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Valve mod - pcp pistol
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BC_Clark View Drop Down
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Posts: 8 		Post Options Post Options   Thanks (0) Thanks(0)   Quote BC_Clark Quote  Post ReplyReply Direct Link To This Post Posted: 07 Sep 2024 at 12:20pm
A thing about dissimilar metal corrosion is it depends on the ratio of surface areas of each metal.
A stainless seat in an aluminium airgun could have no issues but an aluminium seat in a stainless airgun
would be at high risk.
Look up the galvanic series and make sure that the most reactive metal makes up the vast majority.

I find 385 brass to be very good for seats. It machines and polishes well. Bronzes can be more tricky.
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Posts: 1050 		Post Options Post Options   Thanks (0) Thanks(0)   Quote nunga Quote  Post ReplyReply Direct Link To This Post Posted: 07 Sep 2024 at 6:35am
Paul Flick me your address and ill get that bronze sent to you. I will be doing a smelt over the weekend and i will make some bronze while i have the furnace cranked up
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Posts: 135 		Post Options Post Options   Thanks (1) Thanks(1)   Quote xyon Quote  Post ReplyReply Direct Link To This Post Posted: 05 Sep 2024 at 7:42am
Originally posted by nunga nunga wrote:

If it was me doing it i would be looking into 316 stainless for the valve and bronze alloy or brass for the seat. I have both here if you want to play with that. I have 10 and 20mm round 316 bar here. can easily make what ever bronze alloy you want.


Hi, I don't think 316 would be hard enough for the valve stem/shaft, well that would depend of course on how hard you need to hit it and the diameter. FX valve stems (among others) have been known break LOL
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Originally posted by RangerPete RangerPete wrote:

Interesting thread Pauly.
Is this going to be another crossman modification? And what caliber are you using?

I am trying to make as much as I can, but will use a Crosman trigger frame and barrel. I have a steel breech which will save a lot of time, but would like to make a custom breech with a straight pull bolt that has a locking action rather than drop into a slot. very similar to my last build. That way I could get a little creative with open sights maybe.

It'll be .22. I do have a .25 cal FX barrel off an old Bobcat, but of course it'll need chopping down, but had thought about using that for a rifle build.
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Posts: 977 		Post Options Post Options   Thanks (0) Thanks(0)   Quote RangerPete Quote  Post ReplyReply Direct Link To This Post Posted: 05 Sep 2024 at 7:05am
Interesting thread Pauly.
Is this going to be another crossman modification? And what caliber are you using?
Walk quietly, but carry a big stick.
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Pauly5 View Drop Down
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Posts: 1561 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Pauly5 Quote  Post ReplyReply Direct Link To This Post Posted: 05 Sep 2024 at 7:02am
Cool, great info.

In the past, I have used delrin on the shaft which has worked well, but I was thinking of keeping the HP side of the valve stem to a minimum using metal which means the metal head can be made smaller and more streamlined.
I quote some advice given below.
"Therefore you can reduce both major closing forces on the valve:"
1) reducing the static pressure on the valve stem
2) reducing the dynamic pressure on the valve head
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Posts: 1050 		Post Options Post Options   Thanks (0) Thanks(0)   Quote nunga Quote  Post ReplyReply Direct Link To This Post Posted: 05 Sep 2024 at 6:33am
I would highly recommend the bronze alloy as you have to take into account for bimetallic corrosion if you were to use a screwdriver shaft with a stainless steel seat. it would rust out very quickly or weld itself together. be very careful when mixing your ferrous metals
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Originally posted by nunga nunga wrote:

The screwdriver shaft is not hardened only the tips are hardened steel. and you would find it very difficult to machine the hardened steel anyway. you will need grind it.

If it was me doing it i would be looking into 316 stainless for the valve and bronze alloy or brass for the seat. I have both here if you want to play with that. I have 10 and 20mm round 316 bar here. can easily make what ever bronze alloy you want.

Just a thought.

Of course, hadn't thought of brass or bronze. That would make sense.

With the screw driver shaft I don't need to change the diameter at all. I just cut to length then harden it. Giving it a polish afterwards.
I have about 1% metallurgy knowledge, but heat to cherry red or non ferrous state and quench in oil.

I have some 8 and 10 mm 316 round bar, but might take you up on the bronze alloy. Would only need a few small pieces.
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Thanks Xyon, that makes sense, I might go that way. I know I could use HSS drill shanks too, then use the relevant reamer for the hole. But I have no reamers at this stage.

Kruz, I would like to put a reg into it, but they cost about $70 to $80 Euro + delivery each. I should be able to fit one at a later date as the way I have made the body should provide a plenum.
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Posts: 1050 		Post Options Post Options   Thanks (0) Thanks(0)   Quote nunga Quote  Post ReplyReply Direct Link To This Post Posted: 05 Sep 2024 at 5:57am
The screwdriver shaft is not hardened only the tips are hardened steel. and you would find it very difficult to machine the hardened steel anyway. you will need grind it.

If it was me doing it i would be looking into 316 stainless for the valve and bronze alloy or brass for the seat. I have both here if you want to play with that. I have 10 and 20mm round 316 bar here. can easily make what ever bronze alloy you want.

Just a thought.
2nd place HP springer - WFTF World Championships 2014
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