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Disc Filters –- Manual & Automatic
FILTRATION MODULE
SECTION 2
DISC FILTERS – MANUAL & AUTOMATIC
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Disc Filters –- Manual & Automatic
Table of Contents
Table of Contents ......................................................................................................................... 2
1 Introduction ........................................................................................................................... 3
2 Objectives ............................................................................................................................. 3
3 Definitions and Materials ....................................................................................................... 3
3.1 Definitions .......................................................................................................................... 3
3.2 Materials ............................................................................................................................ 4
4 Disc Filtration – The Concept ................................................................................................ 5
5 Manual Disc Filters................................................................................................................ 6
5.1 Arkal Small Filters .............................................................................................................. 6
5.2 Arkal Large Filters ............................................................................................................. 7
5.3 Manual Batteries................................................................................................................ 8
6 Automatic Filters ................................................................................................................. 10
6.1 Automatic Flushing Batteries ........................................................................................... 10
6.2 Spinklin Filters ................................................................................................................. 10
7 Selection and Design .......................................................................................................... 16
7.1 Arkal Manual Disc filters .................................................................................................. 17
7.2 Arkal Automatic Spin Klin filters ....................................................................................... 17
7.3 General notes .................................................................................................................. 18
8 Installation and Operation ................................................................................................... 20
9 Maintenance........................................................................................................................ 22
9 Summary and Conclusion ................................................................................................... 25
11 Questions ............................................................................................................................ 26
11.1 Beginner....................................................................................................................... 26
11.2 Intermediate ................................................................................................................. 27
11.3 Advanced ..................................................................................................................... 28
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1
Disc Filters –- Manual & Automatic
Introduction
Disc filters have been available for agricultural use since the early 80’s and have proven to be
very popular due their reliability, user friendliness and cost effectiveness. Since Arkal pioneered
the way for Disc filtration many have followed – take a look today at the copies available from
manufacturers all over the world. They say that imitation is the best form of flattery!
Advances in materials, design and experience gained has opened up further the applications
where disc filtration can be used.
2
Objectives
The objectives of this Section are
 Summarize the different Disc filters and filtration systems commonly used
 To provide a working knowledge of disc filtration in Agricultural applications
 To present an overview on the types of filter applications and selection of the same
 To ensure a good understanding of the above subjects
 Mention other related subjects which will be covered in other Sections
3
Definitions and Materials
3.1
Definitions
Grooved filter rings
are 3 dimensional colour coded filter elements, made of
polypropylene, and stacked one upon another to provide a filter
element of reduced dimension but with high volume and surface area
characteristics.
Groove design
the number of grooves in each ring is determined by the
circumference of the inner diameter divided by the mesh. As the
grooves need to be parallel – the groove ridges become wider as
they advance to the outer circumference of the ring.
Filtering surface
the grooved ring is a disc-shaped geometrical body. The area
between the outer and inner diameter of the ring is divided by
hundreds of grooves, their number depending on the mesh size.
Grooves are inclined at an angle (tangentially) to the the geometrical
centre of the ring. On each side of the ring grooves are inclined at the
same angle, thus creating a “criss-cross” design when put one atop
the other.
Filtering degree
this is defined as mesh or microns, depending on two factors
1 The number of grooves per ring
2 The depth of these grooves.
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A coarse ring filter element will contain relatively few grooves with an
increased depth of flow path, while a fine meshed filter element will
have numerous shallow grooves.
Filter ring compression
Arkal filters have 3 types of ring compression, depending on the
model of filter
1 Spring – used in small filters
2 Tightening nut – for larger filters
3 Hydraulic pressure – for automatic Spinklin® units
Effective filtering area
the total filtering area/volume is considerably larger than the inlet flow
area of the filter body – therefore head losses will only occur when
clogging has reached an advanced stage.
Air assist flushing
compressed air is employed along with clean filtered water to enable
“aerosol” cleaning of the disc elements that is short in duration and
intense in nature. See later for detail.
Dwell time
with automatic units and multiple filters, the “dwell time” is the interval
between the termination of operation of one back wash valve
solenoid and the commencement of operation of the next. The dwell
time helps to prevent more than one back wash valve activating at a
time, due to delays in the hydraulic command circuits.
3.2
Materials
Filter bodies and covers
Reinforced polyamide, reinforced polyester and
anodised aluminium
“O” Rings and Seals
Nitrile rubber and EPDM
Springs, clamps and bolts/screws
Stainless steel
Disc elements
in Grooved disc style filters are made of polypropylene
with the
Spines
being Acetal and/or reinforced polyamide
Valves
are usually metallic made of bronze, but plastic is
becoming more widely accepted and used.
Usually the manufacturer’s specifications will detail the materials used in the construction.
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4
Disc Filters –- Manual & Automatic
Disc Filtration – The Concept
Disc and Gravel filters would be the most widely used filters in Agricultural applications today.
Because they offer “Depth or Volume” filtration a level of security and comfort is provided that
screen filters cannot. In most instances disc filters can replace gravel filters but due to the
conservative nature of people and a large group of traditionalists, these people prefer to stick
with what they are comfortable with. Because of their light weight, plastic construction disc filters
are easy to handle, install and operate under more corrosive conditions than metallic filters.
Growers like the fact that the discs themselves have a very long life and in many instances do
not need replacing. See Figure 1 below. The same can not be said for screens and sometimes
gravel.
Disc filters are often used as back-up filters on gravel systems, not so much to provide “extra”
filtering but rather to capture any media that may ex-filtrate the mushroom diffusers. (Refer
Section 5 “Gravel Filters – Agricultural”)
Cross section of a
grooved disc –
grooves are on
both surfaces
Figure 1
The excellent filtration obtained through compressed grooved plastic discs is the outcome of a
combination of surface filtration and in-depth filtration, resulting in high precision filtration and
high efficiency.
A revolutionary back washing process adds to the outstanding qualities of the automatic SpinKlin filter – covered in detail later.
The solids retained on the filter accumulate at the intersections between the grooved faces
of each pair of adjacent discs (see Figure 2 below). There is an angle between the grooves of
the "upper" disc and those of the "lower" one. The number of intersections on each groove
varies between 12 and 32, depending on filtration grade. These intersections form larger
cavities, a fact which creates flow turbulence due to the uneven path, with a high probability that
solid particles will be trapped at the next groove-to-face intersection. Furthermore, the
turbulence in the varying paths and the large number of intersections create a situation in which
the particles are eventually trapped, even if some of them were able to escape the first
intersections.
The back washing process of the Arkal Spin Klin filter is characterized by the following features
 Low adhesion between the plastic discs and the solid particles, due to repelling forces
between them (opposed electrostatic polarity).
 Loosening of the discs during back washing and their ability to spin at high speed created by
strong multi-jet sprays.
 Full control of flushing liquid volume, resulting in low consumption.
 Dirt removal using positive rotational and drag forces. No suction forces.
 The only moving parts are the spinning discs which are constantly lubricated by the flushing
liquid.
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This revolutionary back washing process guarantees the full restoration of the initial pressure
differential after back washing is completed.
The Arkal Spin Klin filters are the only filters in which filtration performance does not change as a
result of increasing pressure differential but remains absolutely constant.
Figure 2
Changing shapes of disc
intersections moving
from the outside to the
inside of the disc stack
The creation of many shapes and passages provides a “statistical process” for the removal of
solids., as mentioned in Section 1 of this “Filtration Module”.
5
Manual Disc Filters
5.1
Arkal Small Filters
The Arkal family of small filters consist of:
 20mm
With and without tap
This is an oblique filter with 2 x 20mm BSP male
connections. A shut off valve is an option on the “Filtap”
model. The filter element consists of grooved rings, mounted
on a spine, forming a cylindrical filter body. The rings are
compressed together by a spring seated at the bottom of the
filter body. Direction of water flow is “Out – In”. The filter
cover is a “screw-on” type, locking in a choice of 4 filtering
degrees. This unit has a high resistance to chemicals and
fertilisers. Refer Figure 3.
 25mm
This is a “T” shaped filter available in a short (standard)
and long (optional) version. Construction is similar to
20mm unit above. The 25mm and larger models have
pressure reading check points to measure the PD, during
flow conditions. This eliminates the need to open the unit
to inspect if it is dirty. Refer Figure 4.
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Figure 3
Pressure check points
Figure 4
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Disc Filters –- Manual & Automatic
 40mm
A “T” shaped filter with increased filtration capacity – an
optional ¼” BSP valve is available for the bottom, to drain
sediments and to release pressure. Again this can come in
a long (standard) or short (optional) configuration.
 50mm
Two models being the Dual and Super”P”. The Dual offers
both angle and in-line BSP male connections (standard).
Figure 5
The Super “P” offers superior filtration due to the
tangential entry and cyclonic effect – only available as
angle option, with BSP male connections as standard. The
filter cover is secured to the filter body by a Heavy duty SS
clamp with an “over-centre” locking action. No tools are
required to open it. Again, a ½” drain valve is offered as an
option. The filter body and cover have plugged ½” BSP
ports which are useful for adding valves – for air
release/vacuum breaking and water/chemical/fertiliser Optional drain valve
passage. 6 filtration degrees offered. Refer Figure 5
5.2
Arkal Large Filters
The Arkal family of large filters comprise:
 80mm Twin
This in-line unit has double the capacity of the 50mm Dual
and Super “P”, being made up of two 50mm elements. The
connections are Victaulic™ with Quik Flange™ loose flange
adaptors. Refer to Figure 4. BSP male threads are available
upon request. This has the distinction of being the first 80mm
filter constructed of plastic.
 80mm and 100mm Angle
For medium to higher flows these units are ideally suited for
farm irrigation systems and as a secondary “check filter”. The
angle design offers low head loss and user friendly set up to
be close coupled with angle field valves. Standard equipment
is the 20mm ball valve and 20mm plugged cover for addition
of other valves. The high solid retention capability means
long term operation before cleaning is required. Victaulic™
and Quik Flange™ connections are standard.
Refer to Figure 7.
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Figure 3
Figure 6
Quik Flange™
connections
Figure 7
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 100mm Double Vee
This has double the dirt holding capacity of the 80mm and 100mm Angle filter, being made up of
two of these elements. Victaulic™ and Quik Flange™ connections are standard – with an in-line
flow passage. It is the largest plastic manufactured disc filter available on the market.
Refer Figure 8 below
SS Clamp
Figure 8
Victaulic grooved connection
5.3
Manual Batteries
For high flows that do not require automation, or where the water quality is constant a suitable
solution could be the Manual batteries. The Arkal range offers the Angle or Double Vee
configurations. It should be noted that these can be automated at a later date by retrofitting
suitable back wash valves, solenoids, command accessories and backwash manifolding.
Figure 9
Arkal 3 x 3” Angle battery
(Manual)
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Angle Filter Batteries
Refer to Figure 9 above. The 80mm model filters are standard.
Typically the unit will be fitted with a
 Pressure gauge on a 3 way Sagiv valve
 Air valve (dual purpose)
 Inlet and Outlet manifold
 Victaulic connections
Options are
 Butterfly valves to isolate each filter, being 2 per filter – this allows any individual filter to be
isolated and cleaned during flow.
 Diaphragm backwash valves with no control, for semi-automatic operation. Controllers etc
can be retrofitted, as required
Vee Batteries
The concept is the same as above, except using the 100mm Vee filter instead of the 80mm
Angle. Refer Figure 9a below
Pressure gauge
mounted on 3
way Sagiv valve
Victaulic
connection
OUT
Figure 9a
IN
Command
water filter
4” Back wash
valve
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6
Automatic Filters
6.1
Automatic Flushing Batteries
These are the automatic versions of the 80mm Angle and 100mm Vee batteries described
above. Refer Figure 10 below
Figure 10
Arkal 3 x 3 angle filter battery (Automatic)
Unit comes complete, flange to flange with Air valve,
Pressure Gauge, Back wash valves and manifold, command
water filter, Back wash controller ie ready to plug in.
6.2
Spinklin Filters
Spinklin filters come in 3 different modules
1) 2” or 50mm module
The filter from outside appearance resembles a 2” Super “P” - the connections are 2” BSP or
grooved victaulic, depending on the application. The smallest automatic unit on offer is a 2”
Compact stand alone. Above that the 2” modules can be joined to form batteries with 2 or more
filters. Each module contains 1 spine assembly. The 2” modules are used for lower flows.
2) 3” or 80mm module
These are used in the applications requiring higher flows. For example a 3 x 3” Battery will
usually be mounted on a 6” Inlet and outlet manifold and would be described as a Netafim code
M-336-120-AC
AC control
system
Manifolded
unit
With 3
filters
Of 3”
modules
With 120
mesh rating
On a 6”
manifold
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These are the modules used in the Manifold systems described above and the Star systems.
Each 3” module contains 2 spine assemblies.
3) 4” or 100mm
These are the newest large modules developed for High flows and form the “Galaxy” systems.
Each module contains 5 spine assemblies.
The big advantage of the Spin Klin system above the manual disc systems is its ability to
effectively clean itself with minimal water and at a relatively low pressure (28m). Some gravel
filter manufacturers require 30m to backwash their systems. Refer Figure 10a below
Figure 10a
Galaxy 3 x 4” system
Description of the Back washing Process in a manifold system
In our example we will look at the 2” manifold system to explain the concept. During filtration
stage, water flows through the INLET manifold and is distributed through the 2” back wash
valves, into the 2” Spin Klin filters, passing through the filter elements, and flows out clean
through the OUTLET manifold for consumer use.
 The controller transmits a back flush pulse (as per pressure or differential time, whichever is
first).
 The electrical pulse is transmitted to the solenoid which sends a pressure pulse to the back
wash valve (converting it from filtration to back wash stage).
 The Spin Klin filter piston rises thus decompressing discs, which, in turn, facilitates efficient
cleaning.
At this stage Filter no. 1 is back washed with clean water supplied from the OUTLET manifold,
after being filtered by the other filters in the system. Refer to Figure 11 below. (This process
continues for approximately 15 seconds.) Contaminated water and impurities flow out via the
drain manifold.
On completion of the allotted back washing time, the controller releases the back wash pulse via
the solenoid, which drains the pressure from the chamber of the back wash valve - the piston
closes and recompresses the Spin Klin discs.
Filter no.1, returns to filtration stage. Back washing proceeds to Filter no. 2, as per the same
order of operations, and so forth to all other filters in the system, with intervals of some seconds
between each filter (the Dwell time).
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On completion of back washing all filters, the system returns to its initial state of filtration.
Back wash valve
An Arkal M-324-xxx–yy
battery showing one 2”
module back washing
Figure 11
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For a review of the filtration and back washing mode of the Spin Klin single spine as previously
mentioned in Section 1 “Filtration – Principles and Design” please refer to Figure 12 below
Filtration
1) Contaminated liquid from the supply source enters
the filter element
2) The hydraulic and spring loaded forces compress
the grooved discs.
3) Larger solids and algae are retained on the burst
proof filter element
4) The liquid percolates through the compressed
discs and the smaller solids are trapped in the
intersections of the grooves
5) Outflow of filtered water for irrigation
Figure 12
Back wash
1) A pulse is transmitted by a controller. The inlet is closed
and the drain is opened.
2) The tightening cylinder is withdrawn via hydraulic force
to relieve the pressure from the discs, allowing them to
rotate freely.
3) Spray nozzles driving clean water from the inside are
directed tangentially at the discs, causing them to spin
rapidly.
4) So great is the centrifugal force created by the spinning
action, plus the jets, the dirt is blown and thrown out to
atmosphere vie the drain port of the backwash valve.
Refer Figure 13 below
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Disc Filters –- Manual & Automatic
Figure 13
Exaggerated view of disc
separation and nozzles
blowing dirt out at backwash
Description of the Back washing Process in a 2” Compact system
A popular unit for low flows (8 to 20 m³/hr) is the 2” (50mm) stand alone Compact system.
Refer Figure 14 below
Figure 14
Filtration
Water flows through the inlet valve via the diverter filter and into the 2” Spin Klin where it is
cleaned. The filtered water then flows through the outlet valve to the irrigation system.
Back washing
A hydraulic command is issued from the Back wash controller, based on Time or PD, to the Inlet
valve and Outlet valve to prompt them to change the position of the ports.
1) Inlet valve closes its entrance and diverts water through the diverter filter (perforated screen
type). The drain port opens to atmosphere allowing drain water to exit.
2) Outlet valve closes its downstream port and allows the water ex the diverter filter to enter the
spine assembly to commence backwash.
After the 20 second flush period, valves revert to normal filtration mode. The diverter screen is
cleared of dirt which is then trapped on the discs, ready to be back washed at the next cycle.
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Description of the 2” Back washing valves
Let us now take a closer look at how the back wash valve operates. Refer Figure 15 below. This
shows the newer model 2” “straight through” which is common to the 2” modules – batteries and
Compact.
Figure 15
Filtration
Water flows from port A (main supply) to port B (filter connection). Port C (flushing water outlet)
is closed by the seal.
Backwashing
Command pressure is applied to the bottom side of the diaphragm through port D. The
diaphragm moves up, pulling the sealed body by the shaft. Port A is closed by the seal, thus
preventing flow to the filter. Port C is now open allowing allowing dirty back wash water to be
drained to atmosphere.
Obviously the same principles apply to the 3” and 4” backwash valves.
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Disc Filters –- Manual & Automatic
7
Selection and Design
Some of the principles of Selection and Design were covered in the previous Section “Filtration –
Principles and Design”. We assume you the reader have a general understanding of water
quality and sources.
For manual filters we tend to over design to compensate for the fact that they cannot clean
themselves and that the water quality changes over time. So as “Rule of Thumb” we might say it
is acceptable to design on a “clean flow” head loss of 1 to 1.5 m.
With automatic units we can “work” them harder and design on a higher “clean flow” head loss.
Experience certainly helps, but in the absence of that we need to remain conservative and try to
work with some objectivity and use the Tables supplied by the manufacturer.
It may be useful referring to Arkal’s definition of water quality – see below
There are three parameters which influence filtration quality:
1. Sedimentation
2. Organic Loads
3. Dissolved minerals which solidify reaction oxidation or food for bacteria.
The following chart classifies and defines quality of water. Four categories have been specified
by the letters A through to D, with A being the highest quality
A. Good Quality
 Well water which draws from a steadily flowing aquifer, from a properly maintained well, with
no presence of iron or magnesium.
B. Average Quality
 Rivers, streams, and canals which are slow flowing, or have organized sedimentation
facilities, and are found in cold climates, with a low biological growth.
 Reservoirs in a cold climate - where the pumping point is properly placed - taking into
consideration wind directions and sedimentation possibilities.
 Sewage water after effective sedimentation but without any biological treatment or with
complete biological treatment.
C. Bad Quality
 Sewage water after effective sedimentation and incomplete biological treatment.
 Rivers, streams and canals found in hot climates with a high rate of biological growth and no
chemical treatments.
 Reservoirs in a hot climate with poor placement of pumping point, considering wind direction,
with little or no sedimentation, or a relatively high soluble content that enables the
development of a high organic load.
 Well water which draws from a poor quality aquifer or collapsed well.
D. Very Bad Quality
 Rivers, streams and canals affected by flood flows and having a shortage of sedimentation
facilities.
 Reservoirs where source water is a mixture of sewage or flood water. Poor placement of
pumping point.
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 Sewage water without sedimentation especially when oxidization occurs close to the filter's
inlet
 All types of water containing a lot of dissolved materials which are solidified when exposed to
oxygen - especially when oxidization takes place inside the filters.
As can be appreciated this can be reasonably subjective, so when in doubt call for a Water
Analysis: In all selections a water analysis can be used to confirm selection.
7.1
Arkal Manual Disc filters
As can be appreciated the finer the mesh the higher the head loss and the faster dirt will be
collected in the filter element. So notice the flows mentioned in the Table 1 below will drop as the
mesh increases. This applies to “good” quality water.
Flow Rate (m³/hr) in clean Condition with a 1m Head loss
Table 1
Mesh
Micron (µ)
Colour code
Filter Model
¾”
1”
1½” Super
2” Dual
2” Super “P”
3” Twin
3” Angle
4” Angle
4” Vee
40
400
Blue
80
200
Yellow
120
130
Red
1.8
3.6
7.5
17
17
41
53
53
60
1.7
3.6
7.5
16
16
34
44
52
60
1.7
3.6
7
15
15
30
42
51
60
Mesh and Micron (µ) rating
140
200
100
55
Black
Green
1.6
3
5.5
14
14
28
36
40
50
2.4
4
8.5
8.5
18
25
28
38
600
20
Grey
3
3
10
14
14
20
7.2
Arkal Automatic Spin Klin filters
The Spin Klin automatic filters can handle heavier loads of dirt than can the manual filters due to
the fact that they clean themselves. However there is a limit to what they can do otherwise the
units may spend too much time back washing and less time filtering! Again a conservative
approach is always recommended especially with sources of water that are unknown. There is of
course no substitute for experience and if you are familiar with the quality of the source and how
it can change over time
Netafim’s recommendations for 2” and 3” modules can be found below in Table 2
Both Tables 1 and 2 can also be found in the Netafim Price Book.
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Flow rate per module (m³/hr) for different water quality and Mesh sizes
Table 2
Filter size
2” (50mm)
3” (80mm)
Quality
Bad
Average
Good
Bad
Average
Good
Mesh
40
18
20
25
27
32
36
80
17
19
24
26
31
35
120
16
18
22
22
30
34
140
13
17
20
20
28
30
200*
9
11
14
12
18
20
600*
4
5
7
7
9
11
*For 200 and 600 mesh selections always consult with Netafim Australia Pty Ltd
Notes
1. Spin Klin systems require a minimum of 280 kPa back pressure to ensure effective back
wash. This can be achieved by installing a “blocking” or pressure sustaining valve on the
downstream side of the filter, depending on the pump performance curve.
2. With problematic water and mesh ratings of 200 and 600 “air assist” or “external source back
washing” systems should be considered.
3. The above flows are on a per module basis. Eg. A flow of 32 m³/hr with 120 mesh discs in
bad quality water would require an M-224-120 unit ie. a 2 x 2” system.
4. 2” modules require 8 m³/hr to backwash, 3” modules require 16 m³/hr.
The recommended flow rates for Galaxy systems can be found in Table 3 below
Flow Rate (m³/hr) for Galaxy 4” modules
Table 3
Water Quality
40 to 120 mesh
Good
Average
Bad
Very bad
140 mesh
Good
Average
Bad
Very bad
3 units
4 units
5 units
6 units
7 units
8 units
338
285
201
123
450
380
268
164
563
475
335
205
675
570
402
246
788
665
469
287
900
760
536
328
300
225
150
99
400
300
200
132
500
375
250
165
600
450
300
198
700
525
350
231
800
600
400
264
Notes
1. Galaxy units require only 40 m³/hr per 4” module for back washing.
2. Not suitable for air assist operation
3. Smallest size unit is a 3 x 4” battery.
7.3
General notes
 Pay attention to pressure ratings! Most units are rated to 10 Bar (1000 kPa) although some
are rated to 8 Bar, namely the 4” Double Vee filter. The 2” Dual filter is rated to 12 Bar. With
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this in mind, consider positioning the filter further away from the pressure source ie. up the
hill or along the mainline where static head and friction losses will reduce the residual head to
a workable level. If this is not practicable, then correct placement of pressure relief and/or
reducing valves will assist.
 It is generally not considered sound practice to place filters on the suction side of a main
pump. The seals are not designed to handle negative pressures and if the filter blocks up
damage to the pump can result!
 Wherever possible over design slightly the capacity of the filter, and always be mindful of
possible future expansion. The modular nature of these filters allows relatively easy
expansion of units if set out properly in the first instance.
 2” and 3” Spin Klin systems can come in all plastic construction for corrosive water ie plastic
manifolds, plastic valves etc. Pressure rated to 10 Bar.
4” Galaxy module bodies are usually made of cast aluminium – they can be specially coated
or made from SS 316 for special applications.
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8
Installation and Operation
Installation of the units is generally easy and user friendly since they are relatively lightweight.
Once the selection has been made ie size of unit, auto or manual, mesh rating etc then the
decision on positioning with respect to the pump, fertiliser injector, controller and shed walls can
be made.
With the automatic units normally the following equipment is supplied as standard (on most
models)
1. Pressure gauge mounted on 3 way Sagiv ball valve, with connections to HP (upstream) and
LP (downstream) ports of the filter
2. PD Switch gauge for measuring pressure differential
3. Backwash controller (AC or DC powered)
4. Backwash valves to suit
5. Inlet and outlet manifolds (usually with Quikflange™ connections) plus backwash manifold
(with BSPT connection). A choice of manifold material exists too.
6. Airvalve (2” Dual purpose or 1” Automatic)
7. Hydraulic plumbing and electrical connections already set up
8. The units come with a Manual, spare parts etc
The above points may illustrate how easy it is to work with units these days, a far cry from
yesteryear when everything had to be built up from components. The units are generally self
standing, except in the case of the 2” Compact Spin Klin – here a stand is offered as an option.
Even so the installer should be mindful of other ancillary equipment that may be needed such as
1. Check valve – placed downstream of the filter unit especially when the pump is at a low point
in the block. This enables service work to be carried out on the filter unit.
2. Pressure relief valve – required if the pump can generate pressures in excess of the filter’s
working range
3. Pressure sustaining valve – for the filter’s benefit this valve creates back pressure at the
crucial time for the filter ie. at back washing. The valve may be activated only shortly before
and during the back wash cycle, as required. It can be activated electrically by means of
certain back wash controllers, provided a spare output is available.
With the manual filters all the extras need to be added, and drawings are available. Refer to
Figure 16 below for two options on setting up a 2” Dual filter. This model offers an inline and
angle configuration. Note how the filter bowl can be positioned on its side or upright (or hanging
down). The cover and body in this case has 20mm BSPT plugs which can accommodate valves
and hose connections. The supporting pipe work can be of steel, poly, PVC or other materials
provided it is sturdy enough to support the weight (and vibrations). It is good practice to position
the filter with plenty of room around it to facilitate cleaning and service.
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Disc Filters –- Manual & Automatic
Figure 16
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Disc Filters –- Manual & Automatic
As far as back wash waste water is concerned, peoples preferences will vary and some debate
exists as to what is best practice. Common sense should prevail here. It is not advisable to run
the back wash line so as to return the dirt close to the foot valve. In fact, it is not really good to
put the dirty water back in to the water source at all. Rather direct the water in to a pit or sump,
which can allow the solids to settle out and then perhaps the cleaner liquid can run back to the
source.
Operation of filters should be easy provided the correct selection and installation has been
carried out. A quick check list for initial start up of automatic filters follows
1.
2.
3.
4.
Make sure all connections are secure
Open valve from command water filter to solenoids
Check settings on solenoids and relays (that they are on “Auto” mode)
Adjust settings on back wash controller to
20 to 30 seconds for a flush
About 2 hours between flush cycles
About 15 seconds “dwell time”
About 5 - 7m on the DP switch gauge
5. Pressurise the system and check for leaks
6. Manually operate the solenoids/relays one at a time to check hydraulic circuits.
7. Run the controller through a “Manual” cycle to check electric and electronic circuits
8. Manually activate the DP switch gauge to check and see that it is OK.
9. Adjust the desired pressure setting on the hydraulic pressure sustaining valve (if present)
10. After Steps 6 to 9 above it should be clear whether the filter is back washing effectively or not
11. Measure Upstream and Downstream pressure to calculate DP in a “clean condition”. This will
serve as a benchmark as when to chemical clean the discs. If the DP builds up over time
after the back wash cycle with the same flow, then an acid or chlorine wash of the discs may
be required.
9
Maintenance
For each filtration system, a maintenance program should be put into place. This should include
both in-season and off-season tasks. The frequency of routine maintenance will depend on the
type of filter system and the quality of the water source.
A General Maintenance program will look something like this
Daily
 Inspect system for leaks.
Weekly
 Check head loss across system: should be 7m or less,
 Check back flush controller operates correctly on manual cycle,
 Check automatic back wash operation,
 Check operation of back wash in response to the pressure differential (PD) switch.
End of Season
 Drain filter system,
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Disc Filters –- Manual & Automatic
 Open all filters and inspect discs,
 Wash discs with high pressure water - chemical clean discs if required (see notes following
on next page),
 Check all “O”-rings for damage: replace if necessary,
 Grease all “O”-rings prior to installation using a silicon based product eg Molycote 111,
 Pressurise system and check for leaks,
 Trigger back wash and check operation of all back wash valves,
 Check operation of pressure gauges,
 Check head loss across system under normal flow is less than 4m.
Cleaning Recommendations for Clogged Filtration Discs
Water-formed deposits may cause clogging of the filter discs. The formation of these deposits
depends on the quality of the filtered water and environmental conditions like temperature, pH,
light, duration of filtration etc
Common water-formed deposits are :
 Biological or organic deposits (mostly mucous or oily by touch, beige, brown or green in
color)
 Iron oxide (rust) or other metal oxides.
 Carbonates (white or grey deposit)
 Combinations of the above
If these deposits cannot be eliminated by pretreatment of the water, we recommend the
following cleaning procedure:
Material and equipment
 A well ventilated working place
 2 small containers (1 litre), 2 large containers (15 litre) and a stirring bar, all resistant to
chemicals, preferably of polypropylene.
 Plastic rope or hydraulic tube (8mm) to tie up the discs
 Sodium Hypochlorite (NaOCl), a strong oxidizing liquid, commercial concentration: 10%.
Oxidizes and removes organic and biological deposits
 Hydrochloric Acid (HCI) a very corrosive liquid, commercial concentration: 33%.
Dissolves and removes carbonates, iron oxide, and other deposits.
 Safety equipment: safety glasses, gloves, long pants, long sleeved shirt and shoes


ATTENTION!
WHILE WORKING WITH CHEMICALS
1. Protect yourself with the necessary safety equipment: ie safety glasses, gloves, boots,
long sleeved safety clothing.
2. Work in a well ventilated and spacious area.
3. Follow the manufacturer’s instructions
4. Ensure you have a source of fresh water close at hand
5. Always add chemicals to water, not water to chemicals
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Disc Filters –- Manual & Automatic
Cleaning Organic and Biological Deposits
 Open the filter and remove dirty discs. Hose down with clean water and remove loose dirt.
Attention
Do not open the filter while under pressure!
 Arrange the discs loosely on the plastic rope or 8mm hydraulic tube
 Prepare a Sodium Hypochlorite solution with a concentration of 5%:
1. Pour 5 litres of water into one of the large containers.
2. Add 5 liters of Sodium Hypochlorite (10%) into the water
 Soak the discs in the solution so that both sides are covered. To achieve maximum cleaning
effect, move the discs several times with a stirring stick.
Refer Figure 17 opposite
Figure 17
Chemical washing of
plastic grooved discs and
rinsing in fresh water
 Contact time with cleaning solution - up to 8 hours
 Remove the discs carefully from the solution, put them in the second large container and
rinse them very well with water before placing them back in the filter.
 We recommend flushing the cleaned discs again in the filter to ensure that all chemical
residue is removed.
The cleaning solution can be used for several sets of discs. As the cleaning activity of the
solution deteriorates, it may be necessary to soak the discs for a longer time.
Cleaning Carbonates and Iron Deposits
 Open the filter and remove dirty discs. Hose down with clean water and remove loose dirt.
 Arrange the discs loosely on the plastic rope or 8mm hydraulic tube.
 Prepare a Solution of Hydrochloric Acid with a concentration of 5%:
1. Pour 10 litres of water into one of the large containers.
2. Carefully add 2 litres of Hydrochloric Acid (33%) into the water
Soak the discs in the solution so that both sides will be covered.
NB: Carbonates react violently with hydrochloric acid (foaming, gas evolution).
To reach maximum cleaning effect, move the discs several times with a stirring stick.
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Disc Filters –- Manual & Automatic
 Contact time with cleaning solution: 1 - 8 hours.
 Remove the discs carefully from the solution and rinse them well with water before placing
them back in the filter.
 We recommend to flush the cleaned discs again in the filter to ensure the removal of all
chemical residue.
The cleaning solution can be used for several sets of discs. It may be necessary to soak the
discs for a longer period of time.
Cleaning Complex Deposits
If the composition of the deposit is not known, perform the following test:
 Take 5 discs for the test
 Soak 2 discs in a Sodium Hypochlorite Solution with a concentration of 5%.
Preparation of the solution:
Pour 300ml of water in a small container, then add 300ml of Sodium Hypochlorite (10% NaOCl).
 Soak 2 discs in a Hydrochloric Acid Solution with a concentration of 5%.
Preparation of the solution:
Pour 500ml of water in a small container, then add carefully 100ml) of Hydrochloric Acid (33%
HCl).
 Keep one disc as reference.
 Observe the cleaning process:
If one of the solutions removes all of the deposit, clean the discs in that solution according to the
instructions above
9
Summary and Conclusion
Disc filters are widely used in Agriculture and Industry. The compactness, corrosion resistance
and modularity allows long life and flexibility – many filter manufacturers have started to add disc
filters to their product range, which is a testament to their popularity and cost effectiveness.
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11
Disc Filters –- Manual & Automatic
Questions
These are divided into Beginner, Intermediate and Advanced levels
11.1
Beginner
1) What are the discs in disc filters made of?
2) How many intersections are created on a set of discs with the “criss cross” effect?
3) Which models/sizes of Arkal disc filters have pressure check points already built in?
4) Where would we use Arkal manual batteries (comprising of 3” and 4” Manual filters)?
5) How many and what modules do Spin Klin filters come in?
6) What big advantage does a Spin Klin filter have over a manual disc filter?
7) What keeps the discs compressed in a Spin Klin filter during the filtration process?
8) What flows in normal conditions is the 2” Compact Spin Klin equipped to handle?
9) How many seconds is the back wash action programmed for in the 2” Compact Spin Klin?
10) What pressure is required to back wash a Spin Klin filter?
11) How many spines are there in a 4 “Galaxy module?
12) Where and why do we sometimes use a Pressure Relief valve in a filtration system?
13) With “good” quality water at a maximum flow of 15 m³/hr what filter would we tend to work
with if we are using a manual filter and red discs?
14) If a user wishes to have 200 mesh or 600 mesh discs in their system for the first time, what
should be one of the first things you should do?
15) In which position can we install a 2” Dual manual disc filter?
16) What safety precautions must we take when using chemicals to clean filter discs?
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11.2
Disc Filters –- Manual & Automatic
Intermediate
1) On a gravel system we sometimes use disc filters as a secondary filter close coupled to the
unit. What is the disc filter’s main task in this application?
2) If we had 1” connections and needed a manual filter to handle a flow of 5.5 m³/hr in “Good”
water with 120 mesh discs how would we handle this situation?
3) What lubricates the spinning discs of a Spin Klin during back wash?
4) The 20mm BSPT plugged ports on the 2”, 3” and 4” filters are there for what reasons?
5) Which type of automatic filter needs more pressure to back wash – a gravel filter or a Spin
Klin?
6) What makes the discs “spin clean” so rapidly in a Spin Klin filter?
7) In your own words describe how a 2” Compact Spin Klin filters and backwashes?
8) In your own words describe how a 2” Back washing valve operates?
9) With a flow of 120 m³/hr in “good” quality water and a mesh requirement of 120, what would
be your Spin Klin filter selection?
10) What back wash flow and pressure requirement does an M-336-120-AC (3 x 3” Spin Klin with
120 mesh discs on a 6” manifold with AC control) have?
11) Where and when would you install a Pressure sustaining valve on a Spin Klin system?
12) What sort of pipe work should we use to connect a filter between a pump and the rising
main?
13) What is an acceptable head loss across a filter?
14) What chemicals do we commonly use to clean discs?
15) Do we pour acid into water or water in to acid?
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11.3
Disc Filters –- Manual & Automatic
Advanced
1) Why do we have to consider a “Dwell time” in an automatic filter battery
2) During the filtration process what advantage do you understand a disc filter has over a
screen filter? Please describe in your own words.
3) Where and why would you use an “Automatic Flushing Battery” instead of a Spin Klin?
4) In a 2” Compact Spin Klin how does the “diverter” filter clean itself?
5) We have a flow of 10 m³/hr with “good” quality water requiring 140 mesh filtration. We only
require a manual filter and the pressure is 105m. What is our filter selection?
6) We have a flow of 35 m³/hr in “good” water and require 200 mesh filtration with an automatic
unit – our system pressure is only 20m! Our filter is adjacent to a very big packing shed. How
do we tackle this problem?
7) Another situation calls for a filter to handle 400 m³/hr in “Bad” water using 80 mesh discs.
What is our filter selection?
8) Our water source is fairly acidic and has corroded two gravel filters already. There is no iron
in the water, and we have a moderate loading of sand and algae. We wish to protect drippers
in a system where the main duty point is 90 m³/hr at 65m – the flow rate will double next
year. What would be our filter selection?
9) Describe in your own words to a farmer how and why to go about chemical cleaning of their
discs.
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