INTRODUCTIONIn a power plant the boiler water is circulated in a closed loop by a feedpump driven either by an electrical motor or a steam turbine.The pump takes the water from the deaerator or high pressure heaters and boosts the pressure as high as 5500 psi (387kg/cmz) in supercritical, once-thru boilers. These pumps require a certain mini-mum amount of flow to avoid overheating and cavitation problems.In order to protect the pump when the boiler feed flow require-ment is less than the minimum permissible flow through the feed-pump, a recirculation system is used to return a portion of the high pressure flow back to the condenser or deaerator and from there to the pump. See Figure 1 for a system schematic.Figure 1 - Schematic of typical once-thru,universal pressure, steam-generating plant,showing location of boiler feedpump recircu-lation valve.DEAERATORSUPERHEATERECONOMIZER-P TURBINEL-P TURBINECONDENSERHEATER PUMP9w;g;TERCCI DRAG@ valve of globeconfiguration is shown located near pump discharge with flow to deaerator. An angle CCI DRAG valve is also available, should piping configuration dictate. System s dis-charging to the condenser normally use angle valves.Figure 3 - Actuator control schematicshown is for 3-15 psi modulation signal, with increasing signal tending to close valve.The actuator is fitted with a spring for fail open on loss of air signal. A snap-acting relay is provided to ensure the valve is seated at maximum signal. Th e snap-acting relay is set as shown so the valve modulates between 10% and 100% open.SIGNAL INLET HIGH SELECTOR RELAYPOSITIONERSNAP ACTING RELAY (10% OFF SEAT)REGULATORSETSUPPLY INLET80 PSI MIN / 150 PSI MAXVACTUATOR (FAIL OPEN)rI tem 11819202122232425262728b 293oc 31Description Material/ComponentBodySeat Ring Gasket Seat Ring Disk Stack Guide Bushing Balance Seal Plug Assembly Bonnet/Pressure Bleed Metal Seal Bonnet Flange Bonnet Stud Bonnet Nut Packing Spacer PackingPacking Follower Actuator YokePositioner, Pneumatic Limit Switches (not shown)Packing Stud Yoke Clamp Packing Flange Stem Connector Stem Connector Bolting Filter RegulatorFilter Regulator (not shown)High Pressure Select Relay I/P Transducer Solenoid Valve Snap Acting Relay Actuator Fittings/TubingModulatingStdOptOn-Off StdOpt400 Series SS TFE & 300 Series SS 400 Series SS/17-4 PHX X X X X XNotes:a Recommended spare parts.b Required for applications where the modulation signal is 4-20 mA.c The snap acting relay is used to prevent the valve from throttling less than 10% off the seat The snap acting relay assures 100% actuator loading in the closed position.O P E R A T I O NIdeally the recirculation system would meter the flow in re-sponse to the pump’s requirements. This indicates the need for a modulating control valve, which normally would be closed, but opens automatically on turbine trip. The valve would need to handle water with thermodynamic conditions at the inlet of 2500-5500 psi (175-387kg/cm2) pressure and 300°-500°F (141°-246°C)temperature and, at the outlet, saturation conditions in the rangeof 1 IO°-240°F (41°- 109(387kg/cm2) toatmospheric or vacuum pressure and simultaneously neutralize the effects of-trim erosion due to flashing;-cavitation; and,-mechanical vibration and noise.2. Remain leak tight for long periods of time.3. Modulate automatically and open in case of failure of power to the valve operator.A NEW CCI DRAG@ VALVE HAS BEEN DESIGNED T O M E E T T H E S E S T R I N G E N T R E Q U I R E M E N T S Information required for sizing procedure:l Maximum flow ratel Maximum pressure dropl Pressure drop at maximum flow rate l Vapor pressure of fluid (Figure 4)l Specific gravity at flowing temperature or water temperature (Figure 5)l Inlet pressure and outlet pressureFigure 4TEMPERATURE (°F)Determine:C v = flow coefficient based on pressure drop at Qmax Q m i n = minimum controllable flow (GPM))Procedure:where: P o== Flow (GPM)pounds per sauare inch (psi).1.0100 200 300 400 500WATER TEMPERATURE °FFigure 5These valves are designed for critical pressure steam plants, with pump discharge pressures of 2500 to 5500 psi (175 to 387kg/cm2)and fluid temperatures of 300” to 500°F (141° to 246°C). Thepatented CCI D R A G disk stack in these valves has a special, com-plex pattern disk specifically designed for this service. The only consideration required for sizing is to determine C v required or flow required in GPM. Select the valve from Table 1 which meets or exceeds the required C v or flow.For end connections, refer to Buttweld Ends, Figures 6 thru 9.P R E S S U R I Z E D S E A T P L U GThe pressurized seat plug design is a special form of the balanced plug that is balanced during modulation, but unbalanced when shut off.While the unbalanced and balanced plugs may be applied in either over-the-plug (flow-to-close) or under-the-plug (flow-to-open)configurations, the pressurized seat plug is applied only in aflow-to-close configuration When the valve is completely shut off,the balance hole is closed by the valve stem.When the valve is shut, a tiny bleed path through the bonnet lets pressure build up on top of the valve plug, creating very high seat loading for superior shutoff with a metal-seated valve. This seat loading is in addition to the actuator loading applied to the seat.Once the stem is lifted to uncover the balancing hole, the main valve plug can be opened as easily as any other balanced plugconfiguration. This feature provides superior shutoff (MSS-SP-61).Buttweld EndsANSI B 16.256"31ADIIAFIGURE 7.. . .Include a sketch ot desiredweld end with the order.Control Components Inc.We Solve Control V a l v e Problems.22591 Avenida Empresa l Rancho Santa Margarita l California 92688 USATel.: (714) 858,1877 Fax: (714) 858-1878Sales。