INTRODUCTION
In a power plant the boiler water is circulated in a clod 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. The 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 ud to return a portion of the high pressure flow back to the condenr 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 condenr normally u angle valves.
Figure 3 - Actuator control schematic
shown is for 3-15 psi modulation signal, with increasing signal tending to clo 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 ated at maximum signal. Th e snap-acting relay is t as shown so the valve modulates between 10% and 100% open.
SIGNAL INLET HIGH SELECTOR RELAY
POSITIONER
SNAP ACTING RELAY (10% OFF SEAT)
乡村用英语怎么说REGULATOR
SET
SUPPLY INLET
手诊口诀
80 PSI MIN / 150 PSI MAX
V
ACTUATOR (FAIL OPEN)
r
I tem 1
1819202122232425262728b 293oc 31
Description Material/Component
Body
Seat Ring Gasket Seat Ring Disk Stack Guide Bushing Balance Seal Plug Asmbly 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:
中华好家风征文a Recommended spare parts.
b Required for applications where the modulation signal is 4-20 mA.
c The snap acting relay is u
d to prevent th
e valve from throttling less than 10% of
f the at The snap actin
g relay assures 100% actuator loading in the clod position.无难
O P E R A T I O N
Ideally the recirculation system would meter the flow in re-spon to the pump’s requirements. This indicates the need for a modulating control valve, which normally would be clod, 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 range
of 1 IO°-240°F (41°- 109
单亲家庭
(387kg/cm2) to
atmospheric or vacuum pressure and simultaneously neutralize the effects of
-trim erosion due to flashing;-cavitation; and,
牛仔裤牌子
-mechanical vibration and noi.
2. Remain leak tight for long periods of time.
3. Modulate automatically and open in ca 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 rate
l Maximum pressure drop
l 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 pressure
Figure 4
TEMPERATURE (°F)
Determine:
C v = flow coefficient bad on pressure drop at Qmax Q m i n = minimum controllable flow (GPM))Procedure:
至上励合组合
where: P o
=
= Flow (GPM)
pounds per sauare inch (psi).
1.0
100 200 300 400 500
WATER TEMPERATURE °F
Figure 5
The 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). The
patented CCI D R A G disk stack in the valves has a special, com-plex pattern disk specifically designed for this rvice. 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 G
The pressurized at 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-clo) or under-the-plug (flow-to-open)configurations, the pressurized at plug is applied only in a
flow-to-clo configuration When the valve is completely shut off,the balance hole is clod 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 at loading for superior shutoff with a metal-ated valve. This at loading is in addition to the actuator loading applied to the at.
Once the stem is lifted to uncover the balancing hole, the main valve plug can be opened as easily as any other balanced plug
秋天的好句configuration. This feature provides superior shutoff (MSS-SP-61).
