There are two basic types of pressure pumps in use on pressure washers, the piston pump and the plunger pump. The piston pump is driven with the use of a belt take-off from the drive engine. The plunger pump may be driven with a belt, or a direct drive connection to an electric motor, gas or diesel engine.

A properly designed pressure unloader valve must be installed in the discharge piping. Failure to install an unloader valve could result in personal injury or damage to the pump or system.

Inlet plumbing must be at least the same diameter as the inlet port, preferable one size larger. Keep 90-degree elbows and valves to a minimum, as they add considerable flow resistance to the pumped fluid. Restrictions to the inlet plumbing cause cavitations in the pump, drastically reducing seal or valve life.

Install an inlet strainer twice the rated capacity of the pump and clean regularly. A frequent source of low pressure is foreign matter in the fluid pumped. One small particle will partially hold open a valve, several plug inlet screen or filter. If particles are abrasive, damage to seal assemblies occurs. Line strainer (filters) come in various sizes, shapes and material.

Installation of an in-line strainer with an 80 mesh screen should be mounted between the water reserve tank and pump inlet on a hot water washer. On a cold-water washer with no reserve tank, it should be mounted between pump inlet and water supply connection. They should be inspected regularly and whenever a low-pressure problem develops. The finer the screen mesh, the more protection it provides. On the down side, it also becomes plugged quicker. If it becomes plugged, removing it and washing with clean water corrects the problem.

Low discharge pressure can be a result of problems other than the pump. Some of these causes listed below may appear individually or in combination with one another:

1. Low compression in drive engine
2. Drive belts slipping
3. Unloader valve set too low
4. Unloader valve allowing excessive water to by-pass
5. Heating coil or pressure hose leaking
6. Engine RPM sets too low
7. Dirty inlet or discharge valves on the pump
8. Worn inlet or discharge valves on the pump
9. Air leak in inlet plumbing
10. Worn spray nozzle
11. Inadequate water supply to pump
12. Spray nozzle plugged
13. Undersized spray nozzle
14. Filter between pump inlet and tank outlet plugged
15. Excessively long discharge supply line
16. Worn seals or packing’s on pump
17. Water reservoir inadequate for pump demand

Occasionally particles of plumber’s tape from fittings installed in discharge manifold become lodged between discharge valve seat and discharge valve. Particles passing into and becoming lodged in the seating area of the unloader may cause low pressure at the nozzle. In addition it may cause pressure spikes, cycling of unloader or pump cavitation. Removal of discharge manifold or unloader is required to remove any particles and remedy situation.

An inlet pressure regulator should be installed when the water supply connected directly to the inlet of the pump exceeds maximum inlet pressure established by the manufacturer. It could fatigue inlet seals, resulting in leaking and loss of pressure.

To reduce pulsation and prolong pump and system component life, install a pulsation dampener in the discharge line. The new sealed version eliminates adjustments and operates from 600-3000 PSI. For higher pressures or critical control applications a re-chargeable, bladder type dampener may be required.

Exceeding maximum RPMs of pump for an extended time places stress on both the drive end and wet end of the pump. It may escalate the wear of seals and packing’s, or fatigue drive end components and void the warranty. Most pumps generally tolerate fluctuations of 10% or less. Approval from the manufacturer is recommended for optimum performance and warranty coverage.

A thermo valve protects pumps from premature failure of seals, packings and cups by eliminating heat build-up in closed loop bypass systems. Automatically seats during unloader regulator pressure spikes to prevent fluid bleed. It provides high temperature protection without interruption in flow. If the temperature of the water reaches 145 degrees, it releases the hot water, which is simultaneously replaced with cold water. A thermo valve may be purchased individually, or is available as an optional with bypass hose.

A regular maintenance program extends the life of a pump and decreases downtime. For further diagnosis and maintenance on pump problems, probable causes and solutions, refer to pump manufacturer’s service manual. Follow manufacturer’s recommendations and requirements on installation specifications and instructions on pump repair and replacement of parts.