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Unread 14-02-2014, 14:44
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Re: Compressor gets hot and blows line

Matthew,
Is this the same robot you are asking about in the Labview Forum? If so, there is something seriously wrong with the DSC or your code. The compressor should not come on until the robot is enabled. Neither should the RSL.
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Unread 14-02-2014, 15:16
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Re: Compressor gets hot and blows line

Quote:
Originally Posted by FrankJ View Post
Not only is it good practice, but the relief valve is required to be teed to the compressor with a metal fitting by rule.
Technically, R87 states:
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 agree a metal tee fitting is the best here. However, I think I had a RI or LRI last year state that tubing and plastic fittings would be allowed between the compressor and relief valve as these are considered "legal fittings." Of course, "legal fittings" are not explicitly defined anywhere I can tell.

R77 explicitly allows only:
A. Items available in the 2014 KOP,
...
E. Additional pneumatic tubing, with a maximum 0.160 in. inside diameter, functionally equivalent to that provided in the KOP,
F. Pressure transducers, pressure gauges, flow control valves, and connecting fittings,
...

There is also 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).

I don't read this combination of rules to mean that tubing would be a "legal fitting" to be used in between the compressor and relief valve (it's tubing, not a fitting). I did inspect a robot last year which had a flow control fitting (and tubing I think?) in between their compressor and relief valve. This is clearly an unsafe condition to me - if the flow control fitting was closed, it would prevent the relief valve from doing its job, instead allowing the compressor and fitting to reach higher than 120 psi. I think I had another team using their vent plug in between the two, which presents the same issue. I did require both teams to switch to the standard metal tee implementation (which they had to borrow - maybe part of the problem is these brass fittings are no longer included in the KOP).

To me, using normal push-connect fittings and tubing in between the compressor and relief valve is still potentially unsafe (and in my interpretation illegal), as any sort of blockage (floating thread wrap, melted tubing, etc) which could present itself in this path would prevent the system from venting at 120 psi. The heat from the compressor affecting the integrity of the tubing is another great point.

Al, would you say that the proper interpretation of R87 is that "legal fittings" are only metal tees? Or is the fall back to R8, for unsafe condition? Thanks!

Katie
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Unread 14-02-2014, 15:34
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Re: Compressor gets hot and blows line

Katie,
Your statement is true. Legal fittings are more than brass. However,
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.

implies that best practice places it close to the compressor. Brass is still legal too.
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Unread 14-02-2014, 16:01
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It turns out that the main regulator was tuned backwards. I'd like to blame the freshman that put it in, but I may have told him to so it that way in reflection. Chalk it up to last minute oversight.
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Unread 14-02-2014, 16:05
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Al, I don't think I have posted in the lab view forum. We did have a java issue with motors recently that was resolved by calibrating the talons.
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Unread 14-02-2014, 22:12
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Re: Compressor gets hot and blows line

you might want to have fewer things cantilevered off of the compressor exit port. The material on the compressor is cast, and can crack at the seam of the casting. It looks like you have several heavy components attached.

We usually just have the fitting out of the compressor, the relief valve, and then a tube connector and everything else is mounted to a mounting board.
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Unread 15-02-2014, 14:56
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Re: Compressor gets hot and blows line

Quote:
Originally Posted by Chris Fultz View Post
you might want to have fewer things cantilevered off of the compressor exit port. The material on the compressor is cast, and can crack at the seam of the casting. It looks like you have several heavy components attached.

We usually just have the fitting out of the compressor, the relief valve, and then a tube connector and everything else is mounted to a mounting board.
Alternatively, you could pass the fittings through panels to support them.
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Unread 16-02-2014, 08:24
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Re: Compressor gets hot and blows line

Matthew,
So everything is OK now? When the line blew after only a minute, had the compressor been running for a long time before that? I am asking because one minute is much less than I would consider for the output temp to be so high. For all teams, this little compressor has a duty cycle spec. It really only expects to be run for a short time with a long off time in between so that it can cool down.
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Unread 16-02-2014, 09:22
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Re: Compressor gets hot and blows line

Quote:
Originally Posted by Chris Fultz View Post
you might want to have fewer things cantilevered off of the compressor exit port. The material on the compressor is cast, and can crack at the seam of the casting. It looks like you have several heavy components attached.

We usually just have the fitting out of the compressor, the relief valve, and then a tube connector and everything else is mounted to a mounting board.
While I do not disagree with you in principle, in practice we have run several robots like this without any failures.
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Unread 16-02-2014, 15:33
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Re: Compressor gets hot and blows line

We had a similar problem to this one with our 2011 robot where the tubing would overheat and fail. We found this only occurred during demos following that competition season (it never actually happened at a competition), but nonetheless it got to be quite annoying to have to put a new piece of tubing on every few minutes.

Eventually we mounted one of the kit computer fans so it blew across the compressor, and the change in temperature was drastic.

We did tests and generated a chart based on the results:
https://docs.google.com/spreadsheet/ccc?key=0AqQx991m_YKGdEc3OV9NbG10YmluNjM2UFRhYV9Gb lE&usp=sharing


Long story short, if you can use a fan to cool your compressor, do it.
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Unread 15-10-2014, 09:17
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Re: Compressor gets hot and blows line

We had an interesting related failure last night while we were practicing for the upcoming CAGE Match off-season event.

The students were practicing a maneuver where the intake comes in and out, which means air was constantly being used for 15+ minutes. As I was shouting across the field for them to let the robot rest and have the compressor cool off, I hear a loud pop and the sound of uncapped compressor running. Turns out, the elbow fitting we use to come out of the t-fitting attached to the compressor failed, blowing off the ferrule assembly the tubing plugs into. The compressor was too hot to touch and I suspect the plastic on the 90 degree elbow got warm enough that the metal bit was able to slip past its molded grip.

It was a good reminder for my students why safety glasses are important while working near the robot, and that the Viair compressors shouldn't be run continuously. Because of space constraints, we can't really put a fan on the compressor the way it's mounted right now, but it's definitely something the students will remember next year (if we have pneumatics)
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Unread 15-10-2014, 09:20
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Re: Compressor gets hot and blows line

Quote:
Originally Posted by MechEng83 View Post
We had an interesting related failure last night while we were practicing for the upcoming CAGE Match off-season event.

The students were practicing a maneuver where the intake comes in and out, which means air was constantly being used for 15+ minutes. As I was shouting across the field for them to let the robot rest and have the compressor cool off, I hear a loud pop and the sound of uncapped compressor running. Turns out, the elbow fitting we use to come out of the t-fitting attached to the compressor failed, blowing off the ferrule assembly the tubing plugs into. The compressor was too hot to touch and I suspect the plastic on the 90 degree elbow got warm enough that the metal bit was able to slip past its molded grip.

It was a good reminder for my students why safety glasses are important while working near the robot, and that the Viair compressors shouldn't be run continuously. Because of space constraints, we can't really put a fan on the compressor the way it's mounted right now, but it's definitely something the students will remember next year (if we have pneumatics)
We found that even air blowing across the compressor works wonders. Almost everything on our robot this year was run by pneumatics so our compressor did a lot of work. Even after running through several batteries from practicing our compressor never got hot to the touch.
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