NEW YORK AIR BRAKE EQUIPMENT * BY JOHN HAMILTON Service lap position of the control valve iary reservoir pressure the graduating will next be considered. This is shown valve will move with it, and will cut off in Fig. 52. The movable parts of the communication between ports U and W control valve will assume this position as which will result in the safety valve bealready noted when auxiliary reservoir ing no longer connected to the pressure pressure reduces to the control reservoir in the control reservoir. The reason for until the pressure in the former reservoir this is that if the safety valve should has reduced slightly below the reduction leak, such leakage would not affect the that has been made in the brake pipe pressure in the control reservoir, whereas pressure, and when the pressure in the if leakage existed, and ports U and W locomotive brake cylinders and in cham- were connected, it would result in the bér B of the control valve has increased locomotive brakes releasing for, as alslightly above the pressure in the control ready stated, any reduction in the control reservoir. The triple piston can move valve reservoir pressure will result in a without moving the slide valve, but it release of the lomotive brakes. The concannot move without moving the gradu- trol piston also assumes lap position ating valve. When the triple piston then when the pressure in the locomotive moves towards the slightly lesser auxilbrake cylinders becomes enough greater * Continued from June, 1914, Magazine. than the pressure in chamber D and the control reservoir to allow valves 1 and 1A to close. The exhaust valve now blanks the exhaust port. a slight difference of pressure on either side of this piston will be sufficient to seat the graduating valve as it has not to In lap, the position of the slide valve move the slide valve to do so, this latter is the same as in service position, but the valve being shorter than the distance beposition of the triple piston and graduat- tween the shoulders on the triple valve ing valve is different, the graduating between which it is placed. Therefore, valve having in lap position closed com- the reason that the slide valve is made of munication between the auxiliary reser- this length is to permit of this portion of voir and control reservoir. If no gradu- the control valve lapping after service in all triple valves. ating valve were used, auxiliary pressure applications. This feature is also found would flow to the control reservoir until a considerable difference in pressure existed on each side of the triple piston on account of the resistance offered by the slide valve. When the difference in pressure had become great enough to move the slide valve to close the service ports, all parts would be liable to move to release position. However, with the graduating valve attached to the triple piston, Fig. 53 shows the position the movable parts of the control valve will assume following an emergency application of the brakes. The sudden reduction of brake pipe pressure resulting in the brake valve handle being placed in emergency position will cause the triple piston to move forward the limit of its travel, the stem compressing the graduating spring. The Fig. 54. Automatic Control Valve. Emergency Lap Position matic brake valve will also enter the control reservoir through pipes CR and will increase the presure in this reservoir, and therefore in the brake cylinders, over the pressure obtained during service applications. It will be noted that a port P in the triple slide valve connects the control reservoir pressure with the safety valve. This port is of such a size that the main reservoir pressure feeding through the rotary valve of the automatic brake valve can pass to the control reservoir through pipe CR faster than it can pass through port P to the safety valve, ton and slide valve will remain in the position they assumed following the emergency application, as the pressures in the auxiliary and control reservoirs are equalized at a pressure higher than the pressure in the brake pipe. In fact, if the brake valve had been left in emergency position the brake pipe would contain no pressure. However, the control piston will move to lap position, for as soon as the pressure in the locomotive brake cylinders and in chamber B becomes slightly higher than the pressure in the control reservoir and chamber D, valves 1 and 1A will then seat. The release of the similar to a quick action triple valve, brakes following an emergency application is accomplished in the same manner as after a service application, that is, while the triple piston slide and graduating valves will be moved to release position by the increase in brake pipe pressure, yet the pressure in the control reservoir though admitted to the retain pipe with the triple slide valve in full release this reduction affecting the triple valve on the car next to the engine. An emergency application with plain cylinder cap does not produce any local drop in brake pipe pressure. The quick action cylinder cap is used when such a local reduction in brake pipe pressure is desired as on roads where trains are double headed, the length of the brake pipe between the position cannot escape until the brake brake valve on the first engine and the valve handle is moved from full release or holding position to running position. Fig. 55 shows the operation of the control valve supplied with a quick action cylinder cap during an emergency application. With this attachment, a sudden heavy reduction of pressure in the brake pipe at the brake valve due to the brake valve being placed in emergency position will result in the quick action cylinder cap so operating as to also cause a quick sudden reduction in brake pipe pressure first triple being such that if this device were not used a sudden reduction in brake pipe pressure due to placing the brake valve in emergency position might not cause the first triple valve to operate quick action. Considering Fig. 55, when the triple piston moves the limit of its travel in response to a heavy reduction in brake pipe pressure, the graduating stem will also be forced forward carrying the valve 15 with it, which opens port Q. Brake pipe pressure will then unseat other parts of the control valve is the same as when the quick action cylinder cap is not supplied. The slide valve opens communication between the auxiliary and control reservoirs, and the pressure in this reservoir connects to the safety valve through passage P. The locomotive brakes will be applied no harder with the quick action cylinder cap applied to the control valve than one without it, as the pressure at which the brakes are applied depends upon the pressure in the control reservoir, and this pressure is limited by the safety valve. control reservoir to the exhaust port in the independent brake valve. The brake cylinder pressure in chamber B will then move the control piston to release position, the exhaust valve 7 opening the exhaust port N which allows the brake cylinder pressure to escape to the atmosphere. Exhausting control reservoir pressure does not affect the pressure in the auxiliary reservoir as communication between the two reservoirs is now blanked by the graduating valve 10 which has port J closed, this portion of the control valve being in lap position. The locomo、 |