GE 7FA gas turbines employ compressor bleed valves to protect the axial compressor against stalling and surging conditions during start-up and shutdown. These valves are typically only open during acceleration to rated speed and deceleration from rated speed. Newer heavy-duty gas turbine with complex combustion system arrangements designed to limit emission of harmful gases also employ the compressor bleed valves during very light loading to limit the amount of air entering the combustor.
Compressor bleed valves discharge into the gas turbine exhaust duct. These valves are generally closed during normal operation (with the previous exception) since “dumping” axial compressor discharge into the exhaust reduces efficiency (but it’s MANDATORY during start-up and acceleration to protect the compressor!). Compressor bleed valves are generally either fully open or fully closed; they are not modulated.
For years, these valves have been Keystone K-Lok High Performance Butterfly valves, specially modified by a Keystone distributor. The modification includes removing the wire wrap around the seat, adding a gasket to loosen the seat, and changing the packing to high temp graphoil. The goal is to create a valve that will hold tight against 50 psig hot air, but will require a much smaller pneumatic actuator than a full rated valve. Many plants have encountered performance and maintenance issues with these valves.
Power Valves LLC has worked with ABZ Valves of Madison, KS to develop a valve that will provide improved performance and reliability without aftermarket modification. We have also worked with EasyTork Actuation to couple the ABZ valve with an EasyTork actuator which provides air failsafe operation, minimizing actuator size, eliminating springs, and improving reliability.
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