Correcting a leaking valve and finding power with a better poppet design

[Motorhead]

This got me thinking about the design of the gun I'm building at the moment. I planned on using an o-ring on the valve stem and pondered increasing the dia of the stem and fitting an o-ring on the stem. This would also provide extra closing force once the exhaust port sees pressure. This might fight the hammer in regards to dwell or may be a benefit in a quick valve re-seat? I have seen some other airguns with this design but I can't figure out if it would be a benefit or not ? 

It is documented over and over in many threads on the web that stem groove o-rings work great ! ... but for many designs are limited to modest power tunes or less.
* Trouble being the strength of the poppet stem is at O-ring groove. Heavy hammer strikes on larger head high flow poppet valves can and will either BEND or FRACTURE at the groove when loads are exceeded at the diameter of grooves root.

This is where "If" you wish to seal the poppet stem an external seal within body that allows a straight full length poppet stem is vastly superior.  * Low drag as this thread clearly reads is also very important. 

Now ... IF the machine work is very precise and you are using a Precision ground shaft for stem material, The stem bore to seat is concentric & square keeping alignment dead on ! .... having a precision reamed / lapped hole the stem slides within having a minimal clearance fit, no seal should be required at all.

[Airsnipe]

And I would assume, increasing the size of the valve shaft to the point an o-ring grove is not a weak point would increase the o-ring size and thus the friction of the setup making it undesirable for this application?

[shorty]

I've seen this mod on the marauder forum by braap (first time I ever seen it).
http://www.marauderairrifle.com/forum/viewtopic.php?f=28&t=10781

Seemed interesting at the time (early this year) and saved the link. I didn't think it was important until I was trying to go over 100 fpe with a stock valve.

 The valve stem does leak but it only seemed like it leaked when powering over 80 fpe.

[Motorhead]

I've seen this mod on the marauder forum by braap (first time I ever seen it).
http://www.marauderairrifle.com/forum/viewtopic.php?f=28&t=10781

Seemed interesting at the time (early this year) and saved the link. I didn't think it was important until I was trying to go over 100 fpe with a stock valve.

 The valve stem does leak but it only seemed like it leaked when powering over 80 fpe.

Tell Tail is VERY EASY to find out if stem is leaking.
Place a very small amount of oil or grease on poppet stem, make sure front of hammer is clean & dry ... fire a magazine worth of shots.  Remove hammer and look as the front ... Got oil or grease splatter on it ? STEMS LEAKING !

[Motorhead]

  Over the weekend did a repeat Quad ring and PEEK poppet for the M-rod .177 cal Field Target rifle.

Worked out fantastic being able to back off on hammer spring tension and saving even more air !
Valve in the .177 gun equally loose after @ 3 years of hard use likely having 3x the shots of the .22 cal rifle 
Used the quad right right off finding again just minimal stem drag.  Poppet seal face again at 30* sealing against inside edge of throat.  * It too leaked until @ 800 PSI was bearing against it ... then tight as a drum.

Really liking these small diameter angle seat poppet valves !!! .... Going to be something used in the future for sure 

 

[hpmr2400]

Do you think you can lighten the hammer even more on the .177 version ? Wonder what could be the lightest you can get away with?

[Motorhead]

Do you think you can lighten the hammer even more on the .177 version ? Wonder what could be the lightest you can get away with?

As currently set it's at @ 14 grams. ( was at @19 grams previously )
It is based off my normal 100% nylon 20 gram design. 4 fluted slots running front to back leaving hammer looking somewhat 4 leaf clover like.  Steel stroke / striker replaced with one made of PEEK.
*The .22 first done as shown above hammer went down to @ 20 gram total weight from @ 26 grams previously.

Rifle set up shooting AA 10.3's @ 910 fps and easily does 80+ shots.

Yea, with correct mods one being less poppet head area and a lighter poppet spring you can get away with quite a light hammer.

As stated many times ... light hammers decrease lock time, bounce far less too.  Dwell can become very low saving air extending shot count between fills.

[hpmr2400]

Wow ,14 grams. And shooting 910 fps. What is your reg setting?  Wonder how a 10 gram hammer would do?

I recently reduced my prod hammer to 19 grams, and your right there is quite a difference in the shot cycle. A quick snap.

I think I may look on eBay for some peek rod , I want to experiment .

This is cool stuff, like finesse air gunning lol

[Motorhead]

Wow ,14 grams. And shooting 910 fps. What is your reg setting?  Wonder how a 10 gram hammer would do?

I recently reduced my prod hammer to 19 grams, and your right there is quite a difference in the shot cycle. A quick snap.

I think I may look on eBay for some peek rod , I want to experiment .

This is cool stuff, like finesse air gunning lol

It has been 3 years tuning on the M-rod platform with many a test session coming to an optimum weight for a regulated action in .177 & .22 calibers.  ( .177 cal at @ 1600# using @ 20 gram hammer )  ( .22 cal at 1900# using @ 26-28 gram hammer ) based upon valves utilizing OEM poppets and much softer poppet springs, Opened up intake caps with larger transfer passage sizes.

ONLY sense playing with tapered seat minimal sealing area poppets has the optimum hammer weight required fallen further yet. 
Personally feel weights I'm currently getting away with are very close too or running near minimal weight one could use successfully.  * Also these shared results are with GEN 1 type valve with Flat seats !  Raised fixed sealing diameter Gen 2 or BOTH .25 valves are a different animal and likely won't be able to run at these shared specifications.

* As a tuner, much is shared tho not all the finer details utilized spelled out ... that is what's sold in providing full spectrum tuning services for hire.


PCP's ... More than just cookies !

[lloyd-ss]

Scott,
I have seen those quad o-rings in catalogs but have never tried them. Your first impression in this dynamic application seems to be positive. Care to add any additional thoughts about the  quad o-rings for other applications?
Thanks,
Lloyd

[Motorhead]

Scott,
I have seen those quad o-rings in catalogs but have never tried them. Your first impression in this dynamic application seems to be positive. Care to add any additional thoughts about the  quad o-rings for other applications?
Thanks,
Lloyd

Lloyd,
Had NEVER used them prior to this application. Only did so by suggestion from a Member over on the Marauder forum.
Really never had issue with typical round rings so honestly never had reason to explore X type quad rings.

They sure did the trick here, seal well with minimal drag unlike attempts made with round rings 

[lloyd-ss]

Scott,
Thanks for the feedback.  The dynamic applications always seem to be the hardest to solve.  I might have to pick up a few of them in some popular sizes and see how they work.
Lloyd

[Rocker1]

Good stuff Scott, you are the man no doubts about that sir, you are on a plateau few of us will ever reach.    David

[lloyd-ss]

......................It has been 3 years tuning on the M-rod platform with many a test session ....................
................. As a tuner, much is shared tho not all the finer details utilized spelled out ... that is what's sold in providing full spectrum tuning services for hire.
.....................

Ain't that the truth.  Give 3 cooks the same recipe, and their cakes will still never taste as good as the original.
Lloyd