Selecting a Pressure Reducing Regulator: Key Parameters to Consider

A pressure reducing regulator is used in many industrial applications. In this article, we look at key parameters that must be established to help you make the appropriate selection of a pressure reducing regulator for your application.

Key parameters to consider when selecting a pressure reducing regulator include:

• Outlet pressure to be controlled
• Inlet pressure to the regulator
• Capacity required
• Process fluid
• Process fluid temperature
• Accuracy Required
• Pipe size required
• End connection style
• Required Materials
• Overpressure protection
• Shutoff capability required

Outlet Pressure to be controlled

When you know the outlet pressure, you will be able to establish the following:

• Casing pressure rating.
• Spring requirements.
• Body outlet rating.
• Orifice rating and size.
• Regulator size.

Inlet Pressure to the Regulator

The inlet pressure, both the minimum and maximum pressure, helps establish the:

• Orifice pressure rating and size.
• Pressure rating of the body inlet.
• Main spring (in a pilot-operated regulator).
• The regulator size.

If the inlet pressure fluctuates significantly, it can have an effect on the:

• Accuracy of the controlled pressure.
• Capacity of the regulator.
• Regulator style (two-stage or unloading).

Capacity Required

The required flow capacity affects the following decisions:

• Orifice size.
• Size of the regulator.
• Style of the regulator (direct-operated or pilot-operated).

Process Fluid

It is important to know the fluid properties like its chemical composition, molecular structure, corrosive properties, flammability, impurities, and so forth. These will guide you to select the correct materials that will come in contact with the process fluid.

Process Temperature

Fluid temperature can help determine the materials used in the pressure regulator. For instance, standard regulators use Steel and Nitrile or Neoprene elastomers that are good for a temperature range of -40° to 82°C. For temperatures that are above and below this range, other materials may be required like Stainless steel, Perfluoroelastomer (FFKM) or Ethylenepropylene (EPDM).

Accuracy Required

The accuracy requirement of the process establishes the acceptable droop (proportional band or offset). Regulators can be categorized into the following groups according to droop:

• Rough-cut group – this group generally involves several first-stage, rough-cut direct-operated regulators. This group typically has the highest amount of droop. But some designs are very accurate, specifically the low-pressure gas or air types, such as house service regulators, which include a relative large diaphragm casing,
• Closed-control group – this group normally involves pilot-operated regulators. They provide high accuracy over a large range of flows. Close control applications may include: a) Burner control where the fuel/air ratio is critical to burner efficiency and the gas pressure has a significant effect on the fuel/air ratio; b) Metering devices, such as gas meters, which require constant input pressures to ensure accurate measurement.

Pipe Size Required

In most applications, the outlet piping needs to be larger than the regulator for the regulator to reach full capacity. Knowing the pipe size beforehand makes your work easier in selecting regulator.

End Connection Style

Typical end connections for indicated regulator sizes are as follows:

• Flanged: 1-inch (DN 25) and larger.
• Pipe threads or socket weld: 2-inch (DN 50) and smaller.
• Butt weld: 1-inch (DN 25) and larger.

Required Materials

The regulator construction materials are determined by the application for instance the process fluid properties and other process requirements. Standard materials are:

• Steel
• Aluminium
• Cast iron or Ductile iron
• Bronze and Brass
• Stainless steel

Overpressure Protection

Overpressure protection is usually provided by an external relief valve, or in some regulators, by an internal relief valve. Internal relief is an option that you must select at the time of procuring this equipment. The capacity of internal relief is usually limited in comparison with a separate relief valve. Other techniques such as shutoff valves or monitor regulators can also be utilized.

Shutoff Capability

The required shutoff capability dictates the type of disk material:

• Standard disk materials are Nitrile (NBR) and Neoprene (CR); these materials provide the tightest shutoff.
• Other materials like Nylon (PA), Polytetrafluoroethylene (PTFE), Fluoroelastomer (FKM) and Ethylenepropylene (EPDM), are used when the standard material cannot be used.
• Metal disks are used in high temperatures and when elastomers are not compatible with the process fluid; but, tight shutoff is typically not achieved.

Related articles:

• Pressure Control Valve Operation
• Pressure Regulators: Function & Types
• Pneumatic System Components: Types & Functions
• Valve Positioners: Function & Types
• Directional Control Valves: Function & Principle of Operation
• The Parts and Functions of a Valve