PROPER CONTROL VALVE SELECTION - AN ENGINEER’S …...sizing control valves •primary equipment • subcircuit p can vary between 10 and 40 ft (4.3 –17.3 psi) • 1-2 row heating

PROPER CONTROL VALVE SELECTION -

AN ENGINEER’S PERSPECTIVEDOUG SHOWERS, PE

NOVEMBER 12, 2018

MADISON ASHRAE CHAPTER MEETING

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

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.

SupplyReturn

A BCoil / Heat

Exchanger

Best location

Sub-circuit A-B

TEMPERATURE CONTROL VALVE FUNCTION

SupplyReturn

A B

Sub-circuit A-B

PRESSURE CONTROL VALVE FUNCTION

PDT

SupplyReturn

A BCoil / Heat

Exchanger

Sub-circuit A-B

TEMPERATURE/PRESSURE CONTROL VALVE

FUNCTION

PIC

Pressure

Flow

ControlValve Pressure Drop

Coil and Sub-Circuit PipingPressureDrop

Cons

tant

Pre

ssur

eTEMPERATURE CONTROL VALVE FUNCTION

VALVE CHARACTERISTICS

FROM 2016 ASHRAE SYSTEM HANDBOOKCH. 47

VALVE CHARACTERISTICS

Combined with Heating Coil PerformanceFROM 2016 ASHRAE SYSTEM HANDBOOKCH. 47

REVIEW OF CONTROL VALVE OPTIONS

• VALVE BODY STYLES AND MATERIALS

• PORT SHAPES/CHARACTERISTICS

• ACTUATOR TYPES/FAIL POSITIONS

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

2-1/2” TO 6” IRON/STEEL BODY BALL VALVES• USED FOR MODULATING OR SHUTOFF SERVICE

• BODIES:


• 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


• CLOSE OFF PRESSURE – APPROX. 200 PSI

• NORMALLY FAIL IN LAST POSITION UNLESS SPRING LOADED OR BATTERY OPERATED ACTUATOR IS USED


½” TO 2” BRONZE GLOBE VALVES• USED FOR MODULATING OR SHUTOFF SERVICE

• BODIES:


• 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


• CLOSE OFF PRESSURE – APPROX. 4 TO 365 PSI (FUNCTION OF VALVE SIZE AND ACTUATOR TYPE)



2-1/2” TO 6” IRON/STEEL BODY GLOBE VALVES• USED FOR MODULATING OR SHUTOFF SERVICE

• BODIES:


• 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)


• 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)



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


• QUASI-EQUAL PERCENTAGE, QUICK OPENING

• SEALS

• EPDM, VITON


• CLOSE OFF PRESSURE – UP TO 175 PSI (FUNCTION OF VALVE SIZE AND ACTUATOR TYPE)



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


• QUASI-EQUAL PERCENTAGE, QUICK OPENING

• SEALS

• METAL, BUTYL, EPDM, VITON


• 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

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


• EQUAL PERCENTAGE

• SEALS

• EPDM


• PRESSURE CONTROL DEVICE

• SPRING LOADED PRESSURE DIAPHRAGM

• ACTIVE CONTROL VALVE

• CLOSE OFF PRESSURE – APPROX. 200 PSI (FUNCTION OF VALVE SIZE AND ACTUATOR TYPE)

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

SELECTING THE RIGHT VALVE

• SERVICE – MODULATING, SHUTOFF

• DESIRED PORT CHARACTERISTICS

• EQUAL PERCENTAGE

• LINEAR

• QUICK OPENING

• PRESSURE/TEMPERATURE CLASS

• SHUTOFF PRESSURE

• DIFFERENTIAL VS DEAD-END

ASME/ANSI PRESSURE CLASS


• 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



• 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


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

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

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


• 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


• 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


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

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

CAVITATION, FLASHING, AND CHOKED FLOW

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

QUESTIONS?

• CONTACT INFORMATION

• DOUG SHOWERS, PE

• (608) 236-1119

• [email protected]

Documents

PROPER CONTROL VALVE SELECTION - AN ENGINEER’S …...sizing control valves •primary equipment • subcircuit p can vary between 10 and 40 ft (4.3 –17.3 psi) • 1-2 row heating