This article is a basic guide to understanding the components, accessories and requirements of pressure washer equipment.

All pressure washers work the same way. You need a pump to move the water at a certain flow, a coil to heat the water and a nozzle to pressurize the water. Everything else on the machine is there to make these components work the way you want them to, and to provide safety.

The frame of the machine is designed to hold all the components in a logical configuration to work easily together. It is also designed to be as compact as possible. The tanks hold the water and fuel needed to operate the equipment. The controls provide a means to turn on and off the pump, burner and detergent. They also protect the equipment and the operator.

The operation of the pressure washer is fairly simple. Water is pulled or pushed into the pump with a garden hose or float tank. From the pump, the water is forced out of a nozzle at the end of the spray gun wand at high pressure.

Typical Operation And Requirements:

Pressure
The pressure produced in a pressure washer system is the result of forcing a known volume (or flow) of water through a known size orifice (spray nozzle). Pressure is measured in pounds per square inch psi.

Flow
The flow or volume produced in a pressure washer system is determined by the speed that the pump shaft is rotated rpm. The faster the shaft is rotated, the higher the output volume. Flow or volume is measured in gallons per minute (gpm).

Theoretical Total Impact Force Cleaning Units
For many years, our industry has tried to find an alternate way of defining the amount of "real" nozzle power a pressure washer is able to deliver without simply stating the unit’s motor size or its volume and pressure. As the pressure washer industry and its marketing strategies matured, consumers were introduced to a new terminology to rate a pressure washer’s output. Our industry adopted a simplistic formula that multiplies the gallons per minute of flow times the operating pressure, and in some cases, multiplies the result by 60 (per/hr) to deliver a measurement of cleaning power. This formula was given the name: " cleaning units " (CU) or "units of cleaning power" (UCP).

While this formula was fundamentally a good idea, it did not relate properly to the true effect of a pressure washer’s water spray force that is delivered from the nozzle to the object being cleaned. Flow is not only an integral part of the nozzle output equation, but also the one with the greatest relevance. It is for this reason that the more scientifically correct method to use is the "total theoretical impact force" method. This formula (.0526 x gpm x square root of psi = Theoretical Total Impact) calculates the amount of theoretical impact force in a stream of water expressed in foot-pounds. This measure allows us to compare combinations of pressure and volume accuracy.

Theoretical Total Impact and Nozzle Angle
The above formula refers to a straight stream (0° nozzle). When a straight stream is forced into a fan shape, pressure dissipates from a slit-shaped hole at an angle of projection. This water spray now encounters much more air resistance causing the stream to break up into different sized droplets. The larger the angle of spray, the greater the separation. It is for this reason that a 40° nozzle projection, although covering more surface area at 12" from the object being cleaned will only deliver 12% of the total impact force. In effect, as the degree of stream projection increases, the impact force decreases.

Water Consumption Rate
A reduction in flow in the above calculations can reduce cleaning efficiency. This decrease in effectiveness conversely increases the demand for more cleaning time, which in turn increases water consumption. Higher flows can decrease the amount of water consumption, by increasing the impact force as well as better heat and chemical reaction properties, leading to reduce cleaning time. The physical work performed by this increased flow will more than likely decrease the cleaning time, offsetting water usage.

Inlet Filter
This is a very important component to increase system life and avoid operating problems. A 60 – 120 mesh screen filter is necessary to stop foreign matter from entering the system and scratching plungers, tearing packing, and causing unnecessary wear on all components.

Pump
The pump, which is driven by an electric motor, gas or diesel engine, draws or accepts filtered water through a series of inlet check valves as the plungers move back. As the plungers move forward, the inlet valves close, forcing the water to travel through a series of outlet check valves to the outlet side of the pump.

After the water exits the pump, its flow direction must be controlled with an unloading or regulating valve. A positive displacement pump is always delivering a certain volume of water whether the spray gun is open or closed; therefore a device is needed to control the direction of flow, either allowing the flow to go through the open spray gun, or redirecting (by-passing) the flow back to the inbound side of the pump when the spray gun is closed. Without an unloading or regulating valve, dangerously high pressures will be produced when the spray gun is closed because the water being forced out of the pump has no place to go. Serious bodily injury or property damage could be caused by failure to properly utilize an appropriate unloader or regulator valve in your pressure washer system. As a safety device, at least one pressure relief valve should be installed in the outbound side of the pump to guard against failure of component parts, and the development of dangerously high pressures.

Drives: Belt verses Direct
Direct drives are fine for casual or home use but industrial usage demands belt drives for a variety of reasons. When a direct drive is mounted directly to the engine, the added weight places additional strain on the engine and the mounting bolts. Bolts can wear through and even a minute amount of bolt wear produces additional deadly vibration to the engine. The most important difference, however, is in RPMs (revolutions per minute). With direct drive the pump is coupled directly to the engine drive shaft and is turning at the same RPMs as the engine, generally 3200 to 3400 RPMs, which produces higher temperatures. With a belt drive the pump RPMs are reduced from 3450 to 1725 rpm’s. With a direct drive, anything that happens to the pump happens to the engine. If there is a pump or engine seizure, the concussion will be passed on from the pump directly to engine (or vice versa) yielding damaging stress to the crankshaft.

Frame Construction
Currently frames are built using either painted or powder coated, black iron, aluminum, or stainless steel. Some frames are welded creating a rigid uni-body construction and some are not. Powder coating electrostatically bonds paint to the surface and is stronger than spray painting. All parts are then sent to the welding area. There, frames are put into fixtures to hold them while a welder stitches all the joints. The sheet metal parts are then installed and welded in place. Finally the chassis is ready to be painted.

The paint must be resistant to scratches, sunlight the over-spray of detergents, and still maintain a glossy finish. Proper preparation before painting is also necessary to enable the paint to stand up to this abuse. When a machine component has gone through the production line and is ready to be painted, it is first run through a parts washer. Each piece is hung from a conveyor line and sent through a hot phosphatizer wash. The phosphatizer not only removes the oils and weld splatter, it also etches the steel parts with an acid. The etching process leaves the metal clean and with a miniature pitted surface. This pitted surface gives the paint more surface to adhere to.

Once the part is washed, it is rinsed with clear water and dried. It is now ready for the powder coat paint process. The powder coating paint uses a very special process. The paint itself is almost a plastic. The part to be painted is positively charged with a small voltage and the paint is negatively charged. The paint is a powder, almost like talcum powder. When sprayed from the gun, the powder is attracted to the part and wraps itself around edges to cover the part completely.

Once the part is coated, it is sent into a large bake oven. The oven heats the part to about 315° Fahrenheit and actually melts the powder to a semi-liquid. As it melts, the powder smooths out and flows into a smooth surface, making paint runs, missed areas or thinly painted areas obsolete. After the paint has been baked on, the part is removed from the oven and air dried. As the paint cools, it hardens and makes a hard surface that completely surrounds and protects the steel underneath it.

Detergent Injection Systems
Cleaning detergents may be introduced into the flow of water either inbound or outbound of the pump. An inbound or upstream type of detergent injector simply uses the pump’s ability to draw or suck fluid in to introduce a detergent into the stream of water. Care must be taken to avoid introducing any detergents, which are not compatible with the materials in the pump and downstream components. An upstream injector does allow detergents to be applied to the work surface at the normal high working pressure of the system. An outbound or downstream
type of detergent injector uses a venturi (very similar to that used in an automotive carburetor) to draw a detergent into the water system. A downstream injector requires low pressure to activate detergent flow. Low pressure is achieved by changing to a large sized spray tip, or opening up a large orifice at the outlet end of the spray gun by using an adjustable nozzle or a double lance. There are several advantages to using a downstream injector over an upstream type.

1. Fewer component parts are exposed to the cleaning detergents, extending system life.
2. The operator can control the flow of detergent (on and off) by changing the system pressure at the nozzle. 3. Applying detergents at low pressure is more economical because less detergent bounces off the work surface.

Back-Flow Preventer
A back-flow preventer is placed on machines without float tanks to prevent back-flow in case a city water line ruptures. When using cleaning detergents, care must be taken to prevent these detergents from being back-flushed and contaminating the city water supply. Check your local plumbing codes. An alternative option to a "back-flow preventer" is the use of a water holding tank. If a holding tank is used, be sure not to exceed the negative pressure rating of the pump.