possible high pressure pump?

[SilentCyan]

i was looking at some pressure washers the other day and got to thinking it would be really nice to have a compressor that could reach those kinds of pressures. then i remembered the garden hose compressor idea that i saw somewhere on here(no link at the moment) and thought "hey that would work wouldn't it?"

for anyone who hasn't seen that particular post basically you have a large(ish) tank that is filled from the bottom with water and all the air is pushed through the top and into a gun or storage tank. once the water gets to the top you empty it and start over.

so what do you guys think? would this work? i know some of the nice ones can hit 1500psi.

[POLAND_SPUD]

hmm sure you can do it... (at least I don't see any reason why it wouldn't work) but before you build anything you have to ask yourself one question - 'do I really have access to materials rated to 1500 psi ??'

I find it difficult to get parts rated to 500 psi... and that's the limit of relatively cheap parts... if you increase the pressure more be prepared to pay several times more for your parts

[psycix]

Im not sure if such a thing could also compress air up to 1500.
Air is different then water, and it may leak or not be able to pump/compress air.

[jimmy101]

Using a garden hose as the pressure source you'll only get 40 to 70 PSIG since that is what the household water supply is.

How do you figure to get anything significantly greater than that?

If you were to plumb a pressure washer into the water tank then you might eventually get whatever the pressure washer's max pressure is. But a pressure washer probably moves fairly little water per unit time. It'll take a while to pump up a reasonable sized resevoir with the pressure washer.

There is also the possibility of trashing the pressure washer. The washer is designed to work against fairly little back pressure. Just atmospheric pressure plus whatever the pressure drop through the hose and nozzle is. Put a significant backpressure on the system and you may well burn out the washer's pump, rupture a line, pop a fitting ...

[Brian the brain]

So you're saying it only pumps when the thing sprayes?
I think it builds up pressure..

[sputnick]

I believe Jimmy is incorrect, I am very sure that pressure washers maintain pressure, no pump for around 1000 dollars could generate in excess of 1500 psi instantaneously,

And I would imagine even if that was the case, you would have discovered the nirvana of compressors I am very convinced that it stores the pressure and stores it,

Although to add to that, I do not think that the air pressure is 1500 psi, I would think it would be an enormous ordeal of safety and quality restrictions to make an air/water tank hold 1500 psi, I imagine it is only the pressure of the water flow from the nozzle.

[SilentCyan]

Although to add to that, I do not think that the air pressure is 1500 psi, I would think it would be an enormous ordeal of safety and quality restrictions to make an air/water tank hold 1500 psi, I imagine it is only the pressure of the water flow from the nozzle.

i guess that makes sense but if that were the case would the hoses really need to be rated to 3000psi?

[POLAND_SPUD]

@jimmy101 I suppose that the pressure is constantly in the system.. but anyway these things can provide 3000 psi and more.... that's a lot you know


@SilentCyan I say it again - the idea is nice and it should work... but do you have access to materials to build it and use safely ??

and how are you going to use such high pressures ? gippetto's HP coaxial operates at similar pressures... but that's about it

@everyone else he might have discovered the nirvana of compressors... the only problem is that there are very few members who can safely use pressures above 1000 psi... it's even worst - vast majority of members stick to PVC and 8 - 12 bar which is the max pressure they can get with standard compressors

ohh I've just realized that you can use those 3000 psi to fill HPA setups with tanks and regs.. that would make sense...

but still I think that going from weak 100 psi to 3000 psi is a little bit to much of a leap for the community... for those of you who ever fired a gun at 400 - 500 psi.... would you really feel safe to use 1500 psi ?

[Pookydarts]

Hi guys, I worked at a place that welded polyethylene pipework together and I can tell you that you CAN connect a series of fittings to a pressure washer and use it to pressurise a vessel. (In this case for pressure testing)

We were trying to minimise the air in the whole shebang so that if it went, it didn't go with too much of a boom.

The compressed air could be released from the highest point into a gun, with the right fittings.

(Oh, and they only pump water...)

[Lentamentalisk]

Ok, you guys are largely wrong in this whole deal. I looked into this about a year ago, when I was building my high pressure copper gun. Pressure washers can easily go past 2000psi, depending on the model, but the issue is that they are designed for water, not air. Since water is not compressible, they use a single displacement pump, with a feedback loop. When you turn it on, the pump gets to moving the water in circles, while the sprayer valve is closed, and then when you press the trigger, the loop closes off, and it sprays out of the nozzle. You will notice when using it, that there is a minute delay between pressing down the trigger, and when the pressure washer kicks in.
The only way you can really harness this is by attaching the sprayer nozzle to a tank, and filling the tank with water, and using the pressure off the tank to pressurize your cannon. the problem is that in order to fill up a cannon to 1500psi, you would need a tank approximately 100x the size of your chamber...

In theory it could work, but it would be a pain in the ass to set up, and you would be far better off just buying a HPA tank

[jimmy101]

I believe Lentamentalisk is much closer to how these washers work than those who think they pressurize a chamber.

Besides, just because a pump will generate 5000 PSI doesn't mean it'll move enough material per unit time to be of use. That pressure washer may well be running at high pressure but it is moving a relatively small volume.

Heck, a $10 POS "emergency compressor" for a car is sometimes rated as high as 200 PSI. How do you get that pressure rating from a crappy little 12V motor that's probably smaller than a D batter? Easy, you gear it down a zillion to one then attach it to a tiny piston. That tiny piston will give huge outlet pressures but not actually move much air. It'll take one of those compressors an hour or more to pump up a 100 PSI truck tire.

I suspect a pressure washer is the same. It'll generate very high pressures but the actual piston is so small that it really isn't moving all that much volume.

I've used small hydraulic pumps that'll generate 10,000 PSI but will only move a few cc/minute of water. No resevoir at all on the high pressure side. If the outlet of the pump is closed the motor detects the piston stopping based on the current draw of the motor and shuts off.

[pharmboy]

How a pressure washer gets rated to 5000 PSI is that it's a positive displacement pump. This means that it is capable of moving water against a 5000 PSI force. As water is not a compressable fluid, this pressure builds far faster than with air. Also, sealing is easier with water, because of surface tension. This is the exact reason why it's far easier to render a piping system water-tight than air-tight. And when water at that kind of pressure causes a failure, it's far less destructive than air because of the aforementioned incompressability.

[john bunsenburner]

As maentioned before here it would take for ever to genergate an amount of air that is pressurized to 5000(or even 1000)psi. Your best bet would be to either buil an HPA piston compressor which you feed with a home compressor. It would still take quiet some time to get a large amount of air but it is far more practical than your idea, also it should be cheeper as you dont need (m)any expensive or hard to get materials, just thinks rated for high pressure. There are lots of threads abotu this but feel free to ask if you really need help.