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Homemade high pressure pump

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: SpudBlaster15 » Thu Aug 23, 2007 11:32 am

Ok, the pump is almost complete, I ran into a few issues with the pump body. The hardware store sold me a length of 3/4" pipe that had large grooves cut into the face of the interior, stupid of me not to check before buying it. I am going to exchange it for a smooth piece today. Now, does anyone know what type of lubricant should be used on the o-ring mounted on the pump head? Anything petroleum based poses an ignition/explosion hazard when exposed to 300psi air, so I am unsure as to what I should use.
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Unread postAuthor: paaiyan » Thu Aug 23, 2007 11:34 am

How about a good silicone-based lube?
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Unread postAuthor: jackssmirkingrevenge » Thu Aug 23, 2007 11:37 am

moly lube :D
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Unread postAuthor: SpudBlaster15 » Thu Aug 23, 2007 11:51 am

I am probably going to use this stuff after paaiyan mentioned silicone lubricant.

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Unread postAuthor: joannaardway » Thu Aug 23, 2007 3:40 pm

I'd personally use silicon grease. Much thicker than the spray, it's ideal for moving seals.
It's not very cheap, but it's the best there is.
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Unread postAuthor: Hawkeye » Thu Aug 23, 2007 3:47 pm

Building a check valve into each gun is about the simplest thing to do.
All you need is a threaded 1/8-1/4 brass reducer, a spring from a pen, and a small nail and tiny o-ring.
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Unread postAuthor: SpudBlaster15 » Thu Aug 23, 2007 8:16 pm

Hawkeye wrote:Building a check valve into each gun is about the simplest thing to do.
All you need is a threaded 1/8-1/4 brass reducer, a spring from a pen, and a small nail and tiny o-ring.


Or you could use a spring, a piece of rubber, a 3/4" NPT to 3/4" copper adapter, and a washer and build a check valve into the pump, rather than building several check valves out of similar parts.

*Goes to find some silicone grease*
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Unread postAuthor: schmanman » Thu Aug 23, 2007 8:37 pm

spudblaster, I see how the air gets out (through the one check valve, but you really need a tee there. one for the intake ( flipped the opposite way of the output, so it pulls in air, compresses it, and pushes it out through the other check valve.
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Unread postAuthor: SpudBlaster15 » Thu Aug 23, 2007 8:46 pm

The intake check valve is incorporated into the piston head. Take apart a high pressure (160psi) bike pump and look at the piston head to see what I mean. My design was taken directly from such a setup. Basically, an o-ring seals against a washer on the downstroke of the piston, and allows air passge through a washer with grooves cut into it on the upstroke.

A T fitting with 2 commercial check valves mounted on either end would have way too much dead space, I doubt I would be able to go over 200psi.
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Unread postAuthor: schmanman » Thu Aug 23, 2007 9:34 pm

oops....


couldn't tell from the drawing. :oops:
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Unread postAuthor: Hawkeye » Thu Aug 23, 2007 10:38 pm

You will find that a direct attachment is actually better as your hose attachment will blow up pretty quickly from overheating and pressures beyond its capabilities unless you borrow the hose from a shock pump. Putting a different check valve on each gun is cheap and better in the long run.
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Unread postAuthor: SpudBlaster15 » Thu Aug 23, 2007 11:41 pm

I doubt that I will have overheating/bursting issues with the hose and schrader connection. Both parts are quite robust, and should handle 300psi, which is all I plan to take the pump to. The only part that I am worried about is the hose to pump connection, which replies on 2 hose clamps to hold the hose in place. It may leak, or possibly even come apart, but only time will tell. The pump is assembled and the epoxy is curing, and testing will commence tomorrow morning.
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Unread postAuthor: Hawkeye » Fri Aug 24, 2007 5:56 am

Hose clamps and 300 psi and you're not worried about it bursting from overheating? If the hose is just typical bike pump hose, it will burst pretty quickly if you start stringing shots together before it has a chance to cool.
It will tend to burst right where the hose exits the pump.
Basically think of the hose system as a pressure vessel that needs to go to 300 psi and spike in pressure every time you pump down on the handle.
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Unread postAuthor: Fnord » Fri Aug 24, 2007 6:48 am

I found that typical bike pump hose (the stuff about 1/4 in diameter which doesn't have any type of threads running inside it) will burst at 350-400 psi.

I forgot to disconnect my propane meter from my hybrid once, and the marble I shot decided not to leave the barrel, so the air escaped from the only place it could, which was through the hose walls.
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Unread postAuthor: SpudBlaster15 » Fri Aug 24, 2007 11:03 am

Hawkeye wrote:Hose clamps and 300 psi and you're not worried about it bursting from overheating? If the hose is just typical bike pump hose, it will burst pretty quickly if you start stringing shots together before it has a chance to cool.


I am not too worried, as the pump will be allowed to cool between shots (I am not stupid).
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