cci最小流量阀样本

INTRODUCTION

In 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.

DEAERATOR

SUPERHEATER

ECONOMIZER

-P TURBINE

L-P TURBINE

CONDENSER

HEATER PUMP

9

w;g;TER

CCI DRAG@ valve of globe

configuration 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 schematic

shown 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 RELAY

POSITIONER

SNAP ACTING RELAY (10% OFF SEAT)

REGULATOR

SET

SUPPLY INLET

80 PSI MIN / 150 PSI MAX

V

ACTUATOR (FAIL OPEN)

r

I tem 1

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Description Material/Component

Body

Seat 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 Packing

Packing Follower Actuator Yoke

Positioner, Pneumatic Limit Switches (not shown)Packing Stud Yoke Clamp Packing Flange Stem Connector Stem Connector Bolting Filter Regulator

Filter Regulator (not shown)High Pressure Select Relay I/P Transducer Solenoid Valve Snap Acting Relay Actuator Fittings/Tubing

Modulating

Std

Opt

On-Off Std

Opt

400 Series SS TFE & 300 Series SS 400 Series SS/17-4 PH

X X X X X X

Notes:

a Recommended spare parts.

b Required for applications where the modulation signal is 4-20 mA.

c The snap acting relay is use

d to prevent th

e valve from throttling less than 10% of

f the seat The snap actin

g relay assures 100% actuator loading in the closed position.