Trailer one way Valve

[snailexpress]

(03-07-2021 )alborz Wrote:  Is the a one way valve on trailers?
when the trailer brake is set on the dash, swishing noise is continues for a while. I removed the emergency brake line( red glad hand ) from the trailer and air is pushing out from the trailer side.

You have bad quick release or trailer air tank check valve on the trailer.
How it's work -
You push red dash knob in dash valve will send air pressure signal to TRACTOR PROTECTION VALVE to open air supply to red gland hose.
Air pressure will close trailer quick release valve exhaust to supply pressure to release parking brake and pressurize trailer air tank thru check valve for service brake.
When you pull red dash knob out the dash valve will release pressure from signal line, this cause tractor protection valve to close air supply to the trailer and open exhaust port to bleed air from the red gland hose. Air pressure drop in the hose will cause trailer quick release valve to open exhaust port to bleed air from the air chambers. Spring will apply brakes. Check valve should hold trailer air tank pressurized and not allow air go back in the line.
If you disconnect red gland hose with red dash knob in(break away situation) tractor protection valve SHOULD close trailer air supply due to significant air flow and dash knob will pop up. Or knob will pop up due to air pressure drop to 20 psi or below and close tractor protection valve.
Trailer side will act same as if red dash knob pulled out.