air dryer purge valve

is the purge valve fluttering or is it a constant dump of air pressure? also what air dryer do you have? troubleshooting varies a little from model to model

 

may be bad unloader valve,air flows via control line from compressor to dryer

 

I'm having almost the same problem with FTL 05 Columbia. I did not have pressure at all, I found out that the air hoses were plugged with oil/grease.
I changed the hoses, the governor and the air dryer valve(kit)
apparently it fixed the problem, however the constant air dump goes for a long period of time, which it never did before.
Now the air pressure reach up to 125psi then it releases a constant dump of air down to about 110psi, the pressures back up to 125psi and the cycle start again.
does anyone have any idea why the air dryers dumps the air little by little ??
thank you for your time.

 

Do you know what kind of dryer it is? If it's a Wabco SS1200, it may have a regeneration valve. If it does, it will give a quick burst when it purges, then you get a light purge for around 30 seconds. If this was not the original dryer type, the wet tank may not have enough volume to complete the regeneration, which drops pressure enough to load the compressor and start the cycle over again. To fix it, Wabco has a pressure sensing check valve that replaces the check valve on the secondary air tank. Above 90 PSI, it is no longer a check valve, so air can flow back into the wet tank. This give the dryer more air volume for the regeneration cycle so pressure in the wet tank wont drop below governor cut in pressure.