Q&A 365 - important pneumatic ruling

[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.