Pressure washer terminology guide: 40+ terms explained

Understanding pressure washer terminology is essential for anyone looking to use these versatile cleaning tools effectively. By becoming familiar with terms like PSI, GPM, nozzle types, and pressure washer accessories, BISON can make an informed decision when purchasing and optimizing its performance for various cleaning tasks.

Pressure washer components

Detergent tank

This is a built-in feature in some pressure washers where you can store your cleaning agents or detergent. It allows the pressure washer to mix the detergent with water automatically during operation.

Soap nozzle/Soap tip

This is a specific type of nozzle designed for applying detergents or soap, including inhibited acid solution formulations. It operates at lower pressures to allow for the drawing and mixing of detergent into the water stream.

Adjustable pressure regulator

Change the pressure of the high-pressure spray. Proper pressure regulation protects surfaces from damage and ensures the right output for each cleaning application.

Adjustable spray/Multi-reg nozzles

A multi-reg nozzle that adjusts spray angle (0° to 45° dispersion) by turning the nozzle, and allows chemical solutions to be applied at low pressure.

Axles

Axles support the wheels and bear the machine's weight. They must be strong enough for the unit's weight and long enough to provide stable balance during movement and operation.

Chemical injector

Injects soap or chemicals into the water stream, making cleaning easier and faster. Works with variable-pressure wands to control chemical flow. For pass-through wands, switch to a soap nozzle to use the injector. Most pressure washer chemical injectors are downstream venturi injectors—the chemical is delivered after the pump at low pressure. This protects both pump and cleaning solution, unlike upstream injection methods.

Handles

Most pressure washers include at least one chromed or painted handle. Some models have front handles, others rear handles, for easy moving and loading, plus extra protection for essential components.

Pressure washer gauge

The pressure washer gauge combines a chemical seal and gauges into one unit. A convoluted circular membrane (diaphragm) is sandwiched between two flanges. Pressure exerts force on the diaphragm; a metal push rod welded to its base transmits deflection to linkage, which converts lateral movement into pointer rotation.

Pressure washer hose

There are two types of pressure hoses. Wire-braided high-pressure hose rated up to 4500 PSI, and non-marking gray hose (also 4500 PSI rated) that won't leave rubber marks on surfaces. Both incorporate tightly wound steel braids between inner tube and outer cover, designed to withstand elevated discharge-side pressures without compromising flexibility or safety.

Nozzle

The nozzle is a restriction at the end of the want that creates pressure. Nozzles have different spray patterns that affect the width and intensity of the spray. For example, a 40-degree (white) nozzle will provide a flat spray at about 40 degrees. There are also 25-degree (green) and the most popular 15-degree (yellow) nozzles. Caution operator attention to 0-degree (red) nozzles. It will cut into the wood and cause damage.

For everyday household cleaning tasks such as driveways, patios, and decks, the 25-degree (green) nozzle is the optimal general-purpose choice. Its wider spray distributes pressure more evenly across surfaces, minimizing the risk of damage while still delivering effective cleaning power.

Regardless of nozzle angle, maintaining a standoff distance of 12 to 24 inches is recommended when using wide-angle nozzles in the 25°–40° range. This distance preserves the balance between effective cleaning pressure and protection of more delicate surface materials.

EZ start adjustable unloader

The EZ start adjustable unloader removes pressure in the pump when starting the engine, makes the unit easier to start; less damage to starter motors, especially electric starter engines.

Frame

The frame is critical because it supports the functional components of a powerful pressure washer. The frames will not warp, bend or crack under the most challenging demands. They are also powder coated for extended life in all conditions and to minimize the risk of rust. Many models feature stainless steel frames. The heavy-duty powder-coated frame is compact, portable, and built to withstand years of rugged and rigors of use.

Safety relief valve

The safety relief valve is a design weakness of the pressure washer. The safety relief valve would open and safely relieve system pressure if the unloader fails.

Thermal relief

A technology used to reduce the build-up of hot water inside the electric washer pump when the gun trigger is turned off. When the water reaches the maximum water temperature, the water is circulated through the pump. Some of our pump models are designed for water temperatures of 145°F, 160°F, and some even as high as 180°F. Warm water will be discharged from the pump to the ground. This system prevents damage to the internal pump.

Trigger gun

The high-pressure washer gun controls the water flow. Simply squeeze the trigger to start the flow and release the trigger to stop the flow.

Turbo tip or turbine nozzle

A device that improves the efficiency of high-pressure water by rotating fine water streams at high speed.

Unloader

Relieves pump pressure when the trigger is released (spray blocked) by diverting water back to the inlet side (bypass mode). Prevents pump damage when the wand is not in use.

Running the unit in bypass mode for extended periods will increase the water temperature as the water recirculates. This hot water can damage the high-pressure pump. Most of our units are equipped with a thermal pump protector that drains hot water and introduces cold water, preventing damage to the pump.

Wand

There are two common types of wands: variable pressure and straight-through. The uneven pressure wand allows the user to twist the handle on the wand and reduce the spray pressure. If a chemical injector is connected, soap or chemicals will be automatically injected into the water stream after the pump when the pressure is reduced. Turn up the pressure again, and the injector will stop drawing soap. Besides being convenient, this is the best soap application because it never goes through the pump. Many soaps and chemicals are harmful to high-pressure pumps.

Wheels

Advanced power washers have pneumatic tires with inner tubes instead of hard rubber or plastic tires. Inflating tires with inner tubes provides longer wear time and makes it easier to operate a power washer on most surfaces. In addition, pneumatic tires can absorb vibrations, reducing wear and tear on working parts.

Air filter

Filters the air for combustion in a gasoline or diesel engine. Paper filter elements, oil-saturated foam elements, or a combination can be used.

Pressure washer pump

High-pressure pump

The pump draws water from an external source (usually a garden hose connected to a faucet) and pushes the water with force to create pressures of up to 3000 and 5000 PSI. In comparison, a garden hose produces 40-50 PSI. Some pressure washers have industrial-grade triplex (three plungers) pumps, and some have duplex pumps (two plungers).

Triplex pump

Triplex pumps are high-end pumps used in professional-grade pressure washers. They offer better performance and longevity compared to axial cam pumps.

Axial cam

The device (cam) is used to convert the rotary motion of the electric motor/engine into the reciprocating motion of the pump piston. There are usually fewer parts in an axial cam system, so such units are less expensive.

Gearbox pumps

A gearbox drive consists of a gear reduction box between the pump and the motor; therefore, the operating speed is approximately 1600 rpm, half the speed of a direct drive pump. Slower speeds reduce maintenance costs due to less frequent seal and valve replacements.

Ceramic plunger vs. non-ceramic plunger

The plunger is the moving part of the pressure washer pump, moving back and forth between the rubber seals to create the flow and pressure of the pressure washer system. The material used in all industrial-grade pumps is ceramic. This material has excellent properties, making it incredibly smooth and thus extending the life of the seal. Ceramic also does not wear out. Non-ceramic plungers will wear and shorten seal life.

Pressure washer engine

Engine (gas, diesel, electric motor, or hydraulic power source)

An engine, an electric motor, or an external hydraulic source are the energy sources that drive the high-pressure pump. Which is right for you? In short, gasoline models are more portable and suitable for outdoor use. Electric models, while less portable, are quiet and great for indoor use. Diesel engines are more durable and last longer.

Air-cooled engine

A gasoline or diesel engine cooled by air surrounding cooling fins on the cylinders. A fan mounted on the flywheel drives air and directs it via a cooling shroud.

Electric start

It’s a method of starting an engine using a key.

OHV

OHV technology improves efficiency, runs cooler, and reduces emissions. Same as the “overhead valve,” an improved method of controlling an internal combustion engine’s exhaust and intake valves. OHVI means a more durable industrial version of the OHV engine.

Measurement and Ratings

PSI (Pounds per Square Inch)

Unit of pressure quantifying washer output. Higher PSI means stronger water stream and more cleaning power. Residential machines typically range 1,300–2,000 PSI for light tasks like washing vehicles or furniture; mid-range units handle moderate cleaning; heavy-duty or commercial machines exceed 2,000 PSI for demanding applications. Matching the right PSI tier to your task protects surfaces while ensuring effective cleaning.

Bar

A metric unit of pressure indicates the output of a pressure washer. 1 bar ≈ 14.5 PSI

HP

HP (horsepower) is a unit of work that determines how much power the machine needs to clean the surface. Generally, the more horsepower a machine has, the higher the pressures, volumes, or a combination of both it can deliver. More powerful engines are more capable of completing the job quickly.

RPM

RPM stands for revolutions per minute. The number of revolutions (revolutions) of the engine in one minute.

Water flow (GPM)

Gallons per minute (GPM) is the volume of water used in one minute. Note: pressure cleaning is rated in GPM; steam cleaning uses GPH (gallons per hour), reflecting different throughput scales. Water volume determines how quickly dirt is removed once the debris-surface bond breaks. Higher GPM means faster cleaning; a 4 GPM unit covers more surface area per minute than a 2 GPM unit. For large-scale or time-sensitive tasks, flow rate—not just pressure—can be the decisive variable in overall performance.

Cleaning units

Cleaning power results from combined pressure and flow. Use the formula: Cleaning Units (CU) = Pressure (PSI) × Water Volume (GPM). This combined metric reflects both force and water volume delivered, making it a more accurate single indicator of real-world cleaning performance than PSI or GPM alone.

volt

12V usually generated by batteries for electric start and soft washer pumps. 120V (North America) or 220-240V (Europe, Asia, Australia) is the mains supply for electric pressure washers — check your local voltage before purchasing.

Temperature

This is the temperature range within which the device can be used safely; the specified operating temperature range for the device.

Drive Systems

Belt drive

Belt drives use pulleys and a belt to slow down the pump. With the engine running at 3,800 RPM, the pump will slow down to 1,400 to 1,900 RPM, depending on the pulley and belt settings. This system ensures a long pump life, as the bearings are not subject to much wear, and the pump is isolated from the engine’s heat by the belt and pulleys. The disadvantage of this system is the loss of efficiency due to the additional friction of the belts and pulleys. Plus, adjusting the belt requires more maintenance work. However, all other things being equal, a belt drive should provide the most extended pump life.

Direct drive

The pump is connected to the motor in a direct drive pressure washer system. Therefore, the pump spins at the same speed as the engine, usually around 3,800 RPM. The system has the advantage of being simple, with fewer moving parts; therefore, less expensive. The downside is that the pump rotates as well as the engine, and the bearings experience more wear, reducing the pump’s life.

Other

Cavitation

The impact of thousands of air bubbles collapsing inside the pump quickly pits metal surfaces and seals. Cavitation, also known as pump starvation, is caused by a lack of water at the pump inlet.

GFCI

A ground fault circuit interrupter (GFCI) detects current leakage and immediately cuts power to protect the user from accidental electrical shock (for electric pressure washers only).

2SC

This means a 2-wire compact hose—especially a high-pressure hose for hydraulics and pressure washing.

Female

The receiving end of a quick-connect fitting, typically installed on the hose side. The male plug inserts into the female coupler and locks in place. Also used to describe the internal thread of a pipe fitting. Standard quick-release probe outer diameter: 19.9 mm (common on gasoline and diesel pressure washers).

Epilogue

Congratulations! You've now mastered the terminology of pressure washers. This knowledge empowers you to make informed decisions, whether you're buying, using, or maintaining your equipment.

Remember, if you're a high-pressure washer dealer still navigating these waters, don’t fret. As a professional manufacturer based in China, we're here to guide you. BISON have dedicated specialists ready to address your purchasing concerns and provide tailored solutions.