Parts of a Pressure Washer – Pump, Gun and Wand Labeled

All 21 parts on the diagram

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Whole machine 8

Pump Raises the water to high pressure. The engine turns it.
Engine A small gasoline engine. Its shaft turns the pump.
High-pressure hose Carries the high-pressure water from the pump to the spray gun.
Spray gun Starts and stops the spray with its trigger.
Fuel tank Holds the gasoline for the engine.
Recoil starter Starts the engine by hand. Pull the grip on its rope.
Frame The tube cart that carries the engine and pump. Tip it back by the handle to wheel it.
Wheels Let one person roll the machine to the job.

Gun and wand 5

Trigger Squeeze it to spray. Let go and the spray stops.
Trigger lock A catch that stops the trigger from being squeezed by accident.
Wand A long tube that puts the nozzle well away from your hands.
Quick-connect coupler A collar that slides back to take a nozzle. Let it spring forward and the nozzle is locked in.
Nozzle Shapes the spray. A narrow spray hits harder than a wide one.

Pump 8

Water inlet Where the garden hose joins. A screen inside keeps grit out.
High-pressure outlet Where the high-pressure hose joins the pump.
Unloader valve Sends the water back around the pump when the trigger is released.
Thermal relief valve Lets hot water drip out to cool the pump. It opens when the pump runs too long without spraying.
Detergent siphon tube Draws detergent into the water. It works only at low pressure.
Plunger A smooth rod that slides in and out to push the water. Many pumps have three, side by side.
Seals Rings around each plunger that keep the water in the head.
Check valves One-way valves inside the pump head. One lets water in and the other lets it out.

How this list was compiled: Part names checked on 2026-10-01; a name is kept only when two independent sources use it. (1) A maker's operator's manuals for gasoline pressure washers, https://archive.org/details/manualzilla-id-6088906 and https://archive.org/details/manualzz-id-745829 (spray gun with trigger and trigger lock, high pressure hose, recoil starter, fuel tank, nozzle, detergent siphoning tube, high pressure outlet, water inlet and inlet screen, pump, the cool-down system that the manual also calls thermal relief; its parts list: check valves, thermal relief valve, unloader, pistons and seals). (2) A second maker's operator's manual, https://archive.org/details/manualzilla-id-6198268 (pump, starter grip, spray gun with trigger and safety latch, detergent injector and hose, wand, high pressure hose, unloader, quick coupler, pressure nozzle, water filter and inlet connector, piston packing). (3) A third maker's operator's manual, https://archive.org/details/manualzilla-id-7309415 (unloader valve and what it does, trigger gun, high pressure hose, water inlet, outlet, three-plunger pump, check valves, packings and seals, frame and handle). (4) Two owner's manuals sold under store names, https://archive.org/details/manualzilla-id-7325030 and https://archive.org/details/manualzilla-id-6316069 (trigger locking latch, wand, spray nozzles, muffler, fuel tank, recoil starter, pump, pump inlet, pump outlet, thermal relief valve, pressure hose, check valve, unloader, frame, wheels). (5) Wikipedia, English edition, Pressure washing and Plunger pump, https://en.wikipedia.org/wiki/Pressure_washing and https://en.wikipedia.org/wiki/Plunger_pump (trigger gun, wand, nozzles, unloader valve; a plunger sliding through a fixed seal, valves at the suction and discharge sides). Detail lines are in our own words. Licence: own work

The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work

How it works

These are the parts of a pressure washer with a gasoline engine: the engine and pump on a wheeled frame, the hose, and the spray gun with its wand. Two close-ups follow: the gun, and the pump cut open.

Read the full guide

The machine, the gun, then inside the pump

Numbers 1 to 8 are on the whole machine: the pump, the engine that drives it, the high-pressure hose, the spray gun, the fuel tank, the recoil starter, the frame and the wheels. Numbers 9 to 13 are on the gun: the trigger, the trigger lock, the wand, the quick-connect coupler and the nozzle. Numbers 14 to 21 are on the pump: the water inlet, the high-pressure outlet, the unloader valve, the thermal relief valve and the detergent siphon tube outside, and one plunger with its seals and check valves inside.

Weak spray? Look at the nozzle first. Two of the manuals read list a clogged nozzle among the causes.
The siphon tube draws detergent only at low pressure, so fit the soap nozzle before you expect suds.

Questions and answers

What are the main parts of a pressure washer?

An engine or an electric motor, a pump, a high-pressure hose, a spray gun with a wand, and a nozzle. A gasoline machine also has a fuel tank and a recoil starter, and most sit on a frame with wheels.

What does the unloader valve do?

It gives the water somewhere to go when you let go of the trigger. The pump keeps running, so the unloader valve sends its water back around to the inlet side. On many machines the same valve sets the spray pressure.

Why is water dripping from the bottom of the pump?

It may be the thermal relief valve. When the engine runs for a few minutes with the trigger released, the water in the pump heats up and the valve lets some out. A steady drip while you spray points to worn seals.

How does a pressure washer pump work?

The engine turns a plate or a crank that pushes the plungers in and out. Each stroke draws water in through one check valve and forces it out through another, toward the hose. Seals around the plungers keep the water in.