Unloader and thermal relief valve

I am using a Simpson 4200/4gpm machine. The pump does not come with an outlet for the unloader to cycle water when the trigger isn’t pulled but it does have a thermal relief valve.

The manual doesn’t mention anything about setting up or adding anything to the pump. It only says to not run the machine longer than 2 minutes without the trigger pulled. I never run it longer than several seconds without the trigger pulled.

Should I worry about setting up the unloader to cycle water or not worry about messing with it?

When you say all the way in what do you mean? I have it turned clock wise all the way.

Great machine by the way, huh?

DO NOT do this. Set the unloader with the proper tip and never touch it again.


You only bypass if you have a buffer tank


Please listen to william on this…If pressure washing isnt your specialty then please refrain from giving advice out on setting unloaders.


Which is william?

IBS = William = He knows what he’s talking about. Listen to him.


Sounds like you are referring to wanting to add a line to bypass water back in your tank your pump probably does not have the capabilities to do that it bypasses internally

Yes that’s what I thought. And no mention of it in the manual. Seems fine since I rarely don’t have the trigger pulled or the gun off the hose at the ball valve

One teason to use that unit enough and make enough to upgrade to belt drive w a better pump and pull ofd a bufder tank. Keep the unit u got as a spare thats what i did at least.

When I first started PW last year I was told to turn it all the way in and leave it alone. Now that’s not how it’s done?

Not sure who told you that, but it is incorrect. Set your unloader, then leave it alone

Maybe the vendor wants you back


Guess I’m gonna have to do a search now on how to ‘set’ my unloader.


I agree, probably a good idea to familiarize yourself with the operation of your machine and adjustments and maintenance requirements. The manual is a good place to start . Anything not covered in there is a search or question away on here.
Dont trust ‘the guy at the shop’ to be right everytime or some guy on the internet giving advice on how to set unloaders without first understanding how to set unloaders.

Did a search, still don’t understand the procedure. My machine doesn’t have a bypass, unloader is built in. I haven’t messed with it since I bought it.


The text between the lines below is from the fourth page of Cat’s Data Sheet for your pump, which is available here:

An integral unloader with built-in by-pass is part of the discharge manifold to
provide system pressure regulation and pump protection. This pump also includes
a fixed chemical injector for chemical application.
Pump should be purged of air before commencing with operation. Liquid must
flow through the pump without discharge restriction to assure full system pressure
is reached.
Install a pressure gauge close to the manifold head of the pump to assist in setting
system pressure and to periodically monitor system pressure.
Setting and adjusting the unloader pressure must be done with the system turned
on. Start the system with the unloader backed off to the lowest pressure setting
(counterclockwise direction). Squeeze the trigger and read the pressure on the
gauge at the pump. Do not read pressure at the gun or nozzle. If more pressure
is desired, release the trigger, turn adjusting cap one quarter turn in a clockwise
direction. Squeeze the trigger and read the pressure. Repeat this process until the
desired system pressure is reached. Thread locking nut up to adjusting cap and
tighten set screw. All high pressure systems should have a secondary relief valve.
Set secondary relief valve 200-300 psi above the unloader setting.
NOTE: Pressure is not set at the factory.

See an integral unloader on a Cat pump set here (which I do not vouch for):


The guy in the video is nuts but surely no one here is using crap like that to wash with anyway

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