Pressure Washer Unloader Problem

jay_nj(Zone 6)July 30, 2006

IÂve got a 5 year old 2100psi Sears pressure washer. It has a Tecumseh engine with a Briggs & Stratton pump. I bought it from a neighbor last year  rebuilt the pump 100%. The problem is when IÂve got it running and pull the trigger thereÂs no high pressure kicking in, (incidentally, the unit had this problem when I bought it). IÂve got a low / high adjustable nozzle, (pull for low pressure cleaner application and push for high pressure). In order for me to get the high pressure going, I haved hold down the trigger and then pull and push the nozzle quickly like a shotgun cocking action. IÂm pretty sure itÂs the unloader. I bought a replacement  installed it this afternoon. There was quite a bit of hard water deposit on the old valve. Once in, the machine ran as it should; pull the trigger and high pressure kicked in, but after about an hour, I was back to cocking the nozzle. Anyone have any idea as to why this is happening and how to correct it? Now, the unloader assembly has a rather strong spring in it. IÂm thinking of cutting a small portion off to make it shorter, thus lessening the pressure against the unloader piston. I figure the lesser pressure on the piston may give the valve a bit more sensitivity when it comes time to engage / disengage. But then again, it may have the opposite affect?? IÂm open to suggestions.


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The unloader will be in bypass with the trigger shut. When you open the trigger, the flow of water and/or pressure drop will switch the unloader to flow to the hose and wand. It sounds like you are not getting enough flow out of the high pressure side of your nozzle to switch the unloader. When you pull the trigger in the low pressure setting, the unloader switches to flow to the hose and then you are changing to the high pressure setting afterward. I would start by looking at the high pressure orifice in the nozzle. It may be plugged a bit and restricting the flow enough to effect the unloader shifting. Unloaders are very hard to design and build to perform well, especially with the variations of water they have to work with. The recent price wars on pressure washers has also made for lots of lower price/lower quality unloaders being produced. It is not surprising to see all the problems folks have.

I wouldn't mess with the spring, that is almost always the way that the high pressure is set, so cutting it would probably reduce your pressure, but not solve your problem.

    Bookmark   July 31, 2006 at 9:59AM
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jay_nj(Zone 6)

Hey Booster,

I agree with your thoughts on the nozzle. I actually went out and bought a new wand and nozzle thinking it would solve the problem. Obviously it didnÂt. I will say that the two nozzles are very similar, (low/high  pull push types). Do you think IÂd have better luck using a standard quick change nozzle with a fixed pattern?

I know the pump isnÂt the best quality. I had too much invested into the rebuild when I realized it was completely shot. A new one goes for $175 -- the rebuild ran about $225Â Live and learn.

My drive is fueled by wanting to use the pressure washer to clean the house. Not being a fan of heights, I want to get one of those telescopic wands that reach about 20 feet. But considering the state of my machine, I canÂt very well reach the nozzle to cock every time I need pressure ItÂs frustrating.


    Bookmark   July 31, 2006 at 10:38AM
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The fixed orifice nozzles usually do a better job of being within the rated flow, but the high/low units rarely give the kind of problems that you are seeing. Perhaps your pump just isn't in good enough shape to put out full flow at pressure so the unloader won't shift. The other thing to be sure of is that you got the right size nozzle in the wand. You might want to check your flow into a bucket at high and low pressure to see how you stand compared to rating for the pump and nozzle.

    Bookmark   July 31, 2006 at 10:47AM
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jay_nj(Zone 6)

OK, maybe I need a quick lesson on how the high / low nozzle works. How does the machine know not to put out full pressure when the setting is for low cleaner applications? I would assume if the unloader senses too much of a flow, (or very little backpressure) it knows not to kick in. If thatÂs correct, perhaps my nozzle is over rated (too large) for the flow  which isnÂt all that much @ 2 gallons/minute. If the orifice was smaller, it would yield more backpressure when the trigger is pulled and allow the unloader to kick in? Is that how they work?

    Bookmark   July 31, 2006 at 8:54PM
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The pump is (theoretically) always putting out the same volume, regardless of if it is in bypass, low pressure to the gun, or high pressure to the gun. The pressure comes from the size of the orifice that the flow goes through, smaller orifice, higher pressure at the same flow. When the unloader is in bypass, the flow is just looping within the unloader and pump (and heating up so don't stay in bypass very long). The resistance to flow within the unloader will cause a pressure difference between the input and output of the unloader, which holds the unloader in the bypass position. When you pull the trigger of the gun, the pressure on the pump outlet/unloader inlet drops quickly as the hose fills and the flow goes out the nozzle. The dropping of the pressure allows the unloader to shift to the flow out of bypass, to the gun. When you close the gun, the resulting pressure spike in the hose shifts the unloader to the bypass position.

Since you can get the unloader to shift out of bypass in the low pressure/big nozzle position, it appears that the unloader is working, at least somewhat. It doesn't work in the high pressure/small nozzle setting, so the assumption is that there is not enough flow to drop the pressure in the unloader to get it to shift. This could be caused by too small of a high pressure nozzle or a partially plugged one. It would also make the unit run at too high an operating pressure, which is not a good thing to do. If you have the manual for the unit, it should say what nozzle number to use to get the rated pressure at the rated flow.

Since the pump puts out constant flow, you should get very close to the same gpm into a bucket at low pressure and high pressure. If there is more than about 10% difference, your pump is not very good.

There are also unloaders that shift based on flow, not pressure, so whenever flow is directed to the gun, they shift out of bypass. If your pump was tired, and you had a flow sensing unloader, it may not shift out of bypass, as the flow would be too low.

Happy hunting, hope you find an answer.

    Bookmark   July 31, 2006 at 9:41PM
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jay_nj(Zone 6)

Well, still have the problem. IÂve noticed that everything works as it should for the first few minutes  pull the trigger and the high pressure kicks in. However, seems when the machine heats up, the only way to get high pressure is to cock the high/low nozzle. Today I googled the problem to find that some people recommend lubricating the unloader with white lithium grease. Anyone ever hear of such a thing. IÂm certainly going to give it a try, but I have my doubts about its permanency.

    Bookmark   August 7, 2006 at 10:50PM
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When you say it works well until the unit heats up do you mean with it spraying at high pressure or in bypass. Most of these units will heat up very quickly in bypass, and that can give cavitation, steam and a raft of other things, including heating up the unloader until it sticks, or pump issues.

If it is happening because of running in bypass and heating up, pulling the trigger more often to cool it could help, or you could add a thermal relief valve, which is always a good idea anyway.

    Bookmark   August 8, 2006 at 12:48PM
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jay_nj(Zone 6)

Yes, when I'm spraying. Rarely do I leave in bypass mode for more than 15 seconds. The unit has a working thermal relief valve.

    Bookmark   August 8, 2006 at 1:18PM
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FWIW, my DeVilbiss Ex-Cell 2100psi, 1999 model which I bought new that year, had worked fine the past seven years. I was using it a week ago, however, and the engine died. When I tried to restart it, the rope wouldn't pull.

I emailed msservice, which handles parts for DeVilbiss and others. I described the problem and the tech said it sounded like the pump was low on oil. When I checked it, it was not only low, but almost empty. Unfortunately by the time I discovered that, I had burned up the pump.

All this is to say, check your pump's oil level, even if it has a "never needs maintenance" (hah) pump like I had on mine.

Someone up above bemoaned the fact that new pumps are so expensive. I found an AR model, to replace my cooked pump, that sells all over the internet for $120-$150, for $79 at


    Bookmark   August 23, 2006 at 5:54PM
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