11
Widow’s Creek Units’ 7 & 8 Gland Steam Seal Systems
1. It operates the unloader valve (6b) which is directly connected to the piston rod (3f) and the high-pressure admission valve (6c) by means of the linkage (4).
2. It operates the restoring mechanism (5). The steam valve assembly (6) contains, in a common valve casing (6a), the unloader valve (6b) and the high-pressure admission valve (6c). The unloader valve is built as a seatless valve which can slide up into the discharge bore (6d) beyond the position where it is closed, in order to permit the servo-motor to open the high-pressure admission valve by means of the linkage (4) . The high-pressure admission valve is of the tapered type in order to obtain fine control of the high-pressure steam flow. It is actuated by the walking beam (4a) and it is spring closed against steam pressure by the spring (4b). A fork and guide tube arrangement (4c) prevents the valve stem from turning in order to allow the coupling (4d) to take misalignment of the spring rod (4e) and the steam of the valve (6c) when the valve casing (6a) becomes hot. The restoring mechanism (5) actuated by the piston rod (3f) by means of the link (5a) consists of the lever (513), the roller fulcrum (5c), the dashpot piston (5d) biased by spring (5e), the expansion bellows assembly (5f), the connection (5g) to the between-bellows chamber (2k) of the pressure-sensitive element (2) and the controlled bleed line (5h) which contains the restoring needle valve (5i). The dashpot system is continuously replenished with oil through the leak off line (5k) and any excess oil is drained through the drain line (5m). The suction relief valve (5n) in the dashpot piston (5d) serves to permit rapid action for closing the unloader valve and opening the high-pressure admission valve when the turbine load is decreased rapidly. In case of rapid load increase , the roller fulcrum (5c) will lift away from its guide, having a similar effect as the suction relief valve. A locking device (7) is provided to permit blocking of the regulator in a position where valves (6b and 6c) are both closed. This has been done in order to permit inactivating the regulator in case of malfunction.