[q]I am trying to hook up a lower pressure switch on my 60 gallon shop compressor to use when firing my burners but also keep the high pressure switch on it for other uses, such as air tools. The reason for this is that my kiln burners will use a lot of air constantly for a long time and I was told that it puts a lot of unneeded wear on the compressor/motor to keep cycling it all the way up to 130 psi when I only need 30 psi, so it is best to use a pressure switch like from a water pump, which I have on hand, that cycles from around 30-60 psi. My first attempt at this was unsuccessful and I believe it has something to do with a spring check valve built into the compressor right where the existing high-pressure switch line comes out.
I installed a T right there and ran another line to the low pressure switch, but when I turned off the high pressure switch and turned on the low one, it caused the motor to kick on and off several times really fast before I shut it off. Then when I disconnected the air line to the new switch to remove it, there was no air pressure in that line at all. My guess is that it would not work with the built- in check valve in the compressor since it was rated for a different amount of pressure and a mechanic around here seemed to think the same thing. Anyone have an idea on a better way to do this?[/q]
[a]
On most large commercial compressors there is a small line running off the pressure switch. That is a pressure relief that goes to the head to make it easy to start with less motor load. The lower switch should work but will also most likely need another means of dumping the head pressure on start up as well.[/a]
[a]
Put the low pressure switch on the air tank. Or even further away from the compressor itself, maybe in the line to the burner. Then it’s not affected by the direct boost of the compressor. This boost causes the switch to go on and off. Hope it works.[/a]
[a]
I have a widely adjustable pressure switch on my compressor. It came set to 175, which frankly scared the pee out of me sitting there in the corner. I have reset it down to 125 and I think it would go down to 100 or so. This type of adjustment is fairly common and I think much easier to deal with than valves and separate pressure switches. You are right, compressors get really hot going up to the high end. The biggest damage to any piston system is from the breakdown of oil from heat. You may have to balance the pressure vs. the run time. It will run more frequently, but not necessarily longer when set at a lower head pressure. Check with a compresser shop or Graingers or the like. I know they are out there.[/a]
[a]
Why not just add a small regulator on the line to the kiln burners? Then you still have high pressure for tools when you want as well as adjust the pressure to the burners as needed.[/a]
[a]
There are a lot of calculations that can be done on this. Not only do you have to consider the wear on the compressor you have to consider the power consumption too. Is is cheaper to start and stop a motor than the cost of the wear to the compressor. (Motors use more power during start than they do when they are running) When you have less pressure in the tank, you also have less volume so the compressor will have to run more often. You may spend more money in power than you save on wear in the compressor by going to a lower pressure.
Compressors are like car/truck engines. Starts and stops cause more wear than constant use. Look at a car that has 100,000 city miles and compare it to a car that 100,000 highway miles. I would rather have the Highway miles car. (less stops and starts). I would guess that the maker of your compressor sized the motor and the compressor to the tank. I expect it is set to work the best and last the longest at the set pressures. That’s why you don’t see 12 volt compressors on 80 gallon tanks. My advice would be to use a regulator / valve to supply the pressure you want to you item and let it ride or purchase another compressor set up for lower pressures.[/a]
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