Jim's piston seal article in AGW...

[NickG]

interesting... how does it shoot ?

Not had it in a gun , just wanted to see if I could machine it, its worth a go though.

[Clanchief]

Should do, there's not that much - think of a tight old BSA airsporter o-ring piston head.

But I agree on your priorities... this is just the testing phase

This post and apost 86 are very close to what may in my mind solve some issues.

The long head of the piston seal absorbs energy,,,,,,,as it compresses and tightens up in the comp tube in the reverse stroke also,,,,,,,,not going in to the Airsporter comp tube bleed hole underneath with what it can do to release pressure also.

My Mk3 Airpsorter and all standard internals is very mild to shoot, compared to tuned modern guns it has no hold sensitivity or recoil issues.

Sometimes overthinking and over engineering and theories complicate simple physics. But without this then we wouldn't love airguns.

[NickG]

This post and apost 86 are very close to what may in my mind solve some issues.

The long head of the piston seal absorbs energy,,,,,,,as it compresses and tightens up in the comp tube in the reverse stroke also,,,,,,,,not going in to the Airsporter comp tube bleed hole underneath with what it can do to release pressure also.

My Mk3 Airpsorter and all standard internals is very mild to shoot, compared to tuned modern guns it has no hold sensitivity or recoil issues.

Sometimes overthinking and over engineering and theories complicate simple physics. But without this then we wouldn't love airguns.

I bet your airsporter is a .22 ?

[bmp01]

I guess, keeping the volume low-ish through a valve (compared to a regular TP) would be a challenge?

But maybe it's not as critical IF the valve works. Trapping that energy the pellet side of the valve has got to mean you need less input energy in the first place. Avoid piston crash, yes, but I'm not sure you need the same peak pressures and I'm not sold on minimum transfer port volumes, better to chase dead volumes in lip seals....

BMP01

[crowbar]

I think the piston will reverse faster than the seal due to the drag of the seal and greater mass of the piston.

Another thought is if the piston skirt is pinned to the head in slots this will allow the skirt to act as a inertia weight.

[crowbar]

I think that a valve will increase bounce as it will restrict the air flow and sap energy opening the valve.

This is the problem in the first place in that the transfer port or valve constricts the air flow and the air
has a finite speed.

[Shed tuner]

I think the piston will reverse faster than the seal due to the drag of the seal and greater mass of the piston.

Another thought is if the piston skirt is pinned to the head in slots this will allow the skirt to act as a inertia weight.

the piston only reverses because it is being pushed back by air excerting a force on the seal, so I doubt it...

[Shed tuner]

I think that a valve will increase bounce as it will restrict the air flow and sap energy opening the valve.

This is the problem in the first place in that the transfer port or valve constricts the air flow and the air
has a finite speed.

agree, hence I am working a design of check valve that does not restrict airflow at all

[TonyL]

This post and apost 86 are very close to what may in my mind solve some issues.

The long head of the piston seal absorbs energy,,,,,,,

Sometimes overthinking and over engineering and theories complicate simple physics. But without this then we wouldn't love airguns.

I'd mentioned the possibility of a compressible head (maybe sprung - steel or air) a little while ago on a thread. So that, when the piston reaches the point where the air pressure ahead of it would normally cause it to bounce, only the sprung head moves backwards and not the main piston, reducing / negating surge. As is often the case, it's all been done before and Mick, T20, pointed out that Wonky had played / posted on such an arrangement.

Sometimes (and not wanting to stifle or hold back any advances here) I think it's just nicer to accept some of the limitations and idiosyncrasies of the humble springer. Get the BALANCE right....transfer port dimensions, bore, stroke, piston weight, spring force and, of course, matching that pellet to the powerplant. On many rifles it'll be the transfer port that will be the most difficult to play with - especially the length on guns without sliding comp tubes. As mentioned higher up, we have the choking effect to consider and also, as Jim recently pointed out, the pulse factor, too.

BOING!

[crowbar]

For a valve to not restrict the air flow it would need to be fully open from the start of the pistons release and close when
peak pressure is reached in front valve.

[crowbar]

The air pressure will act on the piston as a whole unit but the piston body and head have a certain amount of
movement between themselves and the greater mass of the piston body will control this movement.

[NickG]

agree, hence I am working a design of check valve that does not restrict airflow at all

Reed Valve ?

[Shed tuner]

The air pressure will act on the piston as a whole unit but the piston body and head have a certain amount of
movement between themselves and the greater mass of the piston body will control this movement.

I disagree - the pressure acts on the piston through the seal.

For a valve to not restrict the air flow it would need to be fully open from the start of the pistons release and close when
peak pressure is reached in front valve.

It would need to open fairly early on, but not necesarily from the outset. You defo don't want it to be shut when peak pressure is reached, just when the pressure differential accross the valve become negative..

Reed Valve ?

Crossed my mind, but I don't think there's space without compromising length / lost volume ?

I think it's time I built what I'm thinking

[greenwayjames]

Some time ago I saw a photo of one of Gerald Cardews W&S Hawks that he used for development work. It was one he had been using to test anti-bounce piston devices. It still worked fine. The Hawk is owned by John Bowkett. As many know I am involved in his facebook fanpage. I will see if I can get permission to put a pic of it either here or over there if anyone is interested?

[hmangphilly]

I know there's no 'one size fits all' answer but where abouts in the stroke would you expect a 25 mm piston to bounce ? ....1-2 mm from the end ? more ?