Next time, when you find yourself at the station, take a minute of your attention and pay it to the inscription, exactly in the middle at the very bottom of the train car, on which you will be whisked off to your next long-awaited vacation. This inscription is not here by chance; it tells us the very mysterious conventional number of the brake air distributor that is installed on this car.
The inscription is visible even if the train is standing at a high platform, so don't miss it.
On this car - "Ammendorf", which underwent a major restoration repair (KVR) at the Tver Carriage Works, an air distributor (VR) conv. No. 242 passenger type. It is now installed on all new and “uncoated” cars, replacing the earlier 292nd VR. It is these devices that belong to the family of braking devices that we will talk about today.
1. Westinghouse Heirs
Passenger-type air distributors used on 1520 mm gauge railways are a kind of compromise between the simplicity of design inherited from the Westinghouse triple valve and traffic safety requirements. They have not gone through such a long and dramatic development path as their cargo counterparts.
Currently, two models are used: air distributor conv. No. 292 and the air distributor conv., which is rapidly replacing it (at least in the Russian Railways fleet). No. 242.
These devices differ in design, but are almost similar in their operational properties. Both devices operate on a difference of two pressures - in the brake line (TM) and the reserve reservoir (R). Both provide additional discharge of the brake line during braking: the 292nd discharges TM into a special closed chamber (additional discharge chamber), with a volume of 1 liter, and the 242nd - directly into the atmosphere. Both devices are equipped with an emergency braking accelerator. Both devices do not have a stepwise release - they release immediately when the pressure in the TM rises above the pressure in the ignition zone established there after the last braking; as they say, they have a “soft” release.
The lack of stepwise release is compensated by the fact that both devices do not work alone on the car (although they can), but together with the electric air distributor conv. No. 305, which introduces electric brake control, and a working chamber with a pneumatic relay, providing the ability to step release.
As an example, consider VR 242, as a more modern one, as well as EVR 305.
Brand new VR 242 on the pneumatic panel in the engine room of the EP20 electric locomotive
The same one installed on a passenger carriage
Let us now turn to the design and operating principle of this device.
Diagram explaining the VR 242 device: 1, 3, 6, 16 - calibrated holes; 2,4 - filters; 5 — piston of additional discharge limiter TM;
7, 10, 13, 21, 22 — springs; 8 — exhaust valve; 9 — hollow rod; 11 — main piston; 12 — additional discharge valve; 14 — stop of the operating mode switch; 15 — operating mode switch piston; 17. 28 — rods; 18 — brake valve; 19 — stall valve; 20 — stop of the emergency braking switch; 23, 26 — valves; 24 - hole; 25 — emergency brake accelerator piston; 27 — valve for limiting additional discharge; UK - accelerating chamber; ZK - spool chamber; MK - main chamber; TM - brake line, ZR - spare tank; TC - brake cylinder
Where does the air distributor begin? It begins with charging, that is, filling the chambers of the air distributor itself and the reserve tank with compressed air from the brake line. These processes occur when the locomotive is started in the depot, when it is standing without air, as well as on all cars, when they are coupled to the locomotive, and the end valve is opened - the train is taken “for air”. Let's take a closer look at this process
Action of BP 242 when charging
So, air from the brake line, under a pressure of 0,5 MPa, rushes into the device, filling chamber U4 under the accelerating piston, then goes up the channel (shown in red), through filter 4, through channel A into the main chamber (MK), supporting it from below the main piston 11, it rises up, with its hollow rod 9 opens the exhaust valve 8, which communicates the cavity of the brake cylinder with the atmosphere. At the same time, air from the filter, along the axial channel of the rod 28, through the calibrated hole 3, goes into the reserve tank (shown in yellow), and from there through the channel into the spool chamber (SC) above the main piston 11.
This process continues until the pressure in the reserve tank, main and spool chambers is equal to the charging pressure in the brake line. The main piston will return to the neutral position, closing the exhaust valve. The air distributor is ready for action.
I’ll write again - the pressure in the TM is unstable, there are leaks in it, small leaks, but they always exist. That is, the pressure in the TM may decrease. If the pressure decreases at a rate less than the service rate, then the air from the spool chamber has time to flow into the main chamber through throttle 3, the main piston remains in place and braking does not occur.
When the pressure in the brake line decreases at the rate of service braking, the pressure in the brake valve decreases quickly enough for the main piston to move downward, under the influence of greater pressure in the spool chamber. Moving down, it opens the additional discharge valve 12.
Action of BP 242 during braking: phase of additional discharge of TM
Air from the main chamber, through valve 12 through channel K, through the axial channel of the rod 28, exits into the atmosphere. The pressure in the brake line and the main chamber decreases even more rapidly and piston 11 continues its downward movement.
Action of BP 242 during braking: initial filling of the brake cylinder
The hollow rod of the main piston 9 moves away from the seal on the exhaust valve, thereby opening the way for air from the reserve tank, which flows through channel B into the spool chamber, the axial channel of the rod 9, channel D and the mode switch passes into the brake cylinder through channel L. At the same time the same air passes through channel D into chamber U2, pressing on piston 6, which cuts off the additional discharge channel from the atmosphere. Additional discharge stops. At the same time, the rod 28 of the piston 6 goes down, the radial channels in it are blocked by rubber cuffs, which leads to the separation of the main and spool chambers. This increases the sensitivity of the air distributor to braking - now reducing the pressure in the brake line at any rate will lead to the lowering of the main piston and filling the brake cylinder.
Action of BP 242 during braking: switching the filling rate of the shopping center
At first, the brake cylinder is filled quickly, through a wide channel, through the open brake valve 18. As the brake cylinder is filled, chamber U16 of the mode switch is also filled through the calibrated hole 1. When the pressure becomes sufficient to compress the spring under piston 15, the brake valve closes and the TC is filled through a calibrated hole in the brake valve at a slow rate. This happens if the handle of the mode switch 14 is turned to position “D” (long-joint). This mode is used if the number of cars in a train exceeds 15. This is done in order to slow down the filling of the shopping centers on the cars, ensuring greater uniformity of the brakes across the train.
On short trains, handle 14 is placed in position “K” (short train). At the same time, it mechanically opens the brake valve 18, and the filling of the shopping center occurs at a rapid pace all the time.
When the driver places the valve in the shut-off position, the pressure drop in the brake line stops. Filling of the brake cylinder will occur until, due to the air flow for filling, the pressure in the reserve tank, and therefore in the spool chamber, drops, becoming equal to the pressure in the main chamber, and therefore in the brake line. The main piston will return to the neutral position. The filling of the shopping center stops, and there is a blockage.
To release the brakes, the driver places the crane handle in position I. Air from the main reservoirs rushes into the brake line, significantly increasing the pressure in it (up to 0,7 - 0,9 MPa, depending on the length of the train). The pressure in the main chamber BP also increases, which leads to the main piston moving upward, opening the exhaust valve 8, through which air from the brake cylinders, as well as from chamber U2, escapes into the atmosphere. The pressure drop in chamber U2 causes the piston 6 and rod 28 to rise, the brake line and the reserve reservoir communicate again through throttle 3 - the reserve reservoir is charged.
When the charging pressure in the surge tank (UR) reaches equal to the charging pressure, the driver places the valve in position II (train position). The pressure in the TM is quickly restored to the pressure level in the UR. At the same time, due to throttle 3, the pressure in the reserve tank has not yet had time to rise to the charging one, charging the air defense continues, but at a slower pace. Gradually, the pressure in the reserve tank, main and spool chambers is set equal to the charging one. The air distributor is then again ready for further braking.
From the driver’s point of view, the described processes look something like this:
A separate element of the VR 242 is the emergency braking accelerator; in the diagram it is located on the left side of the device. When charging, along with filling the main part of the air distributor, the accelerator is also charged - the cavity under the piston 25 and the cavity above the piston are filled with air through the accelerator chamber (AC). The brake line and the accelerating chamber communicate through throttle hole 1, the diameter of which is such that during service braking, the pressure in the accelerating chamber manages to equal the pressure of the brake line and the accelerator does not operate.
Operation of the emergency brake accelerator
However, when the pressure drops at an emergency rate - the air flies out of the brake line in 3 - 4 seconds, the pressures do not have time to become equal, the air from the accelerating chamber presses on the piston 25, and it opens the stall valve 19, opening a wide hole in the brake line from which the air goes into the atmosphere, exacerbating the process. Thus, during emergency braking, when the accelerator is operating, a window in the brake line opens on each car.
To turn off the accelerator (for example, if it malfunctions), use a special key to turn the stop 20, which blocks the accelerator piston in the upper position.
Despite the many written words and letters, in reality this device has a fairly simple and reliable design. In comparison with its predecessor, BP 292, this one does not contain spools, which are still quite capricious in operation, requiring grinding to the mirror and lubrication, and are also subject to wear.
Air distributor 242 is a stand-alone device and can work without assistants. In fact, on passenger cars and locomotives, it operates in conjunction with another device called
2. Electric air distributor (EVR) cond. No. 305
This device is designed to work in the electro-pneumatic brake system on passenger rolling stock. Installed on carriages and locomotives together with VR 242 or VR 292. This is what the brake equipment unit looks like on a passenger carriage
In the foreground is the brake cylinder. A little further, the working chamber EVR 305 is screwed to the rear wall of the shopping center. The electrical part of the EVR together with a pressure switch is attached to it on the left, and air distributor 292 is attached to it on the right. An outlet from the brake line (painted red) is connected to it through a disconnect valve.
EVR 305 device: 1, 2, 3, 6, 9, 10, 11, 12, 14, 18 - air channels; 4 - release valve; 5 — brake valve; 7 - atmospheric valve; 8 - supply valve; 11 - diaphragm; 13, 17 — cavities of the switch valve; 15 - switching valve; 16 — seal of the switching valve; TC - brake cylinder; RK - working chamber; OV - release valve; TV - brake valve; ZR - reserve tank; VR - air distributor
EVR 305 consists of three main parts: a working chamber (RC), a switching valve (PC) and a pressure switch (RD). The pressure switch housing contains release valves 4 and brake valves 5, controlled by electromagnets.
When charging, power is not supplied to the valves, the release valve opens the cavity of the working chamber to the atmosphere, and the brake valve is closed. Air from the brake line, through the air distributor through the channels inside the EVR, passes into the spare tank, charging it, but does not go anywhere else, since its path into the cavity above the diaphragm of the pressure switch is blocked by the closed brake valve.
Action of EVR 305 when charging
When the driver's valve is set to position Va, a positive potential (relative to the rails) is applied to the EPT wire and both valves receive power. The release valve isolates the working chamber from the atmosphere, while the brake valve opens the path of air into the cavity above the RD diaphragm and further into the working chamber.
Action of EVR 305 during braking
The pressure in the working chamber and in the cavity above the diaphragm increases, the diaphragm bends down, opening the supply valve 8, through which air from the reserve tank first enters the right cavity of the switching valve. The valve plug moves to the left, opening the way for air into the brake cylinder.
When the driver's crane is placed in the ceiling, the voltage supplied to the EPT wire changes polarity, the diode through which the brake valve is powered is locked, the brake valve loses power, and the brake valve closes. The increase in pressure in the working chamber stops, and the brake cylinder is filled until the pressure in it is equal to the pressure in the working chamber. After this, the membrane returns to the neutral position and the feed valve closes. The ceiling is coming.
Effect of EVR 305 when overlapping
The release valve continues to receive power, keeping the release valve closed, preventing air from escaping from the cooking chamber.
For release, the driver places the crane handle in position I for full release, and in position II for stepwise release. In both cases, the valves lose power, the release valve opens, releasing air from the working chamber into the atmosphere. The diaphragm, supported from below by pressure in the brake cylinder, moves upward, opening the exhaust valve through which air exits the brake cylinder
Action of EVR 305 during holiday
If, when released in the second position, the handle is placed back in the ceiling, air will stop flowing out of the working chamber, and the emptying of the TC will occur until the pressure in it is equal to the pressure remaining in the working chamber. This achieves the possibility of stepwise release.
This electro-pneumatic brake has a number of features. Firstly, if the EPT line breaks, the brakes will release. In this case, the driver, after performing a number of mandatory actions prescribed by the instructions, switches to using the pneumatic brake. That is, EPT is not an automatic brake. This is a drawback of this system.
Secondly, when the EPT is operating, the conventional air distributor is in the release position, without ceasing to soak up leaks from the reserve tank. This is a plus, as it ensures the inexhaustibility of the electro-pneumatic brake.
Thirdly, this design does not interfere with the operation of a conventional air distributor at all. If the EPT is turned off, then the BP, filling the brake cylinder, will first fill the left cavity of the switch valve, moving the plug in it to the right, opening the way for air from the reserve reservoir to enter the brake cylinder.
This is what the operation of the described systems looks like from the driver’s cab:
Conclusion
I wanted to squeeze freight braking devices into the same article, but no, this topic requires a separate discussion, since freight VRs are much more complex, they use much more sophisticated technical solutions and tricks, due to the specifics of the operation of freight rolling stock.
As for the passenger brake, its relationship with the Westinghouse brake is compensated by additional technical solutions, which on domestic rolling stock provides acceptable performance indicators, a level of safety and manufacturability of maintenance and repair. It will be interesting to compare with “how is it going there” abroad. We'll compare, but a little later. Thank you for your attention!
PS: My thanks to Roman Biryukov for the photographic material, as well as to the site , from which the illustrative material is taken.
Source: habr.com