Four-circuit protection valve

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Four-circuit protection valve

The four-circuit protection valve (English Four way protection valve or Multi-Circuit Protection Valve ) is a component of the multi-circuit air brake system for motor vehicles . It is part of the pressure procurement system and has the task of protecting the individual compressed air circuits from one another. The aim is to prevent a pressure loss in one brake circuit from severely impairing another brake circuit. In principle, there are four overflow valves and non-return valves that separate the individual circuits from one another. The circles are usually divided as follows:

  • Circuit 1: service brake circuit 1
  • Circuit 2: service brake circuit 2
  • Circuit 3: Spring-loaded parking brake and, if necessary, trailer supply
  • District 4: Secondary consumers (air suspension, door control, horn)

If there are more than four circles:

  • Circuit 1: Service brake circuit 1 for the rear axle
  • Circuit 2: Service brake circuit 2 for the front axle
  • Circle 3: trailer control
  • District 4: secondary consumers
  • Circle 5: parking brake
  • Circle 6: Gearbox and clutch
  • Circle 7: air suspension

Since the compressed air brake system is purely an external power brake system, a leak without safeguarding the other brake circuits would lead to a loss of the complete braking effect.

function

The compressed air flows in via the compressor , air dryer and pressure regulator via port 1. When the system is initially pressureless, the reservoirs of the service brake circuits 1 and 2 are first filled equally via the outputs 21 and 22. The two check valves only open from a pressure at which there is already enough compressed air in the containers for several full brakes . Only then is the parking brake circuit storage tank filled via output 23. It is therefore not possible to drive off without sufficient brake pressure, since the parking brake, which is designed as a spring accumulator , can only be released when the two brake circuits already have sufficient pressure. If this circuit has sufficient pressure, the so-called working circuit (compressed air circuit for supplying subordinate units, such as door actuation in a bus) is finally supplied with compressed air through output 24. A leak in one of these circuits, which can no longer be compensated by the compressor, only lowers the total pressure until the respective check valves respond one after the other. For example, a leak in the working circuit would only lower the pressure in the parking brake circuit until the (adjustable) overflow valve of the working circuit closes. The residual pressure prevents the spring accumulator from responding and thus prevents the parking brake from blocking unintentionally. If there is a leak in one of the two brake circuits, the pressure in the other brake circuit is also reduced. Here, too, the (adjustable) overflow valve prevents total failure.

Note on the designation of the connections: In compressed air technology, it is specified that inputs into a component are always designated with 1 and outputs with 2 . The designation 3 is the atmospheric vent and 4 is a supply or control line. If there are several of these, they are numbered with a consecutive second digit, in this case the outputs 21, 22, 23 and 24 for the four compressed air circuits separated from one another.

safety

The four-circuit protection valve primarily defines the priorities of the individual compressed air circuits. The two service brake circuits have top priority, then the parking brake circuit and, at the bottom, the supply of the additional units. If a higher-level circuit loses compressed air due to a leak, the subordinate circuits will only continue to be supplied if the filling capacity of the compressor is higher than the loss. Otherwise these circuits lose their function as soon as their compressed air supply is used up. In this way, it is also achieved that, in the event of a defective service brake circuit, the parking brake closes after not too long and it is no longer possible to continue driving with the service brake failed.

literature

  • Peter Gerigk, Detlev Bruhn, Dietmar Danner: Automotive engineering. 3rd edition, 4th printing. Westermann Schulbuchverlag GmbH, Braunschweig 2000, ISBN 3-14-221500-X .
  • Max Bohner, Richard Fischer, Rolf Gscheidle: Expertise in automotive technology. 27th edition, Verlag Europa-Lehrmittel, Haan-Gruiten, 2001, ISBN 3-8085-2067-1
  • Peter A. Wellers, Hermann Strobel, Erich Auch-Schwelk: Vehicle technology expertise. 5th edition, Holland + Josenhans Verlag, Stuttgart, 1997, ISBN 3-7782-3520-6

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