Some Basic Principles on the Fluid System
The high pressure cleaner’s fluid system is centered on the pump and includes the high pressure hose, unloader valve, safety valve, trigger gun and nozzle as well as the heat exchange coil in that it transports and contains fluid within the system.

Measuring Flow and Pressure
The pump is the heart of the high pressure cleaner. It pushes a volume of water against a restrictive nozzle opening or orifice. The combined action of the pump and nozzle gives fluid in a high-pressure system its two basic attributes, pressure and flow.

Measuring Flow – The flow or volume of water moving through the system is measured as a volume over a period of time. Usually this is gallons per minute or (gpm). Steam cleaner flow is often measured in gallons per hour, and in countries using the metric system flow may be measured in liters per minute.

Flow is usually expressed in gallons per minute (gpm). In some cases – either steam cleaning applications or chemical injection – flow may be expressed in gallons per hour (gph). Cleaning systems produced in other countries may have their flow rated in liters per minute (liters/min).

Note On Conversion: A liter is slightly more than one quart (1.06 quart so four liters will be a bit more than one gallon). Liters per minute can be converted to gallons per minute by multiplying the liters per minute figure by 0.264. Gallons per minute can be roughly converted to liters per minute by multiplying the gallons per minute figure by 3.79.

Measuring Pressure – The force, which pushes water through the nozzle, is measured in pounds per square inch or psi. Most high-pressure cleaners operate in the 500 to 3000 psi range. Where the metric system is used, pressure will be measured in bar.

When we speak of a pump’s ability to produce a certain pressure at a specified flow, what we really mean is that the pump is capable of moving that volume of water through a particular orifice at the specified rate in gallons per minute. Pressure is generally referred to in pounds per square inch (gpm). Equipment manufactured outside of the United States may have pressure expressed in bar. One psi is roughly 14.5 bar. A system producing 1000 psi will be rated at 69 bars.

Water Impact
Flow and pressure together determine the amount of impact a particular cleaner’s water output can have on a surface being cleaned. An increase in flow will result in a greater increase in impact than an equivalent increase in pressure. A high pressure cleaning system with a flow of 2 gpm at a pressure of 750 psi exerts a theoretical total impact of 2.88 foot-pounds. If the pressure is doubled to 1500 psi with the flow remaining constant, the theoretical total impact is 4.0 foot-pounds, an increase of 39%. If the pressure remains constant at 750 psi and the flow is doubled to 4 gpm, the theoretical total impact
is 5.76 foot-pounds, an increase of 100 percent in theoretical total impact or exactly double the impact produced at the 2 gpm flow.

The Formula for Determining Impact
Theoretical total impact is computed by multiplying the flow by the square root of the pressure and then multiplying the result by a decimal fraction, which represents the effect of the nozzle on the water output. This decimal fraction is called a nozzle coefficient. For most nozzles used in high pressure cleaning applications this coefficient is .0526.

Theoretical And Actual Impact
Theoretical total impact represents the impact that will result if the water output strikes a surface exactly at the nozzle outlet. Actual impact varies with distance from the nozzle and with the nozzle’s spray pattern. The greater the distance from the nozzle and / or the wider the spray pattern, the less actual impact the water output will have on the surface being cleaned. Impact is traded off for the amount of area the water spray covers. With fan spray nozzles, the closer the nozzle is held to the surface, the greater the actual impact but the smaller the area cleaned. A zero degree nozzle will have the most actual impact while the wider spray patterns will have decreasingly less actual impact.

Cleaning Efficiency
For the most part any size of cleaner will perform almost any cleaning task. However, the greater the impact, the more rapidly the task can be accomplished. The greater the theoretical total impact, the greater the distance the nozzle can be held from the surface and still do the job. The greater the distance from the surface to the nozzle, the larger the area cleaned in each pass of the spray pattern. The larger the area cleaned effectively, the more quickly the cleaning task is accomplished.

Common Cleaner Sizes
The most common sizes of general-purpose electric motors used for high pressure cleaning equipment-pumping units are 1.5 hp, 3 hp, 7.5 hp and 10 hp. The use of 2 hp high efficiency electric motors in 115 volt powered units is increasing. The 1.5 hp and 2 hp units both operate on 115 volt power supplies while the larger sizes usually are driven by 230 volt power although 7.5 hp and 10 hp motors may use 440 volt and are almost always 3 phase even when 230 volt power is used.

Generally a gas engine will require about twice the horsepower rating as an electric motor to drive the same pump. Each horsepower category is capable of producing a range of theoretical total impact figures depending on the relationship between flow and pressure produced by the cleaning system. Systems in the 1.5 hp range will produce from about 3.5 to 4.5 foot-pounds of theoretical total impact. Systems in the 3 hp range will deliver from 6 to about 7.5 foot pounds of theoretical total impact. Systems in the 5 hp range will produce from about 8.5 to 10.5 foot-pounds of theoretical total impact. Systems in the 7.5 hp range will deliver from about 11.5 to 13.5 foot-pounds. Systems in the 10 hp range can produce from around 14 foot-pounds to 16 foot-pounds.

Flow, Pressure, Horsepower and Impact:

2.2 gpm @ 1000 psi 1.5 hp 3.6 foot pounds Intermittent duty
3.0 gpm @ 750 psi 1.5 hp 4.3 foot pounds Intermittent duty
3.0 gpm @ 1500 psi 3 hp 6.1 foot pounds General duty
3.5 gpm @ 1250 psi 3 hp 6.5 foot pounds General duty
4.5 gpm @ 1000 psi 3 hp 7.4 foot pounds General duty
3.5 gpm @ 2200 psi 5 hp 8.6 foot pounds Medium duty
4.0 gpm @ 2000 psi 5 hp 9.4 foot pounds Medium duty
5.0 gpm @ 1500 psi 5 hp 10.2 foot pounds Medium duty
4.5 gpm @ 2500 psi 7.5 hp 11.8 foot pounds Industrial duty
5.0 gpm @ 2250 psi 7.5 hp 12.5 foot pounds Industrial duty
6.0 gpm @ 1800 psi 7.5 hp 13.3 foot pounds Industrial duty
4.5 gpm @ 3500 psi 10 hp 14.0 foot pounds Extra heavy duty
5.0 gpm @ 3000 psi 10 hp 14.4 foot pounds Extra heavy duty
6.0 gpm @ 2500 psi 10 hp 15.8 foot pounds Extra heavy duty

NOTE: Actual water impact is determined by the spray nozzle pattern and the distance the nozzle is held from the surface being cleaned. Most spray nozzles are a flat fan spray pattern. Fan spray patterns are differentiated by degrees of spread of the spray pattern from the nozzle. The smaller the degree of spread figure, the more water impact will be produced by a fan spray nozzle. The wider the pattern, with a consequently larger degree of spread figure, the greater the coverage. The trade-off then is between the amount of impact and the size of the area covered by the spray. A smaller spray angle provides greater water impact but less spray pattern coverage. A larger spray angle provides less impact but a greater area of coverage.

The Water Supply
The pump must have a steady supply of water at least equal to its discharge volume. This can come from a public water supply, a well, or a source of standing water such as a tank or reservoir. Inadequate or interrupted water flow will cause poor pump performance and eventual damage from cavitations.

Clean Water
A high pressure cleaning system must have an adequate supply of clean water to perform properly. The water supply must be free of foreign particles and contaminates. Foreign material in the water supply can jam system components. Materials such as paper, cellophane or leaves in the float tank can cover the tank’s outlet, causing erratic pump performance or damage. Chemical contaminants or hard water can degrade cleaning chemical performance and reduce system performance by forming a coating of scale inside the system.

A high-pressure cleaner’s water inlet can be fitted with one or more water filters or strainers to clean debris from the water before it reaches the pump. A float tank should be covered to keep foreign objects from dropping into it. Inlet water may be treated with a water softener.

Municipal Water Supplies
Municipal water supplies generally supply water at a flow of 5 to 6 gpm. Therefore any high-pressure cleaning equipment requiring 5 gpm or more should have some kind of tank setup to guarantee an adequate water supply. Under exceptional circumstances, water may be supplied at too high a pressure for the pump to handle. The most common plunger pump types are rated for a maximum inlet pressure of 125 psi. There are several methods of handling improper input pressure problems. If the equipment has a float tank, input pressure will not be a problem.

Standing Water Supplies
A float tank or a standing water supply tank can serve as a sort of buffer between the machine and the local water supply, both guaranteeing a steady supply to the pump and preventing return water flow to the water supply, usually referred to as "backflow." A properly sized regulator may be installed on the inlet side if water supply pressure problems persist with a direct-fed system.

Important: A standing water supply must be positioned relative to the cleaning system in such a way that the pump generates adequate suction or lift to draw the supply into the system. This means that the standing supply must not be too far below or away from the water supply. The distance and height a pump can "lift" water depends upon the type of pump, the size of the line and other factors; however, the best rule for good performance is to demand the least possible work from the pump on the inlet side because the positive displacement pumps used in high pressure cleaning systems are designed to maximize their ability to push water out rather than draw water in.

Water Supply Tanks

Most high-pressure cleaners are connected to a municipal water supply or well using a hose. However, other supplies such as lakes, ponds or tanks may be used. A high-pressure cleaner with an output of more than 6 gpm will probably need a tank or other standing water supply since the cleaner’s output is likely to be greater than the input water flow from the municipal water supply.

The size of a water supply tank, such as a tank on a mobile cleaning unit, limits the amount of time the cleaner can be kept in continuous operation. For example a cleaner with a 5 gpm output will operate for 100 minutes or one hour and 40 minutes from a 500-gallon tank. Then the tank will have to be refilled. If refilled from a residential water tap with a 6 to 8 gpm flow, it will take from one hour to almost one and one half hours to refill the tank. That is, it takes almost as long to refill the tank as it does to empty it. Adding in travel time, this could double the amount of time required to perform a task requiring the use of a water supply tank. At some commercial and industrial locations water may be supplied at higher flow rates or a lift pump may be used to refill the tank. Refilling a 500-gallon tank at a 20 gpm flow rate will require 25 minutes or almost one-half hour. Tanks larger than 500 gallons are generally impractical for mounting on a trailer with a cleaner. Weight is a big factor. A 500-gallon tank full of water will weigh over 4000 pounds. In some cases a separate trailer with a water tank may be used.

Inlet Line and Fitting Types
Most cleaners have a ¾ inch hose connection for the water inlet. This fitting can be adapted to handle other inlet connections but the ¾ female connection is standard. A female connection is designated with an "F" and a male with an "M". Stationary units may e hard-plumbed into the municipal water supply in compliance with local plumbing codes. Leaking is a common problem at the inlet connection when a hose fitting is used. Replacement of the hose washer will generally stop leaking at the inlet fitting. Some systems may use low pressure or quick connects to attach the hose to the system. Leaking in this instance would indicate a missing or bad quick connect o-ring.

Flush the Hose
Before hooking up the hose to the inlet fitting it should be flushed out. To flush the hose, simply let water run through it for a minute or so. If the hose appears to contain a substantial amount of debris, it may be necessary to lift the center portion of the hose above the hose outlet to flush out all the debris.

Flow to the Float Tank or Pump
The inlet plumbing runs from the inlet fitting to the float tank or directly to the supply side of the pump. Water is not under high pressure at this point so high pressure hose is not necessary to run water from the inlet to the float tank. The inlet fitting may actually be on the float tank. If the system does not have a float tank, the inlet line will run directly to the pump inlet. There may be filter or strainer on the inlet line. This will usually be a 50 or 80 mesh brass screen. This filter helps keep debris from entering the system. The hose washer may also include an integrated strainer. Water flows into the float tank, lifting the float ball until the float valve shuts off the water supply to the tank.

The Float Tank

The float tank generally holds about two gallons of water. It is often made of plastic or stainless steel to resist rust and corrosion. Corrosion in the float tank can result in the creation of debris, which can enter the system and cause pump or other problems including damage, which could require component replacement. When the level of water in the float tank falls to a certain point, the float valve allows water flow into the tank again and tank refills until the float rises and the supply is shut off. The purpose of the float tank is to reduce inlet water pressure to zero, allowing for upstream injection of chemical so that chemical can be delivered at high pressure.

Keep the System Clear of Debris
The float tank may have an outlet strainer to prevent debris from entering the rest of the system through the water line. The float tank is usually covered to keep debris from falling into the tank.

However, debris is such as leaves and cigarette cellophanes in the float tank can be sucked against the tank outlet, preventing water flow into the system. This can defeat a vacuum switch, as there would still be suction in the inlet line although there is no water flow. This blockage may allow the burner to ignite without water flow and a steam explosion may result. Bypass flow from the unloader may be diverted back to the float tank rather than to the inlet side of the pump.

The Float

The float valve assembly is designed so that the action of the float riding on the top of the rising water level in the float tank will physically shut a valve and cut off the supply of water to the float tank. When the water level falls, the valve reopens and water is again allowed to flow into the float tank. The float may be made of metal, usually brass, or plastic. It is mounted on an arm that extends out into the tank. The arm generally has male threads on each end to allow easy replacement of either the float or float valve, both of which generally have female threads. This arm may become bent and may need to be straightened or preplaced for proper float valve action.

Float Problems

Some floats have seams that can leak. If the float fills with water to the point where it loses buoyancy and will no longer ride on the surface of the float tank, the float valve will not shut off and water will continue to flow into the float tank. Generally the float tank will overflow in this situation. If the tank does overflow, first check to make sure that the float has positive buoyancy.

If it is filled with water it must be drained. This may be a very slow process if the only way to drain the float is through the same split seam or small puncture that allowed water to seep in the first place. In this situation replacing the float, if a spare is handy. If the float is drained, it must be sealed, usually with silicone, and it will be some time (several hours to a day) before the repaired float can be returned to service. When water flows into the float tank, turbulence is created. This turbulence can be severe enough to cause the float ball to bob up and down, causing problems with the regulation of the water supply. Placing baffles in the tank between the inlet and the float ball often prevents this.

The Float Valve
The float valve consists of a body, usually with a ½" to 1"male inlet fitting, an outlet which may or may not be threaded, a plunger and a short controlling arm on a pivot which translates the up and down motion of the float into the in and out motion necessary to open and close the valve by moving the plunger back and forth in the valve body. The controlling arm pivots on a pin through a hole in the arm and holes through mounting flanges on the valve body. The controlling arm pivots on a pin through a hole in the arm and holes through mounting flanges on the valve body. The controlling arm rides between the two mounting flanges.

The piston will generally be fitted with a rubber stop and/or gasket (these generally are replaceable) to guarantee a good seat when the plunger is pressed into the inlet port. Debris in the port or seat or damage to this stopper or gasket can cause leaking into the float tank. This may be very minor and may not cause the tank to overflow during working hours if the equipment is used regularly. However, if the equipment is kept hooked up overnight, a small leak at the float valve seal can cause the float tank to overflow. A fitting for the float arm is mounted in a slip-proof but adjustable manner to the controlling arm. Usually both the arm and fitting are notched in some manner so that they will fit together in a number of positions when held tightly together by a screw or bolt. This fitting allows the float arm to be adjusted so that the float actuates the valve at the desired water level.

Debris in the tank or damage to the float valve assembly may cause the valve to stick in an open position. This will allow water to run into the tank continuously and the tank will overflow. It is much less likely the valve will become so clogged that water will not pass through. Damage or improper adjustment may cause the valve to not open properly. This can result in pump starvation since the float tank may be completely drained by the pump.

On to the Pump
Water flow from the float tank goes through a low-pressure line to the pump inlet. At this point the water is not yet under pressure so a high pressure hose is not needed for normally used. There may be a chemical injector and a vacuum switch installed on this line. The chemical injector is for upstream injection of chemical. Chemical injected at this point in the system will flow through the pump. The vacuum switch is a control device. If water is not being sucked into the pump, this switch will break the burner control circuit and the burner will not fire. This keeps the boiler from overheating when there is no water flow through the system.