What Makes An Ideal Piston Bumper

[MrCrowley]

I think one area of piston valve designs that is generally overlooked is the bumper. We have some decent ideas about various materials that make good bumpers, and materials that make bad bumpers, but we haven't come close to exploring the best possible materials that would make good bumpers. The idea for this topic came to me while I was thinking about bumpers I can use in my piston hybrid cannon but this thread would be equally important for many building high pressure, or large diameter, piston valved cannons.

So what makes a good bumper? That's not a rhetorical question by the way. I think what most people look for is something that absorbs a lot of force and wont compress under pressure. The last bit is generally what makes things tricky but what exactly are the implications of this? Can some shock absorbing materials still perform well if they're compressed or are they entirely defunct?

I came across this video on YouTube, supposedly showcasing the material that will be used to make cases for the new iPhone. How well would it perform in a spudgun application? Will the compression under pressure render it useless? They do hit the M&Ms with the side of the hammer head for the first demonstration and use the head face for the second demonstration but ignoring this, the material does seem to show some promise.

There's also a variety of other material that will come up in a Google search such as polyurethane polymers and impact gels found in footwear.

I'm sure there are more appropriate absorbers found in the engineering world for very similar applications, does anyone have some examples? I'm not talking about hydraulic or pneumatic absorbers as the former would be difficult to implement in most designs and the latter is already used in some variations to some extent (the air spring) and in other variations would also be difficult to implement. Regardless, I'm more interested in ideas about shock absorbing materials rather than shock absorbing machines.

An external hydraulic shock absorber could be implemented in a hybrid piston design like that of SB15's or mine where it would be external to the pilot system and the spool rod would extend in to a hydraulic cylinder with a piston. I don't think the idea is the most practical as there surely must be some materials that would be suited for placement in the pilot area.

Perhaps I'm wrong and I'm over-reacting about the importance of more bumper related discussion but I thought I'd give it a shot anyway

[jackssmirkingrevenge]

air.

[MrCrowley]

Sweet. Sorted. Let's all go home. We may as well only bother using burst disk valves as well, no need to explore alternatives
I mentioned air springs but they're not preferable for all applications.

Easy to use in hybrid designs but a bit harder for pneumatics, especially typical piston valves (pilot valve that closes early to keep some air in the pilot or your idea above). I think it was ramses who used the air spring in his piston hybrid but there are some disadvantages to using it over a conventional piloted valve. Both SB15 and I have had to rebuild pistons because we couldn't vent the pilot fast enough at first.

I know you like your simple designs Jack, but rarely are they so simple to implement

[Brian the brain]

I have to admit that the first thing that came to mind was indeed "air".

It could come in the form of an airram, diverting the bulk of it away from the pilot via a hose.
That would make it tunable.

Another option would be to use a hydraulic system as seen in....shock ....absorbers?

In other words, compress a large volume of oil through a small adjustable valve.
Works in all sort of dampeners..
Just give the piston some free movement before it contacts the dampener and performance should not suffer any..

[MrCrowley]

Another option would be to use a hydraulic system as seen in....shock ....absorbers?

In other words, compress a large volume of oil through a small adjustable valve.

I did discuss hydraulic shock absorbers in my post

edit: I think the lack of air bumpers shows how difficult or inappropriate they can be to implement in designs. Don't get me wrong, they do have their place but it's no surprise most people go with half a tennis ball instead. Like I mentioned in the first post, I'm looking for discussion on the material side of things rather than the mechanical side. I'm well aware of air bumpers but I think there are better solutions that are easier to implement using synthetic materials.

Edit 2: This topic could even serve to discuss appropriate springs to be used as bumpers as the question came up recently. I myself would be interested in why the springs Fnord and I used in our hybrids failed* and whether there are springs out there that can do the job.

*Not literally "they failed because they were too weak" but more to what would be necessary to stop them from failing (spring constant, compressibility, raw material, spring size and spacing, etc).

Edit 3: Not a whole lot of new talk on this forum, may as well explore and entertain other ideas in intelligent conversation rather than being content with what we know.

[Crna Legija]

im really struggling to fined something for my piston hybrid because I don't have very much room to slow it down in, 20ish mm. i have a few sheets of diffident hardness rubber i was thinking of putting softer ones first and going harder.

[POLAND_SPUD]

Like I mentioned in the first post, I'm looking for discussion on the material side of things rather than the mechanical side. I'm well aware of air bumpers but I think there are better solutions that are easier to implement using synthetic materials.

not to e a dick but there is a reason why you see air springs in serious applications rather than half a tennis ball

[jackssmirkingrevenge]

I know you like your simple designs Jack, but rarely are they so simple to implement

Such is life

Instead of looking for good bumpers, focusing on making the piston as small and light as possible is probably a better route.

[MrCrowley]

Like I mentioned in the first post, I'm looking for discussion on the material side of things rather than the mechanical side. I'm well aware of air bumpers but I think there are better solutions that are easier to implement using synthetic materials.

not to e a dick but there is a reason why you see air springs in serious applications rather than half a tennis ball

Applications like what (I'm curious, not trying to be rude haha)? I'm not against the idea of an air spring but in the current form we apply them they're not always the best method to use. Dampening something that would be on a car is quite different to a hybrid valve so it would be interesting to see if there are other variations of air springs that would be more suitable than the current closed-pilot one.

If the problems me and SB15 had with piston bounce were related directly to lack of flow, and therefore presence of an air bumper, it would seem that air bumpers may not be the best method to use in large bore valves. Perhaps I should be making a topic on the ideal sealing face that can withstand piston bounce. It wouldn't surprise me if I was then told that I should fix my bumper issues rather than try and reinforce the sealing face

Instead of looking for good bumpers, focusing on making the piston as small and light as possible is probably a better route.

Smaller in diameter? As for light pistons, there must be a trade-off somewhere between velocity and energy and I lack the engineering knowledge to decide between the two. A lighter piston would accelerate faster than a heavier one and, depending on its weight, may or may not exceed the energy of a heavier piston. If it does exceed the energy of the heavier piston, there's also things like impulse that need to be taken in to account, correct? These factors would also change how it responds to whatever bumper is in place I imagine. It's generally been said that a lighter piston is better but has this always been in terms of opening time rather than bumper issues?

[jsefcik]

research!!!!

thats what i was always told

[jackssmirkingrevenge]

Smaller in diameter? As for light pistons, there must be a trade-off somewhere between velocity and energy and I lack the engineering knowledge to decide between the two. A lighter piston would accelerate faster than a heavier one and, depending on its weight, may or may not exceed the energy of a heavier piston. If it does exceed the energy of the heavier piston, there's also things like impulse that need to be taken in to account, correct? These factors would also change how it responds to whatever bumper is in place I imagine. It's generally been said that a lighter piston is better but has this always been in terms of opening time rather than bumper issues?

When we talk about collisions, it's momentum rather than energy that is discussed, so we're talking of mass x velocity.

A 50 gram piston at 20 metres per second has the same momentum as a 100 gram piston at 10 metres per second.

In practice though, if you half the weight there will not be a doubling of velocity, so you will be reducing the momentum.

As to diameter, there's an easy weight saving there - a 0.9 inch diameter piston will weigh just 81% of a 1 inch diameter piston of the same length and material.

[Crna Legija]

research!!!!

thats what i was always told

His not asking what should he should use, he is trying to come up with a thread that will help noobs and possibly make a brake though in bumper technology

[POLAND_SPUD]

Applications like what

Well for a start they are used in pneumatic valves and air cylinders

[jackssmirkingrevenge]

...and nail guns

[mattyzip77]

research!!!!

thats what i was always told

:laughing3: :laughing3: :laughing3: :laughing3: :laughing3: