Adjusting unloaders for pressure spikes

[Wayne G.]

I have a 4000psi pump with a pressure sensitive unloader. If I adjust the unloader to where the pump puts out the max psi that the engine can produce, which is about 3700psi, when the gun is closed and it goes into bypass then my pressure spikes to 4300 to 4500psi. Will this practice significantly reduce the life of the pump?

I have heard that the pressure in the system with the gun closed in bypass mode is kept in the high pressure hose between the unloader and the trigger gun, so the pump would not be subject to the pressure spike. Is this true?

[PressurePros]

Wayne, you should turn your unloader down to the operating psi as dictated by your nozzle size. This way you will not lose any flow and the pressure build up in the hose won't be severe.

For example, you are doing decks all day and your nozzle gives you 1000 psi. Open your gun and back off your unloader until the pressure falls below 1000 psi (you have gone a little too far at that point) turn it back up slowly until your reading is once again solid at 1000 psi.

[Russ Johnson]

Unload pressure should be 10% higher than operating pressure. Yours should unload around 4,100.

[Wayne G.]

Ken, thank you for your response. I am confused. My pump is 4gpm at 4000psi. I have a 13hp gas engine that will drive the pump with a 4.0 nozzle and 50' ft of hose to a max psi of 3700. But with the unloader adjusted like this, when the gun is in the closed postion the pressure spikes at the pump to 4300-4500psi. Should I adjust the unloader to where the max psi at the nozzle is about 3500psi so when in bypass the spike is around 4000psi at the pump instead of 4500psi?

[Wayne G.]

Thanks Russ!

[Wayne G.]

Russ - If I want 4000psi at the nozzle. Then what I need is a 4500 psi pump with the appropriate engine to drive it to that capacity and correct nozzle and set the unloader where it runs at 4000psi with the gun open and spikes to about 4500psi with the gun closed...Correct?

[PressurePros]

wayne... question. what are you cleaning at 4000 psi?

[MMI Enterprises]

Hi Wayne...Mind I ask why would you ever feel a need to go from 3.7psi to 4kpsi?.. About anything you need to do up past 3k can be done with a turbo nozzle. Maybe your unit is cold washer and your trying to compensate for lack of heat?
GPM and heat is what cleans things faster not psi.

[Wayne G.]

Ken I am cleaning very dirty aggregate with cold water and no chems.

[Wayne G.]

MMI - thanks for the info. I am currently cleaning a 36,000 sq ft parking lot so a turbo is unrealistic. And 95% of my work is residential, so I can not justify nor do I have the money for a hot water unit. My setup is two cold water units plumbed together so I have 9 gpm and 3600psi at the pumps

[MMI Enterprises]

Regardless, ya think a few hundred will make a difference?
Surface cleaner the way to go and/or a turbo.

Maybe you can discuss and post some pics over here on that new thread I had just posted : Boosting small gpm skids with portable units?

[Beth n Rod]

Originally Posted by Wayne G.

Ken I am cleaning very dirty aggregate with cold water and no chems.

Why? What's around it that you could not use even a simple house wash detergent and far less PSI? What on it?

Beth
p.s. Thanks Russ!

[Wayne G.]

MMI - I have noticed a difference in cleaning at 3600psi vs.3300psi and thought the step from 3700 psi to 4000psi might result in the same difference.

[Wayne G.]

Beth - Thanks for your input. I use 3% bleach and laundry detergent downstreamed at about 8 to 1 to clean houses. And I'm pretty sure this will not help. Any house wash detergent suggestions?

[Barry M]

The proper chemicals ALWAYS help. I use my house wash mix on concrete with great results.