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Got the rest of the fittings this morning, just waiting on the epoxy. Should hopefully be here tommorow. Had a go at casting some pistons, sadly I had no grease so I made two using hot glue as the material, and butter & ac90 for lubricant.
Then I assembled a sort of mock up of what most of the gun should look like, excluding barrel, pilot and shrader. But hopefully you should be able to tell where they will be on the final build. Oh and this is not the actual size of gun either, I used random copper pieces to assemble it so expect the final gun to be smaller, with much less space between the tees & elbows etc.
Ahh why dont my pictures appear on the post
You have to post the "direct url" in the img codes.
That's a new one
Im having trouble getting my piston to slam back, ive made over 5 different piston sizes with no sucess.
Here is the gun so far:
The piston itself:
Where the piston is before pressure:
Where the piston is under pressure:
It seals well enough but when the pilot is opened it doesnt slam back it just sits there and then all the air is released though the pilot valve. This is when I do a test at 20psi as i dont want to epoxy the barrel in until I know that the piston works.
You made a fatal mistake though...
If you are using a hot glue piston, it will not survive forever. It will most likely deform, in which case you need to take it out to replace. Your design doesn't permit removal of the piston though. Also, why doesn't your piston have a sealing face?
Did you epoxy all of the joints?
I know. I wanted it to be mostly maintanance free, like a commercial gun would be but to do that I need a solid piston and well I dont have the right material or proper tools to do that at the moment. The gun itself will probably be in use for about 6 months before I decide to make another one so hopefully It would last. I could also do a piston of epoxy too, but that would be more expensive.
its not finished yet. and it seals well enough for my low pressure tests. my main focus has actually been getting the piston to operate properly first, then sealing the barrel for higher pressures, second.
yes it works pretty well. its airtight and its 4500psi epoxy too so strength is not an issue. I would solder but I dont have any flux or a propane torch to heat up the connections with.
Did you roughen the joints before epoxying them?
yeah I sanded them and didnt brush any of the "copper grit" off either. I put epoxy on the pipes themsleves then went round the seams of the two joints with epoxy, like you would with solder ring fittings.
your piston is way to big you could 1/2 it, and it should meet the seat about 1/2way in the tee. also is the piston a bit bigger than the barrel?
how low is your low pressure testing?, my first homemade piston valve would not fire under 70 psi. also lube it up good
'' To alcohol... The cause of, and solution to, all of life's problems.”
Add me on ps3: wannafuk, 8/11/11 cant wait
Il do that today then
yes by about 1.5-2mm
The trouble is there is a little bevel 1/3 of the way in each side of the tee to stop the pipe from going all the way though the tee. I suppose I could sand it off if nessessary.
Im using some white grease I got from a motorcylcle shop yesterday, seems to work fairly well.
around 40-50 psi, I glue the barrel in with hot glue, then pump to 40 or so psi, release the pilot to see if the piston slams back or not. Do you think I should just epoxy it up and hope it works at high pressure?
Even if there is a sufficient friction on the piston, say 2/3psi will it still function?
can a piece of innertube be used as a suitable sealing head for the piston?
Also my piston takes a while to move forward and seal the chamber, like 2-3 pumps on the floor pump and will not move when the shock pump is used.
Yes it will work fine if you attach it securely.
That is because your piston isn't airtight and your shock pump doesn't have enough air flow. You can fill it to the max of your floor pump then switch to your shocky and it will work then.
Still working on the piston, managed to slide the pipe going to the pilot further out from the piston tee so now The piston has more space. Il keep working on it for a couple of days but the idea of buying a QEV is rather tempting. I know that most are limited to 10bar, but I assume they can operate at higher pressures? I have an SK pheumatics literally down the road so I might go and pay them a visit.
That just created more pilot volume and allowed more acceleration room for the piston... you only harmed it by doing that.
European QEVs have been taken up to 800 psi I believe.
It was nessesary, because now the pipe is not in the the tee as much , so the piston can be the same diameter all the way across its length. When the pipe was fully in, a piston like that wouldnt have moved so it had to have the back at a smaller diameter to fit into the pipe so it could actually move. This is what I believe caused the sealing problems, as the new piston seems to be sealing much better. I hope that all made sense.
Good to know that, I only intend to run at 350psi max, as I cant physically pump any higher with my shock pump. This is with the pump secured the the frame of the gun too.
Well its been a while so heres an update.
Ive redone the gun with comp fittings again, and im currently leak proofing the gun at the moment. I managed to obtain a 1/2bsp QEV and it works at about 50psi min. I think this is because my pilot is a 15mm ball valve and that its too big??
Pictures hopefully late afternoon
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