Weird Pneumatic Issue

Recently We’ve run into a very bizarre issue involving our pneumatics. Both sides have the same everything(spacing, tightness, rubber bands, roughly estimated average K value of said bands and position when we close on an object). However, one isolated system will not operate under 80 PSI. Each system has its own solenoid, tank and piston. Each fitting is cut flat, everything is using plumber’s tape and tightened tight.

Any advice or suggestions is appreciated. We do have an entirely new setup coming in as backup, but using it would remove our backup. Thanks!

Edit: Barin if you reply ur getting locked out of the room tmrw.

Without looking at your system, I would suggest two possibilities:

  1. Lease likely, based on what you describe, you have damaged the air cylinder by accidentally dropping or squeezing the cylinder casings. Disconnect it and see if the rod and piston move freely in the air cylinder.

  2. Most likely cause is a bad solenoid, especially if you are using a double-acting solenoid. The solenoid uses pilot air to push the spool valve back and forth inside the solenoid. Usually this takes about 15-20 psi, but if it is damaged, the spool might be sticking requiring the extra pressure to move it.

You say you used teflon tape on the fittings: if a bit of tape shaved off and got stuck in the spool, this could cause the problem. Tape is not used on the small M3 fittings–instead they seal with a gasket. (tape is used to seal tapered pipe (NPT) connections, which these are not). Proper installation of all the fittings, both on the solenoids and air cylinders is as follows: Ensure the gasket and the gasket mating surfaces are clean, then screw the fitting in finger tight, then using a metric hex key wrench inside the fitting, tighten 1/3 additional turn (120°) to seat the gasket. Unfortunately, VEX does not provide enough instructions with the pneumatics.

ugh. We’d never used pneumatics before. Thanks for your assistance

Are you using a regulator? If its screwed all the way in, then your cutting a lot of the pressure to your system.

Let’s make some clarifications of terminology here, so we all know were talking about the same thing…

This is a regulator. If you screw it in, you increase the pressure of the system. Normally installed just after the air tank, it reduces the system pressure and keeps the pressure steady, as long as the air tank’s pressure is higher. The more you screw it in, the higher the pressure, up to that of the air tank. By using the lowest working pressure that will function, you’ll get the most cycles from your air cylinders.

This is an exhaust flow control valve. If you screw it in, it will slow down (and eventually stop) the flow of air exiting the air cylinder. This provides speed control for your air cylinders. It doesn’t actually affect the cylinder force, but on these small instrumentation cylinders that VEX uses, it sometimes seems like it does. While we use them in industry all the time on larger cylinders, most VEX robots don’t need the speed control, and I would suggest just using regular fittings unless you actually need the speed control.

And by the way, this is an “air cylinder.” I’d lose my job if I started calling this a “piston”, and personally, I think students should be learning proper terminology for parts anyway.