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How to Adjust the Effective Pressure Washer Pressure

I received a great question and thought it deserved an entire post to answer.

The question:

I’m looking for a power washer around 3000 psi for general around the house work. I will occasionally use it to clean vinyl siding and will use it weekly or so to wash the cars. Mostly I want it for the summer to keep things clean around a pool we own.

My big concern is getting a machine that is too powerful for washing cars. I’m afraid of damaging the cars but want a machine that is powerful enough to keep a large concrete driveway clean.

Is there a way of dialing down the pressure from 3000 to say 2000 or lower when using it to wash cars. I’ve never owned a power washer before so I would appreciate your advice. Thanks.

Thanks Patrick for the q.

The gist: You can adjust the force hitting the surface by using different nozzles. Only the $3,000+ commercial pressure washers will have a dial that you can turn to adjust pressure. For a washer around the home you have to use nozzles, which is affordable and simple.

You can definitely have a 3,000 PSI pressure cleaner wash your car – as long as you use the right nozzle.

I’d recommend one of these gas power washers. The Generac 2,700 PSI is the most affordable gas powered, and should easily manage the jobs you want to do with it.

Let’s take a look at the effective pressures for each nozzle:

Nozzles

Nozzles are termed as 0 degrees, 15 degrees, 25 degrees and 40 degrees. The 0 degree nozzle shoots a direct jet of water. The 15 degree nozzle spreads out the water creating more of a sheet of water and so on… With the 40 degree one creating the biggest sheet.

If you’re standing with the tip of your pressure washer wand 1 metre from your house and you’re using a 3000 PSI pressure washer here are the corresponding forces for the different nozzles (assuming no losses over the 1 metre):

  •  0 degree nozzle: house feels 3000 pounds of force or 50 times the force of a garden hose.
  • 15 degree nozzle: house feels 289 pounds of force or 4.8 times the force of a garden hose.
  • 40 degree nozzle: house feels 105 pounds of force or 1.75 times the force of a garden hose.

So if you’re using the 40 degree nozzle and you stand 1 metre from your car you’re only washing your car with about 2 garden hoses of pressure, which is fine and won’t damage it.

Things to Consider

  1. The closer you are to the surface the more effective force. Since the GPM out the nozzle is the same if you’re using the 40 degree nozzle but standing with the nozzle less than 1 inch from the surface – the surface feels the full PSI of the washer.

Here’s how I came up with those numbers (omitting the trigonometry and assuming no losses over the 1 metre from the nozzle to the surface)

Nozzle Forces

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