HPA pump help.

[warhead052]

I have been thinking about making a balanced quick dump valve rifle after seeing all these high powered french ones, and need some help on a hpa pump for it. This pump will be built into the cannon, essentially being the chamber just after the check valve. Here's a picture of the pump, I just need some feed back as to whether it will work or not.

This pump would have a head diameter of around 1/2", stroke length of 24", and be pressurizing a chamber of about 4 cubic inches. Would that be enough to generate about 30 bar?


Yellow is the handle, black is the body and the pump shaft, red is the pump head, and dark red is the check valve. Grey is the springs to hold the check valve shut. And I dunno if you can see it or not, but there is a little hole in the body of the pump near the top for the air to enter to be compressed.

[Hawkeye]

Use a floating o-ring on the piston head. Of course the configuration shown will work as long as you actually have the parts to make it as shown.
I see a lot of vague diagrams that show parts sleeved neatly together with no signs of threads etc. There are usually practical limits to getting the finished product looking eactly like the envisioned product.

[warhead052]

What do you mean by floating oring? I don't quite understand them, all I know is that they move (hence the name floating oring). I can get the parts for this soon, I just need to know the total pressure before I choose a material, I was thinking copper since it can handle high pressure, and can be polished to a shine.

[jakethebeast]

everything can be polished to shine

[warhead052]

Copper looks the best to me though. Has a sort of bronze look to it.

Right now though, the biggest question is how much pressure will be generated, and will I need to make it 2 stage in order to get to my desired pressure.

[MrCrowley]

What do you mean by floating oring? I don't quite understand them, all I know is that they move (hence the name floating oring).

FLOATING PNEUMATIC PISTON SEALS
Floating pneumatic piston seals are reciprocating in nature, but the way in which the seals are effected is unique. Normal reciprocating designs rely on the O-ring being stretched over a piston and then squeezed radially (on the inside diameter, or I.D., and the outside diameter, or O.D.).

In floating O-ring designs, however, there is no radial squeeze on the seal’s cross-section. The O-ring’s O.D. is larger than the cylinder bore diameter. Peripheral squeeze is applied to the O.D. as the O-ring is installed into the bore. Incoming air pressure forces the O-ring against the groove wall, and a seal is effected as shown in Figure 115.

Floating designs offer a number of advantages, including greatly reduced breakout friction and longer seal life. Floating pneumatic piston seals are suited for applications in which the air pressure does not exceed 200 psi (or in hydraulic designs where a small amount of leakage is permissible). Floating O-rings are NOT suitable as rod seals. Gland design measurements for floating pneumatic piston O-ring seals can be found in Table 50. Gland dimensions can be found in Table 51.

You'll need groove cut in the front half of the o-ring groove to allow air to pass through when you pull the pump up like this.

[warhead052]

Thanks Crowley. Make's sense now.

[Hawkeye]

With a 3/4 inch copper pump I can reach 300 psi by basically using the pump like a shock pump.
A 1/2 inch copper pump will be perfect for a hand held high pressure launcher.
With a little creativity the pump could be incorporated like a pump action in the forestock where the pump handle sleeves around the pump cylinder rather than projecting out the end.

[Gun Freak]

You'll need to push on the pump with 105 pounds of force at 30 bar. Is this a project you will actually make or just an idea that probably won't happen?

I'm with Hawkeye, you need to figure out exactly how you are going to make it. Every single part needs to be planned. Yes, that diagram is how a pump works. Duh. Ok, but you need to draw the fittings and plan the check valve (which you should buy, for safety reasons). Also, and very important, how are you going to make the pump head and what will you use for the shaft?

[warhead052]

This is something that may actually be built, so that's why I am being a bit more serious about it.

I was thinking about using an all thread rod for the shaft, 1/4" thick, just for strength. And using washers as the pump head, with a floating oring since that was suggested. The material would be copper, so it should be able to hold 30 bar with no problem, and the check valve would be homemade, with a ball bearing and a spring, as well as a rubber seal for the ball bearing to push against.

If I need 105 pounds of force, then should I make it a lever pump? If so, how would I do that?

[Gun Freak]

Unless you can curl 105 pounds

You'll want a thicker shaft... 1/4" all thread will bend. You need at least 3/8".

[warhead052]

Ok. Well it can't be too big for 1/2" copper, so yeah... 105 pounds is nothing compared to the lifting I do for dance...

[Gun Freak]

I'm sure you could handle it, but it would get really annoying pumping it up every shot. Why not make a PCP?

I tried to do some rough math, and figured you will need a little over 20 strokes to generate 30 bar. Someone might want to check me on that though. Still, 20 strokes is a lot when it is that hard.

[warhead052]

Well, its fine with me. It probably won't be 4 cubic inches, I may reduce it down to about 1 and a half. I got the idea from G-man's 8 and 6mm ones on his youtube channel, so I am going to possibly go through with this.

Edit, what if I used one of those cheapy compressor piston heads as the pump head? That way it has the o-ring built in.

[Gun Freak]

what if I used one of those cheapy compressor piston heads as the pump head? That way it has the o-ring built in.

Stupid idea, you'd need a perfectly sized cylinder.

Get a fridgy?? Mine works wonders.