Glossary of Terms

FNPT/FPT: Female National Pipe Thread is the U.S. standard for measuring female (internal) NPT threads. MNPT pipe sizes do not refer to the actual physical dimension. The outside diameter of a pipe or fitting must be measured and compared to a table for size identification. 

GPM: Gallons Per Minute is the measurement used to determine the flow rate of a hydraulic component. GPM is a key element to a pressure washer or power washer as it describes how much water is striking the target surface or material. Machines with higher GPM rating will have greater ability to flush away solids.

Lance: The lance (also called “wand”) is the tube of metal that attaches to a pressure washer spray gun and holds the spray nozzle at the far end. Lances provide distance between your trigger gun and the spray nozzle so you can clean more effectively from a standing position or a distance away from your target surface. Lances come in a variety of lengths, materials, and styles including insulated lances for hot water machines, non-insulated lances for cold water, telescoping wands, and more.

MNPT/MPT: Male National Pipe Thread is the U.S. standard for measuring male (external) NPT threads. MNPT pipe sizes do not refer to the actual physical dimension. The outside diameter of a pipe or fitting must be measured and compared to a table for size identification. 

Nozzle Size: an industry standard sizing unit for pressure washer nozzles that indicate orifice size and water flow at certain standard water pressure units. Nozzle size does NOT directly correlate to GPM flow rate. It only indicates the relative size of the nozzle orifice.

NPT: National Pipe Thread is the U.S. standard for measuring tapered threads on threaded pipes and fittings. The taper on NPT threads causes them to compress when tightened, creating a seal.

Open Gun: Open guns are a common type of pressure washer spray gun in which water is constantly flowing without a trigger needing to be squeezed. These are generally used in situations where the operator will be pressure washing for long period of time and needs to avoid hand fatigue.

Pressure Relief Valve: A pressure relief valve (also called a “pop-off valve” or “safety relief valve”) is a valve threaded in to the high pressure outlet side of the pump that protects the pump and plumbing system from damage due to pressure build-up. In the event of an unexpected pressure rise, the valve will pop open and release water to relieve pressure. These valves can usually be reset and reused multiple times.

PSI: Pounds per Square Inch is unit of measure expressed in pounds of force per square inch of surface area. PSI is a key element to a pressure washer or power washer system as it describes the force of the water against a target surface or material. Most pressure washer components including pumps, valves, fittings, hoses, guns, nozzles, and accessories have a maximum PSI rating that should not be exceeded to ensure safety of the equipment operator.

Quick Disconnect Nozzle: Quick disconnect nozzles feature a plug that fits into a quick connect socket attached to the end of your lance. This provides the able to quickly change between nozzle sizes and spray angles without the need to unthread and rethread. Quick disconnect nozzles are made of hardened stainless steel and typically feature a plastic grip that is color coded to indicate the nozzle spray angle.

Thermal Relief Valve: A thermal relief valve is a valve threaded into the low pressure inlet side of the pump washer pump that protects the pump from damaging heat buildup. In the event that the pump becomes too hot, the thermal relief valve will open to release hot water and allow cooler inlet water to enter the system. These valves are often considered one-time use and will need to be replaced after being triggered.

Threaded Nozzle: Threaded nozzles (commonly called “screw-in nozzles” or “male nozzles”) are pressure washer nozzles that thread directly to the end of your lance and/or other fittings. The most common size for threaded nozzles is ¼ in MNPT, although they are also available in 1/8 in MNPT for smaller fittings found in duct cleaners, surface cleaners, and other specialty attachments. Most threaded nozzles are made from hardened stainless steel.

Trigger Gun: Trigger guns are the most common type of pressure washer spray gun. They incorporate an internal control valve that is activated by a trigger in the grip. Trigger guns conserve water and allow the operator to navigate a complex cleaning job or job site easier by controlling the release of water with the trigger.

Turbo Nozzle: Turbo nozzles (also called “rotating nozzles”) are pressure cleaning nozzles that use centrifugal force to boost cleaning power. These nozzles house an internal rotor that generates a zero degree spray pattern in a circular motion, creating a very powerful conical spray to help break down tough dirt and grime. Turbo nozzles are sized according to the same industry standard nozzle size chart as regular threaded or quick disconnect nozzles.

Unloader Valve: An unloader valve is a safety bypass device that is common on almost all modern pressure washers and other pressure equipment. An unloader valve allows water to bypass back to the pressure pump while the spray gun is closed or a blockage occurs in the outlet line, protecting the pump and other components from failure due to rapid pressure increase. Most unloader valves also act as a pressure regulator for the output of the high pressure pump.

Weep Gun: Weep guns are pressure washer trigger guns that allow a small amount of water to flow after the trigger is released. This type of trigger gun allows the gun to “weep” or slowly leak to protect from freezing. Weep guns are very common in car wash environments.


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