Excessive Vibration
and Noise in Pump
Vibration from the pump’s feet and the base (where the pump
rests) can cause the pump to be noisy. A
piece of old carpet or rubber between the pump’s base and equipment pad might
reduce the noise.
The bearings might be noisy due to age or high
concentrations of chemicals and heat. A leaky pump seal could damage the front
motor bearing. It is very important to
quickly repair any leaks around the pump to prevent extensive damage.
Many times a noisy pump can come from cavitation. Cavitation
has two possible causes, which are both hydraulically related. The first is that the suction piping is
undersized. If this pipe is undersized,
the amount of water the pump requires to operate properly is reduced. Increasing the pipe size or dropping the size
of the impeller can quiet the pump.
Ensure the pump is level and the suction lines are not
higher than the pump.
Other reason for excessive vibration and noise are given
below:
Foreign material in pump causing imbalance
Bent shaft
Pump cavitation due to vaporization in inlet line
Pump over or under rated capacity
Coupling misalignment
Damaged components: impeller, shaft, packing, coupling
Loose components, valves, guards, brackets
Piping inadequately supported
Suction lift too high
Excessive Wear of pump parts
Wear of pump components is either caused by abrasives being
present in the fluid, chemical corrosion, loss of shaft support (bearing
failure), or operation at a condition for which the pump is not suitable i.e.
cavitation, excessively high temperature or high pressure. To avoid any
abrasive foreign material entering the pump, strainers or filters should be
employed wherever possible and practical.
Abrasive or corrosive action of the liquid cause wears of
pump components.
Incorrect material of construction of parts causes rapid
wear of pump components.
Poor lubrication and overloading practice causes wear of
pump parts.
Looking at the pump internal parts alone may not provide
much help in identifying the cause, thus the importance of knowing what was
occurring in the time period immediately preceding detection of the problem.
Fails to Deliver required
flow rate
Followings are reasons to cause fail to deliver required
flow rate:
Stuck foot valve
Suction lift too great
Relief, bypass, pressure valves leaking
Speed incorrect, belts slipping
Vortex in supply tank
Insufficient NPSH available.
Makeup in suction tank less than displacement of pump
Clogged suction strainer
One or more cylinders not pumping
Air leaking into pump
Broken valve springs
Capacity of booster pump less than displacement of power
pump
Internal bypass in liquid cylinder
Liquid cylinder valves, seats, piston packing, liner, rods
or plungers
Excessive power
consumption
Excessive power consumption can be caused by either mechanical
or hydraulic problems. Mechanical causes include imminent bearing failure, pumping
elements rubbing which can lead to a pump seizure and poor shaft alignments.
Too high viscosity can result in the motor overloading.
Other reason for excessive power consumptions are given
below:
Rotating element binding from misalignment
Specific gravity or viscosity of liquid pumped is too high
Speed too high
Discharge pressure higher than calculated
Electrical or mechanical defect in submerged motor
Higher fluid viscosity than specified
Improperly adjusted packing gland (too tight) causing drag
Incorrect lubrication of driver
Mechanical defects (shaft bent, rotating element binds) on
shaft
Pump running too fast
Stuffing boxes too tight, wearing rings worn
For a rotary lobe pump too high discharge pressure can cause
the motor to overload.
For a centrifugal
pump too high capacity (too low discharge pressure) can cause the motor to
overload.
Insufficient Pressure
Cavitation is caused by
insufficient system inlet pressure to the pump. This can be caused by an inlet
system restriction, excessive fluid viscosity or excessive pump speed. Inlet restrictions
can include dirty or clogged inlet strainers, debris floating in the fluid
supply that covers the inlet piping intake, or rags. If the fluid is cooler
than design temperature, its viscosity may be too high causing excessive friction
in the inlet piping system. Cavitation is frequently accompanied by noise, vibration
and significant increase in discharge pressure pulsation. If a pump is allowed
to cavitate over long periods this will cause damage to the pump components.
Reasons for insufficient pressure
are given below:
Impeller installed backwards
Impeller speed too low
Leaking joints (well application)
Mechanical defects: wearing rings
worn;
Impeller diameter too small
Air or gas in liquid
Excessive lift on rotor element
System head lower than anticipated
Fluid supply exhausted
Fluid vaporizes in inlet line,
fluid may be overheated
Wrong direction of rotation
Loss of Prime
Air leaks developed in suction
line
Insufficient Discharge
Insufficient/Low discharge
pressure can only be caused by loss of flow. Pump discharge pressure is caused
only by the system’s resistance to the flow provided by the pump. Either the
pump is not providing the flow expected or the system is not offering the
expected resistance to that flow. It is possible that flow is being restricted
into the pump (cavitation), usually accompanied by noise and vibration, the
pump is not producing its rated flow (pump worn or damaged), or the pump flow
is bypassing rather than being delivered into the system as intended.
Reasons for insufficient discharge
are given below:
End of inlet line not sufficiently
submerged causing eddies
Excessive lift on rotor element
Speed too low, motor may be wired
improperly or cavitating
Impeller installed backwards
Insufficient NPSHa
Impeller partially plugged
Air leaks in suction or stuffing
boxes and air entry to pump
Bypass valve partially open
damaged
Foot valve of suction opening not
submerged enough
Air leak in inlet line or packing
Wrong direction rotation
Excessive power Consumption
Impeller loose on shaft
Leaking joints
Mechanical defects (wearing rings
worn, impeller)
Net inlet pressure too low
overloaded
Partial air blockage suction or
casing
Strainer partially clogged or of
insufficient area
Suction or discharge valve(s)
partially closed
Loss of Suction Following Period of Satisfactory Operation
Loss of suction can be minor,
causing little short-term damage or sufficiently major to cause catastrophic
damage. Loss of suction means fluid is not reaching the pumping elements or not
reaching them at a sufficiently high pressure to keep the fluid being pumped in
a fluid state. Loss of suction can be interpreted as the inability to prime, cavitation
or a gas content problem.
Reason for loss of suction after
period of satisfactory operation:
Leaky suction line
Air or gas in liquid
Suction lifts too high or
insufficient NPSHa
Water seal plugged
Casing gasket defective
Clogging of strainer
No Discharge
Reason for no discharge in pump is
given below:
Suction lift too great
Packing Failure
Valves closed or obstruction in
inlet or outlet line
End of inlet pipe not submerged in
fluid
Foot valve stuck
Pump damaged during installation
Pump not primed
Wrong direction of rotation
Not enough liquid
Delivery hose punctured or blocked
Discharge head too high
Speed too low
Improper installation
Impeller excessively worn
Incorrect engine speed
Mechanical seal drawing air into
pump
Broken line shaft or coupling
Bypass valve open
Impeller completely plugged
Impeller installed backwards
Impeller loose on shaft
Loose coupling, broken shaft,
failed pump
Pump badly worn
Strainer clogged
Suction lift higher than that for
which pump is designed
System head too high
Worn or oversized stuffing box
bushings
Suction inlet or strainer blocked
Improper or inadequate lubrication
Improper packing selection
Packing too tight
Pump leaking at seal housing
Mechanical seal damaged or worn. Apart
from mis-selection and poor servicing, seal leakage can be due to pump
cavitation, too high discharge pressure, being allowed to run dry and
unexpected solids in the fluid.
Mechanical seals fitted to centrifugal,
rotary lobe and liquid ring pumps can be seen as the weakest point for any pump
leakage and special care should be taken to ensure the correct seal for the
application is installed i.e. mounting attitude; seal face combination and
elastomer selection.
Pump takes excessive power
Engine speed too high
Obstruction between impeller and
casing
Viscosity and / or SG of liquid
being pumped too high
Pump overheating
Cause of pump overheating is given
below:
Engine speed too high
Obstruction in pump
casing/impeller
Impeller damaged
Cavitation due to excessive
suction lift