Instructables

Will letting a pressure washer run without water will tear up the insides of the pump?

Im repurposing it to maybe be a vacuum pump. The outside connections fell to peices and we were going to throw it out, so I might as well recycle it.

Pressure washer pumps will break down if you do not run water through them. Even if you have water hooked up to the pump and let the engine run, you will wreck the pump. There is an unloader which diverts the water when it is not coming out the wand. The pump keeps cycling this water around and around. Even after 10 seconds you can probably feel the pump getting warm. On the better quality pumps, there are ceramic pistons which push the water through and when they get hot and then you finally pull the trigger you shock them with cold water. It can crack a piston which then water can get through and into the oil resivoir . You can also burn up the packing (sealing rings) around the ceramic pistons. If you are thinking about using the pressure pump as a vacuum, I don't think it will work the best because when the pumps are running on water, If the water flow/pressure is not enough it causes cavitation in the pump and it wrecks the packings around the pistons. Pressure washers are usually built to run at 3750 RPM. I don't think that any heat exchanger or anything would lengthen the running time by any sort of a good amount. I doubt that the engine will obtain any damage if the pump does break. Unless ofcourse it is a quick seizure or break. You could possibly sheer the flywheel key or ???. Soooo. Thats my take on it all. Feel free to send me an message if you like with any more questions.
A pressure washer probably will not work as a vacuum pump. First, the intake valves require water pressure to open. They won’t open without pressure. Second, the capacity of the pump is suited for water but is much too small for pumping air. My first vacuum pump was two modified piston refrigerator compressors connected in series, which I used for experiments in sputtered films. Having no vacuum gage, I don’t know the limiting vacuum for this pump, but I could easily create a quarter inch dark space. The intake for the first compressor was a hole in the wall of the piston cylinder. This hole was positioned at the bottom so that when the piston reached the bottom of its stroke, it uncovered the hole and allowed air to enter for the compression stroke. At the top of the cylinder, where the exhaust valve was located, I put a wood valve lifter to help the compressed air exit the cylinder. The piston hit the valve lifter at the top of its stroke. The pump was submerged in motor oil (at the time, I could not find vacuum pump oil) to keep it all airtight. ~Bob~
Re-design5 years ago
Pumps use the water for cooling and lubrication. Running them dry will wear them out very quickly in some cases and in others won't make a difference. I doubt that the motor will be harmed by dry running since it stays dry anyway. I don't know how well it will work as a vacuum pump though.
The Ideanator (author)  Re-design5 years ago
So if I modified it with some sort of oil reservoir and a heat exchanger it would last longer while running dry?
It probably would.
lemonie5 years ago
It'll not be good as a vacuum pump, different design (I should think). Maybe speed-limit it to compensate for lower loading? L
GoodAtIt5 years ago
Yes, dry running a pressure washer will most likely burn up the motor which powers pump. But since your throwing it out anyways, you might as well try and using it as a vacuum pump.
The Ideanator (author)  GoodAtIt5 years ago
So the pump parts themselves most likely wont grind to death right away, just the motor having too much stress? Thats good, I have other beastly motors needing a use.