Q&A 365 - important pneumatic ruling

[Jon Stratis]

I was just going through the latest round on the Q&A, and saw this:

Q. R87 Would pneumatic tubing be considered a "legal fitting" for the purposes of satisfying R87?

A. No.

https://frc-qa.usfirst.org/Question/365/showquestion

And for those who need it,

R87. The relief valve must be attached directly to the compressor or attached by legal fittings connected to the compressor output port. If using an off-board compressor, an additional relief valve must be included on the ROBOT.

I believe this is different from what we saw last year, and something teams should probably be aware of. If I had to guess, they determined that connecting it through tubing is a safety issue, as it's much easier to block tubing (by getting pinched, for example... think of a garden hose with a kink in it) than it is to block a brass T fitting connected straight to the compressor.

Cue the over-hyped outrage we've seen from other Q&A rulings so far this year...

[Thad House]

LRI's at Portland last year said it had to be that way as well. So that was the ruling last year too. We specifically made sure to make ours already compliant like this.

[Tristan Lall]

If I had to guess, I'd say it's an oversight rather than a deliberate safety-oriented ruling (presuming that tubing was considered a fitting last year—I don't remember the specifics). But the ruling is nevertheless clearly stated and enforceable.

Accidentally deadheading the compressor isn't such a terrible thing. Certainly the compressor will stall, but in all likelihood the thermal cutoff or the circuit breaker will trip before the pressure exceeds the structural limits of the compressor or even the pinched tube. In the event that the electrical safety features don't operate, that tube will probably be first to fail (uneventfully), but if not, a compressor seal will probably fail before any structural component.

If it was an intentional decision, perhaps they're concerned about the overheating (especially Viair) compressors softening plastic tubing attached to the compressor head. But if so, the safety issue should be dealt with under R8, because it applies to any tubing running in the vicinity, not just the tubing attached to the relief valve.

[Steven Smith]

I'm not sure if I follow the logic that because other components would fail first, the ruling does not relate to safety.

Regardless of whether the tubing or the tanks would fail first, the sole purpose of including a safety relief valve is to ensure that the entire system stays below the rated working pressure of the components. Connecting the safety relief to the system with flexible tubing that could potentially be kinked by a robot mechanism or any other number of things would render the safety relief worthless, therefore the rule is that it must be connected with rigid fittings.

Seems pretty cut and dry to me?

[Tristan Lall]

Originally Posted by Steven Smith

I'm not sure if I follow the logic that because other components would fail first, the ruling does not relate to safety.

Regardless of whether the tubing or the tanks would fail first, the sole purpose of including a safety relief valve is to ensure that the entire system stays below the rated working pressure of the components. Connecting the safety relief to the system with flexible tubing that could potentially be kinked by a robot mechanism or any other number of things would render the safety relief worthless, therefore the rule is that it must be connected with rigid fittings.

Seems pretty cut and dry to me?

The confusion may lie in my first sentence: I don't think the ruling was necessarily a deliberate attempt to increase safety (even if concerns rules that are clearly safety-oriented). For example, it could be a deliberate attempt to increase reliability, while keeping safety essentially the same.

I don't think it was addressing safety because the additional hazard caused by a tube failure or kink between the compressor and relief valve is minimal, and is adequately managed by the other safety features and regulations.

[AllenGregoryIV]

This is a rule change from last year (actually from earlier this year) and it was intentional on HQ's part for safety reasons.

Our bagged robot is illegal since this rule was not changed until now. We'll be figuring out a way to change it in Dallas.

[artdutra04]

Originally Posted by Jon Stratis

I believe this is different from what we saw last year, and something teams should probably be aware of. If I had to guess, they determined that connecting it through tubing is a safety issue, as it's much easier to block tubing (by getting pinched, for example... think of a garden hose with a kink in it) than it is to block a brass T fitting connected straight to the compressor.

Cue the over-hyped outrage we've seen from other Q&A rulings so far this year...

Originally Posted by 2013 Game Manual

4.1.10.12 R86
The relief valve must be attached directly to the compressor or attached by legal fittings connected to the compressor
output port. If using an off-board compressor, an additional relief valve must be included in the high pressure side of
the pneumatic circuit on the ROBOT.

Same rule as last year.

In fact I'm pretty sure this rule has been the same since they began allowing any COTS compressor besides the original Thomas one, which had two output ports (relief valve had to be attached to one of the two outputs) so the rule in its current form was not necessary.