Operating pressure drop

Patricio

Patricio

New member
Here is a newbie question but I don't have measurements to compare to so I wonder. Never used a pressure gauge on my pressure washers until this week. I would like to know if this is normal and expected. My 3500 psi 5.5gpm PW gives a reading of 3700Psi when there is now flow. When the trigger is pulled the Psi drops to 2400. Normal and expected drop? Reading is taken at the end of a 2' whip line and before the hose reel.
Thanks
Pat L
 
Without the trigger pulled you are at 3700 which is where your unloader is set to go into bypass, thats a good setting so don't mess with that. The first thing I would check is the inlet make sure the screen is not clogged reducing the water flow. Second check the tip and make sure it is a newer one that is not worn out. As tips wear they will cause the pressure to drop because the opening gets larger.

If you still have problems try force feeding the pump with a garden hose to see if there are any air leaks. If you see water dripping from the area behind the head and the body of the pump that is a tell tale sign that the packings are worn and need to be replaced. You can also inspect the check valves to see if there is some debris in them, if they are worn or they oring they sit on is bad this will cause problens as well. Usually if this is the case you will feel a vibration in the hose when you pull the trigger.
 
Your psi will increase by approximately 400 psi by using a #5.5 nozzle instead of a #6 nozzle, at least that what it does on my 5.5 gpm @ 3,500 psi unit. The #5.5 nozzle will more closely match your machine for 3,500 psi cleaning.
 
Thanks David. The pressure washer came with 5.5s but when I ordered an extra set I got 6.0s/. Just tried them and I would say about 400 psi was the difference. What do you see for a difference in pressure between having the trigger open and having it closed? The general opinion seems to be that I am getting a bit much of a difference but what should it be?
 
I was getting maybe a 500 psi spike when I released the trigger, which is your trapped pressure reading. A year ago, I switched to a K-7 unloader which causes the pressure to drop to zero in your hose when the trigger is released and the system goes into bypass. The spikes from the old pressure actuated unloader seemed to wear out the hoses and guns faster so I switched to a flow actuated unloader (K-7). Both unloader types have their strengths and weaknesses.
 
Was the pressure test done AT the head of the pump, or after the pump ?
If the unloader is not unloading, there's more than 1 problem..
frequesntly, the noticeable glitch is an affect, NOT the "cause".
I can send you literature on "all about" unloaders, and talk you through the rest if you like..
I'm Working Saturday (most of the day).

e-mail me.

..and come to my Pressure Washer Troubleshooting School.. when there's one near you..
stay tuned for details on PWI
 
So you are up to 2800psi at the end of 2 foot whip line with a new 5.5 nozzle?

And you have a closed gun pressure reading of 3700psi with the same whip?

Do you have a tachometer on the engine, whats the rpm?

The machine is newish so, if the pump is feed correctly, spinning at the correct speed to produce the desired flow (you can test it with a bucket and stopwatch no nozzle), I am thinking that the unloader is set a little on the low side.

Do you have 4.0 or 4.5 nozzle to test with? The gauge should then read the unloader setting.
 
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I am wondering if the engine is not speeding up enough myself. The unloader has been tightend all the way down. So I would not be able to do anymore there. I have since backed it off a bit.
Thanks
 
Patricio said:
I am wondering if the engine is not speeding up enough myself. The unloader has been tightend all the way down. So I would not be able to do anymore there. I have since backed it off a bit.
Thanks
Click to expand...

With all this testing I hope the guage is accurate (i had one that after some use had wrong readings). Do the bucket test to the determine the flow at the engine rpm. A tiny tach is a good tool to have.
 
Thanks Nigel.
I adjusted the throttle cable. It was loose. Does not look ike it ever slipped. I am guessing it came that way. Snugged it up and now spike is 3750 and with a 5.5 25º nozzle my operating pressure is 3050. Further adjustment gets be to 3100 but thats squeezing every last bit out of it. Not that the 20HP engine seems to care.

So, After all this I still don't know what normal and expected is. Does operating of 3050 PSI seem about right?

Thanks everyone for all the help. I appreciate all the help.

Pat L
 
Should hit 3500psi with a smaller tip (less that 5.5) with the 2 foot whip line .....something still off.

Do the bucket test.

What type of gun are you using?

Tiny tach is the best stethoscope for the situation.

Back the unloader all the way off and run the machine pulling and releasing the trigger,... and while resetting it continue to do this (it may or maynot have a piece of trash in it)

What is the unloader model?
 
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Is this a gear drive? Direct Drive? Belt Drive?

If it is belt drive, check the belts for play, there should not be that much, they could be worn or not tight enough.
 
I will check out all the above. I did adjust a regulating screw on the throttle. It seemed a bit to regulating. Wull test things out tomorrow and try other ideas if that did not do it.
 
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