How many psi should your semi truck be holding in its air tanks?

Answer 1

The ACTUAL legal answer is that cut-out pressure should be between 115 and 130 psi, with cut-in pressure being no more than 25 psi below cut-out pressure. Now, to clear up some inaccuracies..the compressor doesn't stop working when cut out pressure is reached - most (but not all) simply go into an unloaded state. The purge of air you hear when this happens isn't the pop off valves on the tank, but rather, air coming out of the purge valve on the air dryer - the air dryer canister traps moisture and oil before it can get to the primary and secondary tanks, and air is forced through the canister to remove the moisture and oil which was collected in the canister to keep it from becoming oversaturated. The pop off valves on the tanks are not to regulate pressure in the system, but rather, to prevent the tanks from rupturing in the event that pressure regulation system fails and doesn't put the compressor into an unloaded state.

Not sure which of these two answers to go with? I'm the one who has been a truck driver, equipment operator, and holds ASE master medium/heavy duty truck technician certification.

Answer 2

Between 90 and 120 psi. When the air pressure drops below 90 psi the compressor is required to start and refill the air tank. When the pressure gets to 120 psi, the compressor will stop running. There is a relief valve to keep the air tank from having any more pressure than 120 psi.

Answer 3

Between 100 psi and 120 psi