315,716. Associated Telephone & Telegraph Co., (Assignees of Kelly, J. P.). July 16, 1928, [Convention date]. Fluid-presse.-A valve structure for obtaining an automatic brake application in a train stop system comprises a piston having a chamber on one side connected to a second chamber by a restricted opening, the piston being adapted to close a normally open passageway through which the brakes are normally controlled a predetermined time after the second chamber is connected to atmosphere. This automatic valve operates also, after this predetermined time interval, to initiate the application of the brakes unless a manually operated device formed in a single structure with the automatic valve is operated during this interval. If this device is operated after this interval, it releases the brake application after the train has come to rest. The brakes may be applied in emergency by the driver's valve by means of a bye-pass in the automatic valve in the event of the double heading cock which is contained in the automatic valve being accidentally closed. The valve structure shown diagrammatically in Fig. 8 comprises a slide valve 20 normally adapted by means of a port 7<1>, to connect the driver's valve A to the train pipe 10. On an automatic brake application initiated from the track, an electropneumatic vaive EPV controlled by a relay R influenced by the track magnets, is opened and air exhausted from a chamber 71 behind a piston 19 at a greater rate than it is supplied through orifices 23, 24 in the piston and an orifice 22 in a sleeve 73 until the pressure on the right of the piston overcomes a spring 21 and moves the piston to close the orifice 23, thus reducing the air supply to chamber 71 and causing the piston to move to the extreme left. The piston is connected to the slide valve 20 which thus disconnects the driver's valve from the train pipe 10 and connects this latter to atmosphere by means of ports 5<1>, 3, thus initiating a brake application. The relay R closes the circuit of a bell B when it opens the valve EPV and the exhaust from the valve EPV takes place through a whistle 5. If in the time interval between the opening of the valve and when the piston 19 begins to move the driver moves the acknowledging lever 56. the interior 7 of the valve structure is connected by passages 12, 6<1>, 11 to a pneumatic contactor PC which is then supplied with air and opens a second point in the circuit of the valve EPV and closes the circuit of the armature restoring coils 67. 68 of the relay R, thus enclosing the valve EPV and opening the circuit of the bell B, whereupon the driver must restore the acknowledging lever in order that the circuit of the valve EPV can again be completed at the pneumatic contactor contacts. Brake application is thus prevented, the whistle 5 ceases, and normal brake pipe pressure is restored in the chamber 71. Operation of the acknowledging lever 56 when the train has stopped supplies air to the contactor PC by passages 12, 6<1>, 13 and a stop detector SD and the valve EPV is closed and the parts restored to normal condition. The stop detector SD closes the air supply to the contactor PC until the train is stopped. The polarized magnetic pick-up relay R comprises pole-pieces 63. 64 normally polarized by the S pole of a small permanent magnet P and pole-pieces 65, 66 polarized by the N pole thereof. The relay is suspended from a train so that it is brought into the magnetic field of trackway magnets 4. 42 at the exit of each block of a railway signalling system. The polarity of the magnet 4 is such as to cause armatures 58, 59 to rotate in a clockwise direction to open the circuit of the valve EPV and close the circuit of the bell B. The magnet 42 has the opposite effect. The stop detector comprises a piston 122, Fig. 9, in which is adapted to slide a second piston 124 carrying a pivoted valve actuator 121 and is supplied with air through an opening 106 which moves the parts until the valve actuator 12 is moved against the rim 140 of a wheel of the vehicle. If the wheel is stationary the actuator 121 and the piston 124 are stopped in this position and the piston 122 continues to move so that the stem 123 of a valve 113 strikes the actuator and the valve is opened to allow the air acting on the piston to pass by a passage 126 in the piston to an opening 128 in the cylinder. If however the wheel is revolving the actuator 121 is moved so that the stem of the valve does not strike it and is accordingly not opened. When the valve 113 is opened further movement of the piston 122 closes a valve 135 to prevent further movement of the piston 122 and waste of air past the stem 123. The part of the valve body containing the acknowledging valve comprises a cuplike portion 17, Figs. 3 and 7, having a rotary valve seat 47 for the rotary acknowledging valve to which seat the passage 12 leads. The passages 11, 13 also lead through the part 17 to parts 16, 18 respectively. The passage connecting the main valve with the valve EPV, Fig. 8, may be closed by a valve 28 which is provided with a sealed key. The double heading cock 51 is provided in the passage in the main valve leading to the train pipe, and if this should be unintentionally closed a valve 38 is provided, which, on the driver's valve being placed in emergency position so as quickly to release air from one side of a piston 32, through a port 81, is moved to connect the train pipe by means of a bye-pass passage 10<1> and a passage 45 to the chamber behind the piston 32 which is thus forced by train pipe pressure to the extreme left and the slide valve then connects the train pipe to atmosphere through passages 73, 37. Normally, train pipe pressure is supplied to both ends of the piston 32 by passages 81, 80.