pneumatic ram design
Posted: Sat Nov 10, 2007 2:23 am
I've been thinking about high pressure too much lately
. I found a few threads discussing pneumatic rams to increase the performance of small diameter ammo, but they involved using a burst disk or resistance of the projectile and didn't seem to go anywhere. Anyways, my idea is that to get around using a sabot for a given performance with a fixed barrel length, you have to increase pressure. Hpa is limited to 3-4.5k psi, and a standard paintball regulator will take it down to ~800psi for consistent shot to shot performance, and with a pneumatic ram you could increase that to whatever pressure your gun could handle, by changing the ratio of expansion to compression chamber. I picked 6000 psi because that's the highest rated steel fittings I could find. If you were comfortable going beyond the rated pressure given safety factors, you could increase the performance considerably.
To walk through the diagram, the desired chamber volume is 1 cu in at ~6000psi. The volume in the valve housing is ignored for simplicity's sake. To get that pressure from 800 psi, the compression chamber will have to be ~7.5 times the length of 1 cu in. In 3/4" ID pipe 1 cu in is 2.3" long, and the ratio of a 2":3/4" circle is 7.1:1, therefor the compression chamber must be 16.3" long, and expansion chamber 14" long so that the piston doesn't slam the last couple inches when the compression chamber dumps.
First, (1) the compression chamber is filled to 800 psi through the standard piston valve, then that fill line is closed off. (2) The expansion chamber is filled to 800 psi, and the piston moves to the right, venting the air in the middle out (3), and compressing the air in the compression chamber to (4) about 1/7 the volume, which would increase it from 800 to 5700psi. Then the piston valve is fired (5), and the expansion chamber vented (6). The piston will return to its original position when step 1 is repeated.
I can see getting the piston to seal being the most challenging part, but they use o rings in hydraulics that operate at high pressures, so it's possible. Also finding a sealing face that won't be cut by the barrel at that pressure could be difficult. So, difficulties aside, would this work?
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To walk through the diagram, the desired chamber volume is 1 cu in at ~6000psi. The volume in the valve housing is ignored for simplicity's sake. To get that pressure from 800 psi, the compression chamber will have to be ~7.5 times the length of 1 cu in. In 3/4" ID pipe 1 cu in is 2.3" long, and the ratio of a 2":3/4" circle is 7.1:1, therefor the compression chamber must be 16.3" long, and expansion chamber 14" long so that the piston doesn't slam the last couple inches when the compression chamber dumps.
First, (1) the compression chamber is filled to 800 psi through the standard piston valve, then that fill line is closed off. (2) The expansion chamber is filled to 800 psi, and the piston moves to the right, venting the air in the middle out (3), and compressing the air in the compression chamber to (4) about 1/7 the volume, which would increase it from 800 to 5700psi. Then the piston valve is fired (5), and the expansion chamber vented (6). The piston will return to its original position when step 1 is repeated.
I can see getting the piston to seal being the most challenging part, but they use o rings in hydraulics that operate at high pressures, so it's possible. Also finding a sealing face that won't be cut by the barrel at that pressure could be difficult. So, difficulties aside, would this work?