Air compressor pop off valves

I have a 60 gallon compressor in my garage. From the compressor the line goes through a dryer, then a regulator. After the the regulator there is a T one leg of which is a coupler for a hose. The other leg of the T goes to a reel that I have about 12 feet away. Between the compressor and that hose reel there is a length of hose about 12 feet long. I came home the other night and the hose from the compressor to the hose reel was drastically expanded and about to pull off the hose barbs and/or explode. That would be bad.

Since the regulator has a check valve it prevents extra line pressure from returning to the tank. My guess in what happened is that the extra heat in the garage caused the air in the line to expand.

My solution to the problem is to put in another T after the regulator and in that T put in a pop off valve like you have in the compressor tank itself. I ordered a 150 psi valve and put it all together tonight. I had been concerned about the valve not closing before the compressor kicked back in around 90 psi. I was correct.

If I leave the set up as is, if the pop off in the line ever goes the setup is going to continue to spew air and the compressor run until I get home and manually reset the valve.

Ideally I would like to figure out a valve like this one that closes sooner.

Here are my questions:

1. Is there a chart anywhere online that would tell me the pressures at which a pop off closes?

2. Any idea the pressure at which a normal air line would start to expand like it did?

Ideally I need to either:

a. find a valve that opens at less than the answer to question 2 and shuts before 90 psi

or

b. reengineer another solution.

I do realize that I could just shut the valve off at the tank each time I am done using the compressor but I really prefer to have the air line ready to plug in a tool and go.

Any thoughts?

in case anyone is ever curious, a 150 psi pop off valve closes at 45 psi.

Pop-offs come calibrated to different pressures. A serious compressor place should be able to determine what you need and supply one.

your bigger truck's air brake sys. use a pop off valve like your talking bout, may be what you need I would think they would open round 150 and close round 125 or 100

I turn the power off each time I'm done using my compressor. I don't like surprises like the one you found.

I had allowed the drive belts to get loose on my compressor. I hadn't checked the belt tension in years. I was in another room of the shop, with a tractor running, when I noticed smoke coming through the door (my smeller is broken). Belts were so hot I couldn't hold them. Would have been a nasty situation had I been gone.

Also have had hoses blow.

I now have a relay that trips a light & buzzer when I turn off the shop lights. Helps to remind me to turn off the compressor. I hated hiking out to the shop in my underwear at 2 AM to turn it off.

Paul

I'm NOT an engineer with the math to back it up but I REALLY doubt heat expanding the air in the line to that degree was the problem.

You simply had a hose about to fail.

If you were dealing with a non-compressible fluid (hydraulic oil or water, for example) that would be a different matter.

Simply turn off the power to the compressor when leaving the shop and don't worry about it.

My late Uncle was a master electrician and did quite a bit of grain elevator wiring. When I built my new shop in 1984, he supervised it's wiring, and we put in a "night panel" like used in the grain facilities for the heating system and just a couple of essential outlets and an exit light.

To this day, when leaving the shop I pull the main switch and all but a very few essential items are powered down.

That's NOT to say something still couldn't fail and start a fire but it DOES eliminate 95% of the possible things that could fail and start a fire.

Never leave a compressor on overnight! If a hose or something else were to let go, the compressor would run all night and probably be ruined or even worse, start a fire. Unplug the compressor or turn the switch off anytime you aren't there. Having to wait a few minutes for the compressor to fill isn't a big deal. Dave

Your comppressor and application is no differant than 1000s of other shops and in my (slightly) opinionated opinion you are making a lot out of the problem. You had a hose go bad. Hoses never were a forever thing and the quality of the rubber products we buy today is mostly pretty poor. There is no no safety factor like we used to enjoy and todays rubber deteriates quickly epecialy if it came from the land of no quality to begin with. I have gotten rid of all the cheapo hoses in my shop and replaced them with Goodyear. Heat may well have been a factor, it made the allready bad hose even softer but it did not cause line pressure to go into the red zone and burst that I would bet on. Beyond all that there are too many things that can go bad for me to leave my compressors on over night. Over the years I have had 3 sets of contacts weld and thus the compressor wont shut down, several burst hoses like you just experianced, several varius other failures. All this happening during the day while in the shop and a reminder as the other poster said to shut the compressor off every night. If you have no leaks you will have air in the moring anyway, if you do have leaks fix them, its cheaper than pumping air.

My service bench is switched off when I leave the shop.I turned the compressor off at the end of the day when I worked in the Ford garage.I opened the tank drain to blow off water in the morning.My compresser is unplugged when not in use.

The main reason I had assumed the hose expansion was due to heat was because the hose is only about 2 weeks old.

If we assume a given amount of air is trapped in the shop air line, and the temperature rises from 70 degrees to 120 degrees, what will be the pressure change?

Ideal gas law: pV = nRT

Assume the hose does not stretch, so volume is constant. Assume no air is lost, so n is constant.

R is a constant in the formula.

p(1) V = n R T(1)

P(1) = (nR/V) T(1)

P(2) = (nR/V) T(2)

P(2) / P(1) = T(2) / T (1)

but remember that temperature in this formula is expressed as degrees above absolute zero.

Using English units we convert from degrees Fahrenheit (F) to degrees Rankine (R) by adding 459

Starting temp of 70 (F) is 529 (R)
Ending temp of 120 (F) is 579 (R)

Pressure ratio is 579 / 529 or about 1.09

There is thus a 9 percent increase in pressure for a temperature change from 70 (F) to 120 (F). It is unlikely that this caused the hose to balloon.

THANK YOU for doing the math!