Jay Nepa Posted Thursday at 11:48 PM Share Posted Thursday at 11:48 PM I have a 1982 R model I changed the old style air dryer to a new style. Having trouble with the purge going off every 10-15 seconds. Pressure tested the signal line from compressor to dryer no leaks. Do I need a new unloader valve ? Quote Link to comment https://www.bigmacktrucks.com/topic/76398-air-dryer-help/ Share on other sites More sharing options...
Geoff Weeks Posted Thursday at 11:57 PM Share Posted Thursday at 11:57 PM Which AD did you install? No you most likely don't need a new air gov. You likely have either not installed the correct check valve after the A/D if it is the external purge volume type. You could also have other check valve problems causing your wet tank pressure to fall off too quickly/ Why did you change? What problem were you trying to address with a new drier? Quote Link to comment https://www.bigmacktrucks.com/topic/76398-air-dryer-help/#findComment-591124 Share on other sites More sharing options...
Jay Nepa Posted yesterday at 12:37 AM Author Share Posted yesterday at 12:37 AM I had a freeze up and my air operated functions were not working properly. The old style drier was outrageous price for a direct replacement. So I retrofitted a new style dryer. The new air dryer came with a new valve does that need to be installed the parts guy I bought the new dryer from said if I don’t have one now I don’t need one when I put the new dryer on. The old air dryer was an AD2. I tried to post pic but website wouldn’t let me upload pics. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/76398-air-dryer-help/#findComment-591129 Share on other sites More sharing options...
Geoff Weeks Posted yesterday at 12:54 AM Share Posted yesterday at 12:54 AM I can't help if you don't tell me what you put on! How often was it cycling BEFORE you changed the air drier? I suspect it was single check-protection valve and YES you do need it if you replace a AD-2 with an external purge volume drier. In many cases if the air drier can't keep the air free of moisture, it isn't the drier but air system problems (leaks) that keep the system compressing too much of the time. Quote Link to comment https://www.bigmacktrucks.com/topic/76398-air-dryer-help/#findComment-591130 Share on other sites More sharing options...
Geoff Weeks Posted yesterday at 01:00 AM Share Posted yesterday at 01:00 AM Either of these? Bendix AD-SP Meritor Air Drier Quote Link to comment https://www.bigmacktrucks.com/topic/76398-air-dryer-help/#findComment-591131 Share on other sites More sharing options...
Jay Nepa Posted 23 hours ago Author Share Posted 23 hours ago I put on a wabco R 955205. I just put on the pressure controlled check valve on the air tank and it solved the problem. The ad2 had it built into the dryer Thanks for the help. Quote Link to comment https://www.bigmacktrucks.com/topic/76398-air-dryer-help/#findComment-591139 Share on other sites More sharing options...
Geoff Weeks Posted 23 hours ago Share Posted 23 hours ago Ok, did you place it where they tell you in the instructions? It needs to be after the wet tank, in the line to the secondary tank. The original check valve in the secondary tank HAS to be removed and replaced with the valve provided. Anything less and there will not be enough purge air to correctly regenerate the drier bed. This is one of the reasons I don't like external purge driers. Too easy to install wrong. Quote Link to comment https://www.bigmacktrucks.com/topic/76398-air-dryer-help/#findComment-591140 Share on other sites More sharing options...
Jay Nepa Posted 22 hours ago Author Share Posted 22 hours ago I did install it between the dryer and the wet tank MY MISTAKE. I misunderstood the directions. I will have to move it to the secondary tank tomorrow. Quote Link to comment https://www.bigmacktrucks.com/topic/76398-air-dryer-help/#findComment-591141 Share on other sites More sharing options...
Geoff Weeks Posted 22 hours ago Share Posted 22 hours ago Read the instructions! You have to remove the existing check valve on the inlet of the secondary tank and replace with the valve provided. IT MUST be able to take air from the secondary tank back to the drier on purge to regenerate the drier bed. If there is some part you don't understand, post your question and I will try to help. I don't like these external purge volume driers. Too easy to be installed wrong or for the valve to fail. Internal purge driers like the AD-2, AD-4 and AD-9 don't need external source of air volume to purge the drier and regenerate the drier bed. Quote Link to comment https://www.bigmacktrucks.com/topic/76398-air-dryer-help/#findComment-591142 Share on other sites More sharing options...
Jay Nepa Posted 2 hours ago Author Share Posted 2 hours ago Changed the check valve to the secondary tank the way the instructions said. And now it’s back to purging every 15 seconds. Any other ideas or tips ? Quote Link to comment https://www.bigmacktrucks.com/topic/76398-air-dryer-help/#findComment-591181 Share on other sites More sharing options...
Geoff Weeks Posted 2 hours ago Share Posted 2 hours ago (edited) did you remove the factory check valve for the secondary tank? Cycling means the line from the wet tank to the gov is going from cut-out (125psi) to cut in (95 psi) in 15 sec. Why that is happening is the question that needs to be solved. IF the wet tank is not getting back fed from the secondary during purge, it can drop to less then cut in. Again, the drier uses pressure in the wet tank AND the secondary tank to purge and regenerate the drier bed. It can be possible the drier is defective. Get a union and tie the inlet and outlet hoses together (bypassing the drier) and see if it still cycles every 15 sec. If it does, it isn't the drier, if it doesn't you know you have a problem in the drier. You'll need a gauge in the unloader line to see when the compressor unloads. Are you sure you have the inlet and outlet hoses connected to the correct ports on the drier? Edited 1 hour ago by Geoff Weeks Quote Link to comment https://www.bigmacktrucks.com/topic/76398-air-dryer-help/#findComment-591182 Share on other sites More sharing options...
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