Pumps and Pumping Theory
Pump
PUMPS
Based on
PUMPING ACTION
Based on
ORIENTATION
VERTICAL
POSTIVE
DISPLACEMENT
DYNAMIC
RECIPROCATING
DIAPHRAGM
GEAR
SCREW
Electric
Motor
Steam
Turbine
Based on TYPE OF
SHAFT SEALING
GLAND
PACKING
HORIZONTAL
CENTRIFUGAL
ROTARY
Based on NO.
OF STAGES
SINGLE STAGE
MULTI STAGE
AXIAL
Fixed
Speed
Variable
speed
PISTON/PLUNGER
ENGINE ROOM
Steam Reciprocating
Mechanism
MECHANICAL
SEAL
Based on Speed
Variability
Based on
PORTABILITY
PORTABLE (Wilden,
Oil Transfer etc.)
CARGO SPACE
Diesel
Engine
Based on
Location
FIXED
Based on
Prime
mover
OTHER SPACES
Compressed
Air
Hydraulic
Motor
Classification of Pumps
Based on Drive, pumps may be
- Electric Motor Driven
- Steam Turbine Driven
- Steam Reciprocating Mechanism Driven
- Compressed Air Driven
- Diesel Engine Driven
- Hydraulic Motor Driven
Rotodynamic & Positive Displacement
Pumps
Static & Dynamic Head
Pump Performance Characterstics
Slip
Centrifugal Pump Performance Curve
Frictional Losses in Centrifugal Pumps
Actual Performance Curve
Losses in Centrifugal Pump
Centrifugal pump characteristics at
constant speed
Centrifugal pump characteristics
• The effects of throttling discharge valve on discharge pressure, efficiency,
power and npsh can be seen. The throughput of a centrifugal pump alters
with discharge head or back pressure. A slow rate of discharge by a
centrifugal cargo pump can be, explained by increasing head due to a
restricted or very long discharge pipe, high viscosity of the liquid,
discharge to a storage tank sited at a high level or even a partly open valve
on the discharge line. Depending on application, centrifugal pumps can be
designed with relatively flat H/Q curves or if required the curve can be
steep to give a relatively large shut-off head. We can see from the power
curve, that minimum power is consumed by the pump when there is no
flow and when the discharge head is at its highest. This equates to the
discharge valve being closed. Because maximum pressure with the
discharge closed is only moderately above working pressure, a relief valve
is not necessary for a centrifugal pump. It will be noticed that the
efficiency curve for the pump is convex which means that maximum
efficiency occurs at a point somewhere between maximum and minimum
discharge head and throughput conditions.
Losses in Positive Displacement Pump
Rotodynamic pumps (or dynamic pressure
pumps)
• In this a tangential acceleration is
imparted to the fluid. Depending
upon supply head they may
require a positive displacement
pump as a priming device. In
general they would be used for
medium to high discharge rates,
they usually are confined to low
viscosity fluids and generate only
low to moderate pressure
differentials.
Kinetic Pumps (Roto-dynamic)
Centrifugal Pumps
• Rotation of a centrifugal pump
impeller causes the liquid it
contains to move outwards from
the centre to beyond the
circumference of the impeller.
The revolving liquid is impelled by
centrifugal effect. It can only be
projected into the casing around
the periphery of the impeller if
other liquid in the casing can be
displaced. Displaced liquid in
moving from the casing to the
delivery pipe, causes flow in the
discharge side of the system.
Centrifugal Pumps
• The liquid in the impeller and casing of a centrifugal pump is
also essential to its operation. In moving out under the
influence of the centrifugal effect, it drops the pressure at the
centre, to which the suction or supply pipe delivers the liquid
to be pumped. The moving liquid acts in the same way as a
reciprocating pump piston on its suction stroke. Provided that
a centrifugal pump is filled initially with liquid and that flow is
maintained, the suction stroke action will continue. If such a
pump contains no liquid initially, it is as though an essential
part is missing.
Types of centrifugal pumps
•
The volute pump is so called because of the shape of the casing. The object of the
volute is gradually to reduce the velocity of the water after it leaves the impeller,
and so convert part of its kinetic energy to pressure energy. For general purposes
the volute pump is commonly used. In some pumps, diffusers are used. These
consist of a ring of stationary guide vanes surrounding the impeller, the passage
through the diffuser vanes is designed to change some of the velocity energy in
the fluid to pressure energy. The design is used for high pressure as in multi-stage
boiler feed pumps. The diffuser passages are able to convert a larger amount of
the kinetic energy of the liquid as it leaves the impeller into pressure energy. A
single stage diffuser pump is able to deliver to a much greater head than an
ordinary volute pump. The regenerative pump is used where a relatively high
pressure and small capacity are required.
Centrifugal pump characteristics at
constant speed
Centrifugal pump characteristics
• The effects of throttling discharge valve on discharge pressure, efficiency,
power and npsh can be seen. The throughput of a centrifugal pump alters
with discharge head or back pressure. A slow rate of discharge by a
centrifugal cargo pump can be, explained by increasing head due to a
restricted or very long discharge pipe, high viscosity of the liquid,
discharge to a storage tank sited at a high level or even a partly open valve
on the discharge line. Depending on application, centrifugal pumps can be
designed with relatively flat H/Q curves or if required the curve can be
steep to give a relatively large shut-off head. We can see from the power
curve, that minimum power is consumed by the pump when there is no
flow and when the discharge head is at its highest. This equates to the
discharge valve being closed. Because maximum pressure with the
discharge closed is only moderately above working pressure, a relief valve
is not necessary for a centrifugal pump. It will be noticed that the
efficiency curve for the pump is convex which means that maximum
efficiency occurs at a point somewhere between maximum and minimum
discharge head and throughput conditions.
Variable speed centrifugal pump
•
1.
2.
3.
In the case of a variable speed pump:
Head varies as the square of the speed.
Capacity varies directly as the speed.
Power varies as the cube of the speed since
it is a function of head and capacity.
Construction of Centrifugal pumps
• Double eye
Single eye
• In single stage pumps a single impeller rotates in a casing of
spiral or volute form and in multistage pumps two or more
impellers are fitted on the same shaft. Fluid enters the
impeller axially through the eye then by centrifugal action
continues radially and discharges around the entire
circumference. In double inlet pumps fluid enters from two
sides to the impeller eye as if there were two impellers back
to back giving twice the discharge at a given head. In multistage pumps the fluid from one impeller is discharged via
suitable passages to the eye of the next impeller so that the
total head developed (or discharge pressure) is the product of
the head per stage and the number of stages, such a pump is
often used for high pressure discharge at moderate speed
(e.g. turbo-feed).
• The casing usually has the suction and discharge
branches arranged at the back so impeller and
spindle can be removed from the front without
breaking pipe joints. The number of impeller vanes is
not ‘fixed but usually there are six to ten. The volute
casing is like a divergent nozzle which is wrapped
around the impeller and serves two main functions
(1) it enables velocity energy to be converted into
pressure energy, the degree of conversion is
governed mainly by the degree of divergence (2) it
accommodates the gradual increase in quantity of
fluid that builds at discharge from the circumference
of the impeller.
• For the velocity to be constant the volute is made so
that cross sectional pipe area increases uniformly
from cut water to throat. With an impeller having six
vanes then the cross sectional area of volute at No. 1
vane will be 1/6th of throat area as one vane is
pumping 1/6th of the water quantity, similarly 1/3rd
at No. 2 and so on, taking vanes in turn from cut
water to throat. A common fault for repair with
these pumps is the increase of clearance due to wear
at the wearing ring (or sealing ring) faces. This allows
connection between suction and discharge so
drastically reducing efficiency. During overhaul, the
wear ring clearances are checked and if clearances
are more than recommended values, than they are
renewed.
VERTICAL, SINGLE INLET, CENTRIFUGAL
PUMP
• Marine pumps are usually
installed with the shaft
vertical and the motor
above the pump. This
positions the pump as low
as possible for the best
NPSH, takes up the least
horizontal space and leaves
the electric motor safer
from gland or other leakage
Shaft sealing
• In the smaller pumps the
shaft gland seal is by water
cooled ordinary stuffing box.
Stuffing box type glands may
be packed with soft packing.
Great care must be taken on
these packings as they are
very prone to nip and score
the shaft severely if not
properly adjusted.
Mechanical seal
• This consists of a fixed
clamp ring on the shaft
driving another ring cup,
with packing rings on to the
shaft, through driving pins.
Ring cup and rings are free
to slide along the shaft
under the action of axial
springs from the clamp ring.
The cup ring presses on to a
fixed ball ring which in turn
sits in a ball socket joint in
the back plate which bolts
to the pump casting.
Mechanical Seal
Centrifugal Pump – Theory and
Characteristics
Centrifugal pumps are generally used for movement of large volumes of
liquid at low pressures. Higher pressures can be obtained with multistaging
Centrifugal Pump – Theory and
Characteristics
Losses in Centrifugal Pump
Centrifugal Pump – Theory and
Characteristics
Net Positive Suction Head (NPSH)
Net Positive Suction Head Available
(NPSHA)
Net Positive Suction Head Required
(NPSHR)
Cavitation
NPSHA in Reciprocating Pumps
Centrifugal Pumps - Cavitation
Cavitation
Centrifugal Pumps - Priming
Centrifugal Pump - Parts
Centrifugal Pump - Parts
Centrifugal Pump - Parts
Air handling methods
• A separate pipe from the suction pipe of the main
pump is taken to a rotary air pump which is directly
driven by a friction clutch operated spindle as shown.
The rotor revolves in a special variable shaped
chamber which is supplied with fresh water from a
separate water tank attached to the air pump casing.
The discharge pressure of the pump places the air
pump in or out of operation by hydraulic pressure
clutching in/out the operating spindle of the air
pump.
WATER RING AIR VACUUM PUMP
PRINCIPLE
• As the impeller vanes pass the suction
port air is drawn in and trapped
between the water ring and the pump
shaft. This ‘slug’ of air is carried around
and delivered to the discharge port,
hence this pump is a positive
displacement type. Due to the casing
shape the water is made to flow from
and towards the rotor centre during
each revolution. The water motion is
utilised to act as suction and discharge
for the air through appropriate sets of
ports.
Axial Flow Pump
Characteristic curves for an axial flow
pump
Axial Flow Pump
• When large capacity, wide variation of low lift head
at constant speed, conditions have to be met the
horizontal or vertically arranged axial pump is the
most suitable. An axial flow pump is one in which a
screw propeller is used to create an increase in
pressure by causing an axial acceleration of liquid
within its blades. The incidental rotation imparted to
the liquid is converted into straight axial movement
by suitably shaped outlet guide vanes.
Axial Flow Pump
• Axial flow pumps are sometimes classed with centrifugal
pumps although centrifugal force plays no useful part in the
pumping action. A comparison of discharge characteristics
shows that H/Q and working efficiency characteristics for the
two pumps are quite different. Starting from the point of
normal duty, throttling of the discharge of an axial flow pump
reduces the flow but also causes a rise in pressure and power.
With the valve closed and zero discharge, the head can be
about three times greater and absorbed power about
doubled. The action of throttling to reduce throughput would
overload the electric motor and cause operation of protective
devices. If the discharge of the centrifugal pump is closed in as
previously described, the pressure rises by a moderate
amount and power demand actually drops.
Positive displacement pumps
• These are those where the volume of the pump chamber is
alternately increased to draw the liquid in (suction) and
then decreased by forcing the liquid out (delivery). This
maybe done by a reciprocating motion of a piston or
plunger within a cylinder or by a rotary motion of specially
designed vanes, gears or rotors. They do not require a
priming device, in fact they may be used as priming
devices. Positive displacement pumps must be fitted with
relief valve and pressure regulating valve to safeguard the
system. In general they would be used for small to medium
discharge rates, they can pump fluids of a wide range of
viscosity and can develop-especially in the case of the
reciprocating pump-high pressure differentials if required.
Lift Pump
• On high:
The lift pump upstroke
creates a vacuum;
water rises to fill it.
The aspiration height
doesn't exceed nine
metres.
• When attempting to raise
water by use of a vacuum
pump, the weight of the
air is insufficient to raise
the water higher than nine
metres (or 27 feet).
Reciprocating Pumps
• These types of pump operate by using a
reciprocating piston . The liquid enters a
pumping chamber via an inlet valve and
is pushed out via a outlet valve by the
action of the piston or diaphragm.
• Reciprocating pumps are generally very
efficient and are suitable for very high
heads at low flows. This type of pump is
self priming as it can draw liquid from a
level below the suction flange even if
the suction pipe is not evacuated. The
pump delivers reliable discharge flows
and is often used for metering duties
delivering accurate quantities of fluid.
Reciprocating Pump – single & double
acting
•The reciprocating pump is not
tolerant to solid particles and
delivers a highly pulsed flow. If a
smooth flow is required then the
discharge flow system has to include
additional features such as
accumulators to provide even flows.
•Reciprocating pumps designed for
delivering high pressures must
include methods for releasing
excessive fluid pressures. The
pumps should include for built in
relief valves or relief valves should
be included in the fluid circuit which
cannot be isolated from the pump.
Rotary Displacement Pumps- external
gear pump
Internal Gear Pump
• It uses two rotating gears which un-mesh at the suction side
of the pump to create voids which allow atmospheric pressure
to force fluid into the pump. The spaces between the gear
teeth transport the fluid on either side of a crescent to the
discharge side, and then the gears re-mesh to discharge the
fluid.
Lobe-pump
• A lobe-pump like a gear
pump and was the earlier
type of mechanical pumps
used for supercharging of
main engine. Now you will
find it being used as a
sewage pump.
Vane Type Pump
• A Vane Type Pump operation is based
on the principle of increasing the size of
the cavity to form a vacuum, allowing
the space to fill with the incoming
liquid, and then forcing the fluid out of
the pump under, pressure by
diminishing the volume. The sliding
vanes or blades fit into the slots in the
rotor. Ahead of the slots and in the
direction of rotation, grooves admit the
liquid being pumped by the vanes,
moving them outward with a force of
locking pressure that varies directly
with the pressure that the pump is
operating against. The grooves also
serve to break the vacuum on the
admission side. The operating cycle and
the action of centrifugal force and
hydraulic pressure hold the vanes in
contact with the casing.
Single-screw pump or mono pump
•
They consist of only one driven metal
rotor rotating within an elastomer
lined (elastic) stator. Liquid enters the
inlet and as the rotor turns within the
flexible rubber stator forming tightly
sealed cavities between the screw
and the casing and progresses
towards the discharge side of the
pump which moves the liquid toward
the outlet. A. This movement creates
a partial vacuum which draws liquid
into the pump. Pumping action starts
the instant the ROTOR turns. Liquid
acts as the lubricant between the
pumping elements. This pump
produces a constant discharge with
negligible pulsation. This type can
handle highly abrasive liquids and
can also pump liquids containing
fairly large solid particles.
Double-screw pump
• Two screws run either with intermeshing
contact or the screws are driven in phase by
timing gears and synchronized to run with
positive clearance.
Triple-screw pump
Triple-screw pump
• Triple-screw pump has three screw on parallel axis. The central screw is
power driven and drives two outer idler screws directly without external
timing gears. The centre screw is driven mechanically, through a flexible
coupling. The two outer screws are driven by the fluid pressure and act
purely as seals. The screws work in a renewable cast iron sleeve mounted
in a cast iron pump casing. Pedestal bearings at the base support the
weight of the rotors and maintain their axial position
• When the screws rotate, their close relation to each other creates pockets
in the helices. These pockets move axially and have the same effect as a
piston moving constantly in one direction. The liquid being pumped enters
the suction opening, flows through passages around the rotor housing,
and through the screws from each end, in opposed streams, toward the
center discharge. This eliminates unbalanced hydraulic thrust. These
pumps work well at high pressure and with high viscosity fluids (up to
4000 centistokes). . The screw pump is used for pumping viscous fluids,
usually lubricating, hydraulic, or fuel oil.
Hand Pump: (Semi Rotary Pump)
Diaphragm Pump (Wilden Pump)
Diaphragm Pump (Wilden Pump)
• An air valve directs pressurized
air to one of the chambers, this
pushes the diaphragm across the
chamber and fluid on the other
side of the diaphragm is forced
out. The diaphragm in the
opposite chamber is pulled
towards the centre by the
connecting rod. This creates
suction of liquid in chamber,
when the diaphragm plate
reaches the centre of the pump it
pushes across the Pilot Valve rod
diverting a pulse of air to the Air
Valve. This moves across and
diverts air to the opposite side of
the pump reversing the
operation. It also opens the air
chamber to the exhaust.
Eductor
• An eductor is a type of jet pump.
• Unlike other pumps, an Eductor
pump has no moving parts.
• It uses the Venturi effect of a
converging-diverging nozzle to
convert the pressure energy of a
motive fluid to velocity energy
which creates a low pressure zone
that draws in and entrains a
suction fluid.
• It is a device which effectively
utilizes the pressure energy in a
flowing fluid to evacuate,
entrap/suck other fluid and
discharge it to a point as needed
in a system.
Principle of Eductor
A simple eductor pump, as
illustrated, consists of a supply
line, a nozzle, a suction line, a
suction chamber, a diffuser, and a
discharge line.
• After passing through the throat
of the injector, the mixed fluid
expands and the velocity is
reduced which results in
recompressing the mixed fluids
by converting velocity energy
back into pressure energy.
• The motive fluid may be a liquid,
steam or any other gas.
• The entrained suction fluid may
be a gas, a liquid, a slurry, or a
dust-laden gas stream
Applications of Eductors
• Creating vacuum in Fresh
Water Generator
• Mixing Foam and water in
Portable Foam applicator
• Pumping put Engine Room
Bilges,, Steering Flat Bilges
and other Bilges
• Creating vacuum for
Steam Turbine System
• Stripping Cargo tanks in
Oil Tankers
• Drawing water from wells
by supplementing the
centrifugal pump
Mixing Water and Chemicals with
Eductor
1. incoming water stream is
restricted by a nozzle.
2. while the speed of the
outgoing water is decreased by
the inverted funnel shape at
the bottom of the venturi.
3. results in a vacuum in the
middle, where the chemical is
sucked into the water stream.
4. chemical flow regulated by
interchangeable metering tips.
5. water and chemical are
thoroughly mixed as they leave
the outlet.
Rotary Piston Pumps
1.
2.
3.
4.
Radial Piston Pump
Swashplate Piston Pump
Wobble Plate Pump
Bent Axis Piston Pump
Radial Piston Pump
• Radial Piston pumps include a
rotating cylinder containing
equally spaced radial pistons
arranged radial around the
cylinder centre line. A springs
pushes the pistons against the
inner surface of an encircling
stationary ring mounted eccentric
to the cylinder.The pistons draw
in fluid during half a revolution
and drive fluid out during the
other half. The greater the ring
eccentricity the longer the
pistons stroke and the more fluid
they transfer.
Swashplate pump
• Swashplate pumps have a
rotating cylinder containing
parallel pistons arranged radially
around the cylinder centre
line. A spring pushes the pistons
against a stationary swash plate
located at one end of the cylinder
, which sits at an angle to the
cylinder. The pistons draw in
fluid during half a revolution and
drive fluid out during the other
half. The greater the swashplate
angle relative to the cylinder
centre line the further the longer
the pistons stroke and the more
fluid they transfer.
Wobble Plate Pumps
• This pump includes a stationary
piston block containing a number
parallel pistons arranged radially
around the block centre(at least
five). The end of each piston is
forced against a rotating wobble
plate by springs. The wobble
plate is shaped with varying
thickness around its centre line
and thus as it rotates it causes
the pistons to reciprocate at a
fixed stroke. The pistons draw in
fluid from the cavity during half a
revolution and drive fluid out at
the rear of the pump during the
other half. The fluid flow is
controlled using non-return
valves for each piston.
Bent Axis Pump
• Bent axis piston pumps have
a rotating cylinder
containing parallel pistons
arranged radially around
the cylinder centre
line. The cylinder is driven
by an shaft which is
arranged at an angle to the
cylinder axis. the shaft
includes a flange with a
mechanical connection to
each piston. As the shaft
rotates the pistons are
made to reciprocate over a
stroke based on the relative
angle of the shaft and
cylinder.
Running Centrifugal Pumps in Series
and in Parallel
• Case 1. Suppose you are asked to discharge at
a faster rate (with more Q m3/hr) than
possible with a single pump, what do you do?
• Case 2. Suppose you find that during
discharging, that the shore tank is not
receiving the specified amount of cargo due
to increased back pressure, what do you do?
Running Centrifugal Pumps in Series
and in Parallel
• A centrifugal pump will
pump fluid at the point
where the system curve
intersects the pump
curve.
• If you need more
flexibility you can install
another pump and
operate it in either series
or parallel with the first
pump.
• For pumps in series - add
heads, for pumps in
parallel - add flowrates
Running Centrifugal Pumps in Series
• Centrifugal pumps are
connected in series if the
discharge of one pump is
connected to the suction
side of a second pump.
Two similar pumps, in
series, operate in the same
manner as a two-stage
centrifugal pump.
• Each of the pumps is
putting energy into the
pumping fluid, so the
resultant head is the sum
of the individual heads.
• There is no change in the
quantity discharged
Running Centrifugal Pumps in Series
• When two (or more)
pumps are arranged in
series, their resulting pump
performance curve is
obtained by adding
their heads at same flow
rate as indicated in the
figure below.
• If one of the pumps in
series stops, the operation
point moves along the
system resistance curve
from point 3 to point 1 the head and flow rate are
decreased.
Running Centrifugal Pumps in Series
• Centrifugal pumps in series
are used to overcome larger
system head loss than one
pump can handle alone. For
two identical pumps in
series, the head will be twice
the head of a single pump at
the same flow rate. With
constant flowrate the
combined head moves from
1 to 2. In practice the
combined head and flow
rated moved along the
system curve to 3.
• The first pump acts like a
booster pump
Series Operation of Centrifugal Pumps
• Both pumps must have the same width impeller or the
difference in capacities (GPM or Cubic meters/hour.) could
cause a cavitation problem if the first pump cannot supply
enough liquid to the second pump.
• Both pumps must run at the same speed (same reason).
• Be sure the casing of the second pump is strong enough to
resist the higher pressure. Higher strength material,
ribbing, or extra bolting may be required.
• The stuffing box of the second pump will see the discharge
pressure of the first pump. You may need a high-pressure
mechanical seal.
• Be sure both pumps are filled with liquid during start-up
and operation.
• Start the second pump after the first pump is running.
Running Centrifugal Pumps in Parallel
• Pumps are operated in
parallel when two or more
pumps are connected to a
common discharge line,
and share the same
suction conditions.
• When two or more pumps
are arranged in parallel
their resulting
performance curve is
obtained by adding their
flowrates at the same
head as indicated in the
figure.
Running Centrifugal Pumps in Parallel
• Centrifugal pumps in parallel are
used to overcome larger volume
flows than one pump can handle
alone. For two identical pumps in
parallel the flowrate will double
(moving from 1 to 2) compared to a
single pump if head is kept
constant. In practice the combined
head and volume flow moves along
the system curve as indicated from
1 to 3.
• If one of the pumps in parallel or
series stops, the operation point
moves along the system resistance
curve from point 3 to point 1 - the
head and flow rate are decreased.
Parallel Running of Centrifugal Pumps
• Both pumps must produce the same
head this usually means they must
be running at the same speed, with
the same diameter impeller.
• Two pumps in parallel will deliver
less than twice the flow rate of a
single pump in the system because
of the increased friction in the
piping.
• The shape of the system curve
determines the actual increase in
capacity. If there is additional
friction in the system from
throttling (see dotted line in the
following diagram), two pumps in
parallel may deliver only slightly
more than a single pump operating
by its self.
Parallel Running of Centrifugal Pumps
• If you run a single pump only, it will operate at a higher
flow rate (A) than if it were working in parallel with
another pump (B) because it will be operating further
out on the curve requiring increased power. The rule is
that if a pump is selected to run in parallel, be sure it
has a driver rated for single operation.
• Parallel pumps are notorious for operating at different
flows. Often a weaker pump is operating close to its
shut off point while a stronger pump is operating to the
far right of its curve and running out of NPSHA.
Operating Procedures for Positive
displacement pumps
•
•
•
•
•
•
Starting:
Precaution: Never start a displacement pump without
ensuring that all valves on the discharge line are open.
Attempt to turn the pump shaft to ensure it is not
seized.
Ensure that the cocks to the pressure gauges are in line
for indicating the pressure and not open to the
atmosphere.
Open appropriate valves on the discharge side where
the liquid has to go.
Open appropriate valves on the suction side.
On fuel or lube oil transfer pumps you will find a
manually controlled valve (bypass) to regulate pressure,
release the spring load to start the pump at low load.
Starting Procedure for Positive
displacement pumps contd.
• Start the pump and observe for any abnormal sounds, load
on the motor, or pressure build up. (stop the pump
immediately in case of any abnormality)
• If the liquid being drawn is from a distant tank below the
level of the pump, the pump will take some time to draw
the liquid. There will be a change in the running sound
when the liquid reaches the pump. If the liquid is cold the
pump is likely to make more noise.
• Observe pressure as the pump picks up liquid. Adjust
pressure regulating valve to increase the discharge pressure
to normal. Observe leakages at pump lands, valves, and
along the pipe line.
• Incase the pump is having difficulty in drawing the liquid.
Stop the pump and check suction filter. Clean if necessary.
Heat up the liquid if the temperature is low.
Operating Procedures for Positive
displacement pumps
Stopping the pump:
•
•
•
•
Stop the motor.
Shut all valves on the suction and discharge side.
Open bypass valve.
Clean the suction filter if the pump has drawn oil
from dirty tank or the last part of oil tank.
• Record operating times, pressures, soundings as
per standing instructions on board.
Operating procedures for a
Centrifugal pump
• Starting:
• Open the suction valve completely. Keep the discharge valve closed
at this stage,
• Open the air vent and if the water comes out from it, close it (pump
is now said to have been primed).
• If the pump is of the self-priming type with an attached vacuum
pump, keep the air vent closed and open the check valve on the
vacuum pump line.
• Start the motor (pump)
• When the discharge pressure has risen, open the discharge valve
gradually. (For a self-priming arrangement, close the check valve
connecting to the vacuum pump.)
• Changeover suction and discharge as required gradually.
• Monitor suction and discharge pressures, load on the motor,
vibrations, and leakages through valves and glands. If necessary ‘nip
up’ the glands.
•
Operating procedures for a
Centrifugal pump contd.
• Note 1: Starting the pump with closed discharge
valve reduces the starting current on the motor and
prevents damage to the pump parts. Since centrifugal
pump is not a positive displacement type, there is no
danger of build up of excessive pressure. Pup casing
and parts have been design to withstand maximum
pressure the pump can produce in this case.
•
• Note 2: In case the pump looses suction, prime it as
soon as possible. Avoid running the pump without
liquid even for short periods to minimise wear
between the impeller and its guide ring (wearing ring).
Operating procedures for a
Centrifugal pump contd.
• Stopping the pump:
• Incase of a pumps used for bilge or ballast line,
before stopping the pump, you must run the
pump ‘sea to sea’ for some time to flush the
pump and the pipe line of contaminated water.
• Close the discharge valve
• Stop the motor
• Close Suction valves all other valves that were
opened for use.
• Note:
Record starting and stopping times as
per ship board instructions & practices.