regulator – principle of operation - control · pdf file-1-regulator – principle...

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REGULATOR – PRINCIPLE OF OPERATIONREGULATOR – PRINCIPLE OF OPERATION

I. PRESSURE REDUCING REGULATORS

A. OPERATION

1. Point Force Versus Distributed Force2. Force Balance Principle3. Flow To Open Versus Flow To Close Design4. Dome Loaded and Differential

B. PROPORTIONAL BAND (DROOP, PRESSURE BUILD)

1. Cause and Effect2. How Can Proportional Band Work For You?3. How to Lessen the Effect

II. BACK PRESSURE REGULATORS

A. OPERATION

1. Point Force Versus Distributed Force2. Force Balance Principle3. Dome Loaded and Differential

B. PROPORTIONAL BAND (DROOP, PRESSURE BUILD)

1. Cause and Effect.2. How to Lessen the Effect.

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REGULATOR DEFINITIONSREGULATOR DEFINITIONSBACK PRESSURE REGULATOR: Regulator that is designed to relieve pressure above setpoint. Inletpressure is the control or set pressure.

COLD WORKING PRESSURE: The maximum pressure at which a regulator or fitting is allowed to beused at ambient temperature.

DEAD END: When the flow is terminated down stream of the regulator requiring tight shut off of theregulator.

GAS REGULATOR: Regulator terminology normally used to describe inches water column regulator.Always check set pressure before continuing.

INTEGRAL SEAT: A flow control orifice and seat that is an integral part of the body or cage material ormay be constructed from material added to the body or cage; non-removeable/replaceable.

LAPPED-IN: Mating contact surfaces that have been refined by grinding and/or polishing together orseparately in appropriate fixtures.

LOCK-UP: The flow curve between seat shut off and that point when seat lifts off.

PILOT OPERATED REGULATOR: Regulator designed to maintain constant control pressure over a widerange of flowing conditions. Utilizes the system medium via pilot valve to operate main unit.

PRESSURE BUILD: When control pressure or set pressure rises above set point.

PRESSURE DROOP: When control pressure or set pressure falls below set point.

PRESSURE REDUCING REGULATOR: A regulator that is designed to reduce pressure. The outletpressure is the controlled pressure.

PROPORTIONAL BAND: Deviation in controlled pressure as flow rate deviates.

RANGEABILITY: The ratio of the largest flow coefficient (max Cv) to the smallest flow coefficient(min Cv); Rg = Max Cv .

Min Cv

REPEATABILITY: The closeness of agreement among a number of consecutive measurements of theoutput for the same regulator of input under the same operating conditions, approaching from the samedirection, for full range traverse. It does not include hysteresis.

SAFETY RELIEF VALVES: “Coded”; used to protect code designed pressure vessels and pipe systemsagainst over pressure.

SELF-CONTAINED REGULATOR: A regulator which is activated by the fluid flowing through the regula-tor.

SENSITIVITY: The ratio of change in output magnitude to the change of the input which causes it aftersteady state has been reached.

SETPOINT: The controlled pressure at a low flow rate (approximately 2% of Max Cv); flow slightly be-yond lockup zone.

TRIM: Functional parts of a regulator which are exposed to the line fluid. Usually refers to the stem,closure member and seating surface.

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If someone just wants to control his pressure, any of the above three types of valves will do thejob. However, when determining what the application requires (or doesn't need), the followingguide should help determine which valve design would best match the application needs.

KEY:

CRV = Control ValvePOR = Pilot Operated RegulatorREG = Self-contained Regulator

FTC REG = Regulator, Flow-to-CloseFTO REG = Regulator, Flow-to-OpenCRV WP = Control Valve with Positioner

CRV WOP = Control Valve without Positioner

FACTOR CONSIDERED BEST NEXT LAST

Line Size Cost – Thru 1-1/2" REG POR CRV– 2" thru 3" POR REG CRV– 4" and Up CRV POR REG

Cost/Cv – Thru 1-1/2" POR REG CRV– 2" and Up CRV POR REG

Capacity CRV POR REGOutlet Pressure Level Capability CRV REG POROutput Pressure Level Maintenance CRV POR REGof SetpointRangeability FTO REG CRV/POR FTC REGRequirements for External Power – REG/POR CRV(Air or Electricity)Stability CRV REG PORSpeed of Response REG POR CRV WOP/CRV WPAbility to Adapt to System Dynamics CRV POR REGFail-Safe Action CRV – POR/REGAdaptability (Add accessories, CRV REG PORModify Action)Remote Set Point Capability CRV Regulator, POR/REG

Dome LoadedMaintenance Cost/Spare Parts REG POR CRV

HOW TO DIFFERENTIATE BETWEENHOW TO DIFFERENTIATE BETWEENAPPLYING A REGULATOR vs. PILOT-OPERATEDAPPLYING A REGULATOR vs. PILOT-OPERATED

vs. PNEUMATIC CONTROL VALVEvs. PNEUMATIC CONTROL VALVE

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Frs

Dport

Fps

PLUGOUTLET

P2P1INLET

P3Frs

PLUG

P1

INLET

P2OUTLET

P3

Frs

PLUG

OUTLET

FLOW-THRU

CONNEC-TION

P2

P1INLET P1

DEFINITIONSDEFINITIONS1. PRESSURE REDUCING REGULATOR – A “proportional only” control device that controls and responds to

changes in its OUTLET pressure due to flow changes.

Differential regulators are sometimes known as “tracking” or “bias” regulators

P1 - P3 ≈ ∆Pconstant∆Pconstant = Prange spring

setting

Pressure Reducing Regulator

2. BACK PRESSURE REGULATOR – A “proportional only” control device that controls and responds tochanges in its INLET pressure.

P2 - P3 ≈ ∆Pconstant∆Pconstant = Prange spring

setting

Globe Design Flow-Thru Angle Design

3. DIFFERENTIAL PRESSURE REGULATOR – A “proportional only” control device that maintains a CON-STANT DIFFERENTIAL PRESSURE between a reference pressure and the pressure of the controlled fluid.

Differential Pressure Reducing Regulator Differential Back PressureRegulator

Frs

PLUG

OUTLET

P2P1INLET

Frs

OUTLET

P2Fps

PLUG

P1

INLET

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4. EXTERNAL PILOTED REGULATOR – A “proportional + reset” control device that uses a piston or dia-phragm actuated main valve controlled by a separate external pilot regulator that uses the flowing fluid as itspower source.

External Piloted Reducing Regulator External Piloted Back Pressure Reducing Regulator

5. PRESSURE LOADED REGULATOR – A regulator using a fixed volume and pressure of compressible fluidas a spring and set point reference to accomplish pressure reduction or back pressure regulation. Some-times called a Dome Loaded Regulator.

Pressure Loaded Reducing Regulator

6. MINIMUM CONTROLLABLE FLOW – The lowest flow at which a steady regulated condition of the con-trolled variable can be maintained.

7. SETPOINT – The value of regulated pressure at the MINIMUM controllable flow.

8. LOCKUP – The pressure deviation from setpoint pressure when the regulator is fully closed.

9. FLOW COEFFICIENT (Cv) – The regulator capacity in GPM of H2O at 20°C at one psi pressure drop at fullrated travel. Refer to ISA S75.01 and S75.02 for Testing Procedures and Sizing Equations.

10. SPECIFIC GRAVITY – The ratio of the weight of a given volume of a fluid to the weight of an equal volume ofwater (liquids) or air (gases) at “standard” conditions.

OUTLETP2INLET P1

P3

Dport

PLUG

Fps

– HIGH INLET PRESSURE

– INTERMEDIATE PRESSURE

– LOW OUTLET PRESSURE

P

P

P

1

12

2

P SENSING& UNLOADING

2

P

SE

NS

ING

& U

NLO

AD

ING

2

PILOT VALVE

P

SU

PP

LY1

P

LO

AD

ING

12

PISTONMAIN VALVE

OUTLET

P2

INLET

P1

P2 ≈ P3(P3 slightly higher)

= HIGH INLET PRESSURE

= HIGH-INTERMEDIATE PRESSURE

= LOW-INTERMEDIATE PRESSURE

= LOW OUTLET PRESSURE

P

P

P

P

1

12

22

2

UNLOADING

PILOT VALVE

LOADINGP12

“SMALL” RESTRICTION ORIFICE

“LARGE” RESTRICTION

ORIFICE

UN

LOA

DIN

G

DIAPHRAGM MAIN VALVE

P S

UP

PLY

&

SE

NS

ING

1

OUTLET

P2

INLET

P1

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11. PRESSURE (GAUGE) – Pressure above atmospheric pressure.

12. PRESSURE (ABSOLUTE) – The sum of atmospheric and gauge pressure.

13. PRESSURE (OPERATING) – The actual pressure at which a device operates under normal conditions. Thispressure may be positive or negative with respect to atmospheric pressure.

14. RESEAT POINT – In a valve which is opened by an increase in inlet pressure (from an open condition) theleakage just stops as evidenced by the cessation of bubbles passing the sealing element when submerged inliquid.

15. MAXIMUM ALLOWABLE OPERATING PRESSURE – The maximum pressure that the valve may beoperated at, as determined by the manufacturer, taking into account function and a factor of safety based onmaterials of construction.

16. SOFT SEAL – an elastomeric, plastic, or other readily formable material used either in the valve plug or seatring to provide tight shut-off with minimal force – see ANSI/B16.104 for leakage classifications.

17. HARD FACING – A material harder than the surface to which it is applied; usually applied to valve seats toresist galling or fluid erosion.

18. SINGLE SEATED – A valve having a plug with a single seat.

19. DOUBLE SEATED – A valve featuring a plug with two seats.

20. BALANCED – A valve featuring a pressure balanced plug with two seats.

21. SEMI-BALANCED – A valve where the plug is partially pressure balanced.

22. UNBALANCED – A valve where the plug closure number is not pressure balanced; generally single seated.

23. SEAT LEAKAGE CLASSIFICATION – A leakage classification based on ANSI B16.104.

CLASS I. A modification of any Class II, III, or IV valve where design intent is the same as the basic class,by agreement between user and supplier, no test is required.

CLASS II. This class establishes the maximum permissible leakage generally associated with commercialdouble-port, double-seat control valves or balanced single-port control valves with a piston ring seat andmetal-to-metal seats. Use test procedure Type A.

CLASS III. This class establishes the maximum permissible leakage generally associated with Class II, butwith a higher degree of seal tightness. Use test procedure Type A.

CLASS IV. This class establishes the maximum permissible leakage generally associated with commercialunbalanced, single-port, single seat control valves and balanced single-port valves with extra tight pistonrings or other sealing means and metal-to-metal seats. Use test procedure Type A.

CLASS V. This class is usually specified for critical applications where the control valve may be required tobe closed, without a blocking valve, for long periods of time with high differential pressure across the seatingsurfaces. It requires special manufacturing assembly testing techniques. This class is generally associatedwith metal seat, unbalanced single-port, single seat control valves or balanced single port designs withexceptional seat and seal tightness. Use test procedure Type B using water at the maximum operatingdifferential pressure.

CLASS VI. This class establishes the maximum seat leakage generally associated with resilient seatingcontrol valves either unbalanced or balanced single port with “O” rings or similar gapless seals. Use testprocedure Type C.

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P1 = Higher Inlet Pressure

P2 = Lower Outlet Pressure

Frs

F = Force of Range Spring

F = Force of Piston Spring

Pressure Plate

∑Fup

∑Fdown

Fps

PLUG

Dport

Diaphragm

Works by the FORCE - BALANCE PRINCIPLE

rs

F + (P1 x A ) + (P2 x A ) =ps port diaph

∑Fup ∑Fdown=

F + (P2 x A )port

rs

ps

OUTLETP2P1INLET

PLUG MOVES DOWN RANGE SPRING RELAXESTO INCREASE FLOW + +

DIAPHRAGM MOVES DOWN P2 PRESSURE DECREASES

FTC REDUCING REGULATORSFTC REDUCING REGULATORS

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_FFFFFTTTTTCCCCC ––––– FFFFFLLLLLOOOOOWWWWW TTTTTOOOOO CCCCCLLLLLOOOOOSSSSSEEEEE –– –– –– ––

_FTC

_FFFFFTTTTTOOOOO ––––– FFFFFLLLLLOOOOOWWWWW TTTTTOOOOO OOOOOPPPPPEEEEENNNNN –– –– –– ––

_FTO

FTO vs. FTCFTO vs. FTC

“Unstable” asplug nears theseat; i.e. lowflow. Lowerrangeability.

“Stable” as plugnears or departsthe seat; i.e. allflows. Very highrangeability.

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FTO REDUCING REGULATORFTO REDUCING REGULATOR

FTO INCHES WATER COLUMN REGULATORFTO INCHES WATER COLUMN REGULATOR

Large Diaphragm

Force MultiplicationLever

FTO; i.e. stable @ seat.“Soft” springs.

Non-Relieving Pressure Reducing Regulator - “WC”



Pressure Plate

∑ Fup

∑ Fdown

Inlet Pressure Tends To "Push" The Plug Open.

TO INCREASEFLOW

PLUG MOVES RIGHT+

DIAPHRAGM MOVES DOWN

RANGE SPRING RELAXES+

P2 OUTLET DECREASES

RockerArmDiaphragm

PLUG OUTLETP2P1INLET

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_FTO REDUCING REGULATOR



∑F up

∑Fdown

P2

OUTLET

P1PLUG

Inlet Pressure Tends To "Push" The Plug Open. TO INCREASE

FLOW

PLUG MOVES DOWN+



P2 OUTLET DECREASES

CAGE

SEAT

PIS

TO

N

PRESSURE PLATE

P2

P2

_with BALANCED TRIM

P1 P1

INLET

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DIAPHRAGMS —DIAPHRAGMS —How “BIG” are the “FORCES” ?How “BIG” are the “FORCES” ?

PROPORTIONAL BAND -PROPORTIONAL BAND -REDUCING REGULATORREDUCING REGULATOR

P = 100 #/in 2Diaph

Diaph =

Diaph = 6 in.D

F

Diaphπ4

= x D 2A

DiaphP x DiaphA

DiaphF = 2830 #

Diaph =

Diaph = 12 in.D

F

Diaphπ4

= x D 2A

DiaphP x DiaphA

DiaphF = 11,300 #

12 in.6 in.

SETPOINTLESS THAN 10%

_OU

TLE

T P

RE

SS

UR

E

LO

CK

UP

ZO

NE

FULL OPENMECHANICAL LIMIT

PR

ES

SU

RE

“D

RO

OP

”

PR

ES

SU

RE

“F

AL

LO

FF

”

PR

OP

OR

TIO

NA

L B

AN

D

10%20%

30%

40%

0

0 _FLOW CAPACITY HILOW

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P3 = Loading Pressure

P3

Pressure Plate

∑Fdown

∑Fup

Fps

PLUG

Diaphragm


∑Fup ∑F

down=

F + (P1 x A ) + (P2 x A ) =ps port diaph

(P2 x A ) + (P3 x A )port diaph

OUTLETP2INLET P1

PRESSURE LOADED REDUCING REGULATORPRESSURE LOADED REDUCING REGULATOR

P2 ≈ P3

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FTO PRESSURE LOADED REDUCING REGULATOR with

BALANCED TRIMP1 = Higher Inlet Pressure


PL = Loading Pressure

∑F up

∑Fdown

P2

OUTLET

P1PLUG


TO INCREASEFLOW

PLUG MOVES DOWN+



P2 OUTLET DECREASES

CAGE

SEAT

PIS

TO

N

P2

P2

P1 P1

INLET

PL

P = Psp L

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P3 = Loading Pressure Frs

Frs = Force of Range Spring

Fps = Force of Piston Spring

Pressure Plate ∑Fup

∑FdownDport

Diaphragm

PLUG

Fps


down∑Fup ∑F=F + (P1 x A ) + (P2 x A ) =ps port diaph

F + (P2 x A ) + (P3 x A )rs port diaph

OUTLETP2P1INLET

P3

DIFFERENTIAL REDUCING REGULATORSDIFFERENTIAL REDUCING REGULATORSSome applications require that a specified differential be maintained between two separate piping

systems, regardless of the Inlet Pressure variations of either system. The downstream pressure of onesystem may be controlled with a Differential Reducing Regulator to accomplish this task.

As an example, a low pressure steam system must remain 20 psi above an oil distribution line. Byconnecting a high pressure steam line though the Differential Reducing Regulator and loading the oilpressure into the upper spring chamber of the Regulator above the diaphragm, a ratio can be main-tained. By setting the spring adjustment for 20 psi, a 20 psi differential between the steam and oilsystems will then be maintained, even though the pressure of either system may vary. The downstreamsteam pressure is actually being controlled.

The Outlet pressure of the Regulator is the sum of the loading pressure above the diaphragm plusthe Differential Pressure required. With this in mind, sizing of the Regulator is identical to PressureReducing Regulators.

DIFF. REDUCING REGULATORDIFF. REDUCING REGULATOR

P2 - P3 ≈ ∆Pconstant

∆Pconstant = Prange springsetting

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STEAM ATOMIZATION –STEAM ATOMIZATION –DIFFERENTIAL REDUCING REGULATORDIFFERENTIAL REDUCING REGULATOR

DOUBLE-DIAPHRAGM; i.e. OPT-1+8+65DOUBLE-DIAPHRAGM; i.e. OPT-1+8+65

COMBUSTIONINPUT CONTROLSIGNAL

FOS – FUEL OIIL SUPPLYFOR – FUEL OIL RETURNSTM – STEAM SUPPLY

FOS

STM

FOR

STM

FOS

BURNERGUN

BURNER

AIR

DA

MP

ER

FORCEDDRAFT

FANDAMPERCONTROL

COMBUSTIONCONTROL VALVEPF

P1

PL

P2LO

W F

LO

W

VENT

VENT

BACK PRESSURE / RELIEF REGULATOR

DOUBLE DIAPHRAGMDIFFERENTIAL

REDUCING REGULATORW/FLOW-THRU SP. CH.

∆Psizing = P1 – P2; variable

∆Pdifferential = P2 – PL; nearly constant, except for “droop” effect. Set by adjusting range spring.

P1 – Steam Supply Pressure; normally constant.

P2 – Steam Outlet Pressure; variable.

PL – Oil Loading Pressure; variable.

PF – Fuel Supply Pressure.

BURNERLOAD P1 – psig P2 – psig ∆Psizing – psid PL – psig ∆Pdifferential – psid PF – psig

LOW

MED

HIGHLOW

MED

HIGH

125

125

125175

175

175

55

69

8375

94

113

70

56

42100

81

62

40

55

7060

80

100

15

14

1315

14

13

100

90

80120

110

100

PRESSURES

BURNERNOZZLE

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TO MINIMIZE DROOPTO MINIMIZE DROOP

P2

– O

UT

LE

T P

RE

SS

UR

EP

2 –

OU

TL

ET

PR

ES

SU

RE

P2

– O

UT

LE

T P

RE

SS

UR

E

Q – FLOW

Q – FLOW

Q – FLOW

SmallReducing Regulator

Metal Diaphragm

Reduced Port

LargeReducing Regulator

Composition Diaphragm

Full Port

Use a larger body size with higher Cv

– capacity

Use a composition diaphragm material for

an equal body size.

B

A

Use largest port-size available.

C

Regulator withRange Spring

Pressure LoadedRegulator with No

Range Spring

Eliminate the device creating the “proportional effect”.

D

P2

– O

UT

LE

T P

RE

SS

UR

E

Q – FLOW

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TO MINIMIZE DROOPTO MINIMIZE DROOP

RESET = “Correction added to a control loop to offset proportional device setpoint deviation;i.e. Psp ≈ Pdroop + Preset

METHOD CASHCO USES TO “ADD RESET”

A. Go to a “pilot-operated” regulator,B. Go to an “accelerated” regulator, ORC. “Minimize” the “deviation” effect (droop) by going to a control valve and a pressure controller.

P2

– O

UT

LE

T P

RE

SS

UR

E

Q – FLOW

Stiffer Range Spring

Soft Range Spring(10-40 psig)

For overlapping range springs use the “softer” range spring; i.e. lower range spring.EXAMPLE: For a 35 psig setting, use a 10-40 psig range spring rather than a 30-80 psig spring.

EP

2 –

OU

TL

ET

PR

ES

SU

RE

Q – FLOW

“Reset”

P2 = 35 psig

w/o Reset

w/ Reset

Add “Reset” to the “Proportional Regulator”.F

P2

– O

UT

LE

T P

RE

SS

UR

E

Q – FLOW

Short range spring

Tall Range Spring

A longer range spring exhibits less droop.G

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VTA

STORAGETANK

CENTRIFUGALPUMP

BACK PRESSURE /RELIEF REGULATOR

TOSYSTEM

P1

Sizing of Back Pressure (Relief) Regulators follows very closely to previous examples.In Pressure reducing applications, the Regulator is adjusted to maintain a desired pressure

at the outlet of the Regulator. In Back Pressure (Relief) applications, the Regulator is adjustedto maintain a desired pressure at the inlet of the Regulator.

The Outlet Pressure of a Back Pressure (Relief) Regulator is often 0 psig when dischargingto atmosphere, or whatever the pressure build-up would be in discharging piping, or pressureof the receptacle in which discharge is directed.

If the outlet pressure is near zero, for most cases the liquid will be fully cavitating near theoutlet body connection. An angle body design will experience a lower degree of body wearthan a comparable straight body globe pattern in cavitating conditions.

BACK PRESSURE RELIEF REGULATOR –BACK PRESSURE RELIEF REGULATOR –

Common Application –

PROPORTIONAL BAND -PROPORTIONAL BAND -BACK PRESSURE/RELIEF REGULATORBACK PRESSURE/RELIEF REGULATOR

PUMP RECIRCULATION LOOP DESIGNPUMP RECIRCULATION LOOP DESIGN

_INLE

T P

RE

SS

UR

E

0

0 _FLOW CAPACITY HI

SETPOINT

FULL OPENMECHANICAL LIMIT

10%

20%

30%

40%

50%

PR

ES

SU

RE

“B

UIL

DU

P”

PR

ES

SU

RE

“A

CC

UM

UL

AT

ION

”

PR

OP

OR

TIO

NA

L B

AN

D

BACK PRESSURE / RELIEFREGULATOR

LO

CK

UP

ZO

NE

LOW

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BP / RELIEF REGULATORSBP / RELIEF REGULATORS

FLOW-THRU ANGLE DESIGN

GLOBE DESIGN

Frs PressurePlate

Diaphragm

PLUG


= Higher Inlet Pressure

P1

= Lower Outlet Pressure

P2


∑Fdown

∑Fup

OUTLETP2P1INLET

∑ F = ∑ Fup down

(P2 x Aport) + (P1 x Adiaph) = Frs + (P1 x Aport )

Frs PressurePlate

Diaphragm

PLUG

F rs = Force of Range Spring


P1


P2



∑Fdown

∑Fup

OUTLET

FLOW-THRU

CONNEC-TION

P2

P1INLET

P1

(P2 x Aport) + (P1 x Adiaph) = Frs + (P1 x Aport)

-20-

BP REGULATOR


P2 = Lower Outlet

∑F up

∑Fdown

P2

OUTLET

P1

PLUG

Inlet Pressure Tends To "Push" The Plug

TO INCREASEFLOW

PLUG MOVES UP+

DIAPHRAGM MOVES UP

RANGE SPRING COMPRESSES+

P1 OUTLET INCREASES

CAGE

PIS

TO

N

PRESSURE PLATE

P2

P1

with UNBALANCED TRIM TOP/CAGE GUIDED

SEAT

INLET

FTC Flow Direction

2As P varies, the _P w ill vary.sp

1.

2. Dynamic seal _NOT required; no P across seal.∆

-21-



∑F up

∑Fdown

P1

OUTLET

P2

PLUG


TO INCREASEFLOW

PLUG MOVES UP+

DIAPHRAGM MOVES UPP1 INLET IS CONSTANT

CAGE

PIS

TO

N

P1

P1

SEAT

INLET

P = Psp L

FTO Flow Direction

As P varies, the P w ill _NOT vary.

2

sp

1.

2. Dynamic seal _required; P across seal.∆

BP REGULATORwith UNBALANCED TRIM

TOP/CAGE GUIDED

-22-

Frs PressurePlate

Diaphragm

PLUG


∑ Fup

∑ Fdown


P1


P2


P3 = Loading Pressure


F + (P 1 x A )(P2 x A ) + (P1 x A ) port diaph portrs + P3=

P1 P2 OUTLET

P3

INLET

DIFFERENTIAL RELIEF REGULATORSDIFFERENTIAL RELIEF REGULATORS

On heavy machinery, such as a gas compressor, it is important that the pressures beinggenerated by the pressurized lubrication system not exceed the compressed air system pres-sure by more than a specified increment, otherwise oil leakage could occur into the com-pressed gas.

By using a Differential Back Pressure (Relief) Regulator in the lubrication line, the lubrica-tion pressure may be maintained at a specified point above the gaas system pressure. Merelyload the spring chamber above the diaphragm with the gas system pressure, and set thespring adjustment to the point of differential to be maintained.

The Inlet Pressure of the valve is the sum of the Loading Pressure above the diaphragmplus the Differential Pressure required. With this in mind, sizing of the regulator is identical toPressure Reducing Regulators.

DIFF. BP / RELIEF REGULATORSDIFF. BP / RELIEF REGULATORS

P1 - P3 ≈ ∆Pconstant

∆Pconstant = Prange springsetting

-23-

ROTARY GAS COMPRESSOR SHAFTROTARY GAS COMPRESSOR SHAFTSEAL OIL SYSTEMSSEAL OIL SYSTEMS

HIGH PRESSURE— DISCHARGE

LOW PRESSURE— SUCTION

1000 psig

PIOI LOI L

OI L OIL

OIL

OIL

OIL

OIL

O I L

OI L

OI L

OI L

OI L

PI

PIPI

400 psig

420 psig

1020 psig

1020 psid

Gra

vit

y R

etu

rn

FLOWORI FI CE

COMPRESSOR

SHAFT TODRIVER

∆P

= 2

0 p

sid

Diff

Gra

vit

y R

etu

rn

Gravity Return

∆P

= 2

0 p

sid

Diff

HEX

HEX

HP PUMP LP PUMP

DIFFERENTIALBACK PRESSUREREGULATOR

OILRESERVOIR

VENT

HP

P3

P2

P1 P1

P2

P1

OIL

∆P =Size

∆P =sizeP - P =1 2420 psid

LP

DIFFERENTIALBACK PRESSURE

REGULATOR

P1

-24-

PRESSURE LOADED BP REGULATORwith UNBALANCED TRIM

TOP/CAGE GUIDEDP1 = Higher Inlet Pressure


PL= Loading Pressure

∑F up

∑Fdown

P2

OUTLET

P1

PLUG

Inlet Pressure Tends To "Push" The Plug

TO INCREASEFLOW

PLUG MOVES UP+


CAGE

PIS

TO

N

P2

P1

SEAT

INLET

2As P varies, the _P w ill vary.sp

1.

2. Dynamic seal _NOT required; no P across seal.∆

PLP = Psp L

FTC FlowDirection

-25-

_PRESSURE LOADED BP REGULATORwith UNBALANCED TRIM

TOP/CAGE GUIDEDP1 = Higher Inlet Pressure


PL= Loading Pressure

∑F up

∑Fdown

P1

OUTLET

P2

PLUG


TO INCREASEFLOW

PLUG MOVES UP+


CAGE

PIS

TO

N

P1

P1

SEAT

INLET

PL P = Psp L

As P varies, the P w ill _NOT vary.

2sp

1.

2. Dynamic seal _required; P across seal.∆

FTO Flow Direction

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PILOT-OPERATED REDUCING REGULATORPILOT-OPERATED REDUCING REGULATOR

“LOADING” PILOT“LOADING” PILOT

– HIGH INLET PRESSURE

– INTERMEDIATE PRESSURE

– LOW OUTLET PRESSURE

P

P

P

1

12

2

P SENSING& UNLOADING

2

P

SE

NS

ING

& U

NLO

AD

ING

2

PILOT VALVE

P

SU

PP

LY1

P

LO

AD

ING

12

PISTONMAIN VALVE

OUTLET

P2

INLET

P1

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RULE #1: Pressure regulators regulate pressure; they do NOT regulate flow. Theymust be selected for the proper flow rate envelope.

RULE #2: Flow rate and controlled pressure are Integral; i.e. change in flow — changein pressure.

Controlled pressure varies with flow.

The amount of variation in controlled pressure with a given change in Flowis called:

Proportional BandDroop BuildOffset Accumulation

(REDUCERS) (BACK PRESSURE)

RULE #3: The use of composition diaphragms will provide:

Maximum FlowMinimum Droop or Build

RULE #4: PRV and BPV DO NOT fail in the most frequently desired mode.

RULE #5: Regulators are best used in systems where flow changes are small.

RULE #6: DO NOT rely on a regulator as a shut off device.

RULE #7: Never hydrostatically test a regulator.

RULE #8: Reducing regulators, in nearly all cases, have two separate pressure vs.temperature ratings for the inlet and outlet.

REGULATOR RULESREGULATOR RULES

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APPLICATION & SELECTION REQUIREMENTSAPPLICATION & SELECTION REQUIREMENTS

1. SERVICE FLUID.

a. Is it a liquid?, Gas?, Steam?b. What is weight density?, SG?, MW?, Specific volume?c. Viscosity?d. Is it corrosive? Suitable body and trim materials?e. Is it erosive?

2. INLET PRESSURE – P1.

a. Maximum?b. Minimum? Rangeability?c. End connections?d. Suitable products?

3. OUTLET PRESSURE – P2.

a. Suitable products?b. Sizing P1?c. Level of “droop”? *d. Max design pressure? *

4. FLOW RATE.

a. Maximum?b. Minimum?c. End connections?d. Suitable products?

5. TEMPERATURE CONDITIONS.

a. Max inlet – T1?b. Packing design? **c. Gasket design?d. Diaphragm design?e. Seat design?f. Viscosity?g. Suitable body and trim materials?h. Vapor pressure – Pvp? Cavitation? Flashing?

* REGULATOR ISSUE ONLY** CONTROL VALVE ISSUE ONLY

By providing the above five main points of information, all the indicated sub-points can beconsidered as to the “Common Application Practice”, a Cv-Capacity can be calculated, aproduct selection determined, and the SPL-noise level estimated.

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TROUBLE SHOOTINGTROUBLE SHOOTING

PRESSURE REDUCING REGULATORS

PROBLEM: EXCESSIVE SEAT LEAKAGE.

1. Resize application to ensure that we are not mistaking proportional band for excessiveseat leakage.

2. Check inlet pressure, do not exceed allowable limits listed in technical bulletin.

3. Metal seats do not seal bubble tight. If system is dead ended outlet, pressure can in-crease to inlet pressure. Composition seats must be used on dead ended service. (Be-ware of temperature limits.)

4. If unit is cryogenic or is exposed to freezing temperatures, install in inverted position.This eliminates the possibility of condensate freezing above the diaphragm and holdingvalve in open position.

5. Inspect seating areas for foreign matter or nicks in seating surfaces. Replace seats ifnecessary.

6. Check piston spring for damage. If collapsed or broken, replace.

7. Inspect cylinder walls and O.D. of piston for damage. These units must slide smoothlytogether. (No hanging up.)

PROBLEM: LEAKAGE THROUGH SPRING CHAMBER VENT HOLE.

1. Remove spring chamber and inspect diaphragm.

2. If present, remove diaphragm nut and inspect for leakage past pressure plate gasket.

3. For frequent diaphragm failure, resize application, examine system for instability or overpressurization, consider replacing metal diaphragms with composition for longer life.(Beware of temperature limitations.)

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PROBLEM: ERRATIC CHATTERING OPERATION.

1. Resize application to ensure unit is not oversized or undersized for the application.

2. Check inlet pressure for stability (pulsating inlet pressure).

3. Check spring chamber vent hole for pulsation. If pulsation is present, this would indicatediaphragm flutter. Consider a next higher range spring or change diaphragm material todampen.

4. Inspect trim wall of cylinder and O.D. of piston for wear. Replace trim if worn or marred.

BACK PRESSURE REGULATORS

PROBLEM: EXCESSIVE SEAT LEAKAGE.

1. Resize application; is unit being used properly?

2. Metal seats do not seal bubble tight. If valve is expected to seal bubble tight, use compo-sition seating material. Review technical bulletin for lockup ability (this is the system falloff pressure needed to reseat unit).

3. Inspect seating areas for nicks, scratches or foreign matter. Replace seats if necessary.

4. Inspect cylinder walls and piston O.D. Unit must slide smoothly together – no hangingup.

5. A diaphragm that is out of round will pull piston off center causing unit to hang up. Besure all parts are properly aligned.

PROBLEM: LEAK THROUGH SPRING CHAMBER VENT HOLE.

1. Remove spring chamber and check diaphragm for cracks or leaks.

2. If present, remove diaphragm nut and inspect for leakage past pressure plate gasket.

3. For frequent diaphragm failures, resize application and examine system for instabilityand over pressurization. Consider replacing metal diaphragm with composition. (Bewareof temperature limits.)

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PROBLEM: ERRATIC CHATTERING OPERATION.

1. Resize application, confirm data given.

2. Check inlet pressure for pulsation. If present, take steps to dampen surge pressuressuch as installing an accumulator.

3. Inspect trim, cylinder walls and piston O.D. for excessive wear. Marred surfaces cancause units to hang up.

4. If properly sized and system is smooth, take steps to dampen regulator such as compo-sition diaphragm material, higher spring range, etc.

5. A diaphragm that is out of round will pull piston off center causing unit to hang up. Besure all parts are properly aligned.

PROBLEM: REGULATOR CAN'T PASS SUFFICIENT FLOW.

1. Resize application, confirm data given.

2. Review Technical Bulletin for flow expected as given pressure build.

3. If diaphragm material is metal, consider composition material. This can increase capac-ity up to 30% in some cases. (Beware of temperature limitations.)

4. Remove trim and inspect for clogged passages, clean and unplug if necessary. Inspectfor scratched or nicked cylinder walls and piston O.D. This can result in unit hanging up.

5. Check diaphragm (contact factory); getting too high of a diaphragm setting will reducemaximum capacity of unit.

6. If unit is used in below freezing temperatures or on cryogenic application, install unit ininverted position to eliminate freezing of condensate above diaphragm, thus restrictingdiaphragm movement.

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PSAUNIT

PSAUNIT

GN2

LIQUIDSTORAGE

TANK

GN2

LIQUIDSTORAGE

TANKAMBIENTAIR HEX

AMBIENTAIR HEX

OPER. PRESS.= 100 psig

PRIMARY SOURCE

GN2

LARGEPLANT

NORTH

SOUTH

PRESSUREREDUCER REG.

SP = 90 PSIG

SECONDARYSOURCE

GN2GN2

OPER. PRESS.= 100 psig

PRIMARY SOURCE

SECONDARYSOURCE

PRESSUREREDUCER REG.

SP = 90 PSIG

PSA = “PRESSURE SWING ADSORPTION”

TTOO GG AASSDD IISS TTRR IIBB UUTTIIOO NNSS YYSS TTEEMM TEMPERATURE

LIMITING PRESSURE

CONTROL LOOP

ECONOMIZERBP REG

PRESSUREBULDINGHEATEXCH.

LIQUIDSTORAGETANK

PRESSURE BUILDINGREG - LIQUID SIDE

MAINAMBIENTAIR HEATEXCHANGER

AIRSET

TCV+PCVFC

TCV+PCV

V

V REV.

DIR.TC

PC

__LL II QQ UU II DD

VV AA PP OO RR

SRV

CRYOGENIC – LIQUIFIED GASESCRYOGENIC – LIQUIFIED GASES

PSA UNITS IN PARALLEL WITH LIQUID STORAGE UNITPSA UNITS IN PARALLEL WITH LIQUID STORAGE UNIT

LIQUID STORAGE SYSTEMLIQUID STORAGE SYSTEM

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Customer was initially concerned about the effect of a 500 psig pressure drop on a closedcontrol valve on steam service. Cashco's solution lasted eight years.

The rangeability of this system allowed the customer to use the same system for steamtracing and high volume steam cleaning.

11

Our customer had 600 psig superheated steam at 550°F, andwanted to reduce it to 90-100 psig for steam tracing on sulfur tanks. The cus-tomer, however, also wanted a full 1" line volume to allow them to occasionallyclean out railroad cars. We supplied a 1" Ranger with a 764P and a 1" 1000HPwith stellite trim. The 1" 1000HP was piped around the Ranger (like a by-passline). The Ranger and 764P were in the main line. The 1000HP was set at 100psig to supply steam tracing to sulfur. In normal steam tracing service, theRanger was closed by the 764P and all flow passed through the 1000HP. Whenthere was demand on the system to clean rail cars, pressure dropped and the1000HP went towards full open. When the P2 approached 90 psig, the 764P, setat 90 psig, opened the Ranger, holding the pressure at 90 psig.

R.J. Schroeder P. Rogers March 1995

STEAM – PRESSURE REDUCTION

HELPFUL HINTSHELPFUL HINTS

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STEAM-PRESSURE REDUCTION

For Conceptual Use Only!!

MoltenLiquidSulfur

T > 238°F

TR

TR

TR

MELTING &CLEANING

M.P. STEAM

TRACINGM.P. STEAM

SULFURSTORAGE

TANK

P = 100 psig

P = 90 psig2 Max

2 Min

M.P. STEAM

PI PC

764P PneumaticPressure Controller

SP = 90 psig

IAS

SUPERHEATEDH.P. STEAM

1" - Ranger QCTMetal SeatNo Positioner

1" - 1000HP-15+46 m ≈ 1500 #/Hr

.

Melting Point of Sulfur = 238°F

RAILROADTANK CAR

FOR SULFUR

HEX

Drain

Hose

Hose

1 2

P = 600 psig

T = 550°F1

1

m = Max. of 1" dia. pipe

.

SIG

CONDENSATERETURN

CONDENSATERETURN

-37-

B.H. Shiffer P. Rogers March 1995

11

AIR (LOW FLOW) – REDUCING REGULATOR

Purge Air to Pharmaceutical Process Tank —

Inlet = 100 psigOutlet = 2–5 psigFlow = 40 scfhTemp = 70°FCv = .014.

Recommended: 1" Model D, SST body, S36 Trim, 2–15 psig spring range.This valve was “oversized” to reduce the “lockup” zone and eliminate “droop”effect.

Bubble-tight shut-off, lockup within 1 psig.

Because of low flow and relatively high ∆P, the customer was concerned about valve chatter.

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AIR (LOW FLOW) – REDUCING REGULATOR


PUREAIR

P = 100 psig

Q = 40 scfh

T = 70°F

1

1

. 2P = 2–5 psig

R

TANKx

1 2

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BACK PRESSURE CONTROL

1 1

May 1995P. RogersB.H. Shiffer

Back Pressure control for a newspaper ink system

BLACK INK COLORED INKP1 = 100 P1 = 100P2 = 0 P2 = 0Q = 9 GPM Q = 2.3 GPMVisc. = 150,000 SSU Visc. = 150,000 SSUCv = 29.27 Cv = 7.45

Regulator 4" 8311HP 1-1/2" 8311 HPIron Body Iron BodyIron Spring Chamber Iron Spring ChamberS40 Trim S40 Trim75-145 Spring Range 75-145 Spring Range

Because of the double port design of the 8311HP, it can achieve a higher Cv.

Viscosity of the ink.

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BACK PRESSURE CONTROL


INK

INK

INK STORAGE TANK

VISCOUS INK

ATM

PI

PrintingPressNo. 3

PrintingPressNo. 2

PrintingPressNo. 1

INK CIRCULATION PUMP

Back PressureRegulator

100 psig

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This application allowed the customer a tighter control on his regulated pressure (no spring – nofluctuating pressure).

1 1

Robert Schroeder P. G. Rogers August 1995

Autoclave – Tighter Pressure Control

An autoclave was used to mix polymer and then discharge it into aslicing chute. The size of the pellets would vary due to fluctuations ofpurging pressures, causing problems. Cashco supplied a 1000HP-1 withthe spring chamber loaded with air. (Note: The range spring was nearfully relaxed.) When the solenoid opened, a constant pressure supplymaintained proper sized pellets. An added bonus was the installation of a123 back pressure regulator to relieve the pressure when refilling theautoclave.

Their main concern was whether the regulator was big enough. Sizing was done with calculatedfigures from discharge information. Larger units could be done with control valves.

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AUTOCLAVE – TIGHTER PRESSURE CONTROL


IAS

Purge Air

Model 1000HP-1

Model 123

Vent

AUTOCLAVE

SLICER

Product Fill

Pellets

S

P = 60 psigsp

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1 1

S.J. Bishop P.G. Rogers August 1995

Surplus Usage Regulator

This application requires a back pressure regulator but can also bedone with a control valve. Air and water are the most commonfluids. The customer will have a primary and secondary require-ment for the air and water. He never wants to starve the primaryusers, but if there is a surplus the secondary system is supplied.

Never wants to starve system due to secondary usage.

Ensures flow to primary users. Self-contained.

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SURPLUS USAGE REGULATOR


As pressure in primary system decreases due to increased flow demand, the BPV closes off flow to secondary system when pressure falls below 50 psig.

As pressure in primary system decreases due to increased flow demand, the PC outputs a signal to close the PCV. PCV action should be to “fail closed” to ensure that the primary system gets its flow demand first. PC should have broad proportional band.

Back Pressure Regulator - BPV(3 Conn. Body)

Back Pressure Regulator - BPV(2 Conn. Body)

Control Valve – PCV

PressureController

1

1

1

2

2

Primary

Secondary

Primary

Secondary

Primary

Secondary

P = 50 psigsp

P = 50 psigsp

ATO-FC

I/PSIG

IAS

PC

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CONDENSATE SAMPLING SYSTEMCONDENSATE SAMPLING SYSTEM

STEAM DRUMCONTINUOUSBLOWDOWN

Cold Water Warm Water

RETURN CONDENSATE

HP STEAM

BFW @ D/A EXIT

MAKEUP TO D/A

BFW @ECONIMIZERINLET

PUMPEDCOND TO D/A

COOLEDSAMPLE

COOLEDSAMPLE

MODEL 1465

COOLEDSAMPLE

MODEL 1465

COOLEDSAMPLE

MODEL 1465

COOLEDSAMPLE

COOLEDSAMPLE

BFW @ ECONIMIZER EXIT

COOLEDSAMPLE

COOLEDSAMPLE

MODEL 1465

MODEL 1465 AND 1465-80

MODEL 1465 AND 1465-80

MODEL 1465 AND 1465-80

MODEL 1465 AND 1465-80

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NOTES

-47-

1. Reducing regulators control which pressure?

∆PSizing P1 P2 P3 P4 PLoad ∆PDiff

2. Back Pressure/relief regulators control which pressure?

∆PSizing P1 P2 P3 P4 PLoad ∆PDiff

3. What primarily causes “droop” to occur in reducing regulators?

Piston Spring Diaphragm Plug & Seat Vena Contract Range Spring

4. As a “control instrumentation” device, what is a pressure regulator?

Proportional On-Off On-Off Safety Proportional Throttling

5. What is the purpose of the range spring in a differential reducing regulator?

Stability Control Inlet Pressure Control Outlet Pressure Makes FTO

Control Differential Pressure Makes FTC

6. Which is the more “stable” throttling valve?

FTC FTO Both FTC & FTO

Why?

Increased Rangeability Stable @ low flow Stable @ high Flow All of the previous

7. What internals construction will give the smallest body size, lowest cost regulator?

FTO-Metal Diaphragm/Composition Seat FTC - Composition Diaphragm & Seat

Compositon Diaphragm/Metal Seat Metal Seat & Diaphragm

8. Why would stellited seat surfaces be desireable?

Flashing Excessive Partial Cavitation Wet Steam Full Cavitation

Sustained operation @ 5% travel or less Particulates in Fluid High ∆P All Previous

Test Your KnowledgeTest Your Knowledge

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Test Your Knowledge (cont.)Test Your Knowledge (cont.)9. For a back pressure regulator, what is the deviation (due to “build” effect) in controlled pressure if

flow rate is constant?

0% 1-5% 5-10% 10-15% 20% 30% 40%

10. The point where a back pressure regulator cracks open and stabilizes flow is called what?

% Build Setpoint Pressure % Droop Safety Setting Lockup Zone

11. Adding a pilot to a reducing regulator normally accomplishes what?

Increased flow at decreased droop Tighter shutoff Lower flow at increased droop

Decreased rangeability Increased pressure @ decreased droop

12. What is the best seat design & material for best repeatable tight shutoff?

Stellited seats Carbon-filled TFE Virgin TFE Buna-N

Glass-filled TFE FTO-TFE Grafoil

Why?Hardened surfaces Chemical resistance High “creep” characteristic

Resilience-memory FTO stability

13. Given: Pressure Reducing RegulatorBuna-N SeatP1Max = 316 psigP1Norm = 240 psigP2 = 100-110 psigFluid = CondensateT1 = 129°F

Which is the correct statement?

Safety Relief Valve (SRV) or rupture disc is not required because of presence of composition softseat.

Safety Relief Valve (SRV) or rupture disc is not required on low pressure piping systems; onlyrequired on low pressure vessels (tanks).

Safety Relief Valve (SRV) or rupture disc is required because P1 can exceed P2 rating if seat fails.

Safety Relief Valve (SRV) or rupture disc is required because it is liquid flow (if fluid had been agas-vapor, no SRV would be required).

Regulator Nameplate Rating

Inlet 400 CWP 400/100FOutlet 150 CWP 150/180F

ISA/FCI Class VI seat leakage

-49-

NOTES

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