DIY 3000 PSI compressor

[wjr]

I got to thinking when I saw a power washed the other day. On the side it said something along the lines of "3000 psi pressure washer". So, there's got to be a little compressor in there that will compress to 3000 psi... I'd read enough issues of Make magazine to realize this could possibly be modded into something useful, like say, a compressor to fill up paintball tanks!

I'm going to a pawn shot sometime this week to buy one and take a look see at the innards.


Any comments/suggestions? Anyone ever done this before or something similar?

[Tunaman]

The tiny compressor could never handle the volume of a paintball tank...

[Spider-TW]

Surrounded by rednecks...now i r 1.

It would be nice to have a little compressor to fill a tank for testing, even if it took a day to do it. I haven't taken a pressure washer apart, but I would look at two things: one is the seal lubrication, which should be different from air to water service, the second thing is the cooling. It's easy to run the machine continuously with a bunch of water running through it, but if you leave it running all day in air service without cooling it will probably destroy itself.

[Boden]

Ok, Im no smarty-pants, but I think that it is easier to bring fluid(water) up to 3000psi than air. Something to do with fluid dynamics and stuff like that. Take a good look around the interweb(net) before you waste any money. Like I said, I dont know much, but this rings a bell in my head (and yes, It echos).

[angrysasquatch]

Im pretty sure you're right, when an air tank explodes, shrapnel goes everywhere. When a water tank explodes at the same pressure, shrapnel goes.. a couple feet. This means the air tank has more energy, and since your pressure washer is a couple horsepower, it will take longer to get air to the same pressure.

The thing that could make this not work is that the molecules which comprise air are a lot smaller than water molecules. They will most likely get past the seals since it is built to seal against water. Also, the impeller will most likely burn out, since the water it it should be moving is cooling it at the same time.

If you can find a way to overcome these obstacles, first fill the tank to the max of a regular compressor (120 psi?) then use your crazy system since the compressor will fill it to 120 psi in a few seconds while the pressure washer will take a long time (compressor moves a lot of air but can't provide high pressures, pressure washer is the opposite)

[ScatterPlot]

If all else fails you could make an air-over-water system. Have a tube that the pressure washer fills with water, the air that gets squished out is now at 3k psi. However it is a very low volume thing though.

[ScatterPlot]

OK I'm actually interested now. I'm gonna math it out for you guys, be back in a second.

[wjr]

OK I'm actually interested now. I'm gonna math it out for you guys, be back in a second.

Interesting idea. I'm very eager to see what you come up with on this.

[ScatterPlot]

OK mathing done! Had to take back out mah Thermo book, thought I could remember how to do it but alas, no luck

Anyways the results are somewhat surprising.

I assumed a 5 horsepower engine. This may be high or low depending on what you are looking at. This also assumes 100% efficiency, so depending on how much of your 5hp goes to the water stream this may or may not be effective (note: I don't know how engines are rated- the 5hp might be closely related to work done to water stream or it might not). Anyways, turns out time is not a big issue at all.

For a 5hp pump, it will produce enough energy in 19.65 seconds to pressurize a 68 ci tank to 3000 psi (wow I know, that's fast!). This also assumes no temperature increase or decrease- the tank temperature will rise but how much this effects the final answer is beyond me. Also I assume you're using an air-over-water system- I figured out how big that would have to be as well! This would consist of filling a tube full of 125 psi air (from a regular air compressor) with water from the bottom up, with the air going out a hole in the top to a paintball tank.

I checked steel pipe pricing, etc. and all that can be found at McMaster.com. I looked at schedule 80 steel pipe, and it was about $25 for 2 feet. Don't get too excited yet though. I also looked at pressure ratings, and some I looked at would handle 3k psi, some wouldn't. I personally don't know, since I can't match the steel types from McMaster to the random pressure ratings I found on the internet. So how long would this system need to be, you ask? Here's a table:

Diameter, in    Length, ft
0.25		2771
0.5		692.6
0.75		307.8
1		173.2
1.5		76.96
2		43.29
2.5		27.71
3		19.24
3.5		14.14
4		10.82
4.5		8.551
5		6.926

So assuming you can find a 5" pipe that can handle 3000 psi (more for safety margin), it will take you nearly 7 feet to fill a paintball tank. I think 2 strokes through a 3.5 foot tube would work as well. However 5" steel pipe rated at 3000 psi is gonna be hard to find. The thickness required to hold X pressure goes up with the diameter of the pipe (I believe linearly, but I'm not sure). In other words, .25" pipe would not have to be as thick as 5" pipe if they were both holding 3000 psi.

So there you have it. The MAXIMUM values you get for a 5-hp motor. This is not accurate, however, due to losses from the friction in the motor, compressor for water, temperature losses, etc. but here's something close. If someone could get me the flow rate for the 3000 psi water stream that would help get a much more accurate value, but this is it for me for now! Enjoy.

[wjr]

Hmm... so, the numbers may be off, but it sounds like it's feasible, right? I at least might be able to get a few shots. It'll be fun to work on anyways.

This weekend I'll go check what horsepower it is.

I'm thinking that instead of buying pipe I might want to buy a scuba tank. According to your calculations I'll need a tank that's 35cf. I'm going to look around for one that's close to that size.

But I'm not really understanding this part:

This would consist of filling a tube full of 125 psi air (from a regular air compressor) with water from the bottom up, with the air going out a hole in the top to a paintball tank.

I understand the concept of the air-over water tank (I think), but how would this work to compress air to 3000 psi?

[ScatterPlot]

Hmm... so, the numbers may be off, but it sounds like it's feasible, right? I at least might be able to get a few shots. It'll be fun to work on anyways.

This weekend I'll go check what horsepower it is.

I'm thinking that instead of buying pipe I might want to buy a scuba tank. According to your calculations I'll need a tank that's 35cf. I'm going to look around for one that's close to that size.

But I'm not really understanding this part:

I understand the concept of the air-over water tank (I think), but how would this work to compress air to 3000 psi?

Imagine a pipe full of air, with a little water at the bottom. Water inlet at the bottom, air outlet at the top. As the pressure washer pumps water in the bottom, air gets squished into the top. If there is enough air to be able to be compressed, then eventually the pressure exerted by the water coming in (at a known 3k psi) will equal the pressure of the air at the top. Add an outlet to the top to connect a tank, and you can fill it.

The scuba tank idea would work pretty well for this application- however you will need to find some way to keep all the water and moisture out of the air. With only one inlet, it will be hard to do. Also, the water in the tank will eventually rust and corrode it out- water in compressed air vessels is a BAD thing. Read that again- it will kill you. That's why all air compressors have a water drainage valve on the bottom. They will explode when they start to rust.

[KayleAGD]

OK I'm actually interested now. I'm gonna math it out for you guys, be back in a second.

Nerd.... :rofl:

Anyway, Really you just sounded like Tom k .. Basically what he is proposing is a genisis system with a water drive and one stroke. actually it would be more realistic to make a booster with a larger drive system to run on 100psi. But yes it would work.

[ScatterPlot]

Nerd.... :rofl:

Anyway, Really you just sounded like Tom k .. Basically what he is proposing is a genisis system with a water drive and one stroke. actually it would be more realistic to make a booster with a larger drive system to run on 100psi. But yes it would work.

Haha, wow, that's actually a compliment! Good thought on using the booster system to work from just the 100 psi. I've thought about that kind of thing before, and I do get a lot of crap from less, say, technical minded people when they think about an air-powered air pump

[Ghola]

3k psi hand pump anyone?

http://www.airforceairguns.com/handpump.html

[matteusz]

3k psi hand pump anyone?

http://www.airforceairguns.com/handpump.html

Now that is the new cheap way to fill your tank. You hook the pump up to the tank and your buddy (who lost a bet to you recently) to the pump! 230$ and all your air is free from then on (provided you are good at betting).

Back on topic. I like the water over air idea. Couldn't you put an intermitent water trap between the top of the pipe and the paintball tank? That is all they do on air line where several numatic devices are run from a central compressor.

Booster system more economical mmmmmmmm.