and for cleanliness and bacterial content
and appropriate remedial action taken.
Permanent on-line monitoring should be considered.
10.6 Pressure test and storage fluids
Ready mixed pressure test and storage emulsions are designed as
dual function fluids for PRS and their component parts. They should
be compatible with OEM recommended hydraulic operating fluids
and sealing arrangements.
Pressure test and storage fluids inhibit ice crystal formation at very
low temperatures and typically contain both liquid and vapour phase
corrosion inhibitors and offer protection against freezing
temperatures during storage and transport.
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11 ELECTRICAL SYSTEMS AND DATA LOGGING
11.1 System construction
11.1.1 Control system
PRS control system components should be designed in line
with harmonised standards i.e. BSEN 1710 Equipment and
components intended for use in potentially explosive
atmospheres in underground mines, and IEC 61508-1
Functional
safety
of
electrical/electronic/programmable
electronic safety-related systems.
Ingress Protection (IP) rating, positioning and orientation of
the system components should be designed to obviate any
contamination from external source, such as fluid leakage.
Components requiring inspection or maintenance should be
positioned and accessible.
Ventilation arrangements are designed to minimise and dilute
accumulations of methane within PRS. Methane potentially
occurs towards the rear of the PRS during normal operations
and increases towards the return end of the face; location of
the electrical components and interconnecting cables should
take cognisance of this.
Automatic detection of the presence of methane must be
provided within the last support at the return end of the face,
to provide continuous monitoring and alarm at an appropriate
level.
Electrical system components must be located and maintained
to prevent physical damage during PRS operations throughout
their full operating range.
To avoid dismantling and reassembly of electrical systems,
electrical equipment should remain in situ, where practicable,
when the support is fully collapsed and during transport.
Cables between PRS, when disconnected, should be looped
and any open ports blanked to prevent ingress of
contamination.
Interconnection of the system components should be made by
OEM interconnecting cables or hose cables, or those of an
approved type.
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11.1.2 Cables
To minimise the ingress of dirt and water, top entry
orientation for cable glands or plugs and sockets should be
avoided.
Cables between PRS should be wrapped in an additional
protective cover and suitably restrained collectively within and
between each support.
PRS interconnecting hose cables having staple lock type
retention must have hydraulic rated staples fitted.
Staples designed for electrical applications should not be fitted
to hydraulic circuits.
Electrical system hose cables should be colour coded or their
outer coverings should be moulded differently to differentiate
from hydraulic services.
11.1.3 Power supplies
The adequacy and stability of PRS power supplies should
reflect the range of voltage transients typically experienced
during coal face operations, for example, variations in supply
voltage during start up of large capacity plant.
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To ensure system stability, PRS power supplies should
typically include constant voltage transformers (CVT) or
uninterruptable supply units (UPS).
All systems must include a failsafe electro-hydraulic safety
(dump) valve assembly designed to operate on the detection
of any safety critical event or loss of electrical supply. Only
authorised persons must be permitted to reset any electrohydraulic safety (dump) valve system.
11.2 Lighting
PRS systems and coalface lighting should have separate power
supplies to prevent intersystem faults.
The two
•
•
•
•
systems should be integrated and take cognisance of the:
cable routing between and within PRS.
mounting and location of junction boxes for 110V supplies.
labelling/identification of 110V components/cables.
provision of staggered supplies to avoid the total loss of
lighting associated with one supply and be clearly marked
• provision of suitably labelled, lockable means of isolation
for maintenance.
The light fittings should be positioned to:
• avoid glare
• avoid entanglement with controls leading to inadvertent
operation
• afford access to PRS controls or components
• avoid damage during normal operation.
11.3 PLC & data logging
The PRS programmable logic controller (PLC) provides a
management facility for the safe operation of the coal face, and
allows the operators and technicians to observe and interrogate the
system during its operation.
The PLC is safety critical within the management system. See “The
use of computers in safety critical applications” (ISBN 0 7176 1620
7) and “The TickIT Guide” (ISBN 0 580 36943 9).
Differing levels of security provide access to the operating systems;
these should be password protected in the following hierarchy:
•
•
•
1.9.3.795.
1 – free access to observe the various displays and menus.
2 – technician password for parameter and the system
changes/operation.
3 – OEM password for manufacturer system changes.
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To eliminate irregular use and facilitate planned changes a password
protocol should be maintained.
Embedded critical system software changes should only be
undertaken by the OEM. Planned software changes should be
agreed with OEM and include testing and commissioning of the
system.
The construction layout and design of the system displays should
clearly differentiate between safety and operational information.
The PLC system should record and store PRS data for several
support cycles and include a fault log. Memory capacity should be
commensurate with the system complexity and retain and restore
data in the event of supply interruptions.
11.4 Data logging system
The PLC should be connected to the mine data network by a
dedicated facility, the face switchgear, an integrated face
management package or other medium.
Data connection, protocol and system software should interface with
high speed fibre optic systems to transmit both PRS static and
dynamic information to aid and improve operational performance
and early detection of safety critical problems or events.
Data transmitted from the PRS PLC should interface with the surface
network systems improving face performance monitoring and
diagnostics.
This information is typically presented using
appropriate screen mimics of the PRS system rather than by the use
of coded systems.
A record of the data transmitted to surface should be retained and
stored using a stable medium, having the capacity to store an
appropriate historical log; routine replication should be undertaken.
PRS system software and architecture enables automatic generation
of reports for analysis of system performance for both safety and
operational requirements.
The safety related information logs should include any:
•
•
•
1.9.3.795.
operation of the electro-hydraulic safety (dump) valve
operations of any electro-hydraulic safety (dump) valve
override facility
operation of any emergency stop
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•
•
•
•
•
•
•
•
failure of the electro-hydraulic safety (dump) valve to
operate on an emergency stop
detected system fault configured to trigger a electrohydraulic safety (dump) valve operation
failure of the electro-hydraulic safety (dump) valve to
operate
any support operation function, without an associated
manual or automated command
initiation of any automated sequence
cessation of an automated sequence
manually requested support commands
position of the coal cutting machine.
These events, and any PRS control unit commands that have been
manually or automatically generated, including any system fault
detection, should be identified, endorsed with an accurate time and
date stamp, and recorded.
Self diagnostics or supervisory programmes (watchdog) to alert
users to status and stability changes should be an integral part of
the PRS system and give early warning of degradation in the
transmission system.
Secure remote access to the data system facilitates OEM expert
assistance to proactively and reactively view available data and
allow appropriate changes to software via a data download.
The security and operation of this practice should be controlled and
covered by specific rules. Commissioning should include areas
affected by the software change.
11.5 System connection integrity
Electronic circuits can be easily damaged by some insulation test
equipment and OEM procedures for insulation and continuity testing
should be adhered to.
During assembly incremental testing of the system should be
undertaken and a record of results maintained to ensure any
degradation of the system is apparent during routine maintenance,
or when fault finding. Any test results should be compared against
OEM recommended parameters.
11.6 Hydraulic flow/pressure monitoring
Variable speed drive motors and pump systems provide increased
performance by negating transient peaks in fluid delivery and are
preferential to conventional fixed speed systems.
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System integrity is verified by pressure and flow monitoring.
Return line monitoring should be installed close to the face and at
intervals along the face line to determine levels of leakage on the
system when operations are idle, and the return line pressure under
operational conditions. Monitoring enables rapid identification of
loss of containment.
Systems may include restart timers to initiate smooth recharge of
the hydraulic system following pressure loss and should be
configured with the minimum time to afford the greatest level of
protection.
11.7 Filtration & electronic monitoring
Filtration monitoring should be provided on the pumping station
and/or power packs and on both the pressure and return filters.
To facilitate routine filter element changes, systems with
replaceable filter elements should include at least two units to allow
easy change over. These types of systems should be equipped with
pressure differential monitoring on the filter system, to give early
impending blockage alert.
Automated systems should be installed in preference to simple
manual replaceable element types. These can be configured to
automatically change between units on detection of a pressure rise
across the filter and purge the blocking element, or can be
configured to change over and purge on a cyclic basis.
11.8 Oil mixture electronic monitoring
On line continuous monitoring of the fluid condition should be
installed to facilitate routine testing of the mixture as part of the
system management.
11.9 Installation
The installation of PRS may take place without the electronic control
system being installed at that time and utilising a temporary
hydraulic supply; to remove the hydraulic pressure from the PRS a
separate emergency stop system must be made available
throughout installation.
11.10 Commissioning
PRS installations must be comprehensively commissioned. A written
log of all checks undertaken, will determine if the equipment has
been installed in line with the OEM guidelines and installation
drawings. The log should detail verification of system configuration
to ensure that only required system options are enabled.
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This log should form part of the commissioning system to confirm
that all safety critical equipment is operational and functioning in
accordance with design parameters.
Commissioning commences as PRS are being installed. The function
of the individual PRS stop button should be verified prior to the
electronic control scheme being initiated to operate the PRS
hydraulics.
Proprietary test devices used to prove the functions of individual
PRS control units, supplied by the OEM, should be deployed prior to
connecting the control unit to the PRS.
The completed commissioning document should record any defects
identified on the system and corrective actions taken and
documented in line with the mines planned preventative
maintenance (PPM) scheme.
11.11 Salvage
PRS salvage is a high risk activity and must be systematically
undertaken in accordance with an approved methodology including
safe systems of work and risk assessments. Personnel assigned to
such work should be trained and competent to carry out the task.
The salvage of PRS may take place without the benefit of the
electronic control system and utilising a temporary hydraulic supply;
to remove the hydraulic pressure from the PRS a separate
emergency stop system must be made available throughout the
face line during salvage.
Operation of the in support valves will be required to remove the
PRS. The operation of these valves must always be carried out
from a safe area outside of the high risk zone using a hand held
remote control supplied by the OEM.
Further guidance can be found at:
Mineral Products Qualifications Council - NOS
Guidance on the design, installation and use of free-standing support
systems (including powered supports) in coal mines
Guidance on the support of salvage faces in coal mines
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