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Anatomy of the Pressure Washer Water Pump
Water Pump

You’ve been using your new pressure washer for a week now; cleaning everything in sight. You are confident that the device will serve you for a long time, because the dealer emphasized that the unit you bought uses a triplex water pump--probably the best in its class—which delivers up to 5,000 pounds per square inch (PSI) pure pressure.

A pressure washer is only as good as its water pump — the heart and soul of the machine. Understanding how it works goes a long way towards proper maintenance and long service life. The designer will tell you it is an engineering marvel and highly reliable.

Any pump rated 1000 PSI and above is considered a high-pressure pump. Pumps are rated at the maximum pressure at a specified flow rate (in gallons per minute, GPM). When this flow is forced to pass a constriction in a nozzle, the desire pressure is created.

The various flow rates are created by varying the speed of the pump (RPM), the diameter of the cylinder or the stroke, which is the distance a plunger or piston travels within the cylinder.

The standard pressure washer pump today is the reciprocating plunger/piston type pump. Reciprocating means the ability to convert a circular motion, such as that of the crankshaft to linear, like the push-pull motion of the plunger or piston. The difference is that the plunger type uses static packing or seal while in the other type, the seals move back and forth together with the piston.

The major parts of a water pump are the following:

  • Adjustable pressure regulator – controls the water pressure output from the pump
  • Water inlet – where water comes in from the water supply through a hose
  • High-pressure outlet – connects to the high-pressure hose which is usually made of reinforced hard rubber
  • Unloader valve – allows the water to circulate within the pump when the spray gun is idle or controls the direction of the flow of water exiting the pump

Pressure washer pumps comprise two parts which are bolted together. These are:

(1) The crankcase which contains an oil bath for the crankshaft and the connecting rods; and
(2) The manifold, which is the section where water flows.

Cams on the crankshaft allow the reciprocating movement of the connecting rods. The plunger guides attached to the connecting rods extend through the crankcase into the cylinders of the manifold.

On the manifold are two inlet ports on the lower side and two outlet ports on the upper side.

The information supplied here will not make you a water pump expert; however, the basic understanding gained should allow you to troubleshoot the machine during those rare breakdowns if properly maintained. Look out for the occasional loose bolts, worn-out seals and the lubricating oil.

Simple cleaning and drying of your pressure washer including the water pump after each use should be observed. It will reciprocate by giving you headache-free operation for a long time.


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