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Author Topic: Valve seat material?  (Read 497 times))

Offline rkr

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Valve seat material?
« on: January 24, 2023, 08:29:29 AM »
I made a new valve block for my .45 Evanix from aluminium and I'm having huge trouble in getting the PET-P/Ertalyte poppet valve to seat. Is aluminium a poor choice of valve seat material or is it just me not doing it right? Or is it PET-P that's the problem? The old valve block which I guess was iron or low grade steel didn't have such problems with PET-P. It's 10mm straight face poppet in conical valve seat and 9mm valve tunnel.
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Online nervoustrigger

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Re: Valve seat material?
« Reply #1 on: January 24, 2023, 11:30:57 AM »
I donít have a lot of experience with aluminum valve bodies but I canít fathom why aluminum would present unique challenges for the poppet to seal off against it.  A couple of things come to mind as Iím reading your description.  The first one is just that a tapered seat demands precise concentricity of both the poppet (stem to poppet OD) and valve (stem bore to tapered seat).  If you have the parts in your hand and pull the stem and spin the poppet lightly against the seat with your fingers, does it feel perfectly uniform throughout a full 360deg rotation?
 
The other thing is that while PET-P machines to a very clean surface finish, I get a tenacious wire edge at the corners.  And of course for a tapered valve seat, the very corner of the poppet is the critical sealing area.  If you havenít already tried, what I would do is take a Sharpie and color both the corner of the poppet and the valve seat, and then apply a light abrasive (e.g. J-B compound) and grab the stem with a drill and spin it against the seat for a few seconds.  Then clean away the abrasive and inspect both surfaces where the Sharpie was removed with the aid of magnification.  If the ring on either part lacks uniformity or smoothness, you can continue with the abrasive until they do.
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Online nervoustrigger

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Re: Valve seat material?
« Reply #2 on: January 24, 2023, 12:18:26 PM »
Quick questionÖI was just looking at the dimensions, a 10mm poppet over a 9mm throat.  Is that small of a sealing margin known to have worked in the past?  For example, At 3000psi operating pressure, Iím calculating a compressive load of 15,500psi carried by the rim of the poppet.  According to an https://www.matweb.com/search/DataSheet.aspx?MatGUID=281e3a595e624a06bf49d9c6138092e5]example datasheet for PET-P[/url], that may be exceeding the compressive strength rating of the material.
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Offline Motorhead

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Re: Valve seat material?
« Reply #3 on: January 24, 2023, 12:51:55 PM »
I have used Aluminum seats on many of my custom valves & retrofits.  ( 7075 or 4064 is best. 6061 T6 also works )  * Poppet stem material must be HARD !!!
Have found a Concave seat surface of @ 15* really helps center the poppet head.
The poppet head when machined needs to have a very crisp unbroken edge along the side to bottom ( Stem side ) so that the contact making the seal is a very thin margin.
As used this thin margin will quickly flatten out a tad once pressure and some cycles happen.
* Ideally using PEEK for the head, size it @ .060" larger than throat .. IMO

Manufactured CONCENTRIC in all dimensions is critical in having the assembled valve seal correctly.
« Last Edit: January 24, 2023, 01:29:36 PM by Motorhead »
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Offline Firewalker

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Re: Valve seat material?
« Reply #4 on: January 24, 2023, 02:40:21 PM »
I just made a peek poppet for my AEA, it has an aluminum seat as well and I had to chuck up the poppet in a drill and burnish it into the seat to get it to seal.

I pulled it out to look at it and the poppet barely had a mark on it and the aluminum seat still had the anodizing on it.

Delrin seems to seal easily in comparison.
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Offline Motorhead

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Re: Valve seat material?
« Reply #5 on: January 24, 2023, 07:52:18 PM »
I just made a peek poppet for my AEA, it has an aluminum seat as well and I had to chuck up the poppet in a drill and burnish it into the seat to get it to seal.

I pulled it out to look at it and the poppet barely had a mark on it and the aluminum seat still had the anodizing on it.

Delrin seems to seal easily in comparison.
Indeed it does ... PEEK will allow faster opening and a crisper shot cycle & if air filling gun is kept clean I won't wear out for the life cycle equivalent of many Delrin ones.
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Offline rkr

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Re: Valve seat material?
« Reply #6 on: January 25, 2023, 02:25:40 AM »
Thank you for the feedback. This is a 2mm stem valve and I use similar valve in my .257 Evanix - 8.0mm poppet in a 7.0mm valve tunnel where it has worked great for hundreds of shots while giving big reduction in hammer force needed. The difference is that I have PEEK poppet in that valve.

Now that you mention problems in machining PET-P, I do recall my earlier valve in this gun which also had PET-P poppet developing leak in range that was caused by the poppet. The seat is as concentric as I could make in my lathe so I think the problem may be in poppet material and my ability to machine it. Perhaps I should try Delrin/acetal poppet, or would I be better off with PEEK? Delrin seals easier and with 2mm stem there's much less force slamming it back to seat so it might just work.

Come to think of it, what was that new material that's even harder than PEEK that people were using for poppets?
« Last Edit: January 25, 2023, 02:32:38 AM by rkr »
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Offline Motorhead

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Re: Valve seat material?
« Reply #7 on: January 25, 2023, 02:43:05 AM »
Harder than PEEK
I mien dang ... peek good as it works, something even more requiring of precision to actually work sounds like a bit much honestly.

I do recall last year conversations about some semi transparent yellowish material, but don't remember material name .. or ever played with it.
Dug around ... PEI

« Last Edit: January 25, 2023, 02:56:20 AM by Motorhead »
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Online nervoustrigger

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Re: Valve seat material?
« Reply #8 on: January 25, 2023, 03:01:26 AM »
A while back I put together this comparison of some commonly available plastics. 

Code: [Select]
           comp.  tens.   Izod               water           Ball  coeff.   wear
            str.   str.   impact   hardness   abs.  density indent friction factor
           -----  -----  --------  --------- ------ ------- ------ -------- ------
UHMW-PE     2000   3100  no break  D62-D66    0      0.034    5700  0.14     0.1
PTFE           ?   3900    3.5     D50        0      0.078       -  0.09    4080
ABS         5000   6500    7.0     R105       0      0.038   13500  ?        ?
polycarb.  12000   9500   13.0     M70, R118  0.12   0.043   16500  ?        ?
nylon 6/6  12500  11500    0.6    M85, R115  7      0.042   20000  0.25     162
 w/30% GF  20000  27000    2.1     M101       0.7    0.049   30000  0.31     150
acetal     15000   9500    1.0    M88, R120  0.2    0.051   19500  0.21     340
PET-P      15000  12400    0.5     M93, R125  0.07   0.051   19500  0.20     121
PAI        19000  13000    1.0     M113, E75  0.35   0.053       ?  0.35     637
PEEK       20000  16000    1.0     M100,R126  0.1    0.047   27500  0.27     467
 w/30% GF  26000  15000    1.4     M103       0.1    0.056   37500  0.25     187
PEI        22000  16500    0.5     M112       0.25   0.046       ?  0.39     605

Sources:
http://sterlingplasticsinc.com/materials/
http://www.matweb.com
[url]https://www.polytechindustrial.com/products/plastic-stock-shapes[/url]

The yellow material Scott is referring to is PEI which has a slightly higher compressive strength and hardness than PEEK.  It machines very nicely even with my amateurish hand-sharpened HSS cutter.  An example:



It seems to work very similarly to PEEK in terms of how easy it is to knock open.  And likewise, similarly unforgiving of surface quality.  Less expensive, though it's not like it takes a lot of material for a poppet.
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Offline rkr

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Re: Valve seat material?
« Reply #9 on: January 25, 2023, 03:45:15 AM »
I did the sharpie trick (or actually polishing paste on the seat) that Nervoustrigger suggested and indeed there's a section of poppet edge that's not touching the seat properly. I guess that was the problem although I can't quite understand how i managed to do that when spinning the poppet in a lathe. Still, that PEI sound quite interesting, perhaps I'll give it a go in the future as the PEEK rod I have is only 9.5mm in diameter so I need to order something bigger anyway.
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Offline Firewalker

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Re: Valve seat material?
« Reply #10 on: January 25, 2023, 12:19:40 PM »
I did the sharpie trick (or actually polishing paste on the seat) that Nervoustrigger suggested and indeed there's a section of poppet edge that's not touching the seat properly. I guess that was the problem although I can't quite understand how i managed to do that when spinning the poppet in a lathe. Still, that PEI sound quite interesting, perhaps I'll give it a go in the future as the PEEK rod I have is only 9.5mm in diameter so I need to order something bigger anyway.

I don't know if you had the same issue I had when turning peek on my lathe but I got chatter when cutting the bevel and had to use sandpaper to remove the chatter marks.

I was feeding very slowly, almost burnishing the bevel when the cutter took a nice bite out of the peek but unlike soft metals, the chatter was only 1 chip on the face, not a washboard pattern at all.
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Offline Motorhead

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Re: Valve seat material?
« Reply #11 on: January 25, 2023, 01:12:15 PM »
Yup ... RAZOR sharp HHS tooling I've found best for such materials.
Minimal rake and place on work piece center line of ever so *slightly lower for best finish.
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Offline Firewalker

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Re: Valve seat material?
« Reply #12 on: January 25, 2023, 01:26:14 PM »
Yup ... RAZOR sharp HHS tooling I've found best for such materials.
Minimal rake and place on work piece center line of ever so *slightly lower for best finish.

C6 Carbide with a LOT of rake did it to me. I dont use HSS, I find it creates more work for me. I have a flat C4 bit I can shape to cut the bevel with the rod chucked up.... maybe that will help?
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Offline rsterne

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Re: Valve seat material?
« Reply #13 on: January 25, 2023, 02:21:09 PM »
Great subject for the Workshop, thanks for posting, also the chart of materials....  8)

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Offline rkr

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Re: Valve seat material?
« Reply #14 on: January 25, 2023, 02:53:25 PM »
I made a 10.5mm delrin poppet and it sealed right away. So, poor machining from my part.
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Offline Motorhead

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Re: Valve seat material?
« Reply #15 on: January 25, 2023, 03:36:16 PM »
I made a 10.5mm delrin poppet and it sealed right away. So, poor machining from my part.
Indeed higher yield materials shape shift easier and there for seal easier.

So folks understand while reading this post ....
We go to harder materials because it takes less strike energy to get poppet to come off the seat, wears far better yielding greater service life.
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Offline rkr

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Re: Valve seat material?
« Reply #16 on: January 25, 2023, 03:49:58 PM »
I made a 10.5mm delrin poppet and it sealed right away. So, poor machining from my part.
Indeed higher yield materials shape shift easier and there for seal easier.

So folks understand while reading this post ....
We go to harder materials because it takes less strike energy to get poppet to come off the seat, wears far better yielding greater service life.

Exactly, and what I'm doing now is to keep the energy needed to get the poppet off the seat and reducing the energy needed to keep the valve open - or shall we say reducing the valve closing force. It will be interesting to see what the results are.
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Evanix Blizzard .257/.357 - 160/230 fpe
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Offline Firewalker

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Re: Valve seat material?
« Reply #17 on: January 25, 2023, 04:40:36 PM »
I made a 10.5mm delrin poppet and it sealed right away. So, poor machining from my part.
Indeed higher yield materials shape shift easier and there for seal easier.

So folks understand while reading this post ....
We go to harder materials because it takes less strike energy to get poppet to come off the seat, wears far better yielding greater service life.

I'm using this peek poppet in an AEA VARMINT and the bolt is incredibly hard to pull. Just using this poppet, I have been able to back off the hammer spring 4 full turns and keep the same velocity, 850 fps.

The bolt is still stiff but it's now not such a chore, the trigger lightened up a smidge too. I also got 4 more shots off a fill which may not seem like a lot but I'll take it!
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Offline Motorhead

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Re: Valve seat material?
« Reply #18 on: January 25, 2023, 04:49:35 PM »
I made a 10.5mm delrin poppet and it sealed right away. So, poor machining from my part.
Indeed higher yield materials shape shift easier and there for seal easier.

So folks understand while reading this post ....
We go to harder materials because it takes less strike energy to get poppet to come off the seat, wears far better yielding greater service life.

I'm using this peek poppet in an AEA VARMINT and the bolt is incredibly hard to pull. Just using this poppet, I have been able to back off the hammer spring 4 full turns and keep the same velocity, 850 fps.

The bolt is still stiff but it's now not such a chore, the trigger lightened up a smidge too. I also got 4 more shots off a fill which may not seem like a lot but I'll take it!

Yup easier to open
« Last Edit: January 25, 2023, 04:52:15 PM by Motorhead »
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Offline Tack Driver 10

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Re: Valve seat material?
« Reply #19 on: January 27, 2023, 03:56:09 PM »
I've experimented with most of the material available.
Even tried glass filled Peek and Pet P but found it abrasive to the seat.
I cut the valve seat concave and then polish with a hard felt bullet.
A little oil and light abrasive takes out any imperfections in short order.
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