10-2747_best practices for regulator selection

7/30/2019 10-2747_Best Practices for Regulator Selection

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Regulator SelectionPractices

Regulator SelectionPractices

an s a es o voan s a es o vo


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PresentersPresenters

Vince Mezzano

Keith Erskine


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IntroductionIntroduction

The purpose of this presentation is to provide an overview of

Pressure Regulator operation, discuss selection criteria, and

dispel common misconceptions which may lead to

suboptimal selection and performance.


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Sample Data SheetSample Data Sheet

SampleDataSheet


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Sizing and Selection InformationSizing and Selection Information

Required

Process Data

P1, P2, Fluid Properties, Temperature, Flow Rate

Piping Specs

Materials, Connection Type and Size, ANSI Rating,

Design Pressure and Temperature Functionality

Back Pressure or Pressure Reducing

Minimum Accuracy Requirements


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Definitions:Definitions:

Upstream pressure is P1.

Downstream pressure is P2.

Differential Pressure is the difference between upstream

and downstream pressure.

UpstreamPressure (P1)

Downstream

Pressure (P2)

Delta Pressure

PCV Set @ 10 psig


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A pressure regulator is a device that matches the

downstream flow demand while maintaining the

downstream pressure constant.

The simpler a system is the better it is. Regulators are simpler devices than control valves

Performs the function of a VALVE, ACTUATOR, CONTROLLER, AND

What is a Pressure Regulator?What is a Pressure Regulator?

Process-powered (does not need external power sources, its WIRELESS!)

Field Adjustable

Normally No Feedback (technology exists to communicate with BPCS strictly position feedback

only)

Regulators can be more cost effective than Control Valves.


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Types of RegulatorsTypes of Regulators

Pressure ReducingRe ulator Self Contained

Pressure ReducingRegulator with External

DifferentialPressure Reducing

ISA Symbols

S5.1

Pressure TapRegu ator witInternal and

External PressureTaps

BackpressureRegulator with

External Pressure

Tap

BackpressureRegulator, Self

Contained


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Specific Regulator Types / Definitions:Specific Regulator Types / Definitions:

Pressure Regulators can be used to control downstream pressure, upstream pressure,

or differential pressure.

Pressure Regulators that control upstream pressure are typically referred to asbackpressure regulators. (Relief Valves not ASME certified)

Pressure Regulators in differential pressure service monitor both upstream and

downstream pressure and hold a constant pressure differential.

There are two types of pressure regulators: Direct-Operated and Pilot-Operated.Self-

Operated regulators are mounted in-line and do not have any external to the process.

A Pilot-Operated regulator is mounted in-line and has a sensing line connected to the

process.


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Direct-Operated RegulatorDirect-Operated Regulator

Also called Self-Operated Pressure Regulator(Vince Mezzanos First Choice)


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Three Essential ComponentsThree Essential Components

1. Restricting Element (a valve, disk, or plug)

2. Measuring Element (a diaphragm)

.


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Self-Operated RegulatorSelf-Operated Regulator

Loading - Spring

Regulator has three basic

components:

Sensing - Diaphragm

Restricting - Valve


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Force BalanceForce Balance

1. Pressure = Force/Area (lb/In)

2. Force = Pressure*Area (lb)

3. Spring Force (Fs)= K*X (lb) 1 Inch

FS = 100 Lb

Ad=10 in

P1 = 100 Psig

Q = 50 SCFH

P2 = 10 Psig

D =

Fs = 100 lb/in x 1 in = 100 lbFd = 10 psig x 10 in = 100 lb

At Equilibrium

K= spring rate (lb/In)

X= Compression (In).

Fs=Spring Force (lb)

Fd= Diaphragm Force (lb)


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Increasing DemandIncreasing Demand

0.90 Inch

FS= 90 Lb

=

As flow demand increases, downstream pressure decreases.

Fs= K * X (lb)

P1=100 Psig

Q = 200 SCFH

P2 = 9 Psig

.1Valve travels = 0.10 in


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Actual Performance Droop/OffsetActual Performance Droop/Offset

P2Psig

11

109

8

Ideal

Actual

10%20%

Droop is the amount of deviation from the set point at a given flow,Expressed as a percentage of set point.

Flow scfh

0 50 200 300 500

P1 = 100 psig


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Droop due to Diaphragm EffectDroop due to Diaphragm Effect

Assume:At rest

Fs=Fd=100 lb & Ad=10 inFs=P2(Ad), Solve for P2P2=Fs/Ad=100 lb/10 inP2=10 lb/in

Diaphragm area increasesfrom 10 in to 11 inasit travels downward.P2=99 lb /11 inP2=9 lb/in


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Spring Effect Reduces P2 furthermoreSpring Effect Reduces P2 furthermore

Recall:

1) The effective diaphragm area is 10 in at rest.

2) The Spring Force is 100 lb.

3) P2 desired is 10 lb/in.

Now assume that the diaphragm travels downward 0.10 in to open the valve fully.

The effective area of the diaphragm increases from 10 in to 11 in.

In order to load the regulator with 100 lbs of downward pressure, the spring mustbe compressed 1 in, if the spring has a rate (K) of 100 lbs/in.

Fs=K(X)

Fs=100* (1-0.1)= 90 lbs. Solve for P2 by equating Fs=Fd

Fs=P2(Ad) P2=90 lbs/11 in=8.2 lbs/in due to the diaphragm and spring effects.


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Light Spring Rate Improves AccuracyLight Spring Rate Improves Accuracy

A light spring rate of 50 lb/in will open twice as far as it did with a heavy spring

rate of 100 lb/in.

For example#1 using heavy spring rate of K=100 lb/in, Solve for compression X, initially

Fd=P2(Ad)=10(10) lb Fs=K(X) X=Fd/K X=100/100 = 1 in

When P2 dropped from 10 psig to 9 psig.

Fd=P2(Ad)=9(10) lb Fs=K(X) X=Fd/K X=90/100 = 0.90 in

For example#2 using light spring rate of K=50 lb/in, Solve for compression X, initially

Fd=P2(Ad)=10(10) lb Fs=K(X) X=Fd/K X=100/50 = 2 in

When P2 dropped from 10 psig to 9 psig.

Fd=P2(Ad)=9(10) lb Fs=K(X) X=Fd/K X=90/50 = 1.80 in

Therefore, a spring with a range of 2 to 10 psig is more accurate than a spring with a range of 9 to 20 psig. If

the set pressure of the PCV is 10 psig, the 2 to 10 psig spring will provide better

accuracy or less droop.


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Spring Effect on AccuracySpring Effect on Accuracy

P2

Psig

11

10

98

Ideal

Light spring

Heavy spring

Flow scfh

0-50 200 300 500

P1 = 100 psig

400

10% Offset 300 scfh


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Pilot-Operated RegulatorPilot-Operated Regulator

Loading Style (two-Path Control)

The pilot is simply a pressure amplifier. It detects a smallchange in downstream pressure and it increases the LoadingPressure 20 times as much.

The pilot regulator uses upstream pressure as its supply,reduces this pressure, and loads the main regulatordiaphragm with sufficient pressure to compress the mainspring and open the regulator up to full travel.

Use Pilot Pressure Regulators on large flow capacity andclean service.


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Question #1Question #1

The upstream pressure (P1) is 100 psig and a differentialpressure is 20 psid.

What is the downstream pressure (P2) of a pressure regulator?

a) 120 psig

c) 20 psig

d) None of the above

b) Delta Pressure = P1-P2 Solve for P2=80 psig


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Regulator SizingRegulator Sizing

The manufacturers formulas and tables shall be used to size and

select pressure regulators.

The regulator shall be sized no more than 10% droop at maximum

.

Regulators should never be used in cavitating or flashing liquid service.


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Regulator Applications & Typical SizesRegulator Applications & Typical Sizes

Pressure Reducing

Back-Pressure/Relief

Differential Pressure

Sizes 1 to 8, up to ANSI 600

Where?

- Boiler/Furnace/Burners Fuel Gas

-

- Instrument Air Supply- Compressor Fuel Gas

- Water Systems

- Natural Gas Distribution

- Steam Supply- Lube Oil Systems, Pipelines, Farmtaps,

Residential


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Why Use a Pressure Regulator?Why Use a Pressure Regulator?

Non-critical applications

Quick speed of Response

Economic solution

No external energy source required

Low maintenance device

Reliable solution to control pressure


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True or False.

Heavy spring rate provides the most accuracy (least droop)than light spring rate.

a) Falseb) True


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Backpressure RegulatorsBackpressure Regulators

A backpressure regulator maintains a desired upstream pressure by varying the flow in

response to changes in upstream pressure. A pressure relief valve limits pressure buildup(prevents overpressure) at its location in a pressure system. The relief valve opens to

prevent a rise of internal pressure in excess of a specified value. The

pressure at which the relief valve begins to open pressure is the relief pressure

setting. Relief valves and backpressure regulators are the same devices.

.

(relief applications) are not ASME safety relief valves.

Backpressure Regulator Selection

Backpressure regulators control the inlet pressure rather than the outlet pressure.

The selection criteria for a backpressure regulator is exactly the same as for apressure reducing regulator.


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Which of the following answer reflects the ISAsymbol of the Pressure Regulator?

a)Self-Operated PCV with internal tap.

b)Self-Operated PVC with external tap.

c)Backpressure PVC with external tap.

d)Backpressure PCV with internal tap.

e)None of the above.


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General Sizing Guidelines:General Sizing Guidelines:

Pressure Ratings: Remember regulators can have different ratings

between upstream and downstream. Make sure not to exceed the

rated casing pressure.

Spring selection: Choose the spring with the lowest spring rate

.

Orifice diameter: Choose the smallest diameter that will handle the

required flow.


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Common Misconceptions

Pressure regulators control pressure; they do NOT regulate flow.

Flow rate and controlled pressure are linked together; thus change in flow

change in pressure.

Regulators are best used in systems where flow changes are small.

Regulators are NOT shut off devices. All regulators with elastomeric seats are bubble tight, but wear or damage to seats could

increase leakage.


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DO NOT hydrostatically test a regulator.

Reducing regulators, in most cases, have two separatepressure/temperature ratings for the inlet and outlet.

Common Misconceptions

Failure Mode Depends on the component that fails No air or power failure basis


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Control Valve or Regulator?Control Valve or Regulator?

Regulator Advantages

Self Contained Faster Speed of Response

Less Complicated

Control Valve

Advantages Larger Size, Pressure, andTemperature Capabilities

Trim Selections (Severe

Ease of Maintenance

Flow Turndown

Service)

Material Selection

Fluid Versatility

Remote Interface andFeedback


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Upstream pressure = 200 psig.Differential pressure = 50 psig.

What is the set point ofa pressure regulator?

a)150 psigb)200 psigc)250 psigd)None of the above

UpstreamPressure (P1)

DownstreamPressure (P2)

Delta Pressure

PCV Set @ xx psig


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Fuel Gas Compression PackageFuel Gas Compression Package

Instrument Supply Instrument Supply

First Cut

source: SEC caterpillar compressor skid


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For Vapor Service, how does one know if the valve is ina Cavitation or Flashing Service?

a) Downstream pressure is greater than Vapor Pressure.b) Upstream pressure is greater than Vapor Pressure.

c owns ream pressure s ess an apor ressure.d) Upstream pressure is less than Vapor Pressure.e) None of the above.


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Summary:Summary:

Pressure Reducing Regulators

a) Direct-Operated

b) Pilot-OperatedBackpressure Regulators (Relief Valves not ASME certified)

Three Components on Pressure Regulators1) Loading (Spring)

2) Sensing (Diaphragm)

2) Restricting (Valve or Plug)

Droop, Proportional Band, or Offset.


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Contd Summary -Self-Operated RegulatorContd Summary -Self-Operated Regulator

Simplest and most cost effective final control element

Offer the fastest speed of response

Used on applications that require low flow capacity.

10%-20% Droop.


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Contd Summary - Pilot-Operated RegulatorContd Summary - Pilot-Operated Regulator

Fast speed of response

Handles high flow capacity

Larger body sizes, up to 8x6

More economical option to valve-actuator controller

- roop.


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Website:

http://www.fisherregulators.com/

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