Pump Project

[saefroch]

As some of you may or may not have noticed, I've mentioned building a HPA pump of my own for some time now. Well I'm here to officially say I've made significant progress. It works. And it's two-staged as of 10/23/10. I've injected up to 300psi so far, and at that inlet pressure I can reach 1,000psi very quickly!

Stroke length: 23.75"
Pump head diameter: .495"
Dead volume: ~0.0122 cubic inches
Max pressure: ~1,200psi with cycling 200-80psi injection (my gauge only goes to 1,000psi)



As requested, the (now old) pump head.


This is in the discussion section only because I see this as very much a work in progress. If some mod feels it belongs in the showcase... well yeah. The new addition to my sig comes from this project.

I HAS TWO-STAGE!!!!!!!!!!



And the new pump head. Threaded connection to the handle, via a 1/4" steel rod. Keep in mind that o-ring is only 1/16" thick, and also that there is almost no other dead volume in the pump, because of the coaxial construction.

[clemsonguy1125]

Looking good, whats outer tube(I cant think of the name) made from.

[saefroch]

Type 304/304L Stainless Steel.

[Lockednloaded]

looks great, it looks like you may be standing on your gauge though, and you wouldn't want to damage such a nice 1000psi gauge.

Also, do you have a pic of the pump head we could see?

[lozz08]

Yes, head pics would be nice. What kind of a check valve are you using? I need to get one rated for that kind of pressure as I intend to make one of these.

[saefroch]

Will get pictures of the pump head, afraid to touch most of it right now, I just took it up to 700psi for a test dry-fire at that pressure, and either that pressure or the temperature thus created made my piston valve open slowly.

EDIT: Pump head picture added to the first post.

I am not standing on my gauge, you can't see it in the picture but when it rests flat the gauge is pointing up at maybe a 20degree angle.

Currently using a check valve from McMaster, it's the large brass part you see in the picture. Rated to 1,000psi.

EDIT: Just investigated, firing error was likely due to degradation of the scotch tape on the back of the piston I've been using to decrease the size of the equalizer hole. Which means...

After operation at ~680 psi, the o-ring on the front of my piston is still attached.

[lozz08]

Did you use your drill press again to shape that piston head? Can't wait to get my drill press as it will open up a lot of possibilities for me.

[saefroch]

Yup, drill press to make the pump head. Be sure to drill the holes in the pump head for the air travel first.

My o-ring is degrading so far now that the pump is almost out of commission. I figured out what that hissing sound is... it's the o-ring letting the dead volume gas leak backwards when I begin the up-stroke. Probably something to do with the heat and all the rubbing it's experiencing... I'll be buying a bunch of replacements. Thank goodness that's a standard size o-ring. Hopefully if I clean out all last bits of the Vaseline I used originally to lubricate it, the next few won't degrade so quickly.

EDIT: o-ring replaced, and not degrading under the 5W-30.

[lozz08]

If I were you I would clean the inside of the metal barrel with a petrol-based cleaner like shellite, with a long hard-bristled brush. The o-ring could be getting messed up by bits of crap on the inside of the barrel.

Also, you could cool it very effectively by sleeving the barrel in a larger pipe, and filling the gap with water.

Also you might want to get a better lube than vaseline- try grease, or fine graphite.

[saefroch]

I think graphite was found not to work. So far as I can tell, the pump shaft is clean as can be, very smooth. It seriously looks like it's dissolving into something... or rubbing off somehow uniformly. In any case, it's getting too small to be of much use.

I'll look into cooling, thanks for the suggestion.

I'm currently using 5W-30 in the Trident, and it works amazingly. It's like those people know what they're doing after all... O-ring's not dissolving, and I haven't needed to re-grease it yet.

[Hawkeye]

Careful what you grease a piston with. Remember anything that has the potential to diesel under presure is a bit risky. That's why air tool oil is I believe mineral oil based.

[saefroch]

Good point. Good thing I already tested the 5W-30.

[lozz08]

A possible solution is to find an o-ring of the same size that is made from viton rubber. That would last for some time.

It's interesting that you're using that motor oil as lube. It's supposed to be able to kind of dissolve impurities as well, meaning that jus changing the oil would completely clean the pump.

I wonder what kind of pressure you could get out of a pump with a 1/4" head...

[Gippeto]

Nice pump. 700psi is a bit 'o fun ain't it.

With regards to the wear on the o-ring, what's your cylinder/piston clearance at?

You could reduce the dead space by reducing the allowable movement of the o-ring...it' doesn't need to move hardly at all.

I would suggest silicone based oil. Available as "chamber oil" where ever you buy airguns.

Alternatively, silicone grease ...dielectric grease at the auto parts store, divers grease, Molykote 55, etc. Even used by plumbers.

[saefroch]

I can certainly order o-rings from Viton rubber, but they're almost $1 each. With a 1/4" head... I don't know. Dead volume wouldn't drop much because I can't drill a hole smaller than 1/16" but in theory it would be easier to pump... but it probably wouldn't make a difference in final pressure or usefulness for that matter. You'd have 1/4 the displacement per stroke.

I'm a peanut at 132lbs and I can push this almost to its current dead volume & leak limitations.

I think my clearance is .05" or should be.

After the heck of a time I had making the first head, I might just stick with the current one or just stick another o-ring or two onto the head to reduce dead volume instead of making another.

I'll keep an eye out for silicone grease, though I doubt I'll see any since I don't often visit any store that sells airguns.

I'll be actually shooting at 700 psi soon, hopefully by Monday. Watch this space, and this space