The Ultimate Pressure Washer Dictionary

Do pressure washer terms have you scratching your head?

We get it. With lots of specialised parts and equipment, keeping all the terms straight can be a challenge.

Check out our glossary of pressure washer terms below and never get your pressure switch and unloader valve mixed up again.

Pressure Washer Term Glossary

AC – alternating current. An electric current that reverses direction at regular intervals and continuously and regularly varies in magnitude. (See alternating current).

Acidizing – Use of an inhibited acid solution to remove hard water or chemical scale from the heat exchanger coil.

Accumulator – a pulsation dampening device relying on a diaphragm and gas-filled cylinder to lessen the effect of pump pulsation on the system. A shock absorber for water.

Adjustable Nozzle – a nozzle which may be adjusted for higher or lower pressure output or wider or narrower spray pattern. An adjustable nozzle may allow either variable pressure or spray pattern or both.

Air Band – adjusts or regulates the air intake on a gun-type burner to provide the right amount of air to mix with atomized fuel oil for proper combustion. The air band controls the amount of excess air introduced into the combustion chamber.

Air-Cooled Boiler – a boiler design which uses air being forced into the combustion chamber to insulate the heat exchanger. The air passes around the outside of the boiler but inside the wrapper and is preheated before it reaches the combustion chamber, contributing to more efficient combustion.

Air-Cooled Engine – a gasoline or diesel engine which is cooled by air forced around cooling fins on the cylinders. The air is moved by a fly-wheel-mounted fan and directed by the cooling shroud enclosing the fan.

Air Cone – insert in air tube of gun-type burner to restrict and direct flow of air for proper combustion.

Air Filter – filters air supplied for combustion in gasoline or diesel engines. May use a paper filter element or an oil saturated foam element or a combination of both.

Air Tube – tube at end of gun-type burner in which electrodes and fuel nozzle are mounted.

Air Valve – air valve on coil to allow purging water from coil with compressed air to help prevent freezing in cold weather.

Alkaline – substance with a pH below seven. Also called a base or basic solution. The opposite of an acid.

Alternating Current – AC. An electric current that reverses direction at regular intervals and continuously and regularly varies in magnitude. Type of current as supplied by electric utilities or generators. The reversal of direction is measured in cycles per second or hertz. (See AC, DC, Direct Current).

Aluminum Brightener – hydrofluoric acid. a hazardous chemical used to clean aluminum. Must be neutralized or it can attack the surface being cleaned.

Amp Draw – The demand for electric current flow by a specific application such as an electric motor.

Ampere – amp. Equal to the current that passes in a resistance of one ohm when a potential difference of one volt is applied. Refers to the quantity of current flowing or volume of current flow.

ASME – American Society of Mechanical engineers – sets standards for boilers and pressure vessels.

Bacharach Smoke Tester – method for checking the amount of smoke in flue gasses using paper which discolors depending on the amount of smoke. The darker the paper, the more smoke.

Backflow -flow out of the cleaner into the water supply. Water and chemicals may be pushed or siphoned back into the water supply.

Backflow Preventer – essentially a check valve which allows water flow in one direction only – into the system. This device is mounted on the inlet line. Backflow prevention is required in some municipalities as a requirement for hooking up to the municipal water supply.

Back Pressure – any pressure back against the head or outlet side of the pump. Increasing backpressure over a period of time can indicate scale is forming in the coil.

Baffle – or baffle plate. Steel insert in pancake coil which breaks up flame and flow of hot air, allowing for slower escape from the coil and more efficient heat exchange. Different manufacturer’s coils may have different baffle designs.

Bearing – a support or guide for a rotating or oscillating element such as a shaft. Ball bearings are most common.

Blower – a fan that forces air into the combustion chamber in the volume needed for proper combustion.

Boiler – the hot water cleaner’s burner and coil assembly is essentially a boiler.

Boiler Controls – devices used to control boiler operation or prevent boiler operation in unsafe conditions. Boiler controls may include thermostats, flow switches, pressure switches, high temperature limit switches, or vacuum switches.

BTU – British thermal unit. Heat needed to raise temperature of one pound of water one degree Fahrenheit.

Buna N – Buna-nitrile A type of rubber used in hoses, “O” rings, and seals.

Burner – a device for converting fuel to heat energy.

Bus – a rigid conductor in an electrical circuit used to connect several circuits. Bus bar.

Bushing – in mechanical terminology a replaceable tube or sleeve mounted in a housing and used as a bearing. In electrical terminology a lining for a hole intended to protect and insulate conductors passing through it. May also refer to pipe fittings. An example is a reducing bushing with male threads and smaller female threads to allow insertion of a smaller pipe or fitting.

Bypass – water flow directed away from hose and gun and back to inlet side of pump or the float tank. The result of unloader action on closure of trigger gun.

DC – direct current. Unvarying electrical current with a single constant direction. The type of current supplied by a battery.

Deliming Pump – used to inject water softening or scale inhibiting solution into cleaner’s fluid system to reduce liming or scaling.

Detergent – type of cleaning chemical whose action lifts soil and holds it in suspension or emulsion in water. May be acid or alkaline.

Descaling – removal of hard water or cleaning chemical residual scale from inside of coil. Usually involves removal of scale buildup from the inside of a coil with an inhibited acid solution.

Descaling Pump – special pump used to pump acid solution through coil to remove scale. Used instead of the high pressure pump to prevent damage to the pump by the acid solution.

Diaphragm Pump – a pump design which uses the action of a diaphragm rather than pistons or plungers to compress and move fluid.

Direct Current – DC. Unvarying electrical current with a single constant direction. The type of current supplied by a battery.

Direct Drive – motor or engine connected directly to pump. Pump runs at motor speed. Motor rpm determines pump speed.

Double Lance – lance with two tubes, generally one with small nozzle orifice for pressure washing and one with larger nozzle for chemical application. (See dual lance, variable pressure lance).

Downstream – on outlet or discharge side of pump. Chemical delivered on the downstream side of the pump is usually through a venturi injector and at low pressure. Downstream chemical is consequently also called low pressure chemical even though it is delivered on the high pressure side of the pump.

Down-Fired Burner – vertical boiler configuration with burner firing downward into the combustion chamber from the top of the boiler. These boiler designs are usually air cooled with air passing around the outside of the boiler before reaching the combustion chamber.

Drip leg – Pipe in gas inlet plumbing extending vertically downward and capped. The drip leg allows water and debris to settle out of the gas flow before entering the gas control valve.

Drum Kit – packaging of concentrated detergent with liquid and powder components which when mixed with water makes a 55 gal. drum of regular strength cleaning chemical.

Drum-Mount – cleaner (usually cold water) designed for mounting on a standard 55 gallon drum.

Drum Pump – pump used to pump chemical out of a drum. May be manually operated or driven by a motor.

Dual Lance – double-tubed lance for washing and chemical application. (See double lance, variable pressure lance).

Dump Gun – trigger gun which deflects water to larger orifice reducing pressure instead of sending flow into bypass.

Duplex Pump – two-cylinder pump.

Easy Start Valve – valve which relieves system pressure during start-up to reduce load on motor or engine.

Electric Motor – motor which uses electrically generated magnetic fields to turn a shaft.

Electrodes – two rods with ceramic-insulated bases used to provide ignition for an oil -fired burner. High voltage current arcs across the gap between the tips of the two electrodes to ignite the mixture of atomized fuel oil and air in the combustion chamber.

Electromagnetic Field – a condition existing near an electromagnet or current-carrying conductor which manifests itself as a moving charge or magnetic pole. This field can interact with other magnets or magnetic fields.

Emulsion – Mixture of two mutually insoluble substances in which one is suspended in the other. For example, an oil suspended in rather than dissolved in a liquid, like fat is suspended in milk. Cleaning chemicals emulsify grease and oil so these soils may be washed from the surface being cleaned.

Excess Air – air provided to combustion zone in excess of amount theoretically needed for combustion.

Filter – any of a variety of porous substances or devices used to remove particles from air or fluid.

Foam – cleaning chemical and water solution injected with air to create a foam which ideally should be the consistency of shaving lather.

Foaming Brush – brush accessory used to apply foaming chemical to a surface.

Foaming Head – injector nozzle used to apply foaming chemical to a surface.

Foot Pound – measure of force or work. One foot pound is the amount of work required to move one pound one foot. in one second.

Float – or float ball. Rides on the surface of the water in the float tank. This movement activates the float valve. The sensor which activates the float valve.

Float Valve – a mechanical valve which responds to level of fluid in float tank as indicated by the float.

Float Tank – intermediate source of water supply for pump. Holds incoming water supply. Allows for upstream chemical injection or high pressure injection by reducing inlet line pressure to zero.

Flocculation – a chemical technique for separating oil from water. The forming of aggregated or compounded masses. The binding of oil into masses for separation from water.

Flow – volume of water moved by pump. Measured in gallons per minute for pressure cleaning and gallons per hour for steam cleaning. 1 gpm equals 60 gph. May also be expressed metrically in liters per minute.

Flow-Actuated Unloader – Valve which responds to changes in flow rather than pressure to put water into by-pass.

Flow Switch – a switch which responds to changes in the volume of flow. Used as a burner control to shut off the burner when there is no or a reduced flow of water through the coil. Water flow moves a magnet which actuates a reed switch to open the circuit to the solenoid valve when sufficient water flow is present. Other types of flow switches use different types of sensors.

Flow-Through Gun – a trigger gun design in which water flows through piping in the grip to reach the valve.

Four Cycle Engine – a gasoline engine in which each of the four operations, intake, compression, expansion and exhaust takes up a full stroke of the piston. Two full revolutions of the crank shaft are required for a full cycle.

Four Pole Motor – electric motor with two stator windings. Each winding has two magnetic poles, making such a motor a four pole motor. The motor shaft turns at about 1750 rpm.

Fuel Filter – filter for gasoline or fuel oil. Many types are used.

Fuel Nozzle – atomising nozzle for fuel oil. These nozzles are rated in gph of fuel flow at 100 psi.

Fuel Oil – refers to specific grades of refinement of crude oil. No. 2 diesel fuel is a fuel oil.

Fuel Pump – pressurises fuel for oil-fired burner.

Fuel Tank – generally refers to fuel tank for heating oil in hot water machine. Also refers to gasoline and diesel tanks for internal combustion engines.

Fuse – protects against excess electrical current. A device containing a piece of metal that melts when excess current is applied, breaking the circuit.

Gas Jet – machined nozzle, usually brass, used in natural gas or LP burners.

Gpm – Gallons per minute, measure of flow generally used in pressure cleaning.

Gph – Gallons per hour. Measure of flow generally used in steam cleaning. Gpmx 60. Also used to measure flow of fuel through fuel nozzles in oil burning equipment.

Grains of Hardness – measure of water hardness. Indicates the number of grains per gallon of calcium carbonate.

Ground – a conducting connection between an electric circuit and the earth or some other conductor.

Ground Fault Circuit Interrupter – shuts off electric power if device’s ground fails. Measures the flow of current into the device and to the ground and if the two do not match breaks the circuit almost instantaneously. Often referred to as GFCI.

Gun – pistol grip handle for wand. May or may not have trigger mechanism for water shut-off.

Hardness – refers to minerals naturally present in a water supply. “Softer” water has lower concentrations, “harder” water higher concentrations. Water hardness varies from one locale to another. Harder water is more likely to cause excessive coil scale. Commonly measured in grains. A greater quantity of cleaning chemical is required for cleaning with hard water than with softer water.

Hex Nipple – male threaded fitting to connect two pipes. Fitted in the center for handling with a hex wrench: (See close nipple, nipple).

High Pressure Hose – outlet hose. Generally reinforced with one or more tightly wound steel braids between tube and cover to handle high pressures.

High Side – high pressure side. Outlet or discharge side of pump.

Hobby Machine – small cold water machine designed for sale to homeowners.

Horizontal Cleaner – hot water machine with burner and coil parallel to the ground.

Horsepower – about 550 foot pounds of work per second or 746 watts of power.

Hose – Inlet side supply hose is usually garden hose. Outlet hose is high pressure or steam hose. High pressure hose delivers water under pressure and consists of tube, reinforcement, usually wire braid, and cover. Garden hose is used to convey water from source to pump inlet. Other types of low pressure hose or tubing may be used in the inlet side of the system.

Hose Barb – a hollow, tapered connector on which a length of low pressure hose or tubing is fitted. Generally used for chemical inlet lines. Usually hose is slipped over the barb and then secured with a hose clamp.

Hose Guard – a length of spring or rubber at inlet and/or outlet end of hose to prevent excessive bending and resultant wear and failure. Also called a bend restrictor.

Hose Reel – device that winds or holds hose for storage.

Hot Water Cleaner – high pressure cleaning equipment which uses hot water to increase cleaning effectiveness.

Up to 2 weeks.

Lance – a length of tubing or pipe, usually metal, connecting the gun with the nozzle. The lance may be of almost any length although 36″ is considered the optimum for reach, safety and ease of use.

Lift Pump – pump used to move water from a tank or reservoir to a level where it can be handled by the cleaner’s positive displacement pump.

Live Swivel Coupling – a coupling that will swivel when under pressure.

Low Side – low pressure or inlet side of the pump, upstream, before fluid gets to the pump. Fluid is not yet under pressure.

Magneto – source of spark for engine ignition. Usually belt-driven.

Magnetic Contactor – an electrically operated switch for operating with low amp draw or low voltage. Used to control another circuit of different amperage or voltage.

Metering Valve – allows control of the amount of chemical entering the system. (See Chemical valve).

Millivolt Generator – uses a heat differential to generate a very low voltage. Consists of two and pilot dissimilar conductive metals joined at the ends. When the two junctions are maintained at different temperatures a current proportional to the temperature difference is induced. (See pilot generator).

Mole – a device, usually with rotating nozzles, for cleaning pipe. Also called a pipe cleaning nozzle or tool.

Multiple Pass Coil -a coil type in which heated air passes around coil pipe several times before exiting out stack. These units may also be air-cooled with the inlet air passing around the outside of the coil wrapper before entering the combustion area.

Nipple – threaded connector for two pipes or threaded fittings.

Nitrile – A rubber material used in hoses and ‘O’ rings.

Nozzle – A restrictive orifice or hole at end of wand. “Squeezes” water to increase velocity and, consequently, impact. The smaller the opening the higher the pressure rating.

Nozzle degrees of spread – Spread of the stream of water from a nozzle measured in degrees of a circle, a half circle is 180 degrees. Zero degree nozzle gives a straight stream. Common are 15, 25, 40, 60 degree. (See Theoretical coverage).

Nozzle Pressure – Pressure of the system measured at the nozzle.

NPT – National Pipe Thread. A standard for threads on pipe fittings.

Number 2 Fuel Oil – Also number 2 diesel. The standard fuel used in oil -fired burners. Other fuels such as Kerosene and other fuel oil weights may be used as well.

OD – Outside Diameter. The distance from outside to outside across the center of a pipe or hose.

Oil Bath Pump – Pump with lubricant-filled crank-case. Crankcase is usually half-filled with lubricant and motion of connecting rods spreads oil over all surfaces requiring lubrication.

Oil Seal – seal which keeps oil in dry side of pump.

Operating Pressure – Pressure at which a device or component is rated for safe operation. In hydraulics in the United States one-fourth the rated burst pressure.

“O” Rings – circular rings, usually rubber or similar material, used as seals in valves and connectors.

Overhead Valve – Gas engine type with valves on top of cylinder.

Orifice – an opening or hole as in a nozzle. Precisely machined to a predetermined size.

Oxygen Percentage – The percentage of oxygen in flue gases.

Packing – seal in pump cylinder to keep water contained in wet side of pump. (See “V” packing).

Pancake Coil/Helical Coil – A coil design with one or more wound “pancakes” of pipe at the end of the combustion chamber away from the burner.

Parts Washer – contained washer designed for washing grease and oil from parts. May use a solvent-type chemical.

pH – Measure of alkalinity or acidity of water or chemical solution on a scale of 0 to 14 with 7 neutral and 14 most acid.

Pilot Generator – millivolt generator which generates enough voltage from heat of pilot light to keep pilot valve open. (See millivolt generator, thermocouple).

Pinpricking – practice of piercing the cover of a steam hose to prevent vapor buildup and resultant bubbling of the cover during use of the hose at high temperatures.

Piston Cups – high pressure seal or packing on piston pump. Packing floats with movement of piston allowing the piston to function as an inlet check valve.

Piston Pump – pump pistons carry packing or cup with them as they move through cylinder.

Plunger Pump – Usually ceramic plunger pump. Plungers move through stationary packing.

Portable – A cleaning system which can be moved from place to place. May be carried or moved on wheels.

Positive Displacement Pump – pump designed with the primary purpose of pushing a flow of water. The pump is designed to expel as much water as enters the pump. May have little ability to lift water vertically.

Pop-Off-Valve – or pressure relief valve that releases water to atmosphere when a set + pressure is reached. A safety valve.

Ppm – parts per million. A measure of concentration of another substance in a fluid.

Ppb – parts per billion.

Pressure – measured in psi or bar (metric). Since fluids are essentially non-compressible a measure of potential energy rather than compression.

Pressure-Actuated Unloader – valve that sends pump output into bypass when pressure increases above a set level.

Pressure Gauge – used to measure pressure, attaches to pump port or other fitting.

Pressure Nozzle – restrictive nozzle on high pressure cleaner. Size of nozzle orifice relative to amount of flow produced by pump determines output pressure.

Pressure Regulating Unloader – unloader valve designed for and used to regulate output pressure. (See pressure actuated unloader)

Pressure Regulator – regulates incoming pressure of gas to the burner. LP gas, is usually supplied at a pressure too high for proper combustion.

Pressure Regulating Gas Valve – multipurpose gas valve designed to reduce gas input pressure to level required for combustion.

Pressure Relief Valve – valve which vents water to atmosphere or bypass when system pressure reaches a preset limit. (See pop-off valve).

Pressure Spike – momentary increase in pressure resulting from interruption of water flow. Will occur on closure of trigger gun valve.

Pressure Switch – switch which uses pressure-driven plunger to activate microswitch. Can be used as a boiler safety device or for complete system shutdown.

Prime – water in the pump head and cylinders needed to initiate pump action.

Probe – a sensor, often of temperature, which provides information to a measuring device such as a thermostat.

Psi – pounds per square inch. a measure of pressure.

PTO – power takeoff. Connection for using tractor or other engine-driven machine to drive a device such as a pump.

Pump – a device which moves fluid through a combination of suction and displacement, that is the water is sucked into the pump and then pushed out. The pump’s action imparts energy to a stream of water.

Pump Head Pressure – water pressure at pump outlet.

Pump Saver – thermal relief valve that dumps hot water to atmosphere when the water overheats in bypass. The expelled hot water is replaced with cold water and the valve resets itself.

Pulsation – a vibration or throbbing. Deviation from steady stream in flow of water as a result of pump action. Pulsation is measured in psi as the range between the lowest and highest pressures achieved in the pulsation cycle.

Pulsation dampener – any device used to reduce pulsation.

Pulse Hose – a length of soft hose to absorb pump pulsation.

Reverse Osmosis – filtration process in which particles are removed from fluid by forcing the fluid through a fine filtering membrane.

Rotating or Rotary Nozzle – a device consisting of a zero degree nozzle or nozzles spun by the force of water flow to increase the surface coverage of the high impact straight stream nozzle or nozzles.

Rotor – rotating electric magnet in an electric motor.

Rpm -revolutions per minute. Measure of the speed of any rotating device.

SAE – Society of Automotive Engineers, set standards for hydraulic system components such as hose, pipe and tubing.

SAE 100R1 and R2 – ratings for hydraulic hose, the R1 and R2 in this instance denote the number of metallic wire braid enforcements.

Safety Factor – The ratio of burst pressure to operating pressure. The United States standard for hydraulics is 4 to 1 that is a component with 4000 psi burst pressure would be rated with a 1000 psi operating pressure.

Safety Valve – A pressure relief valve installed in a high pressure cleaning system to protect against over pressurization.

Schedule 40 & 80 Pipe – SAE ratings for types of pipe used in coil manufacture. Schedule 80 is thicker, with a higher burst and operating pressure, and is becoming more common Schedule 40 has been standard for most coils.

Side Valve Engine – older gas engine type with valves at side of cylinder.

Skid Mount – Pressure washer mounted on a skid, usually metal, for transportation by fork lift.

Solenoid Valve – Type of magnetically or current operated valve.

Solvent – cleaning chemical which dissolves soil from the surface. Usually volatile.

Squirrel Cage – Type of electric motor rotor. Also type of fan used in some burner blowers.

Strainer – filter. Usually of fine mesh screen.

Single phase – type of alternating current. Current supplied for household use in single-phase.

Stack Temperature – The temperature of flue gases escaping through the stack from the combustion chamber, temperature can vary from place to place in the stack.

Stack Thermometer – A dial thermometer used to read stack temperatures.

Starting Load – the load on a motor or engine at the time it starts.

Starting Windings – smaller windings on rotor of electric motor used to facilitate starting.

Stator – stationary electromagnet in an electric motor.

Steam – water vapor.

Steam Cleaner – cleaner which uses expansion of vapor from water superheated in the system to propel water out of an

expansion nozzle. Does not actually use steam to clean.

Steam Explosion – explosion that results when superheated water goes to steam. Steam cleaner action is simply a controlled steam explosion.

Steam Hose – hose designed for use at high temperatures. Usually pinpricked to prevent vapor buildup under the cover.

Steam Nozzle – an expansion nozzle used with a steam or combination cleaner to control and shape the vapor explosion that results when superheated water is exposed to the atmosphere.

TEFC – totally enclosed, fan-cooled electric motor enclosure.

Teflon Tape – tape used to make a waterproof seal in threaded fittings. Should not be used in fuel line fittings.

Temp Limit Switch – or high temperature limit switch. A boiler control used to prevent overheating. When the switch reaches the maximum temperature it opens, breaking the burner circuit and turning the burner off.

Thermistor – temperature sensor which relies on difference in electrical resistance at different temperatures to measure temperature.

Thermocouple – a device for measuring temperature. Consists of two dissimilar conductive metals joined at the ends. When the two junctions are maintained at different temperatures a current proportional to the temperature difference is induced. Can be used to generate a very low voltage current.

Thermopile – a collection of thermocouples used to generate electricity. (See pilot generator, millivolt generator).

Thermoplastic – plastic designed to withstand higher temperatures, usually around or in excess of 200 degrees Fahrenheit. Used for hose.

Thermostat – controls burner activity to keep heat exchanger temperature at desired level.

Thermowell – a hollow fitting to allow a temperature sensing probe to be mounted in a high pressure system. The fitting protects the sensitive capillary probe from system pressure.

Three phase – type of electric current which can most easily be understood as three single phase alternating current power supplies.

Three phase motor – electric motor running on three phase current, self starting.

Three Pole Switch – electrical switch with three positions. Used as a combination switch to control pump and burner operation.

Timer – switch used to delay machine shutdown.

Torque – A measure of motor or engine power based on the ability to move a weight one foot from the center of the shaft. Related to horsepower. measures the ability of a motor to start against a load.

Trigger Gun – A hand-held device that opens valve to allow flow to nozzle when trigger is depressed.

Triplex Pump – A three-cylinder pump.

Truck Wash Gun – trigger gun designed for washing vertical surfaces without causing undue operator fatigue.

Tubing – Used in some coils, differs in I.D. and O.D. from pipe of same SAE rating.

Turbolator – A sort of baffle arrangement that causes turbulence in a burner flame.

Two Step – A cold water washing process that uses an acid on first application that is neutralized on the second wash.

Two Cycle Engine – A simple engine that requires only two strokes or one revolution of the crankshaft to accomplish intake, compression, expansion and exhaust functions.

Two Pole Switch – A simple switch with only two lugs or terminals for wiring connections.

V Packing – high pressure seals in a plunger pump.

Vacuum Switch – switch which relies on pressure differential to move a diaphragm.

Venturi Injector – or siphon injector, creates pressure differential in the line to draw chemicals into system.

Vertical Cleaner – Hot water machine with boiler mounted vertically.

Volt- the electromotive force that will cause a current of one ampere to flow through a conductor with a resistance of one ohm.