COMPLETE REVISION June 2007
Process Industry Practices Process Control
PIP PCECV002 Pressure ressur e Regul Regula ators tor s Selection Selection Guide uid elines lin es
PURPOSE AND USE OF PROCESS INDUSTRY PRACTICES In an effort to minimize the cost of process industry facilities, this Practice has been prepared from the technical requirements in the existing standards of major industrial users, contractors, or standards organizations. By harmonizing these technical requirements into a single set of Practices, administrative, application, and engineering costs to both the purchaser and the manufacturer should be reduced. While this Practice is expected to incorporate the majority of requirements of most users, individual applications may involve requirements that will be appended to and take precedence over this Practice. Determinations concerning fitness for purpose and particular matters or application of the Practice to particular project or engineering situations should not be made solely on information contained in these materials. The use of trade names from time to time should not be viewed as an expression of preference but rather recognized as normal usage in the trade. Other brands having the same specifications are equally correct and may be substituted for those named. All Practices or guidelines are intended to be consistent with applicable laws and regulations including OSHA requirements. To the extent these Practices or guidelines should conflict with OSHA or other applicable laws or regulations, such laws or regulations must be followed. Consult an appropriate professional before applying or acting on any material contained in or suggested by the Practice.
This Practice is subject to revision at any time.
© Process Industry Practices (PIP), Construction Industry Institute, The University of Texas at Austin, 3925 West Braker Lane (R4500), Austin, Texas 78759. PIP member companies and subscribers may copy this Practice for their internal use. Changes, overlays, addenda, or modifications of any kind are not permitted within any PIP Practice without the express written authorization of PIP.
PRINTING HISTORY
May 1999 June 2007
Issued as PCECR001 Complete Revision
Not printed with State funds
COMPLETE REVISION June 2007
Process Industry Practices Process Control
PIP PCECV002 Pressure Regulators Selection Guidelines Table of Contents 1. Introduction.................................2 1.1 Purpose............................................ 2 1.2 Scope ...............................................2
2. References ..................................2 Process Industry Practices ...................... 2
3. Ap plic ati ons ................................ 2 4. Sizing and Selection...................3 5. Noise Reduction ......................... 3
Process Industry Practices
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PIP PCECV002 Pressure Regulators Selection Guidelines
1.
COMPLETE REVISION June 2007
Introduction 1.1
Purpose This Practice provides guidelines for the application and selection of pressure regulators.
1.2
Scope This Practice describes the recommended guidelines for proper application, sizing, selection, and noise reduction of pressure regulators.
2.
References Applicable parts of the following Practices shall be considered an integral part of this Practice. The edition in effect on the date of contract award shall be used, except as otherwise noted. Short titles will be used herein where appropriate.
Process Indus try Practices (PIP) – PIP PCCCV002 - Pressure Regulators Selection Criteria – PIP PCECV001 - Guidelines for the Application of Control Valves
3.
Applications 3.1
Typically pressure regulators are used to regulate utilities such as air, nitrogen, fuel gas, blanket gas, steam, water, lube oil, and fuel oil.
3.2
Regulators can be used to control downstream pressure, upstream pressure, or differential pressure.
3.3
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3.2.1
Regulators that control upstream pressure are typically referred to as backpressure regulators.
3.2.2
Regulators in differential pressure service monitor both upstream and downstream pressure and hold a constant pressure differential. The differential pressure can be induced across process equipment ( e.g., a heat exchanger), across a separate restrictive orifice, or across the regulator itself.
Pressure regulators can be used for the following reasons: 3.3.1
Regulators are generally less expensive than a control valve and controller to purchase and install.
3.3.2
Remote monitoring is not required.
3.3.3
Frequent setpoint adjustment is not required.
3.3.4
No control medium is available ( i.e., instrument air, nitrogen, electricity, etc.).
3.3.5
Tight shutoff is not required.
3.3.6
The processes can tolerate some offset (droop) between the manipulated variable and desired setpoint.
Process Industry Practices
COMPLETE REVISION
PIP PCECV002 Pressure Regulators Selection Guidelines
June 2007
4.
5.
3.4
There are two types of pressure regulators; self-contained and pilot-operated. Selfcontained regulators are mounted in-line and do not have any external connections to the process. A pilot-operated regulator is mounted in-line and has a sensing line connected to the process.
3.5
Pilot-operated regulators can offer more accurate regulation and higher capacity than self-contained types but are more expensive. 3.5.1
Typically the pilot is close coupled with the regulator, but can be located remotely from the main valve to mitigate the effects of shock and vibration.
3.5.2
The small passages of the pilot are subject to plugging, so pilot-operated regulators should be specified for clean services only.
3.6
Regulators should not be used for toxic service because a diaphragm rupture or internal pressure relief could allow the process to vent to the environment
3.7
Regulators are not recommended for cavitating or flashing liquids (for a discussion of cavitation and flashing, see PIP PCECV001.)
Sizing and Selecti on 4.1
The manufacturer’s formulas and tables should be used to size and select pressure regulators. This information is needed to size the regulator, inlet pressure range, outlet pressure and flow rates.
4.2
The regulator should be sized to be 50-60% open at normal flow.
4.3
Generally the droop should be less than 10% at the point of maximum flow. Droop is the deviation of the controlled pressure from the set pressure which occurs because regulators are proportional-only controllers.
Noise Reductio n 5.1
Noise produced by regulators should be considered and should stay within established noise exposure limits (typically less than 85 db).
5.2
Generally, a control valve with noise-abatement trim would be a better choice if noise is a concern (for further discussion, see PIP PCECV001.).
5.3
The aerodynamic noise can be reduced by limiting the flow velocity below the sonic level. This can be accomplished using multistage regulators or regulators in series to keep the pressure ratio less than 2:1 ( i.e., less than the critical pressure ratio) across each stage.
Process Industry Practices
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