Eliminating Feedwater Control Valve Damage
The feedwater control valve (located downstream of the high-pressure feedwater heaters) performs the critical function of controlling the feedwater flow rate over a wide range of service conditions.
During startup and shutdown, the feedwater control valve restricts flow by controlling near the closed position. The pressure drop across the valve is high, which can cause severe cavitation and noise. Over time, these severe service conditions will damage a control valve. Even a properly designed valve will not work well unless it is connected to a correctly sized actuator. An undersized actuator will cause unstable flow conditions while an oversized unit has a slow response to input signals.
Flowserve has successfully addressed these issues with specially engineering multi-stage multi-path, or MSMP, designs. MSMP trim channels the flow through a series of orifices to reduce the pressure in stages. This prevents cavitation from occurring inside the valve. The velocity of the feedwater is kept low to prevent erosion of the valve body and to reduce noise and vibration.
MSMP trim is customer-designed for the full range of service conditions. MSMP trim prevents cavitation when throttling near the seat but acts like a conventional control valve when controlling near the full-open position. As the pressure drop across the valve decreases, the cavitation also decreases and then stops. To maintain flow rate with decreasing pressure drop, the valve will open further and expose flow paths without orifices. The orifices are not needed at this flow condition because cavitation has stopped.