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Trailer Park Brake Control Valve with Single-Button Design.

Park Release Valve (PRV) – new generation Trailer Parking Brake Control Valve for safer parking and trailer shunting is an integral part of ZF’s Intelligent Trailer Braking Platform.

  • Patented one-button design with easy 3-step push/pull operation of Park, Drive, and Release functions.
  • Trailer emergency brake function is incorporated within the iEBS modulator – the trailer spring brakes are automatically activated when detaching the supply line between truck and trailer.

How does PRV work?

Park (P) – red button pulled out to top position. Parking brake applied, trailer spring-brakes are safely activated on a coupled or uncoupled trailer.

Drive (D) – red button set to middle position. Parking brake released, trailer is ready for drive-off.

Release (R) – red button pushed in to bottom position. Parking brake of an uncoupled trailer released for towing / shunting without external air supply.


  • When the red supply line is connected, the device will automatically switch from release / shunt position to drive position without any manual intervention.
  • For the parking brake release minimum pressure 1 ± 0.5 bar is required.
  • When the trailer is coupled, a pneumatic engagement mechanism prevents the unintended actuation of the release / shunt function, though the release function works only when the trailer is uncoupled, when is coupled – it doesn’t work.
  • In case of leakage / rupture of the supply line (red coupling) during driving or uncoupling of the trailer, the trailer spring brakes will be automatically activated.
  • After emergency braking the brake can only be released if the supply line (red coupling) pressure is above 4 bar.

Product Variants

Product number
971 003 001 0
971 003 003 0
971 003 029 0
Supply port 1-1
8x1 mm tube
10x1 mm tube
8x1 mm tube
Delivery port 2
8x1 mm tube
8x1 mm tube
8x1 mm tube
Reservoir port 1-2
8x1 mm tube
8x1 mm tube
8x1 + pressure test connection (M16x1.5)

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