The double safety valve (Fig. 1 a) is designed to separate the supply line into two autonomous circuits (auxiliary and parking brakes) and automatically turn off the damaged circuit in order to maintain the necessary pressure in the healthy circuit.

It consists of a housing 1, a central piston 2 with two check valves 3, two thrust pistons 4 and springs 5, 6, 7, respectively, thrust pistons, a central piston and check valves.

Double protective valve

In the initial position before starting work (Fig. 1 b), the central piston 2, under the action of springs 6, occupies the middle position.

In the working position (Fig.1, c), when air is supplied from the condensate receiver to the I inlet, compressed air through the hole in the piston 2 presses the check valves and enters the II outlets and III.

If one of the circuits is damaged (Fig. d), the pressure in it drops and the central piston 2 moves towards the damaged circuit under the influence of the pressure difference, rests with its seat against the check valve 3 and presses it against the piston 4, turning off the damaged circuit.

The secondary circuit check valve remains open and compressed air from the supply line continues to flow into the undamaged circuit.

A double safety valve maintains a good compressed air pressure within 520...540 kPa in the event of a faulty one circuit.

When the pressure at the inlet to the valve rises above 540 kPa, the spring 5 is compressed under the action of compressed air acting on the check valve 3, the valve comes off the seat and the excess compressed air is bled into the damaged circuit.