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GIwasB4
6/16/2020 1:21pm
6/16/2020 1:21pm
There been a few power washer threads and I have not found this answer. Who makes a power wash unit which is self priming? In other words I would like to stick a hose in a tank or barrel of water in my trailer. Anybody have one that works that way? All the offerings from the big box stores say they will not work that way, need to be hooked up to a pressurized water supply.
Bosch makes a line of pressure washers with an optional "self-priming" kit.
The Shop
I think some people would be surprised at how many pressure washers won't work unless you have them hooked to pressure. Like, 20+ psi of water system pressure. Likely higher end ones will, but a lot of box store ones won't. And our new 6hp Kohler powered Simoniz won't. I ended up getting a small 1" gas powered pump to feed ours when in the woods. Will find other uses for it also
Believe this is close to what you are looking for, the 20V version doesn’t seem to pull a ton of pressure but I think the 40V version does like 450psi
All of my Ryobi gas units Bought From Home Depot worked with A gravity fed tank. That is until recently when I bought a new pump for the Honda/ryobi washer I have. Hooked it up to my 25 gallon tank like I always have for years and no dice. I removed a plastic filter on the Pumps inlet to improve flow but it still did not work. Would really like to know how to get this pump to work with a gravity fed source.
Pit Row
You need a source of water that is preferably higher than your pressure washer so it flows. Flow is all you need. Atmospheric pressure is more than enough to allow your pressure washer to work. I would put a valve on the side of your tank and hook your hose up that way. Going out of the top will require the pump to pull a vacuum - why you asked about a self priming washer. Dont limit what you can buy when you can just put a valve on the side of the tank.
Some pressure washers definitely need pressurized feed. If one thinks they all don't, they just haven't experienced it yet. Take it from those of us who have been there with it. I think it has to do with spring loaded check valves in the inlet side of the pump, that need a certain amount of pressure on them before the check opens and water can get through the pump. They are not all the same.
You only get 0.4psi per foot of elevation. Unless you really jack it up there. Even 10 feet up is only 4psi.
If you had a garden hose hooked to the bottom of a 5' high 50 gallon barrel, and another one hooked to the bottom of a 5' high 5000 gallon tank, each full - it would take the same pressure from your thumb to stop water coming out the end of the hose.
Physics & all that.
The 14psia doesnt include factoring in the weight of the water itself. The pressure will increase from there. P=h times the specific weight of the water. So whatever that calculation is divided by the area in square inches of your valve opening will give you your pressure.
If we assume pressure coming out of the tank is 20psig, its actually got 34.7 pounds of force per square inch when you consider the atmospheric pressure. Assuming you have a 1/2” id hose, you take the 34.7psia x .196in.sq. and you get 7.3 pounds of force acting on the check valves in the pressure washer. I dont know of any little check valves that would require that much force. Id also imagine the vacuum at the pump inlet would also help open the check valve.
Our new one - I temporarily hooked a 2" gas water pump up, between the tank it was hooked to, and the washer, to get it to work & get out of our jam on first use in the middle of the woods. 2" pump was only idling. The top of the water in the tank was likely 8' above the pressure washer inlet. It would not pump just hooked to the tank. It would, with the extra pump in between. And when I shut the pump in between off, to check it out further, the pressure washer stopped pumping even with gravity pushing big volume through the 2" pump. That's when we saw the fine print in the trouble shooting part of the manual about requiring a water feed with 30psi. I doubt you'd need quite that much - but you definitely need pressure, and more than gravity will get you. With some pressure washers.
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