Below is a guide given on piston and plunger pump fault diagnosis.
Check nozzle for wear. Do not adjust regulating valve as can lead to pump damage.
Check suction and discharge pipework for leaks. Use bonding sealant for connections where possible
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.
Check pipework connections
Check belt teeth, belt tension and belt type
Worn bearings or loose connecting rods. Service drive end as soon as possible.
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.
Belt slippage. Check belt tension & belt wear.
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
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
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.
Ensure flexible hose is on the inlet of the pump and pulsation dampener fitted on the discharge of the pump.
Seals or Cups
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
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
Split manifold designs of pumps have adapters within the pumps. Check O rings when servicing seals and valves and replace them as required.
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.
Positive Displacement Pump Repair
As the leading European supplier of positive displacement pumps we are experts in their repair