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Valve mod - pcp pistol
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Pauly5 View Drop Down
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Posts: 1410 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Pauly5 Quote  Post ReplyReply Direct Link To This Post Posted: 09 Sep 2024 at 10:06pm
Well I tried cutting one of my donor screw drivers and it was hard. The hacksaw had trouble biting into it. It made a small nick, so I just put it in the vice and it snapped on the nick.

Doing pest control I was always up in ceilings and sparkies often forget stuff and they do like to have expensive screwdrivers which are decenyly hardened. So I have a couple I can wreck. So this will be my valve stem.
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Pauly5 View Drop Down
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Posts: 1410 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Pauly5 Quote  Post ReplyReply Direct Link To This Post Posted: 07 Sep 2024 at 8:26pm
So should I remake that valve seat in brass and the harder material for the moving part of the valve. Poppet valve?
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Originally posted by nunga nunga wrote:

Thats because 385 brass as a lot of lead (around 3%) compared with other types of brass which makes it very good for machining it is also know as free machining brass. But it is a lot softer as well so i dont know how it would handle been used on HPA valve seat.

If you have had good results using it BC_Clark then i would be happy to mix up a batch for you paul, like i said i have everything here and i will be smelting other stuff this weekend anyway.


Some of my most powerful and highly stressed valves have been with 385 brass seats
so I can say that normal HPA usage is no challenge.
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nunga View Drop Down
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Posts: 1009 		Post Options Post Options   Thanks (1) Thanks(1)   Quote nunga Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 2024 at 5:49pm
Thats because 385 brass as a lot of lead (around 3%) compared with other types of brass which makes it very good for machining it is also know as free machining brass. But it is a lot softer as well so i dont know how it would handle been used on HPA valve seat.

If you have had good results using it BC_Clark then i would be happy to mix up a batch for you paul, like i said i have everything here and i will be smelting other stuff this weekend anyway.
2nd place HP springer - WFTF World Championships 2014
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Posts: 6 		Post Options Post Options   Thanks (0) Thanks(0)   Quote BC_Clark Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 2024 at 5:20pm
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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nunga View Drop Down
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Posts: 1009 		Post Options Post Options   Thanks (0) Thanks(0)   Quote nunga Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 2024 at 11:35am
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
2nd place HP springer - WFTF World Championships 2014
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xyon View Drop Down
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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: 04 Sep 2024 at 12:42pm
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
---
My favourites
springer - Diana 52
PCP - FX Wildcat III
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Pauly5 View Drop Down
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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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RangerPete View Drop Down
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Posts: 884 		Post Options Post Options   Thanks (0) Thanks(0)   Quote RangerPete Quote  Post ReplyReply Direct Link To This Post Posted: 04 Sep 2024 at 12:05pm
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: 1410 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Pauly5 Quote  Post ReplyReply Direct Link To This Post Posted: 04 Sep 2024 at 12:02pm
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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