do you mean in a boiler system? in a potable water system air is purged through a faucet or fixture. if you are talking about recharging or replenishing an air chamber, (to prevent water hammer) then you would have to drain the sysem the refill it. if you are referring to a boiler , you would open a drain valve on the affected zone while the recirc. pump is running until the air is discharged. you can usually hear the air moving throught the system.
