300 psi compressor ??

[picclock]

Possibly not the correct forum - mod please feel free to move.

I'm struggling to get a 300psi low air volume compressor. I need this to set/check safety valves and proof/leak test some equipment which will run at 160psi or less. In my ignorance I bought one of these 12v 300 psi car inflater type pumps, but even with the hose blocked off and no leaks it barely makes 200 psi - I would send it back but it was so cheap its just not worth it.  I've had a couple of crazy thoughts, like making an air powered pressure step up device, or enclosing duff pump in housing and pressurising the housing from my main compressor (100-130 psi) thus adding that pressure to the output. Considered using CO2 but the volume of the device is quite large, and I may have to do this test many times before I am satisfied (some of the home brew sites state a CO" cylinder can be picked up for as little as £17 - If this is the case then that may be the simplest option).

Any advice or suggestions most welcome.

Best Regards

picclock

 

[awemawson]

Those Chinese 'pounds per square inch' just don't come up to standard compared to British ones 

[Pete.]

Bloody dangerous proof-testing with compressed air. What you going to do if it fails the test?

Fill whatever you are testing to the brim with water and gently warm it up. Pressure will soar without the inherent dangers of an uncontrolled release of compressed air. If there's a failiure all you'll get is a dribble of water not flying parts.

[picclock]

@ pete

Your quite right. The main assembly has already been proof tested using paraffin and a hand pump I made, however some parts can not be tested under those conditions. So this final test is to check rotating mechanical seals and other fittings, all rated well in excess of these pressures.

As an aside I used this method with water once and pumped up this job to 400 psi. I thought I would let it sit a while and check for any pressure loss. So I went to have a coffee and the sun came out from behind the clouds and brightly shone on my test piece. When I got back the pressure was heading northward of 900 psi     - way over the limits - so I don't  leave things like that anymore.

@awemawson

Even the gauge on this chinese pump reads about 20 psi low so I guess that goes with the low output. To be fair it was very cheap and is probably fine for inflating tires and stuff.

Best Regards

picclock

[Pete.]

Aah, sorry to presume your ignorance of the dangers, ut so many just don't realise. Better to be said so that others also understand.

[fixerup]

I like to use these pump   http://www.dudgeonjacks.com/index_files/Page556.htm
I fill the parts to be tested with water, making sure all the air is out of every cavity. then pump to the desired  test pressure, close the valve and watch for water leak or pressure drop. If it fails it is very boring to watch just a small dribble of water, no big bang like air pressure

Cheers
Phil

[picclock]

@fixerup

 Although I can test a lot of the parts that way I can't use that method for checking the leakage on rotary/mechanical seals and suchlike as they have to be turning and it is not possible to do that with the pressurised chamber filled with liquid.

The pumps are very similar to the one I made for myself. My one will pump (with some effort) to 1000 psi. Its mounted on a board so that I can stand on it and the handle can be extended with a piece of tube. The clear tube is the liquid intake, normally paraffin now, and the outlet in the picture is the reinforced flexible hose. At the time I made it, some years ago, I was not aware that such things could be purchased. The valve seats and piston seals are all o'rings and are still original. Highly functional, but not exactly a 'looker' 



Best Regards

picclock

[David Jupp]

Air powered step up device - sounds like a gas booster.  Small ones are widely used by Divers for topping up SCUBA cylinders.  They are not very complicated, most of the ones I've seen work at much higher pressures than 300 psi.

I would have thought that a 300 psi version ought to be a reasonable workshop project, won't need a very big boost ratio.  They tend to be noisy.

[fixerup]

Picclock
Your hydrostatic pump looks good to me and you have built it  yourself.   Well Done!
Even with the store bought pump $$ , I have to stand with both feet on the mounting board to get to 1000psi + .  The lever is about  3' long.

Instead of buying one, I would of learn more making one.

Could you please explain the use of parafin ( candle wax ?)

Thanks!
Phil

[David Jupp]

Paraffin = UK term for kerosene.

[DaveH]

Highly functional, but not exactly a 'looker' 

picclock

Well it looks a good 'looker' to me 
 
DaveH

[picclock]

@ fixerup
As David Jupp has said, paraffin is the UK term for kerosene.  When I first started I used water with car anti freeze to stop corrosion. But with complex parts there would often be liquid trapped inside and after a few weeks the anti freeze mixture would cause discoloration or even rust on susceptible materials. The switch to paraffin (kerosene) eliminated all of that and has the added benefit of lubrication and limited rust prevention.

Best Regards

picclock