Neyveli Control Valves

PNEUMATIC HOOK UP DIAGRAM FOR SH/RH CONTROL VALVES

Limit SwitchesUSED TO INDICATE THE OPEN OR CLOSE POSITION OF THE CONTROL VALVE

LIMIT SWITCH

AIR LOCK VALVEUSED TO MAINTAIN THE VALVE IN STAYPUT CONDITION ON SUPPLY AIR / SIGNAL AIR FAILURE

AIR LOCK

USED TO MAINTAIN AIR PRESSURE AT INLET OF POSITIONER

AIR SET

PNEUMATIC POSITIONERA FEEDBACK DEVICE THAT RECEIVES A PNEUMATIC SIGNAL FROM A CONTROLLER COMPARES THAT SIGNAL TO THE ACTUAL POSITION OF THE VALVE . THE POSITIONER SENDS OR BLEEDS AIR PRESSURE TO OR FROM THE ACTUATOR UNTIL THE CORRECT VALVE POSITION IS ACHIEVED.

PNEUMATIC POSITIONER

SOLENOID VALVEUSED TO MAINTAIN STAYPUT VALVE POSITION ON SIGNAL AIR FAILURE

VOLUME BOOSTER USED TO ENABLE FASTER OPENING ( IN LARGER VALVES AND BIGGER ACTUATORS )

VOLUME BOOSTER

CONTROLLER COMPARES PROCESS PARAMETER WITH SET VALUE AND GIVES SIGNAL

CONTROLLER

I /P CONVERTERUSED TO CONVERT ELECTRICAL SIGNAL TO PNEUMATIC SIGNAL

I / P CONVERTER

POSITION TRANSMITTERUSED TO INDICATE THE PERCENTAGE OPENING OF THE VALVE

TYPICAL CONTROL VALVES IN BOILERSUPERHEATER SPRAY CONTROL VALVEREHEATER SPRAY CONTROL VALVESOOT BLOWER PRESSURE REDUCING VALVEFULL LOAD FEED WATER CONTROL VALVELOW LOAD FEED WATER CONTROL VALVEDEARATOR LEVEL CONTROL VALVE

SPRAY STATION ARRANGEMENT

FLASHING

DOWNSTREAM PRESSURE IS

FLASHING & CAVITATION PHENOMENON

HOW TO CONTROL FLASHING REDESIGN SYSTEM TO AVOID FLASHINGDISCHARGE INTO LARGE VESSEL AND AWAY FROM ANY CRITICAL SURFACES.HARD FACING OF TRIM & DOWNSTREAM PASSAGE

CAVITATION- PR IN THE VENA CONTRACTA BELOW VAPOUR PR AND PR RECOVERY ABOVE THE VAPOUR PR .

- VAPOUR BUBBLES FORM WHICH THEN COLLAPSE AS PR RECOVERS

IMPLOSION OF VAPOUR BUBBLES CAN ERODE METAL SURFACES IN BOTH THE VALVE BODY AND DOWNSTREAM PIPING , AS WELL AS CAUSE NOISE.

HOW TO ELIMINATE CAVITATIONBY USING ANTI CAVITATION CAGEWITH MULTIPLE CAGESUSING RETAINER OR CAGE WITH A TORTUOUS PATHBY USING MULTI-STAGE PRESSURE DROP VALVE

LINEAR CHARACTERISTIC USED WHEN MAX. P IS TAKEN ACROSS THE VALVE.

WHEN UPSTREAM PRESSURE IS CONSTANT

USED RARELY

EQUAL PERCENTAGE CHARACTERISTICUSED WHEN MAX. P IS TAKEN IN PIPING & SYSTEM

HIGH P LOW Q , LOW P HIGH Q

WHEN VALVE IS OVERSIZED BECAUSE OF LIMITED DATA , =% IS BEST

MOST COMMONLY USED

LEVEL CONTROL VALVESCONSTANT P ACROSS VALVE - LINEAR CHARACTERISTIC USED

P AT MAX. LOAD > 0.2 P AT MIN LOAD - LINEAR CHARACTERISTIC USED

P AT MAX. LOAD < 0.2 P AT MIN. LOAD - =% CHARACTERISTIC USED

PRESSURE CONTROL VALVES LIQUID SERVICE - =% CHARACTERISTIC

GAS SERVICE , SMALL VOLUME FLOW - =% CHARACTERISTIC

GAS SERVICE , LARGE VOLUME FLOW- LINEAR CHARACTERISTIC

GAS , P AT MAX. LOAD > 0.2 P AT MIN . LOAD - LINEAR CHARACTERISTIC

GAS , P AT MAX. LOAD < 0.2 P AT MIN. LOAD - =% CHARACTERISTIC

FLOW CONTROL VALVES WIDE RANGE OF FLOW SET POINTS - LINEAR CHARACTERISTIC USED

SMALL RANGE OF FLOW SET POINTS - =% CHARACTERISTIC USED

TYPES OF CONTROL VALVES USED BY BHEL -TRICHYSUPERHEATER SPRAY CONTROL VALVEREHEATER SPRAY CONTROL VALVESOOT BLOWER PRESSURE REDUCING VALVEFULL LOAD FEED WATER CONTROL VALVELOW LOAD FEED WATER CONTROL VALVEDEARATOR LEVEL CONTROL VALVE

SUPERHEATER SPRAY CONTROL VALVE The moderation of temperature of superheated steam is achieved by spraying water into the steam . Quantity of spray is controlled by the spray control valve . Feed water at about 182 kg/sq.cm pressure and 240 C temperature is regulated and supplied to the system at a pressure of 170 kg/sq.cm . It can be noticed that the pressure drop across the control valve is only moderate . However , selection of control valve for this application should be done taking the following factors into consideration . Valve will be operating at minimum condition most of the time .As such the valve plug will be close to the seat for a long period of time causing erosion of the seat and plug .So the resultant valve offered should ensure around 15% opening at the minimum operating conditions . Equal Percentage characteristic is needed for this service .A cage design valve enables maximum pressure drop to take place in the cage rather than in the seat and thus protects the seat ring . This ensures continuous trouble free operation .TYPICAL OPERATING PARAMETERS OF SH SPRAY CONTROL VALVEInlet pressure : 182 kg/ sq.cmOutlet pressure : 170 kg/ sq.cmOperating temperature : 240 Deg. CFlow rate : 34.5 Tons / Hr.

REHEATER SPRAY CONTROL VALVEIt handles a higher pressure drop when compared to the superheater spray control valve.In order to avoid cavitation , erosion , vibration and noise associated with this service , a multi stage pressure reducing valve is needed for this service .Typical operating parameters are given below .Inlet Pressure : 170 kg/ sq.cmOutlet Pressure : 100 kg / sq.cm Operating Temperature : 240 Deg CFlow rate : 15 tons / hr

SOOT BLOWER PRESSURE REDUCING VALVEThis control valve design requires high pressure- temperature class design due to the very critical nature of the application.Soot blowers are operated occassionally during the day . This leads to temperature cycling of the valve . In addition to the temperature cycles , high pressure drops create high noise levels and can cause excesive wear and vibration to occur in the trim .Hence a special low noise / anti-vibration trim with better noise attentuation features is required for this application.Typical operating parameters for this applicationInlet Presure : 175 kg / sq.cmOutlet Pressure : 30 kg / sq.cmOperating Temperature : 420 Deg. CFlow rate : 8 tons/ hr

FULL LOAD FEED WATER CONTROL VALVEIt handles a relatively large volume of flow . When the boiler is in full load operation or near it , this valve will be in continuous operation . Since this valve takes over from low load feed control valve after having achieved a steady operation : the pressure drop across this valve is less .A cage guided valve , 12 x 8 size , for this application ( for 210 MW/ 250 MW) and 16 x 12 size for 500 MW plant is used.A Balanced trim construction enables to meet the high shut off requirements with conventional actuators . The valve design should handle large volume of flow ( higher Cv for given body size) keeping flow velocities very much within limits.Typical operating parameters for this valve are Inlet Pressure : 233 kg / sq. cm Outlet Pressure : 228 kg / sq. cm Operating Temperature : 240 Deg . C Flow quantity : 720 Tons / hr

LOW LOAD FEED WATER CONTROL VALVEAt boiler start up , the feed water is to be fed at low pressure and consequently the low load feed control valve handles very high pressure drops . Because of this high pressure drops ,there are chances for the feed water to flash / cavitate . The internals of the valves are to be carefully selected to meet these severe service conditions . The trim is made of hardened stainless steel / SS316 with Stellite overlay .A cage guided 6 x 4 size ( for 210 / 250 MW units ) and 8 cage guided valve for 500 MW plant is used . Typical operating parameters of this control valve are given below .Inlet Pressure ; 233 kg / sq. cmOutlet pressure : 100 kg / sq.cmOperating Temperature : 240 Deg. CFlow quantity : 200 tons / hr

DEARATOR LEVEL CONTROL VALVEThe purpose of this valve , as the name implies , is to maintain a correct level in the deaerator . This valve performs its function by varying condensate flow into the deaerating vessel in response to load and a level signal . The service conditions confronting these valves vary directly with the plant load .The service conditions faced are mild when compared to spray control valves and low load feed water control valve .A cage guided valve is recommended for this application .Typical operating parameters for this valve are Inlet Pressure : 19.6 kg / sq.cmOutlet Pressure : 13.8 kg/ sq.cmOperating Temperature : 49.2 Deg. CFlow rate : 523.3 Tons/ hr

TYPES OF CONTROL VALVES USED BY BHEL -TRICHYSUPERHEATER SPRAY CONTROL VALVEREHEATER SPRAY CONTROL VALVESOOT BLOWER PRESSURE REDUCING VALVEFULL LOAD FEED WATER CONTROL VALVELOW LOAD FEED WATER CONTROL VALVEDEARATOR LEVEL CONTROL VALVE

SUPERHEATER SPRAY CONTROL VALVE The moderation of temperature of superheated steam is achieved by spraying water into the steam . Quantity of spray is controlled by the spray control valve . Feed water at about 182 kg/sq.cm pressure and 240 C temperature is regulated and supplied to the system at a pressure of 170 kg/sq.cm . It can be noticed that the pressure drop across the control valve is only moderate . However , selection of control valve for this application should be done taking the following factors into consideration . Valve will be operating at minimum condition most of the time .As such the valve plug will be close to the seat for a long period of time causing erosion of the seat and plug .So the resultant valve offered should ensure around 15% opening at the minimum operating conditions . Equal Percentage characteristic is needed for this service .A cage design valve enables maximum pressure drop to take place in the cage rather than in the seat and thus protects the seat ring . This ensures continuous trouble free operation .TYPICAL OPERATING PARAMETERS OF SH SPRAY CONTROL VALVEInlet pressure : 182 kg/ sq.cmOutlet pressure : 170 kg/ sq.cmOperating temperature : 240 Deg. CFlow rate : 34.5 Tons / Hr.

REHEATER SPRAY CONTROL VALVEIt handles a higher pressure drop when compared to the superheater spray control valve.In order to avoid cavitation , erosion , vibration and noise associated with this service , a multi stage pressure reducing valve is needed for this service .Typical operating parameters are given below .Inlet Pressure : 170 kg/ sq.cmOutlet Pressure : 100 kg / sq.cm Operating Temperature : 240 Deg CFlow rate : 15 tons / hr

SOOT BLOWER PRESSURE REDUCING VALVEThis control valve design requires high pressure- temperature class design due to the very critical nature of the application.Soot blowers are operated occassionally during the day . This leads to temperature cycling of the valve . In addition to the temperature cycles , high pressure drops create high noise levels and can cause excesive wear and vibration to occur in the trim .Hence a special low noise / anti-vibration trim with better noise attentuation features is required for this application.Typical operating parameters for this applicationInlet Presure : 175 kg / sq.cmOutlet Pressure : 30 kg / sq.cmOperating Temperature : 420 Deg. CFlow rate : 8 tons/ hr

FULL LOAD FEED WATER CONTROL VALVEIt handles a relatively large volume of flow . When the boiler is in full load operation or near it , this valve will be in continuous operation . Since this valve takes over from low load feed control valve after having achieved a steady operation : the pressure drop across this valve is less .A cage guided valve , 12 x 8 size , for this application ( for 210 MW/ 250 MW) and 16 x 12 size for 500 MW plant is used.A Balanced trim construction enables to meet the high shut off requirements with conventional actuators . The valve design should handle large volume of flow ( higher Cv for given body size) keeping flow velocities very much within limits.Typical operating parameters for this valve are Inlet Pressure : 233 kg / sq. cm Outlet Pressure : 228 kg / sq. cm Operating Temperature : 240 Deg . C Flow quantity : 720 Tons / hr

LOW LOAD FEED WATER CONTROL VALVEAt boiler start up , the feed water is to be fed at low pressure and consequently the low load feed control valve handles very high pressure drops . Because of this high pressure drops ,there are chances for the feed water to flash / cavitate . The internals of the valves are to be carefully selected to meet these severe service conditions . The trim is made of hardened stainless steel / SS316 with Stellite overlay .A cage guided 6 x 4 size ( for 210 / 250 MW units ) and 8 cage guided valve for 500 MW plant is used . Typical operating parameters of this control valve are given below .Inlet Pressure ; 233 kg / sq. cmOutlet pressure : 100 kg / sq.cmOperating Temperature : 240 Deg. CFlow quantity : 200 tons / hr

DEARATOR LEVEL CONTROL VALVEThe purpose of this valve , as the name implies , is to maintain a correct level in the deaerator . This valve performs its function by varying condensate flow into the deaerating vessel in response to load and a level signal . The service conditions confronting these valves vary directly with the plant load .The service conditions faced are mild when compared to spray control valves and low load feed water control valve .A cage guided valve is recommended for this application .Typical operating parameters for this valve are Inlet Pressure : 19.6 kg / sq.cmOutlet Pressure : 13.8 kg/ sq.cmOperating Temperature : 49.2 Deg. CFlow rate : 523.3 Tons/ hr