Pressure washer build help

Hello! I just recently built my first gas pressure washer.

I’ve got an AR RRV4G40 (4GPM 4000PSI) pump with a VRT3-310 unloader, and my engine is a 16HP 420cc Duromax XP16HPE.

No buffer tank is being used, by-pass is recirculated back to the inlet.

While setting unloader, I cannot get operating pressure to reach 4000psi. Operating pressure will reach 3000psi (3200psi bypass/spike pressure) and any further adjustment to the unloader only increases my spike/bypass pressure.

The engine is operating at 3400rpm during testing as displayed on the tachometer.

Throttle lever at 9/10 as the engine reaches 3600 rpm, full throttle.

Inlet water pressure at end of the hose is 60PSI and supplying 4+GPM.

No air is leaking into the inlet to the best of my knowledge, as it holds 60PSI without leaking water, using brand new #4 orifice general pump nozzle 105084.

With that all being said, what could be causing my machine to not reach full operating pressure? Could it be that I’m testing at only 9/10 throttle? I don’t want to run the pump at 3600rpm and damage it. I consulted with the company that sold me the pump and they told me it could be the shutter valve in the unloader sticking open.

REF #21-#25

The unloader is brand new though.

If anybody has had this issue before and can chime in or has any tips it is greatly appreciated!

Thanks - Phillip, Triton Pressure Washing

That’s terribly difficult to read.

1 Like

Yeah sorry first post, I’ve fixed it.

take off black handle of unloader, theres additional adjustment available by loosening nuts.

Thanks for your reply @Redjess, I have taken the handle off and adjusted the locking nuts to their lowest position already. the problem isn’t that the unloader is bottoming out, but that when I try to increase the pressure only my spike pressure increases after 3000PSI.

Those gauges are pretty inaccurate, if you’re getting 3000psi you have more than enough for pretty much anything.

You’re most likely right, the quality of this gauge seems a Lil iffy to me. this is what I had grabbed some amazon garbage, Ultimate washer doesn’t even sell the same one on their site.
I just needed one quick so I could set the unloader, you have a gauge you can recommend? was thinking to get a comet and mount it directly off the unloader using a tee, or just use the coupling off this gauge.
yeah, you are also right about 3000psi being enough, I just wanted to try and get the full performance out of my machine to maybe reduce cleaning times… also going to be using it for downstreaming a bit until I get my softwash setup and want to be able to get chemical up high and i assume it’d be easier to do so at 4000psi.

Alrighty, I was saying the same darn stuff three years ago so here’s the lowdown.

GPM is king, PSI is secondary. If you get a full 4gpm at 3000 after 200’ of hose, you’re set. Get a small buffer tank ASAP so you can run bypass instead of having to hit the trigger every half minute. Downstream washing height comes from the proper shooter tip that runs about 100psi instead of 4000psi.


Okay, I gotcha you have a good point. ill keep it at 3k.
As for running a buffer tank I’ve read I shouldn’t with a direct drive pump because of low inlet pressure off buffer tank and need either gear or belt-driven pump? I was thinking to just plug off the inlet port and run the bypass to dump to the ground though, or set up 2 valves on the bypass ports so i can switch between dump or inlet bypass if I need to drop the gun for a few minutes.

So part of your issue might be running the motor at 3400 rpm instead of 3600. Most direct drive pumps are rated for 3600. So they will put out less gpm. Less gpm results in a lower peak pressure in the same tips.

Not really a huge deal; as others have pointed out, 3000psi is plenty. But you are probably missing out on some flow, that’ll help a bit with efficiency. You should be able to run that motor at 3600 no problem.

It is quite likely that your motor is not actually producing 16hp, even though it is advertised as 16hp.
At least my guess…

Edit: @Philaroo

okay thanks, ill test it out tomorrow at 3600 and see if that helps.

@charc0al yeah, I wouldn’t doubt that to be honest.