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How an AR High Pressure Plunger Pumps Work

October 12, 2015

What a AR high pressure plunger pumps actually do is move a column of water to create a flow. Pressure results from a restriction on than column of water as is the case when the water passes through a nozzle. When we speak of a pump's ability to create a certain pressure at a certain flow, what we really mean is that the pump is capable of moving that amount of water per minute through a nozzle or restriction which actually creates the specified pressure.

In order to create a flow of water, most pumps used in the pressure cleaning industry rely on a system of valves and cylinders. The movement of a plunger or piston in the cylinder draws water through the inlet valve and the upstroke expels it through the outlet valve. The valves basically direct the water through the pump by preventing backflow.

The simplest valve design consist of a spring and poppet and is hydraulically operated by differences in pressure on either side of the valve. When pressure against the valve exceeds the ability of the spring to hold the poppet closed, the valve opens. On the opposite stroke, water itself presses the poppet against its seat, holding the valve closed and preventing flow of the water in the wrong direction.

The flow of water through the pump can be controlled in three ways, by increasing or decreasing the bore of the cylinder, by lengthening or shortening the stroke of the piston or plunger or by increasing or decreasing the speed at which the pump operates.

Types of AR High Pressure Pumps

Pumps are differentiated in several ways: whether they are driven by a crankshaft or wobble plate, how many cylinders, whether they are piston (cup) or plunger pumps, the method of crankcase lubrication, and whether they have a hollow or solid crankshaft.

The crankshaft pump, with three cylinders (tri-plex plunger pump) uses a crankshaft similar to an automobile’s crankshaft. The plungers are perpendicular to the input shaft. The wobble plate pump, also called an axial pump, replaces the crankshaft with a cam (plate) which drives the plunger. The plungers are parallel to the input shaft.


Cavitation occurs when air is literally sucked out of the water being pumped during the suction phase of the pump’s operation. If the water supply is inadequate, a vacuum results creating an air bubble which then collapses or implodes against the inner surfaces of the pump. This can take small chips out of the plunger (or even crack the solid ceramic plunger). Deteriorating the efficiency and ultimate life. Cavitation can also result when water is very warm because, in low pressure situations, water can vaporize at temperatures substantially lower than the sea level boiling point of 212 degrees F.

Pump materials vary. Plunger pump cylinder heads can be made of a variety of materials including aluminum, brass or stainless steel. While aluminum is adequate for many applications, brass is best for use with soap solutions and stainless steel is generally recommended for the most severe environments. Some pumps may have cast iron heads or brass nickel plated for extra strength under high pressure conditions.

To learn how to avoid cavitation read How To Avoid Cavitation Damage.


AR pumps are all classified as a wet crankcase plunger type. The wet crankcase is similar to the arrangement for lubrications of an automobile's crankshaft. The crankshaft is submerged in oil. Wet crankcase pumps require much less frequent lubrication. Generally, manufactures recommend an oil change after the first 50 hours and 500 hours of operation then after. AR's recommended oil to use is a 30W non-detergent oil. Our service technicians recommend that the operator check the pumps oil (crankcase) after each use. This will avoid any unnecessary warranty claim or downtime for the contract cleaner.


Pumps may be mounted to several different power sources. The most common of these are gasoline engines (direct, gearbox or belt drive), electric motors (direct, coupler or belt drive). Of these options the most common mounting configuration are direct and belt drives.


As the desired pressure and flow increase, so does the amount of power required to drive a pump. Also, generally it requires a gasoline engine rated at approximately twice the horsepower of an electric motor to get the same performance out of the same pump under continuous operation.

To determine what horsepower is required to operate a pump at a desired flow and pressure, simply multiply the psi (pounds per square inch) and gpm (gallon per minute) figures you want together and divide the result by 1450 to determine the required electric motor horsepower for pumps. To roughly determine the required gasoline engine horsepower, simply multiply the figure by two.


AR high pressure plunger pumps can be operated at other than their rated or maximum volume by simply reducing the speed of operation or rpm. A simple formula can be used to determine the rpm requirements for a desired volume. Cross multiply the rated rpm by desired flow (sum) and divided by rated flow. Giving approximate rpm pump must run for desired flow.

Basic Troubleshooting:

There are several reasons for pump failure and most are generally connected with improper usage.

  1. Damage to pumps can occur to insufficient water supply or sudden increase in water temperature, both of which can cause cavitation. Additionally, over-revving the motor, which some operators try as a way to improve pump performance with more viscous liquids or with inadequate water supplies, can damage the pump.
  2. Contamination of water supply, using the pump with chemicals it is not designed for, or operation of a pump in dusty environments can also result in pump damage.
  3. Improper adjustments to the unloader valve can cause extreme high pressure spikes which can stretch a brass head or even blow it off although this would be an absolute worst case. Each AR pump is designed to obtain a hydrostatic rating four times the maximum rated working pressure. The most common symptom of an over adjusted unloader valve is a broken connecting rod (over pressurization).
  4. A very common pump problem is valve clogging due to a small piece of debris that had entered the water supply. On most AR pumps the valves are readily accessible and the offending particle can be easily removed. Often only a few valve caps need be removed to get to the unitized valve.

Proper care and good sense should make for long pump life.

Ten Series of AR High Pressure Plunger Pumps:

Wobble Plate Series: XJ, SJ, RM

Crankshaft Series: XT, XM, RK, XW, SX, SH, RS

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