| 摘要 |
1,136,566. Propelling vehicles. DOWTY MINING EQUIPMENT Ltd. 21 July, 1966 [30 July, 1965], No. 32685/65. Heading B7L. [Also in Division F2] A telescopic hydraulic device for fixing adjacent a track 13 and which is engageable with the passing wheels of a rail vehicle to effect retardation or acceleration thereof comprises a piston 14 and cylinder 11 defining a chamber 19, 25 which communicates with a low pressure connection 22 through a pressureresponsive valve 24 carried by the piston and with a high-pressure connection 32 through a mechanically-operated valve 33 carried by the cylinder, the latter valve being actuated by an hydraulic telescopic tappet 45, 54. Extension or collapse of the tappet is controlled by either a vent valve 56 or a lock valve, which is constituted by an orifice 49 normally closed by the end of a relief valve piston 43 within the pressure responsive valve. On depression of the piston 14 by a vehicle moving below the critical speed, valve 43, 49 remains closed and maintains the tappet fully extended. Valve 24 initially remains open. The lower end of the tappet engages a cup 66, Fig. 3, and compresses a spring 68 until the action of ball detent 63 is overcome and sleeve 59 of the mechanicallyoperated valve 33 released. The compressed spring then urges the sleeve downwards until parts 64 and 65 of said sleeve and a spigot part 34 of the valve become aligned to allow highpressure flow from connection 33 to enter chamber 19. The piston is forced upwardly to exert an accelerating force on the vehicle, the valve 24 closing and lock valve 43, 49 opening to permit collapse of the tappet on upward piston movement. A ring 57 secured to the piston, Fig. 3, engages a flange 60 on the valve sleeve 59 and lifts the latter to its previously closed position shutting off the highpressure supply towards the end of the piston extension stroke. If the piston is depressed by a vehicle moving above a critical speed, pressure responsive valve 24 is closed by the pressure differential due to flow through it, valve flange 42 moving from the larger 37 to the smaller 36, of two stepped bores in the piston wall. Further flow from chamber 19, 25, now at high-pressure and producing a retardation on the vehicle, takes place through a flap non-return valve 27, 28. Large back pressure may raise the relief valve piston to produce a by-pass passage through valve 24 and to vent the tappet, thereby preventing actuation of the mechanically-operated valve on contraction of the piston and cylinder. The vent valve 56 is provided to permit collapse of the tappet in the event of failure of the highpressure source to cause closure of valve 24 and opening of the lock valve. |
