proper control valve selection - an engineer’s …...sizing control valves •primary equipment...
TRANSCRIPT
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PROPER CONTROL VALVE SELECTION -
AN ENGINEER’S PERSPECTIVEDOUG SHOWERS, PE
NOVEMBER 12, 2018
MADISON ASHRAE CHAPTER MEETING
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LEARNING OBJECTIVES
• BETTER UNDERSTANDING OF CONTROL VALVE FUNCTION
• REVIEW OF CONTROL VALVE OPTIONS
• SELECTING THE RIGHT VALVE
• SIZING CONTROL VALVES
• WHEN TO USE PRESSURE INDEPENDENT CONTROL (PIC) VALVES
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BETTER UNDERSTANDING OF CONTROL VALVE FUNCTION
• FLOW CONTROL (2-POSITION – OPEN/CLOSED)
• TEMPERATURE CONTROL (MODULATION OF FLOW TO AFFECT ENERGY TRANSFER)
• PRESSURE CONTROL (MODULATION OF FLOW TO AFFECT PRESSURE OR PRESSURE
DIFFERENTIAL AT A GIVEN POINT)
• COMBINATION TEMPERATURE/PRESSURE CONTROL
• CONTROL VALVES CAN CHANGE THE FLOW RESISTANCE OF THE SUB-CIRCUIT ONLY!
• INDIRECTLY AFFECTS FLOW IN OTHER PARTS OF THE SYSTEM.
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SupplyReturn
A BCoil / Heat
Exchanger
Best location
Sub-circuit A-B
TEMPERATURE CONTROL VALVE FUNCTION
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SupplyReturn
A B
Sub-circuit A-B
PRESSURE CONTROL VALVE FUNCTION
PDT
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SupplyReturn
A BCoil / Heat
Exchanger
Sub-circuit A-B
TEMPERATURE/PRESSURE CONTROL VALVE
FUNCTION
PIC
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Pressure
Flow
ControlValve Pressure Drop
Coil and Sub-Circuit PipingPressureDrop
Cons
tant
Pre
ssur
eTEMPERATURE CONTROL VALVE FUNCTION
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VALVE CHARACTERISTICS
FROM 2016 ASHRAE SYSTEM HANDBOOKCH. 47
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VALVE CHARACTERISTICS
Combined with Heating Coil PerformanceFROM 2016 ASHRAE SYSTEM HANDBOOKCH. 47
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REVIEW OF CONTROL VALVE OPTIONS
• VALVE BODY STYLES AND MATERIALS
• PORT SHAPES/CHARACTERISTICS
• ACTUATOR TYPES/FAIL POSITIONS
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½” TO 2” BRONZE BALL VALVES• USED FOR MODULATING OR SHUTOFF SERVICE
• BODIES:
• AVAILABLE IN 2 PORT, 3-PORT MIXING, AND 3-PORT DIVERTING CONFIGURATIONS
• NPT OR SWEAT END CONNECTIONS
• CLASS 125 TO 250 PSIG WORKING PRESSURE (FUNCTION OF FLUID TEMPERATURE)
• AVAILABLE IN STAINLESS STEEL FOR CERTAIN APPLICATIONS
• BALL/PORT CHARACTERISTICS
• NORMAL, FULL, EQUAL PERCENTAGE
• BALL MATERIALS – BRASS, CHROME-PLATED BRASS, STAINLESS STEEL
• SEALS
• EPDM, VITON
• TEMPERATURE RANGES (0OF TO 250OF)
• CLOSE OFF PRESSURE – APPROX. 200 PSI
• FAIL OPEN, FAIL CLOSED, FAIL LAST POSITION
• COMMERCIAL VALVES VS. INDUSTRIAL GRADE VALVES
• STEAM AND CRYO SERVICE OPTION MAYBE AVAILABLE FOR INDUSTRIAL VALVES
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2-1/2” TO 6” IRON/STEEL BODY BALL VALVES• USED FOR MODULATING OR SHUTOFF SERVICE
• BODIES:
• AVAILABLE IN 2 PORT, 3-PORT MIXING, AND 3-PORT DIVERTING CONFIGURATIONS
• NPT OR CLASS 150/300 ASME FLANGED END CONNECTIONS
• CLASS 150 TO 275 PSIG WORKING PRESSURE (FUNCTION OF FLUID TEMPERATURE)
• AVAILABLE IN CAST IRON, CAST STEEL OR CAST STAINLESS STEEL
• BALL/PORT CHARACTERISTICS
• NORMAL, FULL, EQUAL PERCENTAGE
• BALL MATERIALS – BRASS, CHROME-PLATED BRASS, STAINLESS STEEL
• SEALS
• EPDM, VITON
• TEMPERATURE RANGES (0OF TO 250OF)
• CLOSE OFF PRESSURE – APPROX. 200 PSI
• NORMALLY FAIL IN LAST POSITION UNLESS SPRING LOADED OR BATTERY OPERATED ACTUATOR IS USED
• COMMERCIAL VALVES VS. INDUSTRIAL GRADE VALVES
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½” TO 2” BRONZE GLOBE VALVES• USED FOR MODULATING OR SHUTOFF SERVICE
• BODIES:
• AVAILABLE IN 2 PORT, 3-PORT MIXING, AND 3-PORT DIVERTING CONFIGURATIONS
• NPT OR SWEAT END CONNECTIONS
• CLASS 125 TO 250 PSIG WORKING PRESSURE (FUNCTION OF FLUID TEMP)
• AVAILABLE IN CAST STEEL OR CAST STAINLESS STEEL FOR INDUSTRIAL VAVLES
• PORT CHARACTERISTICS
• EQUAL PERCENTAGE, LINEAR, QUICK OPENING
• CAGE-GUIDED VALVES
• SEALS
• EPDM, VITON
• TEMPERATURE RANGES (0OF TO 250OF)
• CLOSE OFF PRESSURE – APPROX. 4 TO 365 PSI (FUNCTION OF VALVE SIZE AND ACTUATOR TYPE)
• COMMERCIAL VALVES VS. INDUSTRIAL GRADE VALVES
• STEAM AND CRYO SERVICE OPTION MAYBE AVAILABLE FOR INDUSTRIAL VALVES
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2-1/2” TO 6” IRON/STEEL BODY GLOBE VALVES• USED FOR MODULATING OR SHUTOFF SERVICE
• BODIES:
• AVAILABLE IN 2 PORT, 3-PORT MIXING, AND 3-PORT DIVERTING CONFIGURATIONS
• CLASS 125 ASME FLANGED END CONNECTIONS
• CLASS 125 TO 250 PSI WORKING PRESSURE FOR CAST IRON (FUNCTION OF FLUID TEMPERATURE)
• CLASS 150 TO 275 PSI WORKING PRESSURE FOR CAST STEEL (FUNCTION OF FLUID TEMPERATURE)
• PORT CHARACTERISTICS
• EQUAL PERCENTAGE, LINEAR, QUICK OPENING
• CAGE-GUIDED VALVES
• SEALS
• EPDM, VITON
• TEMPERATURE RANGES (0OF TO 250OF NORMAL, UP TO 400OF WITH SEAL SEATS AND TRIM)
• CLOSE OFF PRESSURE – APPROX. 20 TO 80 PSI (FUNCTION OF VALVE SIZE AND ACTUATOR TYPE)
• COMMERCIAL VALVES VS. INDUSTRIAL GRADE VALVES
• STEAM AND CRYO SERVICE OPTION MAYBE AVAILABLE FOR INDUSTRIAL VALVES
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GENERAL PURPOSE BUTTERFLY VALVES (2” TO 60”)• USED FOR SHUTOFF SERVICE (NOT RECOMMENDED FOR MODULATING SERVICE)
• BODIES:
• CAST IRON, DUCTILE IRON, CAST STEEL, ALUMINUM
• AVAILABLE IN 2 PORT AND 3-PORT (2-VALVES LINKED TOGETHER) CONFIGURATIONS
• CLASS 125 OR 250 ASME FLANGED END CONNECTIONS FOR CAST IRON
• CLASS 150 OR 300 ASME FLANGED END CONNECTIONS FOR CAST STEEL
• PORT CHARACTERISTICS
• QUASI-EQUAL PERCENTAGE, QUICK OPENING
• SEALS
• EPDM, VITON
• TEMPERATURE RANGES (0OF TO 250OF)
• CLOSE OFF PRESSURE – UP TO 175 PSI (FUNCTION OF VALVE SIZE AND ACTUATOR TYPE)
• COMMERCIAL VALVES VS. INDUSTRIAL GRADE VALVES
• STEAM AND CRYO SERVICE OPTION MAYBE AVAILABLE FOR INDUSTRIAL VALVES
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HIGH PERFORMANCE BUTTERFLY VALVES (2” – 54”)
• USED FOR MODULATING OR SHUTOFF SERVICE
• RELATIVELY HIGH CV VALUES
• BODIES:
• AVAILABLE IN 2 PORT AND 3-PORT (2-VALVES LINKED TOGETHER) CONFIGURATIONS
• CLASS 150 OR HIGHER ASME FLANGED END CONNECTIONS (FUNCTION OF FLUID TEMPERATURE)
• AVAILABLE HIGHER PRESSURE CLASSES USING CAST STEEL OR CAST STAINLESS STEEL FOR INDUSTRIAL VAVLES
• PORT CHARACTERISTICS
• QUASI-EQUAL PERCENTAGE, QUICK OPENING
• SEALS
• METAL, BUTYL, EPDM, VITON
• TEMPERATURE RANGES (0OF TO 500OF)
• CLOSE OFF PRESSURE – UP TO 1480 PSI (FUNCTION OF VALVE SIZE, PRESSURE CLASS AND ACTUATOR TYPE)
• STEAM AND CRYO SERVICE OPTION MAYBE AVAILABLE FOR CERTAIN VALVES
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PRESSURE INDEPENDENT CONTROL (PIC) VALVES(1/2” – 16”)
• USED FOR MODULATING
• BODIES:
• SAME AS BALL OR GLOVE VALVE OPTIONS
• CAN BE TWO VALVES IN SERIES WITH PRESSURE CONTROL VALVE/DEVICE UPSTREAM OF CONTROL VALVE
• PORT CHARACTERISTICS
• EQUAL PERCENTAGE
• SEALS
• EPDM
• TEMPERATURE RANGES (0OF TO 250OF)
• PRESSURE CONTROL DEVICE
• SPRING LOADED PRESSURE DIAPHRAGM
• ACTIVE CONTROL VALVE
• CLOSE OFF PRESSURE – APPROX. 200 PSI (FUNCTION OF VALVE SIZE AND ACTUATOR TYPE)
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ACTUATORS• MOVEMENT TYPE (LINEAR VS ROTARY)
• LINKAGES TO ACHIEVE MOVEMENT OF EITHER TYPE
• ENERGY SOURCE
• COMPRESSED AIR (15 TO 100 PSIG)
• LOW VOLTAGE (24 VAC)
• FLOATING POINT VS ANALOG
• WITH OR WITHOUT FEEDBACK
• LINE VOLTAGE (120 OR 240 VAC)
• MOVEMENT ACTION – 2-POSITION OR MODULATING
• FAIL POSITION
• SPEED OF ACTUATORS
• TIME DELAYS
• FEEDBACK OPTIONS
• OPEN/CLOSED POSITION SWITCHES FOR 2-POSITION VALVES
• ANALOG FOR MODULATING VALVES
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SELECTING THE RIGHT VALVE
• SERVICE – MODULATING, SHUTOFF
• DESIRED PORT CHARACTERISTICS
• EQUAL PERCENTAGE
• LINEAR
• QUICK OPENING
• PRESSURE/TEMPERATURE CLASS
• SHUTOFF PRESSURE
• DIFFERENTIAL VS DEAD-END
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ASME/ANSI PRESSURE CLASS
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SELECTING THE RIGHT VALVE
• CHARACTERIZED BALL VALVE
• ROTARY VALVE (90 DEGREE ROTATION)
• MORE FLOW THAN A GLOBE VALVE AT THE SAME SIZE
• LARGER CV
• BETTER SHUTOFF
• LARGE GLOBE VALVE = POOR SHUTOFF
• RECOMMEND USING MULTIPLE SMALLER CHARACTERIZED BALL VALVES INSTEAD
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SELECTING THE RIGHT VALVE
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SELECTING THE RIGHT VALVE
• COMMERCIAL VALVES
• SOME OPTIONS
• TRIM TYPE, MATERIAL
• SPRING RETURN, VOLTAGE, SIGNAL TYPE, FEEDBACK
• INDUSTRIAL VALVES
• MANY OPTIONS
• DIFFERENT TRIM TYPES TO REDUCE NOISE OR HANDLE CAVITATION, VALVE MATERIALS
• SELECTION SOFTWARE AVAILABLE FOR USE
• SMART VALVE POSITIONERS
• HART COMMUNICATION, DIAGNOSTICS
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SELECTING THE RIGHT VALVE
VALVE TYPE RECOMMENDED FLUIDS SIZE RANGE CV RANGE
SHUTOFF
PRESSURE
RELATIVE
COST
BRONZE BALL VALVE WATER <200oF, LPS 1/2" - 2" 1.2 - 77 200 LOW
CI/CS BALL VALVE WATER <200oF, LPS 2" - 12" 16 - 4200 200 MED-HIGH
BRONZE GLOBE VALVE WATER <200oF, LPS 1/2" - 2" 0.7 - 46 4 - 80 LOW
CI/CS GLOBE VALVE WATER <250oF, LPS, HPS 2 - 6" 51 - 347 4 - 100 MED-HIGH
PIC VALVE WATER <200oF 1/2" - 16" 3.4 - 2460 200 MED-HIGH
GP BUTTERFLY VALVE WATER <200oF, LPS 2-1/2" - 60" 300 - 190,000 175 LOW
HP BUTTERFLY VALVE WATER <400oF, LPS, HPS 2" - 60" 160 - 160,000 600 HIGH
NOTE - ALL VALUES VARY BY MANUFACTURER
VALVE COMPARISON TABLE
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SIZING CONTROL VALVES
• VALVE AUTHORITY
• SIZE FOR 25-50% VALVE AUTHORITY
• THIS MEANS THAT 25-50% OF THE SUBCIRCUIT PRESSURE DROP IS DUE TO THE VALVE
• OVERSIZED VALVES HAVE POOR VALVE AUTHORITY
• VALVE PRESSURE DROP △P = FUNCTION OF FLOW (Q) , SPECIFIC GRAVITY (SG), AND FLOW
COEFFICIENT CV
• CV = Q (SG/△P)0.5 OR △P = SG (Q/CV)2
• FOR WATER (SG=1), CV = FLOW (GPM) AT 1 PSI PRESSURE DROP
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CONTROL VALVE AUTHORITY
• CONTROL VALVE AUTHORITY (N) = RATIO OF VALVE △P/SUBCIRCUIT △P
• IDEAL AUTHORITY IS WHEN N < 0.5
• 0.25 < N < 0.5 IS USUALLY ACCEPTABLE
• UNSTABLE CONTROL RESULTS WHEN N < 0.25
• OVERSIZED VALVES RESULT IN LOW VALVE AUTHORITY
• CAN ALSO BE DESCRIBED AS TOO MUCH GAIN IN THE VALVE
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SIZING CONTROL VALVES
• RULES OF THUMB FOR TERMINAL DEVICES
• SUBCIRCUIT △P USUALLY < 10 FT. (4.3 PSI)
• SIZE MOST VALVES FOR △P BETWEEN 1.5 AND 2.2 PSI BUT NO LOWER THAN 1.1 PSI FOR GOOD
CONTROL AUTHORITY
• SOME UH/CUH COULD HAVE SUBCIRCUIT △P AS HIGH AS 25 FT (10.8 PSI)
• SIZE UH/CUH VALVES FOR △P BETWEEN 3 AND 5 PSI BUT NO LOWER THAN 2.7 PSI FOR GOOD
CONTROL AUTHORITY
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SIZING CONTROL VALVES
• PRIMARY EQUIPMENT
• SUBCIRCUIT △P CAN VARY BETWEEN 10 AND 40 FT (4.3 – 17.3 PSI)
• 1-2 ROW HEATING COILS ARE AT THE LOWER RANGE
• 6-10 ROW COOLING COILS ARE AT THE HIGHER RANGE
• FOR ACCURATE SIZING, CONSIDER DETERMINING SUBCIRCUIT PRESSURE DROP AND SELECTING VALVE FOR UP TO 50% OF SUBCIRCUIT △P.
• RULE-OF-THUMB METHOD:
• SIZE HEATING VALVES FOR △P BETWEEN 3 AND 5 PSI BUT NO LOWER THAN 3 PSI FOR GOOD CONTROL AUTHORITY
• SIZE COOLING VALVES FOR △P BETWEEN 3 AND 9 PSI BUT NO LOWER THAN 3 PSI FOR GOOD CONTROL AUTHORITY
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SIZING CONTROL VALVES
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INSTALLATION
• RULE OF THUMB IS NO MORE THAN TWO SIZES SMALLER THAN PIPE
• IF MORE THAN 2 SIZES, NEED STRAIGHT PIPE UPSTREAM AND DOWNSTREAM VALVE TO AVOID
CAVITATION
• NO AGREEMENT ON STANDARDS OR RULES
• CONTROL VALVE TEST STANDS HAVE AS MUCH AS 20D UPSTREAM AND 10D DOWNSTREAM
• USUALLY NOT PRACTICAL IN THE REAL WORLD
• BEST PRACTICE IS TO HAVE 2/3 OF STRAIGHT RUN UPSTREAM OF VALVE
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CAVITATION, FLASHING AND CHOKED FLOW
• CAVITATION AND FLASHING
• CAVITATION AND FLASHING OCCURS
WHEN PRESSURES WITHIN THE VALVE
(@ P2 LOW - BEFORE RECOVERY)
DROPS BELOW THE VAPOR PRESSURE
OF THE FLUID AT A GIVEN
TEMPERATURE
• CHOKED FLOW FOR NON-
COMPRESSIBLE LIQUIDS OCCURS AS A
RESULT OF CAVITATION OR FLASHING
• CHOKED FLOW FOR COMPRESSIBLE
GASES OCCURS WHEN VELOCITY
THROUGH THE PORT REACHES MACH 1
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CAVITATION, FLASHING, AND CHOKED FLOW
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WHEN TO USE PRESSURE INDEPENDENT CONTROL (PIC) VALVES
• FOR LARGE UNBALANCED SYSTEMS
• FOR SYSTEMS WHERE LOAD OR △P VARIES
• PROPERLY SIZED PRESSURE DEPENDENT VALVE CAN ACCOMPLISH THE SAME THING
• RESPONSE MAY BE SLOWER
• CONSIDER WHETHER TO USE ON ENTIRE SYSTEM OR ONLY LARGE VALVES
• NECESSARY FOR TERMINAL VALVES TO BE PRESSURE INDEPENDENT?
• COST IS MORE COMPETITIVE THAN IN THE PAST