1,112,319. Brakes for winch drums. G. A. BLACK. 19 May, 1966 [15 June, 1965], No. 28342/65. Heading B8B. [Also in Division F2] An unbalanced double drum winder of a pithead winding gear, has a braking system whereby the maximum braking torque available to each drum at any instant during the wind is sufficient to induce an angular retardation of the same magnitude, which is the same for each drum whether the drums are coupled together or not. The maximum braking torque available varies as the winding proceeds, but at any instant, corresponds to the same angular retardation of the drums. Each of the two drums has an identical braking system controlled by a driver's single control valve 4 and an emergency trip valve 5. The circuit for one drum, shown on the left of the Fig. comprises brake release cylinders 3 operable to compress springs 6 which normally urge the brake into the applied position. Fluid is supplied to the cylinders 3 by a pump 1 via a pressure relief valve 2. The pressure level of the fluid in circuit is controlled by either of the variable relief valves 8, depending on the direction of drum wind. Each valve 8 is controlled by a pivoted lever 9 engaging a cam 10 which rotates approximately one revolution to a complete wind and a three-way valve 13 operated in conjunction with the winder brings the appropriate valve 8 into service. A centrifugally-operated valve 11 permits relief of pressure from the circuit provided valve 4 or 5 is open, when the speed of wind reaches a predetermined minimum. The valve 11 causes a by-pass of the valves 8. Valves 12, 15 permit an initial surge of fluid pressure and then a slow leak away. A valve 14 is provided to open the circuit to atmosphere to brake that particular drum whilst the other drum is still controlled by the valve 4 or 5.
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