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Piston and Plunger Pump Fault Diagnosis

Below is a guide given on piston and plunger pump fault diagnosis. 

Problem

Possible Cause

Remedy

Low Pressure

Worn Nozzle

Check nozzle for wear. Do not adjust regulating valve as can lead to pump damage.

Air Leak

Check suction and discharge pipework for leaks. Use   bonding sealant for connections where possible

Pressure Gauge

Gauge could be worn, or have particle ingress.

Relief Valve / Regulator Issue

Check settings cover system performance. If the system is outside of the range the valves will not function correctly.

Check for ingress of solids.
Check internal parts and piston stems. Reset Primary valve and relief valve.

Seats or Valves Worn

Replace as required

Suction Filter Clogged

Clear Suction Strainer

Insufficient NPSH Available

Suction pressure is incorrect meaning the pump is cavitating. Ensure all valves are open, check the liquid temperature. To correct increased fluid in the tank, check for air ingress, remove unnecessary bends,   increase pipe diameter, install feed pump.

A flexible hose is recommended to be 3”-6” before pump inlet.

Leakage

Check pipework connections

Belt

Check belt teeth, belt tension and belt type

Noisy Pump

Knocking Sound

Worn bearings or loose connecting rods. Service drive end as soon as possible.

Suction Sound

NPSH requirements are not being met.
  Ensure all valves are open, check the liquid temperature. To correct increased fluid in the tank, check for air ingress, remove unnecessary bends, increase pipe diameter, reduce fluid temperature, install feed pump.

Screeching Sound

Belt slippage. Check belt tension & belt wear.

Oil Leak

Worn Crankcase Oil Seals

Replace more frequently when bearings and crankshaft   oil seals are replaced

Worn Crankshaft Oil Seals

Oil contaminated. Ensure seals are replaced with   bearing replacement

Bearing Wear

Bearings can be worn by crankcase oil. Seal and packing wear results in liquid traveling along plunger rod allowing oil and water mix. Replace bearing as soon as oil leak is noticed.

Plunger or Piston Wear

Replace plunger and pistons. Increase frequency of seal   service to reduce plunger or piston wear

Drain Plug / Oil Gauge Leaking

Check tightness. Ensure O rings are replaced on the drain   plug and oil gauge

Pulsation

Insufficient NPSH Available

Suction pressure is the incorrect meaning pump is cavitating. Ensure all valves are open, check the liquid temperature. To correct increased fluid in the tank, check for air ingress, remove unnecessary bends,   increase pipe diameter, reduce fluid temperature, install feed pump.

A flexible hose is recommended 3-6” at the pump inlet.

Inlet or Discharge Valves worn / sticking

Check liquid viscosity, lubricity, and presence of particles. Seal flushing may be required in between operations.

 

NPSH requirements are not being met. Check PH of liquid is between 5-9.

Discharge Pipework

Ensure flexible hose is on the inlet of the pump and pulsation dampener fitted on the discharge of the pump.

Seals or Cups

Scored Plungers

Check for Chemical wear, hard water, and abrasive particles. Increase service intervals as high wear to low and high-pressure seals can cause the male adapter to come into contact with the plunger.

Scored Cylinders or Sleeves

Cups worn causing damage to cylinders and sleeve.   Increase service interval of cups and replace cylinders and sleeves
 
 

Sleeves and rods must always be smooth otherwise they will prematurely wear any seals.


 Cups and seals should be replaced when a drop in pressure is noticed

Inlet pressure too High

Maximum inlet pressure for piston pumps is 40psi (2.75   bar) and plunger pumps is 60-70psi (4-4.8bar). K Style pumps can accept higher inlet pressures.

High Fluid Temperature

Check liquid is in line with pump handling capability.  Fluid heating may occur from prolonged operation in bypass mode.

Pump Dry Running

Check Fluid level and that NPSHR is being met. Check  inlet pipework, and filters for blockage, long suction lines, and presence of   air ingress

Seals Installed Incorrectly

Seals will not hold pressure if installed incorrectly.

 

Keep V Groove on the spring side or packings towards liquid or high-pressure side.

 

NBR or FPM cups assembly must be towards liquid or high-pressure side.

Water in Crankcase

Spraying / Air Condensation

Protect pump from direct spray with ventilated enclosure if necessary. Contaminated oil will damage bearings and other components within the drive.
 
  Change oil every 3 months or after 500 hours.

Worn Seals or V Packings

This can allow fluid to travel along the plunger rod leading to the scoring of the oil seal allowing the water and oil to mix.
 
 Increase service intervals

Water Leak

Worn Seals or V Packings

Seals wore and require replacing.


  The symptom is low pressure. Can be caused by chemical incompatibility, excessive   pressure and temperatures

Worn Sleeves or Cylinders

Increase frequency of replacement and ensure O ring on piston   do not allow water ingress which can cause further damage

Worn Adaptor

Split manifold designs of pumps have adapters within the pumps. Check O rings when servicing seals and valves and replace them as required.

Damaged Plunger

Can be caused by Thermal Shock, Chemicals or abrasives.   Worn packings can allow the male adaptor to travel along the plunger causing damage to it. Examine plunger when installing seals and replace if needed

Manifold Wear / Damage

Check chemical compatibility of fluid and any cleaning fluids used. Operation with worn seals and o rings can accelerate manifold wear. Erosion can be limited by freshwater flushing between pump use.

 

Manifolds can be damaged by overpressure which may be caused by high inlet pressure, relief valve or regulating valve failure or blockage within the pump.

 

Ensure an external relief valve is installed in the system with an internal relief valve and regulating valve.
 
 
  If the pump is to be stored for long periods, ensure the pump is drained and filled with 50% water and glycol mix.

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