A single protective valve maintains pressure in the receivers of the tractor vehicle in case of an emergency decrease in pressure in the trailer supply line, and also prevents compressed air from escaping from its line when pressure drops in the brake drive of the tractor vehicle, preventing automatic self-braking of the trailer.

The valve is adjusted to bypass air and from port I to port II when pressure reaches 550 kPa in port I.

Single safety valve operation

Compressed air through outlet I enters cavity A under membrane 3.

After reaching a pressure of 550 kPa, compressed air, overcoming the force of springs 6 and 7, lifts the membrane 3 and passes into the sub-valve cavity B, from where it flows through the check valve 2 to terminal II of the trailer supply line.

When the pressure in outlet I is below 545 kPa, the membrane 3, under the action of springs 6 and 7, falls onto the saddle and disconnects outlets I and II; at the same time, check valve 2 closes and prevents the reverse flow of compressed air from port II to port I.

The opening pressure of the valve is set by adjusting screw 8.

When screwing it in, the valve opening pressure increases, when turning it out, it decreases.

Single safety valve

Replacing the single safety valve

The single safety valve is replaceable in case of the following faults:

  • - violation of the tightness of the valve. An external sign is air leakage through the terminals and in the places where the cover is attached to the valve body;
  • - mechanical damage to the valve body, cover and membrane, disrupting its normal operation

Tools will be required: keys 22x24, 27x30

Removing the 28 single safety valve

We prepare the car and release air from the receivers 19 of the parking brake circuit

Unscrew the union nut of the pipeline coming from the receiver 19 from the fitting of the single protective valve 28 and disconnect the pipeline from the valve

Unscrew the safety valve 28 from the tee connecting the safety valve control valve 27

Installing a single safety valve 28

We wind the protective valve 28 onto the valve tee 27

Note: The airflow direction arrow on the body of the single safety valve must point towards valve 27

Connect the pipeline from the receiver 19 to the safety valve and tighten the union nut

Removing single safety valve 10

We release air from the receiver 19 of the parking brake system

Unscrew the union nuts of the inlet and outlet pipelines from the fittings of the single protective valve 10

Disconnect the pipelines from the valve and remove the valve

Installing a single safety valve 10

Connect the pipelines to the safety valve 10 and tighten the union nuts of the pipelines

Note: The arrow of the single safety valve must point in the direction of the compressed air flow from the compressor

We start the engine and create pressure in the pneumatic brake actuator. We check the tightness of pipelines and protective valves. Air leakage is not allowed

Disassembly and assembly of a single safety valve

You will need tools: a vice, soft jaws, a 12x13 wrench, a 10 socket wrench, a screwdriver, special pliers I801.23.000-01, dishes for fuel and lubricants, a brush

Single Safety Valve Disassembly

Installing the valve in a vise

Single Safety Valve Disassembly

Using keys 13, a socket wrench 10, we unscrew the adjusting screw 15 and the lock nut 14

With a screwdriver, unscrew the screws 13 fastening with washers 12 of the cover

Remove cover 11, spring plate 10, spring 9, piston 8, membrane 7

Remove thrust ring 1, bushing 2, spring 3, valve body 4, valve ring 5

Remove the body from the vise

Promwe wash the valve parts in diesel fuel, blow them with compressed air and check their technical condition

Valve Assembly

We install valve ring 5, valve body 4, spring 3, bushing 2 and thrust ring 1 into body 6

We install the membrane 7, the piston 8, the spring 9, the plate 10 of the spring into the body 6

Note: coat the spring with Ciatim-221 lubricant

We install the cover 11 on the valve body 6, insert the fastening screws 13 with spring washers into the holes of the cover 11 and the body

We screw in the fastening screws 13 with spring washers 12 and screw the adjusting screw 15 into the cover, tighten the locknut 14

Remove the valve from the vise and test the valve

Test order:

Connect the device according to the scheme

single safety valve testing

Open the tap 7. Set the pressure reducer on the pressure gauge 1 to 539 kPa (5.5 kgf / cm2).

We achieve the position with the adjusting screw 3 so that the receiver 6 begins to fill. Close faucet 7 and open faucet 5.

We close the valve 5 and open the valve 7. Using the reducer 8, we set the pressure of 736 kPa (7.5 kgf / cm2) on the pressure gauge 1. Gauges 1 and 4 should show equal pressures.

During the test, device 2 should not show a decrease in pressure

Secondary check the adjustment, as mentioned above, and correct the adjustment, if necessary