10-2747_Best Practices for Regulator Selection
Transcript of 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
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- 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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Question #2Question #2
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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Question #3Question #3
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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Question #4Question #4
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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Question #5Question #5
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/
More Information