Low piston pilot valve volume

[tghhs]

Hey guys been thinking about this one, as a way to reduce pilot volume for faster opening times. As you see the piston extends out the pack of the "T". This is so that the surface area when the piston is clossed will be just slightly larger than than the surface area on the seal side of the piston. This will make the difference between the closing force and opening force minimal allowing for faster opening times.

this has probaly already been thought of, but what do you think? will the extra effort produce better performance?

[inonickname]

I can see that making your piston heavier, and therefore increasing the amount of time it takes to completely open.

For a lower pilot volume and weight solution I use a piston shaped like a cup with a tube on the inside for it to travel on.

[Technician1002]

Depending on the piston valve seat to the piston OD, this can actualy slow the piston. When the piston snaps open, the volume in the pilot area gets quickly compressed. Unless you are also using a very large and fast pilot valve, this sudden compression will slow the piston.

This may be a good thing as it reduces the impact force into the bumper.

In my piston cannons, I try to keep the pilot area compression to about 2:1 or less, so if the piston unseats at 1/4 the chamber pressure, the piston is fully open with the pressure near 1/2 the chamber pressure. To find actual parameters, absolute pressure and gas volume needs considered.

I've never needed a super small pilot area for high performace piston valves. I use a close ratio so the pilot area pressure is very low before the piston unseats. This limits the pressure rise in the pilot as it opens.

At higher pressures with a very small pilot area, the piston will open slower and may reclose early as the chamber pressure rapidly drops and the pilot rises fast. Can you say honk?

Listen to a proper operating hiss boom on my Mouse Musket. It pops open and has less than a 1:2 compression ratio in the pilot and uses a small pilot valve. (blowgun)

[tghhs]

I can see that making your piston heavier, and therefore increasing the amount of time it takes to completely open.

For a lower pilot volume and weight solution I use a piston shaped like a cup with a tube on the inside for it to travel on.

Do you mean something like this?

@Technician: Hmm yeah there's something i had considered, thanks

[inonickname]

Yes, except in mine the pilot in/out port ran through the center of the black part. Just a bit simpler.

[tghhs]

Cool Well thats how i'm gonna build my next valve then

[MrCrowley]

Depending on the piston valve seat to the piston OD, this can actualy slow the piston. When the piston snaps open, the volume in the pilot area gets quickly compressed. Unless you are also using a very large and fast pilot valve, this sudden compression will slow the piston.

This may be a good thing as it reduces the impact force into the bumper.

In my piston cannons, I try to keep the pilot area compression to about 2:1 or less, so if the piston unseats at 1/4 the chamber pressure, the piston is fully open with the pressure near 1/2 the chamber pressure. To find actual parameters, absolute pressure and gas volume needs considered.

I've never needed a super small pilot area for high performace piston valves. I use a close ratio so the pilot area pressure is very low before the piston unseats. This limits the pressure rise in the pilot as it opens.

At higher pressures with a very small pilot area, the piston will open slower and may reclose early as the chamber pressure rapidly drops and the pilot rises fast. Can you say honk?

Listen to a proper operating hiss boom on my Mouse Musket. It pops open and has less than a 1:2 compression ratio in the pilot and uses a small pilot valve. (blowgun)

Hmm that's quite interesting. Both my 1.5" pistons housed in 2" tee's open pretty much as soon as I trigger my sprinkler valve and all I hear is a loud bang, but you get quite a nice popping noise for such lower pressure, low bore and late delay on the firing.

I've never really thought about pilot pressure getting compressed because I figured it couldn't be compressed as it'd be well out of the pilot volume by the time the piston is fully open. I guess when you have such a large pilot valve you don't have the compression problem you described as much.

[Hubb]

I've never really thought about pilot pressure getting compressed because I figured it couldn't be compressed as it'd be well out of the pilot volume by the time the piston is fully open. I guess when you have such a large pilot valve you don't have the compression problem you described as much.

Even if the air is dumped from a pilot area, there is still going to be the atmospheric pressure remaining, which is still going to be compressed. Like Tech said, this can either be a good thing or a bad thing.

The ideal solution to remedy this is to use some sort of vacuum, however, that gets complicated very quickly and is usually not feasible. The alternative that pneumatic spudders have come up with is to use a larger pilot valve (which is why it is recommended all the time). If the valve is large enough, the atmospheric pressure will be purged from the pilot area as the piston retracts, resulting in no performance loss.

Now, with that said, the design in the original post (considering that the piston is sealed as to not allow chamber pressure to enter the outer area of the pilot in the diagram) will sill have atmospheric pressure. This pressure will still be compressed, even with the smaller actual pilot area, resulting in the same results I mentioned above.