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Need pump help

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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Need pump help

Unread postAuthor: RBurke83 » Tue Mar 05, 2013 4:29 pm

Hey guys, just got done building my new pump and I seem to have an intermittent problem with the air chuck. Is this air chuck just useless for this application? Its a Milton industries lock on air chuck. Sometimes it pumps fine, other times it only puts like 100 psi into the launcher and the rest just pressurizes the line. What type of chuck do u guys use for homemade high pressure pumps? I really dont want to cannibilize my track pump as its perfect for lower pressure shots.
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 05, 2013 5:00 pm

looking good :D

why did you use a plank instead of a pipe, looks uncomfortable.

As to a chuck, these are great: http://www.ebay.com/itm/Evo-PRESSURE-LX ... 5d3a82c00d

Shame to buy the whole pump just for the chuck though.

For high pressures, you really want something that threads onto the schrader, a friction fit will pop off below 200 psi typically.
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Unread postAuthor: RBurke83 » Tue Mar 05, 2013 5:12 pm

Thanks Jack! The 2x4 is a temporary solution, though i feel plenty safe with it's strength. I had originally purchased a 1/4npt to 1/8th npt adapter thinking a schrader must be 1/8th,...alas it's not, some strange thread pattern i guess. this air chuck is nice, for a car or bike, but without attaching it to anything, it leaks beyond 240psi. So right now the pump is great up to a male 1/4npt fitting on the end of the hose. Just have to do some searching for a thread on chuck on the interweb. Thanks for the suggestion!
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Unread postAuthor: RBurke83 » Tue Mar 05, 2013 5:21 pm

I took the chuck apart, and found it to be a slightly odd design. The pin is floating and has no spring behind it, either gravity drops it onto the sealing face, or a decent rush of air through the hose. It may be time to mod this thing!
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 05, 2013 5:21 pm

Yeah, schraders have a quaint thread:

Metric: 7.7 mm OD, thread root diameter is 6.9 mm × 0.794 mm pitch.

Imperial: 0.305 in OD, thread root diameter 0.271 in × 32 tpi (threads per inch)

Maybe this will do as a solution that won't break the bank:

http://www.ebay.com/itm/90-Degree-Press ... 23180eb419

The male fitting is also for a schrader but it can be epoxied or hose-clamped into another fitting to fit the pipe.
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Unread postAuthor: CS » Tue Mar 05, 2013 6:10 pm

The tips that come on the end of blowguns fit the thread of a schrader valve.

Image

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Unread postAuthor: jackssmirkingrevenge » Tue Mar 05, 2013 6:33 pm

CS wrote:The tips that come on the end of blowguns fit the thread of a schrader valve.


Not very well, surely - that thread is usually 1/8" BSP...
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Unread postAuthor: Zeus » Tue Mar 05, 2013 6:51 pm

The little adapters do though, third and fourth down have the right threading for it.
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Unread postAuthor: RBurke83 » Tue Mar 05, 2013 8:49 pm

I will try them, i have a few of those adapters kicking around. Another problem is the gun fires if i don't get the pump off of the schrader in time, kinda scary. My track pump seems to blow itself right off of the valve as soon as I flip it's lever...I may just end up destroying that pump to get the chuck from it.
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 06, 2013 1:42 am

RBurke83 wrote:Another problem is the gun fires if i don't get the pump off of the schrader in time, kinda scary.


This is the great thing about the shock pump head, you can depress the schrader stem independently.

Another solution is to have a pump head that seals against the schrader lip but doesn't depress the stem, that way the schrader acts as a check valve - the problem is that you have around 50-70 psi cracking pressure, so the pressure in the chamber will be lower than that on the pump gauge.
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Unread postAuthor: RBurke83 » Wed Mar 06, 2013 1:07 pm

If I used the schrader as a check valve as you say, would pressure eventually equalize between pump and chamber, or would I always need to have pressure 50-70psi higher on the pump end? As of now, I feel ok about pump and launcher at 400psi, but I'm not sure about the pump at 470.
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 06, 2013 3:11 pm

RBurke83 wrote:If I used the schrader as a check valve as you say, would pressure eventually equalize between pump and chamber, or would I always need to have pressure 50-70psi higher on the pump end?


yes

As of now, I feel ok about pump and launcher at 400psi, but I'm not sure about the pump at 470.


if it can take 400, it can take 470... its never that marginal.
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Unread postAuthor: RBurke83 » Thu Mar 07, 2013 6:15 pm

Ok so I cannabilized my Blackburn trackpump for the chuck. I successfully threaded and epoxied the chuck into a brass male/male 1/4npt adapter. No leaks, so I first went to my previous high psi for the gun and old pump which was approximately 210psi. No issues, dry fired it in the garage. My next test was to set some new bests while testing the gun/pump system. Went to 300 psi, left the pump attached to the gun, ate dinner, came back and it was still @ 300psi. Dry fired in garage. Later I decided to keep pushing and I took the launcher up to approximately 350-360 psi. No issues, I left and came back 5 min later, still 360 - I put literally one more pump in the gun and the chuck was blown partly off the schrader but still depressing the valve...Needless to say the gun fired in my bedroom and my ears are still ringing an hour later hehe. Jack ur right, for high pressures, a thread on chuck is totally neccessary. Could have been dangerous if ammo was in the barrel.
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Unread postAuthor: jackssmirkingrevenge » Fri Mar 08, 2013 1:13 am

RBurke83 wrote:Jack ur right, for high pressures, a thread on chuck is totally neccessary.


[youtube]http://www.youtube.com/watch?v=MCQ7VLoY7bQ[/youtube]

;)
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Unread postAuthor: RBurke83 » Sat Mar 09, 2013 6:08 pm

Alright, I am pretty pleased with myself right now. I have come up with a way to have a quick connect schrader, that doesn't screw on and also releases the gun from the pump without bleeding air. In a few minutes I'll take some pictures and start a new thread.
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