Compressor gets hot and blows line
 

So when we enable the robot the compressor kicks on, the pressure builds in our high pressure tanks, gets to 65 psi, holds there for ~20 seconds, then the line coming out of the compressor blows out. The line and compressor are very hot when this happens. Any ideas?

Re: Compressor gets hot and blows line
 

How much air storage to do have? And does the compressor have a fan on it? The VIAIR really needs one if it is going to be running for any extended period of time.

Re: Compressor gets hot and blows line
 

Compressors create heat when they compress air. In normal usage the heat is dissipated and doesn't cause a problem. If however the compressor is on for a long period of time, like in practice, there can be enough heat generated to soften the hose and create failure.

In good practice to connect the pressure relief valve and pressure switch directly to the compressor with brass fittings. This helps isolate the hose from the heat. The more metal between the hose and the compressor the better.

Re: Compressor gets hot and blows line
 

How many tanks, of what size, are you trying to fill?

To that end, note the compressor in the lower left-hand corner of the robot: coupler, tee to relief valve, couple, tee to pressure switch, couple, tee to pressure gauge, then the quick-disconnect to a hose.

We also added the medium-sized muffin fan from the KOP blowing across the compressor and fittings, which helps a lot.

Re: Compressor gets hot and blows line
 

We found that this happens as well. Mounting a 12V server fan pointed right at it keeps it as cool as a cucumber... or at least one that has been sitting on the counter. We had to run without the fan last night, and remembered just how hot it got.

Re: Compressor gets hot and blows line
 

Not only is it good practice, but the relief valve is required to be teed to the compressor with a metal fitting by rule.

Re: Compressor gets hot and blows line
 

Does the tubing pull out of the compressor or does the line fail by producing a bubble and then blow out at the soft spot?
If it produces the bubble then the compressor is likely running continuous for several minutes (~10 or longer). It sounds like the high pressure relief valve is not calibrated. This is supplied uncalibrated and needs to be adjusted by the team to release at 125 psi. A compressor that runs for an extended period will blow out the line. It does this by heating the tubing to a temperature where it fails under pressure. To calibrate, loosen the locking ring on the valve, it is the lower hex hardware on the valve. Then power the robot and enable, short the pressure switch which should run the compressor continuously. With an accurate pressure gauge on the high pressure side, watch for the pressure to rise to 125 psi and listen and feel for air escaping the top of the valve. If it does not, turn the top counter clockwise until air is vented from the valve. If air is released at a lower pressure, then turn the top clockwise until 125 psi is reached when it vents. Tighten the locking ring without letting the top of the valve rotate. Remove the short across the pressure switch and see if the compressor shuts off when the pressure reaches ~120 psi.

If it simply pulls out of the fitting, one of two things are occurring. Your gauge is not accurate and you are exceeding 150 psi and failing at the fitting. Or the fitting could be bad and not securing the tubing. Once inserted you should not be able to pull out the tubing without pressing the release ring first.

Re: Compressor gets hot and blows line
 

That sounds like your main regulator is not plumbed correctly.
On the regulator there is an arrow on one of the ports. The high pressure tubing must go into the port that is at the tail end of the arrow, and only that port. The other three ports are kept at working pressure ~60psi.

Re: Compressor gets hot and blows line
 

You're missing a few important pieces of information. How long is the compressor on when it's building pressure in your high pressure tanks? What gets to 65PSI, low pressure gauge or high pressure gauge? How much air storage do you have on the high pressure side?

I suspect you've mis-plumbed something or have a leak somewhere, causing the compressor to be on much longer then expected.

Re: Compressor gets hot and blows line
 

Mark I think has the solution. I did not consider the regulator in backward. It is designed to vent to atmosphere any excess pressure on the output port.

Re: Compressor gets hot and blows line
 

We are pressurizing 3 of the 41in^3 tanks.

The setup

VI Compressor-->Tanks (with pressure switch, and pressure gauge installed on the tanks -->Regulator (60 psi) ----Splits to two paths

Path A: ---> 30 psi regulator -->solenoids
Path B: ----> Solenoids

Re: Compressor gets hot and blows line
 

Let me check the regulators, and get back to you.

Re: Compressor gets hot and blows line
 

The high pressure side gets to 65 psi.

The compressor is on a minute or so, and gets to 65 psi, stays there, and half a min later or so blows the line.

~120 in^3 of air stored on te high side. No tanks after the main regulator.

Re: Compressor gets hot and blows line
 

Like many have said, we always use lots of brass fittings at the beginning of the line from the compressor and put the required fittings on there as well, this helps because the brass dissipates the heat before it reaches the tubing.

Re: Compressor gets hot and blows line
 

Reverse the polarity to the compressor?

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.

Re: Compressor gets hot and blows line
 

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

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.

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.

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.

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.

Re: Compressor gets hot and blows line
 

Alternatively, you could pass the fittings through panels to support them.

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.

Re: Compressor gets hot and blows line
 

While I do not disagree with you in principle, in practice we have run several robots like this without any failures.

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.

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)

Re: Compressor gets hot and blows line
 

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.