GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Topic started by: Ronno6 on July 28, 2024, 08:28:11 PM
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Not certain as to where this should be posted............
O-rings are typically used in applications in which they are pretty much encapsulated....like in grooves in glands or loading bolts
that contain 3 sides with the other part in the system..loading port, shaft, etc contact and contain the remaining side.
I am trying to use one as a valve seat, between a valve poppet and back wall of the valve chamber, by bonding the O-ring into the ID of a washer.
I had purchased some "bonded sealing washers" from McMaster and they worked great........for about 10 shot cycles.
Then the O-ring in the center seemed to extrude into the valve's discharge hole around the stem.
The O-ring has a 5.8mm ID and the hole in the valve is maybe 6mm, so the mean diameter should be 7.3mm ergo larger than the hole.
The hardness of the O-ring that is used is spec'd as 85A durometer.
The sealing washer was only rated for 200psi gas, and in a Daisy 850 SSP gun, that inna gonna cut it, and I verified that.
So, I machined a then washer using brass and super glued in an O-ring.
The tricks there were getting the washer thin enough so that the O-ring protruded on both sides. and gluing it in without getting super glue on the sealing surfaces.
The 70 durometer buna O-ring is 1.5mm cross section, (about .059") and the brass washer is .030" thick.
So far it is working.
However, owing to the failures of the purchased sealing washers, I don't know if I can trust my part....
This gun is from the west coast, so I don't want to ship it to the owner only to have it fail.....
Thoughts???
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Hum...
Any way you could put the O-ring on a shoulder on the poppet instead of trying to use it as a seat?...
Then you would retain something solid to keep the ring from extruding into the discharge port...
Otherwise you are completely dependent on your adhesive AND ring material to prevent the inevitable of the o-ring following the path of least resistance, which is right out the exit...
In which case, a solid rubber washer bonded to the face of the seat area would be a better bet-far more surface area bonded to the seat...
Jesse
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Mr. Jesse,
Dunno about sealing on a shoulder....
The original valve used the hard plastic poppet sealing against a cup-shaped rubber seat with a raised ridge around the center, ala O-ring.
But it was all molded as 1 piece.
The current design casts a raised ridge in the metal valve seat area around the center .
I had attempted to make a valve seat washer out of brass but could never get the system to seal.
I punched a sealing washer out if friction tape to seal the brass seat against the valve end wall, but the system
still leaked...not sure which side of the seat leaked...
I may revisit the brass seat style, but use a Bengamin valve stem that has a rubber-esque sealing surface.
However, the poppet stem is larger O.D. than the original, and I really don't have a way to chuck it up to turn down.
So, I suppose I can enlarge the stem thru hole in back of the valve, but then I am committed to that design.....
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Mr. Jesse,
Dunno about sealing on a shoulder....
The original valve used the hard plastic poppet sealing against a cup-shaped rubber seat with a raised ridge around the center, ala O-ring.
But it was all molded as 1 piece.
The current design casts a raised ridge in the metal valve seat area around the center .
I had attempted to make a valve seat washer out of brass but could never get the system to seal.
I punched a sealing washer out if friction tape to seal the brass seat against the valve end wall, but the system
still leaked...not sure which side of the seat leaked...
I may revisit the brass seat style, but use a Bengamin valve stem that has a rubber-esque sealing surface.
However, the poppet stem is larger O.D. than the original, and I really don't have a way to chuck it up to turn down.
So, I suppose I can enlarge the stem thru hole in back of the valve, but then I am committed to that design.....
You've probably already looked, but there wouldn't happen to be a U-cup or similar that would fit your application?....
The combination between the port size and valve ID would have to be just right though...
https://www.mcmaster.com/products/o-rings/u-cup-seals~/ (https://www.mcmaster.com/products/o-rings/u-cup-seals~/)
https://www.mcmaster.com/products/o-rings/rod-seals-1~/ (https://www.mcmaster.com/products/o-rings/rod-seals-1~/)
Maybe even one of these?...
https://www.mcmaster.com/products/o-rings/rod-wipers~/ (https://www.mcmaster.com/products/o-rings/rod-wipers~/)
Sorry, that's all I've got :P
Jesse
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Mr. Jesse,
Yup.
The OEM seal is 1/2" OD X 1/4" ID but pretty thin in the seat area........maybe .050" or so..... but about 3/16" lip...
Speaking from memory....
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About the only idea I have left is turning a seat from Teflon-*might* be soft enough to seal-yet it can be machined (a lot better than I expected-although I haven't found out if the check valve I made seals yet either... :o)...
Edited to add:
I recall seeing a video where a fellow was making compressed air engines-he molded his own piston seals...
IIRC, he 3D printed the molds, and filled them with some type of 2-part rubber compound?...
Had to degas the mixture to not get voids-again IIRC he did that by sicking it into a large glue syringe, capping the end, and pulling the plunger back to create a vacuum...
I don't recall it that well, and have no idea where I found it...
Maybe it was a video posted here?... ???
In the Back Room?...
I can't remember now...
Jesse
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Well I'll be danged-Google still works...
This was the guy; don't have time to dig up which vid ATM but it's one of his:
https://www.youtube.com/@TomStantonEngineering (https://www.youtube.com/@TomStantonEngineering)
Jesse
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Mr. Jesse,
I have some Delrin that I can use to fashion a seat..... I will give that a try.
I had used the brass as the current design has the plastic poppet sealing against a metal seat cast into the valve body.
I am pretty sure that the Benji stem will seal against a brass seat, but may have to silicone the seat into the valve..
I'm not sure how well friction tape seals.......
I may also try a rubber sealing washer, but would probably need to retain the edges with a ring of some sort.
I would think,tho, that if a flat washer would work, Daisy woulda used one to begin with...