Testing has shown that every valve we’ve got (SMC dual coil, Festo, RexRoth, etc.) ALL bleed air out their exhaust ports (albeit slowly) in normal operation. We’ve tried a number of copies and they all act the same. Tiny amounts for sure, but we can watch the air “slowly sink ino the West” as we watch!
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You can see this effect by adding a short hose to the exhaust(s), and covering it (them) with your thumb(s) for a few seconds. It’ll always “pfffft” slightly when released. WHICH port moves back and forth on the SMC dual coil units depending on which side is active, but they all do it. (We had hoped it was only an effect of the single coil units, but no such luck… Darn…)
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We wanted to go without a compressor, but how the heck have you guys kept your compressor-less system from bleeding itself low/dry, expecially from just waiting around for the round to start??? Our application’s need is just too close to the storage capacity to risk wasting even a little bit of the stored air!
I’m assuming this has to do with the piloted valves’ design(s).
As a soluion, I’m considering tying all the vents together, and hooking on a freshly made copy of my old Servo Controlled Valve on the output to "seal the system " until we need to use it (see: http://www.chiefdelphi.com/media/photos/26363 ) , but there’s got to be a faster/better way than resorting to that! [Making a Servo Controlled Valve] will take time to implement, which we can’t really afford right now this close to ship.
Any proven solutions out there?
adTHANKSvance!
Keith McClary
Chief Engineer, Team 1502 “Technical Difficulties”
Last year we ran a compressorless system for one 3/4" bore x 6" cylinder which we ran at 40 (or maybe 20) psi. We had two clippard storage tanks, and were able to get 40-50 throws after letting it sit for 5 minutes (to simulate the match starting). Now, the cylinder never had to do any work though, it was used as a ball stop so it only took mininal side load.
We had some minimal leaks at start, but made sure all the solenoids were wired nicely (make sure the tubes are cut nicely) and double checked everything. We eventually got it to a workable level.
Because of the leaks there isn’t really a good way of knowing beforehand if it will work. You will just have to finish the pnuematics, clean them up to be as efficiant as possible and test it.
Last year, we had a pneumatic cylinder which controlled the angle of our cannon. We used a rexroth valve which was a non-piloted valve, which does not require pressure on both sides of the valve.
If you tie all the outputs together, and vent this when you vent the individual cylinders, this may solve your problem.
Yea we’re at that stage now. I’m sure this is NOT a dirt or bad assembly problem. I’ve proved that those piloted valves definitely consume a bit of air in normal idling operation.
Hi Mike!
That sounds promising. What was the part number (and cost) for the Rexroth valve you used?
I’m STILL curious though: Up to now, has everyone really just “topped it off and prayed that they’d start the round soon” whenever they ran compressor-less??? I find that hard to believe.
Keith McClary
Chief Engineer, Team 1502 “Technical Difficulties”
Maybe that or a bit higher with the SMC dual coil, significantly higher (up to twice that) with the single coil valves.
The grey Festo was definitely the worst case (Rexroth a close second), and the grey Festo WAS the one we wanted to use.
Things work great the second we pull of the compressor. But if the round start takes more than a few minutes from compressor disconnect, we’re starting to get marginal on air. That delay happens often enough at regionals that it concerns me. That’s why I’m seeking either non-leaking valves, or some kind of a “digital cork” stop-gap solution. I’m not comfortable with any “quick, let’s start or we’re toast” design.
(At least it’s good to know that we’re not the only ones that see this problem.)
Keith McClary
Chief Engineer, Team 1502 “Technical Difficulties”
I am on the same team as Imax, and I’m the pneumatics captain.
I encountered this problem with the new SMC dual coil solenoids this year, and if you want to go that route I discovered that the problem significantly lessens (if not dissappears) when you remove the small gasket (there are two, one more flat, one smaller and more rounded). Having only the flatter gasket seemed to help.
I remember last year trying to use the Festo valve and having a lot of problems. I really just don’t like it. I ended up going with the Rexroth, and not having any port problems.
My situation may be different, but I was using the Rexroth after the SMC (In Series, to slowly adjust the throw of the actuator). Here’s what I did (a little bassackwards):
I had the SMC valve as usual, but EA and EB were ported into P on the Rexroth, and the A from the Rexroth was plugged (Actually achieved by running a piece of tube out of it into a plugged piece of brass T). That’s the best way I could manage to control the exhaust.
Hope it helps, but if you have any more questions, just ask.
Two years ago I also did a compressorless system with just one SMC valve, and honestly, it just came down to making sure there were absolutely no leaks, and I simply had to keep putting the valve back together to make sure all seals were tight. So it’s possible. (I was using like a 1 1/2 inch throw, and got well into the 90 on two tanks).
An excellent suggestion! I’ll try a series valve string. (That’s an easy test.) Who knows? It may at least SLOW the leak enough to work for this year.
Thanks for the offer, but that’s the one I tried already (see above). It too slowly bleeds out its exhaust port. It was better than the Festo, but worse than the SMC dual coil. (It’s also too late for mail swaps before ship, but we appreciate the thought!)
We’re definitely overweight right now, so I have to solve this one so I can delete the compressor. (That’s over four pounds!)
No more overnight shipping now (no mail on Monday), so unless someone else has some really slick trick we can try in the next two days with whatever we have on hand (or can get from a hardware store), I may have to resort to whipping up another “digital cork” servo-valve again.
** Any other suggestions, anyone?**
Keith McClary
Chief Engineer, Team 1502 “Technical Difficulties”
Who knows? It may at least SLOW the leak enough to work for this year.