Questions about operation of pneumatic valves

[Abrakadabra]

We are using the standard SMC double solenoid valve sold by VexPro.
We are controlling it using the WPILib DoubleSolenoid Java class.
We are using the controlled piston to hold a latch in place for our catapult.

Issue: When we go over a Stronghold defense roughly, sometimes the solenoid changes state on it's own, with out being commanded by the software (i.e. - the catapult fires)

Further detail: We latch the catapult by pulsing the solenoid in the "forward" direction for a second or two, and release it by pulsing the solenoid in the "reverse" direction, again for only a second or two. At all other times, including when the catapult is latched, the solenoid is set in the "off" position, with the understanding that the valve is piloted, and should hold its last position even when the solenoid is unpowered.

The solenoid definitely switches position, as after the misfire, the latch is fully moved to the unlatched position (and is held there by air pressure). So this is not a case of the latch simply "slipping its grip".

Question 1: Is it possible for a mechanical shock (such as might be caused by going over a Stronghold defense) to cause the unpowered piloted valve to be jarred sufficiently to actually switch positions? Or should we be looking more at the electronics as a possible culprit?

Question 2+: What are the pros and cons of "pulsing" a double solenoid versus just keeping it powered in the desired direction? Would it be possible for 8 continually-powered solenoids on the PCM to exceed the max 500mA current rating of the PCM? (We are only using three right now). Does keeping the solenoid constantly powered shorten its life in any appreciable way?

Thanks for your ideas!

[headlight]

SMC Specification sheet for the series of solenoids you are using: http://content2.smcetech.com/pdf/SY3.5.7.9000.pdf

It looks like each solenoid will use at most 0.45 watts. I don't think keeping the solenoid powered will notably reduce the lifespan of the solenoid valve.

We exclusively use single action solenoids and leave them powered for significant portions of the match. We have observed that when hitting a defense hard it will momentarily pulse the solenoid. I suspect that it might actually be hitting it with enough force to pop the spool back, but I haven't done any tests to confirm. According to the spec sheet they're rated for impact (maybe they meant shock?) at 150m/s^2.

[adciv]

SMC solenoids will not be damaged by being continuously powered during the match. We routinely run these (and all our double solenoids) powered in the desired direction (simplifies coding).

Recommend you double check your wiring for any potential short circuits, especially right around the PCM.

[feverittm]

I would agree with the other posters. In your configuration (double solenoids) you will only have 4 energized at a time (the other 4 are in the other direction). So the power would be less. We have routinely left our solenoids energized to force a mechanism into the hold position with not adverse effects.

A few ideas:
Is this repeatable on you home practice defenses? If so then you have a place to experiment...
What is the orientation of the solenoid valve relative to the shock induced by the field? Can you change this orientation and does it change the behavior?
Can you 'shock mount' the solenoid (cable tie it to a hunk of foam to dampen the shock).
If you leave the solenoid energized in the direction that hold the latch closed, does it change the behavior?

Have Fun!

[FrankJ]

We always use single solenoids unless we need the bi state feature. But yes, as you found out, bouncing a dual solenoid valve just right can cause it to shift. As others suggested, leaving the solenoid energized will stop that behavior. I have solenoids in the plant the stay energized for years without damage.

[GeeTwo]

Most solenoid valves, including the VexPro ones you are using, have a small button to manually switch the state. Is it possible that in the banging around some part pushed that button?

[Abrakadabra]

Thanks for all the replies! This is an issue that has just recently appeared, so it could very well be a wiring issue, but now that we know it's safe to keep the solenoids powered, we'll try that as a first approach. And knowing that mechanical shock can indeed be an issue, we will try the shock mounting remedy as well.