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Valve mod - pcp pistol |
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nunga 
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Joined: 08 Mar 2013 Location: Pukekohe Status: Offline Posts: 1006 |
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 Posted: 04 Sep 2024 at 11:33am |
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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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2nd place HP springer - WFTF World Championships 2014
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Pauly5
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Joined: 10 Mar 2013 Location: Titahi Bay Status: Offline Posts: 1398 |
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Posted: 04 Sep 2024 at 12:02pm |
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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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RangerPete
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Joined: 18 Apr 2023 Location: Cambridge. Status: Offline Posts: 874 |
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Posted: 04 Sep 2024 at 12:05pm |
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Interesting thread Pauly.
Is this going to be another crossman modification? And what caliber are you using? |
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Walk quietly, but carry a big stick.
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Pauly5
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Posted: 04 Sep 2024 at 12:23pm |
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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xyon
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Joined: 20 Dec 2016 Location: Canterbury Status: Offline Posts: 135 |
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Posted: 04 Sep 2024 at 12:42pm |
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  |
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My favourites springer - Diana 52 PCP - FX Wildcat III |
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nunga
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Posted: 06 Sep 2024 at 11:35am |
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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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2nd place HP springer - WFTF World Championships 2014
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BC_Clark
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Joined: 15 Feb 2024 Location: Auckland Status: Offline Posts: 6 |
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Posted: 06 Sep 2024 at 5:20pm |
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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
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Posted: 06 Sep 2024 at 5:49pm |
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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.
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2nd place HP springer - WFTF World Championships 2014
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BC_Clark
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Posted: 07 Sep 2024 at 7:50pm |
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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Pauly5
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Posted: 07 Sep 2024 at 8:26pm |
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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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RangerPete wrote: