Relief Valve

[pruo95]

Rule R87 states that "the relief valve must be attached directly to the compressor or attached by LEGAL FITTINGS connected to the compressor output port." What does it mean by LEGAL FITTINGS?

[kmusa]

T's, pipe nipples, elbows, etc. Not Tubing.

With the old style compressor, since there were 2 outlet ports, the rule was that the relief valve was to be installed in one of them.

With the current one (Viair 90C), there is only one outlet port. A suitable T, or nipple and T will get you the additional port for the relief valve, as well as the port to power your pneumatics.

Remember R75 - All pneumatic items must be COTS pneumatic devices rated by their manufacturers for working pressure of at least 125psi (with the exception of R77-D).

-Karlis

[SpeedFreed]

Actually, LEGAL FITTINGS only refers to the fitting's allowed everywhere else in the pneumatic system.

This is backed up by our robot last year which had its relief valve on the opposite side of the chassis as the compressor, making it easy to access.

As well, this year we are using tubing T's to split to everything we need in the high pressure side, so that to save weight from not using so much brass. This includes the relief valve.

Our coach, an LRI, suggested it, in addition to it getting us though inspection last year.

[EricH]

Originally Posted by SpeedFreed

As well, this year we are using tubing T's to split to everything we need in the high pressure side, so that to save weight from not using so much brass. This includes the relief valve.

Our coach, an LRI, suggested it, in addition to it getting us though inspection last year.

Last year is not this year--and even with an LRI saying it's OK, I'd be skeptical. And here's why: "Legal Fittings" doesn't include tubing. R77F versus R77E. YMTC on this, but if you make it to Champs, expect Al to weigh in with your LRI on this one (your LRI mentor loses if Al disagrees).


Now, I've got a slightly better, and definitely legal solution on the brass stuff: "T" the relief valve immediately off the compressor using brass. Run tubing off the other branch of the "T".


BTW, this doesn't apply if you're using "relief valve" to refer to the "vent plug valve", AKA "dump valve". If that is the case, carry on, but learn to use the right terminology.

[Kevin Selavko]

I think SpeedFreed is talking about his ball valve because he was talking about its accessibility.

[Jaxom]

Originally Posted by SpeedFreed

This is backed up by our robot last year which had its relief valve on the opposite side of the chassis as the compressor, making it easy to access.

As well, this year we are using tubing T's to split to everything we need in the high pressure side, so that to save weight from not using so much brass. This includes the relief valve.

Our coach, an LRI, suggested it, in addition to it getting us though inspection last year.

If you are actually talking about the pressure vent plug, this was fine. If you really did mean the pressure relief valve, you dodged a bullet; it was not legal last year to use any tubing between the compressor and the valve. I saw multiple teams have to move their relief valve so that tubing was not in the path to the compressor. R86 was pretty clear, and Q448 of the Q&A verified the requirement.

Now, this year isn't last year, but given that R87 this year has the same language, I don't think you're going to get away with having tubing in the path. I'll require the relief valve to be moved if I see this as an inspector.

[Gregor]

Just for curiosity's sake, why does the pressure relief valve have to be attached to the compressor with fittings (i.e. no tube in between), other than "because the rules say so."

[EricH]

Originally Posted by Gregor

Just for curiosity's sake, why does the pressure relief valve have to be attached to the compressor with fittings (i.e. no tube in between), other than "because the rules say so."

What happens if the PRV is connected with tubing and there's a jam between the compressor and the PRV? Not too hard to do with tubing, mind you, particularly if you don't practice FOD control, or are a bit careless with the handling. Let's just say someone is heatshrinking some wire near the compressor, is a little careless, and manages to melt tubing closed.



Right. Pressure buildup, possibly to well over 125 psi. After all, the pressure switch will probably be down beyond the PRV as well, so it won't register that increase and shut off the compressor. Insert potential catastrophic failure of the pneumatics system here.

With fittings, you get a connection that is very difficult to jam, as well as being resistant to heat, pulling out, etc., and quite probably more resistant to bursting if someone still manages to get a nice jam going.

[FrankJ]

The rules say so is the best answer. Next reason is it is a good best practice. Much for the reasons that Eric described.