Pressure Washer Question

[16again]

Bought this brand new about 8 months ago. Finally started it up last week.
Simpson ALH4240 pressure washer.
Darn thing is a beast! Works great

Cat 67DX39G11 Pump
If I let go of the trigger on the wand or the hover wand, the valve on back of pump pushes out water like crazy!
What the heck does this mean? I’m NOT a pressure washer guy at all.
Is this normal?
Do I need to replace the part (not the pump) I’m pointing to?
Educate me, please.
Thanks

 

[scooby074]

Not the thermal valve releasing is it? You dont want to dead-head the pump for more than a minute or two at the most.

 

[16again]

Not the thermal valve releasing is it? You dont want to dead-head the pump for more than a minute or two at the most.

Honestly, I don't know. Seems that as soon as I let go of the trigger, that part is blowing water like crazy. Water that comes out is quite warm and this is not a hot water pressure washer.

 

[thool]

I have the 3GXT30 and that looks like the thermal relief valve. As @scooby074 stated, you don't want to run the unit without spraying. I give mine 30 seconds max, then either spray or shut it off. After every session, I allow hose pressure to push water through the pump for a few minutes to help cool it, by squeezing the trigger without a tip on the wand.

I'd contact Cat Pumps and see what they have to say.

 

[scooby074]

Honestly, I don't know. Seems that as soon as I let go of the trigger, that part is blowing water like crazy. Water that comes out is quite warm and this is not a hot water pressure washer.

Very likely its the thermal then. You arent feeding it hot or warm water are you?

Also curious did you change the jets on the gun/are the jets the right size? If you arent feeding it hot water I wonder if your somehow restricting the gun from flowing enough which causes the pump to re-circulate the already pumped water which causes it to warm up. You want the water to go through one way and out the nozzle to keep things cool

 

[16again]

Very likely its the thermal then. You arent feeding it hot or warm water are you?

Also curious did you change the jets on the gun/are the jets the right size? If you arent feeding it hot water I wonder if your somehow restricting the gun from flowing enough which causes the pump to re-circulate the already pumped water which causes it to warm up. You want the water to go through one way and out the nozzle to keep things cool

No hot water being used. Straight from the spigot (city water) 3/4" water line. Plenty of water and pressure right from here.

This only happens when I stop using the wand or even when I stop using the hover wand. I want to say that it takes about a minute before it blows. That said, this thing has enough pressure that I'm actually considering turning it down.

Really want to do the roof. Trying to figure out how to start the unit and get up on the roof BEFORE it starts blowing out. I'm hoping that its only a weak (defective) thermal valve. Trying to figure out which one to order. After looking online figured I'll just call in the morning and let them tell me which one. Only a few bucks, I'll just swap it out.

 

[LopezBart]

This only happens when I stop using the wand or even when I stop using the hover wand. I want to say that it takes about a minute before it blows. That said, this thing has enough pressure that I'm actually considering turning it down.

You cannot let the pump dead-head for very long w/o either tripping the thermal protection or getting close to it.

From your owner's manual page 15:

DO NOT stop spraying water for more than two minutes at a time. Pump operates
in bypass mode when spray gun trigger is not pressed. If pump is left in bypass
mode for more than two minutes internal components of the pump can be
damaged

As they say in the computer biz: RTFM

 

[scooby074]

No hot water being used. Straight from the spigot (city water) 3/4" water line. Plenty of water and pressure right from here.

This only happens when I stop using the wand or even when I stop using the hover wand. I want to say that it takes about a minute before it blows. That said, this thing has enough pressure that I'm actually considering turning it down.

Really want to do the roof. Trying to figure out how to start the unit and get up on the roof BEFORE it starts blowing out. I'm hoping that its only a weak (defective) thermal valve. Trying to figure out which one to order. After looking online figured I'll just call in the morning and let them tell me which one. Only a few bucks, I'll just swap it out.

Edit: It looks like you have an internal unloader, im more familiar with the external unloader models. Im wondering if your unloader is unloading? Try loosening the unloader knob and see if you have any changes. Im wondering if something is stuck inside. Sometimes loosening and retightening the unloader can jiggle the valve inside and get it moving again

This guy converted his SImpson / Cat internal, into an external with the dump. You can see what were talking about here.

Still get in the habit of using larger nozzles to reduce pressure instead of the unloader though

Good discussion about orifice number and pressure

 

[16again]

@scooby074 Thank you

 

[scooby074]

@scooby074 Thank you

No problem, hope it helps a little bit.

Id start with troubleshooting the unloader knob on your existing setup and go from there.

 

[mike93lx]

Paging the pressure washer oracle

@fatfillup

 

[Hohn]

You cannot let the pump dead-head for very long w/o either tripping the thermal protection or getting close to it.

From your owner's manual page 15:



As they say in the computer biz: RTFM

Bart nails it again.

All that pump work has to show up somewhere. When you are pumping water in circles through a lot of restriction, it gets HOT.

 

[fatfillup]

The part in question is a thermal relief valve that is designed to dump water at 140 degrees F. Kinda like the thermostat in your cooling system.
When the trigger is shut off, a small volume of water circulates through the pump, unloader and back into the pump. It heats up due to friction and will eat away at the pump seals.
One thing that will cause the water to heat up quicker is if the unloader isn't going into bypass. When the trigger is released, the engine should speed up a bit and sound like there is no load. If the motor is lugging down when the trigger is released, then the unloader is not going into bypass and the water will get hot much quicker.

As to roof cleaning, if asphalt shingles, NO HIGH PRESSURE!!! HIgh pressure will wash the pebbles off the shingle and expose the asphalt to UV light and will degrade quicker.

Good discussion about orifice number and pressure

First video about adding an external unloader is a temporary solution to buying the wrong equipment to do the job. Yeah it will work for a bit but unloaders are wear items and when the internal unloader starts bypassing water when the trigger is open, you will be buying a new pump anyway. And dumping the water on the ground is wasteful especially in areas where water is not plentiful.

Second video, I couldn't watch for long. Guy is diving into minutia about quick couplers and guns that just doesn't matter. I assume his name of Obsessed Garage should explain where he is coming from, take everything to the n'th degree and keep on going. Didn't make it to nozzle size but it is critical for sure. You can always use a bigger nozzle and get less pressure and not hurt anything

 

[Hohn]

The part in question is a thermal relief valve that is designed to dump water at 140 degrees F. Kinda like the thermostat in your cooling system.
When the trigger is shut off, a small volume of water circulates through the pump, unloader and back into the pump. It heats up due to friction and will eat away at the pump seals.
One thing that will cause the water to heat up quicker is if the unloader isn't going into bypass. When the trigger is released, the engine should speed up a bit and sound like there is no load. If the motor is lugging down when the trigger is released, then the unloader is not going into bypass and the water will get hot much quicker.

As to roof cleaning, if asphalt shingles, NO HIGH PRESSURE!!! HIgh pressure will wash the pebbles off the shingle and expose the asphalt to UV light and will degrade quicker.

First video about adding an external unloader is a temporary solution to buying the wrong equipment to do the job. Yeah it will work for a bit but unloaders are wear items and when the internal unloader starts bypassing water when the trigger is open, you will be buying a new pump anyway. And dumping the water on the ground is wasteful especially in areas where water is not plentiful.

Second video, I couldn't watch for long. Guy is diving into minutia about quick couplers and guns that just doesn't matter. I assume his name of Obsessed Garage should explain where he is coming from, take everything to the n'th degree and keep on going. Didn't make it to nozzle size but it is critical for sure. You can always use a bigger nozzle and get less pressure and not hurt anything

Great post. A small external unloader with a surge tank can save your PW pump if you have extended periods of not spraying.

The hotter water will cavitate the pump, and cavitation can eat through almost anything.

As for nozzle size, you just need to know that the orifice number represents gpm at 4000psi. Unless you need 4000 psi (you don’t) and have a machine rated that high, the orifice number should always be larger than your pump’s gpm rating.

I run an oversized 4 gpm CAT 66dx on only a 9hp Honda. Since I don’t have the hp to pull full pressure at this flow, I run oversized nozzles to get the pressure down to 2500psi. A #5.5 nozzle puts me around 2200 psi. A 4.5 gets me about 2500psi.

You be surprised how effective 2200psi is when it’s a full 4gpm.

The original pump gave this machine a rated 3.5gpm/3800 psi. Going bigger on flow and lower on pressure for the same engine was a decision in hindsight that worked much better than I thought it would.

 

[16again]

@fatfillup, thanks for the info.
I called CAT pumps. Very helpful, gave me the needed information and I ordered the proper thermal relief valve.
My roof is concrete just like the rest of the house. I clean it with the hover wand. Going to look into lowering the pressure with different tips. Guy at CAT pumps said the same thing.

 

[scooby074]

The part in question is a thermal relief valve that is designed to dump water at 140 degrees F. Kinda like the thermostat in your cooling system.
When the trigger is shut off, a small volume of water circulates through the pump, unloader and back into the pump. It heats up due to friction and will eat away at the pump seals.
One thing that will cause the water to heat up quicker is if the unloader isn't going into bypass. When the trigger is released, the engine should speed up a bit and sound like there is no load. If the motor is lugging down when the trigger is released, then the unloader is not going into bypass and the water will get hot much quicker.

As to roof cleaning, if asphalt shingles, NO HIGH PRESSURE!!! HIgh pressure will wash the pebbles off the shingle and expose the asphalt to UV light and will degrade quicker.

First video about adding an external unloader is a temporary solution to buying the wrong equipment to do the job. Yeah it will work for a bit but unloaders are wear items and when the internal unloader starts bypassing water when the trigger is open, you will be buying a new pump anyway. And dumping the water on the ground is wasteful especially in areas where water is not plentiful.

Second video, I couldn't watch for long. Guy is diving into minutia about quick couplers and guns that just doesn't matter. I assume his name of Obsessed Garage should explain where he is coming from, take everything to the n'th degree and keep on going. Didn't make it to nozzle size but it is critical for sure. You can always use a bigger nozzle and get less pressure and not hurt anything

Yeah I know the external unloader is a bit of a hack. I had a much longer reply that I deleted half of that said that. I was trying to get the OP up and running with what he had to do the job he was planning. Minimal added expense

And yes. Obsessed Garage is difficult at the best of times, I picked his vid so as to hopefully show the OP in more detail what difference orifice size can make as hes still learning. There were a couple Landa vids that were 2:00 long on the subject, but lacked the minutia that might have helped OP.

 

[L.Cheapo]

I have the exact same machine. As stated above, operating as intended. I believe the manual states not to let the pump deadhead for more than 2 minutes. If I stop spraying mine for a minute I can feel the temperature of the water increase through the hose. I try not to let it happen for more than a few seconds or I shut the machine off.

 

[fatfillup]

Another way of adjusting pressure on cold water gas engine machines is to slow the motor down. It will pump less water and pressure will drop.

Hohn, you are absolutely correct in not needing 4000 psi for most tasks, probably for no task around the house. Higher pressure is easier to sell then higher volume and that is why the industry makes such a big deal on pressure. Higher pressure just wears everything out faster, guns, quicks, nozzles, pumps, etc.

There are 4 main factors that affect cleaning. In order of importance IMO
1. hot water, hot always cleans better then cold. Sometimes the difference is huge, like grease and oil, other times it is minimal, like cleaning your residential sidewalk (note, residential folks rarely need hot water unless you are a motorhead.
2. Volume, the higher the GMP, the faster you can get your work done. Kinda like the difference of hauling stone in your pick up verses a dump truck. Both will get the job done, just one is much faster
3. Chemical, the right detergent will speed up your job
4.Pressure, least important factor in most jobs. Most soils will move at 1500 psi, more pressure doesn't speed the process up much.

People walk into my shop and ask for as yellow nozzle. I ask what size. They respond yellow. I respond, I stock 10 different sizes of yellow nozzles and they all fit the same quick coupler. Then the questioning begins to determine what machine they own. Too small will over amp an electric motor pretty quick.

 

[16again]

New thermal relief valve installed. If I get a chance this weekend, I'll test it out. Thank you everyone for the help.
Photo is the offending part.
New one is now in its place.