After some discussion with team members and mentors, I wanted to ask for other teams’ experiences with pneumatics.
Is it possible to make a pneumatics system with absolutely no leaks? If not, how minimal of a leak have you guys had in the past?
This question is mainly directed to teams that do not use a compressor on their robot.
Impossible to be leak free.
With 3x medium clippard metal tanks we leak down about 15 psi per hour.
There are a lot of things you do to get low leak rates. Happy to share if you’re interested.
Here’s one team’s standard
Yes please.
As far as a leak rate standard, your best best is to decide how much pressure drop you’re willing to start a match with, then aim for less than that over a 3 hour period. If you can at least hit that mark, you should be covered for the worst scenario FRC could reasonably throw at you.
Firstly, get a tubing cutter. Anything else is going to deform the tube or not cut square. You could probably get similar results with a razor or knife, but you’d end up spending more than the $4.25 in bandages and stitches.
Secondly, if you’re reusing fittings, make sure you clean up the threads with a brass brush so you don’t see any leftover teflon or sealant. Pre-applied sealant can be reused a couple of times, but unless you’ve been counting it’s best to just clean it off.
Thirdly, use teflon tape or thread sealant on all the tapered threaded fittings. If you’re using teflon tape, wrap it by pretending that you’re screwing the fitting in, and use just 2 wraps. More is not better with teflon tape.
For tightening fittings, finger tighten them first, then use a wrench to tighten them 2-3 more turns. Don’t tighten more than this, or you’ll risk damaging things. NPT thread fittings are tapered and it’s entirely possible to split or crack things if you over tighten them.
The above two only apply to tapered fittings. If your fitting has a o-ring, gasket, or similar above the threads, then that’s what makes the seal, and you shouldn’t use sealant, just wrench it till it’s reasonably tight.
Serious leaks can be found by sticking a piece of tubing in your ear and hunting around with the other end near fittings. Or a spray bottle with soapy water. Spray it around a fitting and look for bubbles.
Slow leaks, you’ll probably have to hunt down by isolating systems. Make up a dead end with a push fitting and a correctly size pipe cap. Use it to block off the output of your tanks so your system is just tanks and a compressor. Check for leaks. Then add the regulator, then individual valves or manifolds, then cylinders. It can be a time consuming process, but eventually you’re get most of the leak sources found and fixed.
Honestly, we have never been able to achieve a leak proof system.
Our practice bot and comp bot this year are as close as we’very ever come.
At 120psi, we loose less that 10 lb. in 4 hours. That is the longest we have gone without using the pneumatics, so our actual loss rate is unknown.
Right now we are completely satisfied with its performance!
If its a non-mobile application, pneumatic system will be probably leak proof. In FRC robots, there will be leak, the best one can do is to minimize the leak rate.
I disagree, but 15 PSI per hour is plenty fine and no need to go further.
Leak-proof is different from leak-free, and considerably more difficult.
Kevin covered most everything I had in mind. I would just add two things.
First,* if practical to do so*, submerging components under water can identify multiple leak points accurately and quickly.
Second, push-to-connect fittings have a limited number of cycles that they’re rated for, so they must be checked just like all other fitting styles. The oring that makes the seal in PTC can be damaged or wear out. Consider this carefully when reusing storage tanks with molded-in PTC fittings!
I worked with a team this weekend in diagnosing their pneumatic system leaks, during which they said that they had used soapy water on ‘all the connections’ but had not checked any PTC fittings. Guess where the leaks were?
Perhaps ‘impossible’ was the wrong phrase… wildly impractical is probably more accurate. A better question might be ‘how do you make a pneumatic system that leaks as little as reasonably possible?’
One quick way to isolate leaks is to set the working pressure regulator to zero. Fix all the leaks of the storage pressure side.
While push fittings have a life, I wouldn’t obsess too much on that. If it not sealing, more likely trash or something wrong with the tube than a worn out O-ring. Do make sure the tube is cut square with no imperfections on the sealing area.