Membrane cylinder
Diaphragm cylinders are in connection with the mechanical wheel brakes and are part of the air brakes in vehicles. Depending on the size and the applied pressure, they ensure the required braking force in the service brake system. They convert pneumatic energy into mechanical energy that acts on the brake calliper in the case of disc brakes and presses the brake pads against the brake discs. With drum brakes, the piston acts on a slack adjuster, which transfers the force and thus presses the brake shoes against the brake drum.
Variants of the membrane cylinder
The common membrane cylinder
The simple diaphragm cylinder is an integral part of the service brake and is now often located on the front axle of the towing vehicle. In the cylinder itself there is a spring that pushes the plate to which the rod is attached inwards, into the membrane . On the other side of the membrane is an empty space. If the brake pedal is now pressed, compressed air flows into the empty space and pushes the membrane outwards. This compresses the spring and pushes the rod outwards. This mechanical energy then acts on the brake caliper, whereby either the brake pads are pressed against the brake disk in the case of the disc brake, or the brake shoes are pressed against the brake drum in the case of the drum brake. This brakes the vehicle. If you let go of the brake pedal again, the air escapes from the cylinder and the spring pushes the plate and the diaphragm back into their starting position. The braking effect decreases again.
Piston Cylinder
The piston cylinder is the predecessor of the diaphragm cylinder. The difference is that a piston is built into the piston cylinder and not a membrane. The way it works is the same. When the brake pedal is pressed, compressed air flows into the empty space of the cylinder and compresses a pretensioned spring via the piston. The linkage is also pushed outwards, acts on the brake shoes and brakes the vehicle. If the air escapes again, the pre-tensioned spring pushes the piston back into its starting position and pulls the rod back again. The braking effect decreases. The piston force depends on the piston area and the pressure acting on it. The piston cylinder is not only available as a pushing cylinder, but also as a pulling cylinder. When the cylinder pulls, the piston is compressed when the compressed air flows in in the other direction and pulls the rod in further, which then brakes. If the air escapes, the piston relaxes and pushes the linkage outwards again. The braking effect decreases.
The piston cylinder as a brake cylinder is hard to find these days. It was often installed in single-circuit compressed air systems, especially in the agricultural sector, because a piston cylinder can achieve a greater stroke than a diaphragm cylinder. This also results in other areas in which the piston cylinder is used, e.g. B. when opening and closing flaps via compressed air or tensioning, lifting, switching at other points. If the bellows of the cylinder breaks or the seals are leaking, there are repair kits available. Since the shell of the cylinder is riveted, it is very difficult or impossible to change the piston or spring inside. If there is damage inside, the entire cylinder is often replaced. The membrane cylinder is much cheaper to purchase, which is why the entire device is often replaced if the membrane cylinder is defective, although the individual parts can theoretically be replaced.
Spring-loaded cylinder
A spring-loaded cylinder is responsible for the parking brake. Without compressed air, the spring is expanded and the brake is firm. The brake must be released when starting the tractor or when connecting the air supply to a trailer. As soon as a stable compressed air circuit has built up, the spring in the spring-loaded cylinder is compressed by the compressed air and the brake is released. This also gives a protective function. Should the compressed air circuit break down or become leaky, there is no longer any braking force via the brake pedal or the handbrake. The spring-loaded cylinder, on the other hand, brakes the entire train as soon as there is a drop in compressed air, because the compressed air escapes, the spring expands again and thus pushes the linkage outwards, which releases the brake. This serves as a protective function. If the vehicle has to be towed after an accident, the spring-loaded cylinder must be released manually. To do this, you use the mechanical release device that is attached to the cylinder, consisting of a hexagon screw and a needle bearing . There is a cap at the end of the spring-loaded cylinder that must be removed. Underneath it there is a mounting hole for the needle bearing. After inserting the needle bearing, the hexagon nut is screwed counter-clockwise onto the needle bearing. This pulls the inner piston outwards without the influence of compressed air and preloads the spring, which releases the brake.
Double membrane cylinder / combination cylinder / tristop cylinder
In addition to the cylinder types mentioned above, the combination cylinder (also called double-membrane cylinder or tristop cylinder) is a hybrid of the two. This hybrid form occurs both in the towing vehicle and in the trailer. The double diaphragm cylinder is the cheaper option and is often used in trailers. It combines the functions of a diaphragm and a spring-loaded cylinder and looks like a spring-loaded and a diaphragm cylinder, which are connected by a clamp. As long as no compressed air circuit has built up, the trailer is braked because the spring in the spring-loaded cylinder-like part of the combination cylinder presses a membrane into the starting position and thus also presses the linkage outwards. As soon as a compressed air circuit has built up, the empty side of the membrane fills with compressed air and compresses the spring, so that the linkage is brought back inside by the other spring in the cylinder and the brake is free again. If the service brake is now operated with the brake pedal , air also flows into the membrane-like empty space of the cylinder and compresses the second spring again via the membrane, which pushes the linkage outwards again and brakes the trailer. If you let go of the pedal, the air escapes again and the spring pushes the membrane back again, the rods are drawn in again and the braking effect decreases. If the compressed air circuit should collapse, all of the air escapes from the double diaphragm cylinder and the spring from the spring-loaded part opens up again, pushing the linkage outwards and braking the trailer (see spring-loaded cylinder).
There is also the option of manual release with the double diaphragm cylinder. Here it works exactly the same as with the spring-loaded cylinder. By turning the hexagon nut on the needle bearing, the piston is pulled outwards without the influence of compressed air and the spring is pretensioned until the diaphragm cylinder part is stronger and the spring of the spring-loaded cylinder part compresses so that the brake is released. In contrast to the diaphragm cylinders or piston cylinders, if there is a defective combination cylinder, attempts are made to repair the damaged areas and, if necessary, also to use new diaphragms, since the cylinders are more expensive to purchase than the individual diaphragm, piston or spring-loaded cylinders and therefore have to be thrown away would be uneconomical.
Individual evidence
- ↑ Breuer, Bert 1936-, Bill, Karlheinz H .: Brake Manual Basics, Components, Systems, Driving Dynamics . 5th edition 2017. Springer Vieweg, Wiesbaden 2017, ISBN 978-3-658-15489-9 .
- ↑ Matthias Becker: Compressed air brake combination brake cylinder. (No longer available online.) Archived from the original on November 25, 2017 ; accessed on November 30, 2017 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
