How Does a Pressure Washer Pump Work? [ANSWERED]

A pressure washer is simply a water pump. It is powered by a motor that draws in water, pressurizes it, and then releases it through a cleaning attachment. They are available in two types: axial and triplex. Axial pumps are better suited for commercial use.

Pressure washers are great for speeding up that cleaning job. They take the hassle out of spraying down an area. Yet, have you ever wondered how they work?

Let’s take you through the mechanics of your pressure washer. Also, we will touch on why you need oil for your machine. Read on to learn all this and more.

pressure washer on driveway

Related Reading: Are Pressure Washer Hoses Universal? [ANSWERED]

How a Pressure Washer Works

The basic principle of a washer is to force water through a constricted space. This compression is what causes the pressure. Imagine what would happen if you took your hand and made the opening of your garden hose smaller. You would feel the water building up and trying to push its way through the narrow opening.

In effect, this is what a pressure washer does. It just does it using a motor instead of your hand.

  1. The pump starts to draw in water from your source.
  2. A cleaning solution, such as detergent, flows into the washer via an additional hose. (This step is optional).
  3. As the water enters the pressure washer, the pump mixes the water and detergent. This mixture is heated to between 125–155°F. (Some washers are unable to heat the solution)
  4. The pump forces the solution through the pressure hose. As the water flows through the pump and up the hose, it is compressed.
  5. Water is then squirted out of the cleaning attachment. Though the pump and pressure hose pressurize the water, you can add even more compression with the nozzle.

Pressure washers not only do an outstanding job of cleaning, but they also use less water than a garden hose. On average a standard hose uses around 24 gallons of water a minute. A pressure washer uses a tenth of that (2-4 gallons per minute).

When it comes to maintaining your washer, give it a good clean after every use. Also, check if you need to replace the oil.

The 4 parts of a pressure washer

A pressure washer consists of several components. These are created to pump water through the unit while pressurizing it. Then the water is released through a trigger at a highly compressed rate.

All pressure washers are fundamentally the same. There are usually five parts that make up the washer (you will find that there are units with extra features).

  1. Inlet Hose

This is the component that you connect to your faucet. It has an in-built filter to prevent debris from getting into the water pump.

  1. Motor

The motor will be powered either by gasoline or electricity. Usually, the smaller washers are electrical and have a rating of 1,300 PSI or higher. Larger machines (2,000 PSI or more) are run using gasoline. These are ideal for commercial jobs. However, they are noisier than the electrical models.

It’s the job of the motor to push the water through the pump.

  1. Water Pump

The water pump is where the action happens within the washer. First, it extracts the water from your water supply (e.g. your faucet). Then it pushes the water out in a pressurized stream. Pumps can push through up to 2 gallons of water a minute.

  1. Pressure hose

A pressure hose pulls the water up to the cleaning attachment. It is reinforced with plastic and wire meshing. This hose needs to have a higher pressure rating than that of the pump. Safety precautions dictate that you should always use a hose with a rating 3 times higher than your pump.

For example, if your pump is rated at 1,500 PSI then your pressure hose has to be 4,500 PSI.

Related Reading: How Much PSI Is Necessary In A Pressure Washer? & Is 2000 PSI Safe for Washing a Car?

What Is Pressure Washer Pump Oil

Within your washer are moving parts. Like any engine, these can suffer from friction as well as wear and tear while in motion. To extend the life of your washer, you need to make sure you are keeping it well-oiled.

Here are a couple of more reasons why you need pump oil:

  • It’s part of your warranty agreement: Carefully read the warranty card that came with your pressure washer. A failure to perform standard maintenance on your machine can void your warranty.
  • The cost of repair: Axial pumps have a higher wear-out rate than the triplex version. However, triplex pumps are easier to repair. The repair cost for these is also cheaper than axial pumps. Usually, with axial pumps, you can easily replace the seals, but if the wear and tear is more widespread, then it’s better to buy a new unit.

When should I replace the pressure washer pump oil?

How often you do an oil change on your pressure washer depends on much you use it. To ensure you are maximizing the life of your unit, replace the oil every 3 to 5 months. Another rule of thumb is to swap out the oil after 200 hours of work use.

If you seldom use your washer, then you could get away with replacing the oil less often. In this situation, an oil change every six months or once a year is okay.

Look to see if the oil within your washer is milky. That is a sign that it is being contaminated and you need to do urgent repair work on the unit.

What oil should I use?

When changing the oil in your pressure washer you should use 30w non-detergent oil. There is some debate around if it’s okay to use other oil. For example, in temperatures above 40OF, you could get away with using all-purpose engine oil.

Always check your user manual for the recommended oil type. After all, you don’t want to invalidate your warranty.

When buying oil, there are three options you could choose from. Look at the label on the bottle for one of these indicators:

  • ND: This means non-detergent
  • Pump Oil: An oil created with water pumps in mind.
  • For classic cars: Usually made from low-detergent or non-detergent oil. However, it is more expensive than ND oil

There is no set rule as to which of these oil types is the best for your pump. You can try them all and settle on the one that is your favorite.

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How to do an oil change in your pressure washer

When it comes to swapping out the oil in your pressure washer, the procedure is similar across all types and brands.

  1. Turn on your pump and let it run for several minutes.
  2. Remove the oil. You can do this either by draining it out, using a suction gun, or pumping it out with a hand pump.
  3. Store away the used oil in a container. It can be recycled at a specialist center.
  4. Put the drain plug back in. Fill your pump with the new oil.

When replacing the oil, you don’t want to overfill the pump. Doing so runs the risk of leaks which can damage your washer. Take your time. Don’t rush through the process.

Continue Reading: Does A Pressure Washer Use Regular Gas?


A pressure washer pump is made to extract water from a source and then push it through a compressed hose. The water is then released through a cleaning attachment. Using this type of pump for cleaning is not only effective at removing stubborn dirt it also uses less water (up to 4 gallons per minute) than a garden hose (24 gallons per minute).

Oil is used in most pumps to reduce friction and extend the life of the unit. The standard oil is 30w non-detergent oil. Yet, there are situations where you could use all-purpose oil.

Take your time to maintain your pressure washer and you will have a unit that lasts for countless cleanup jobs.