When specifying a pressure regulating valve, pipe size and pressure range will get you to a shortlist. Getting to the right valve requires working through flow profile, media compatibility, operating conditions, and compliance requirements. Errors at the specification stage tend to surface as process instability, premature failure, or compliance issues that are considerably more expensive to resolve than they would have been to avoid.
This guide covers the key selection criteria in the order they should be addressed.
What Is a Pressure Regulating Valve?
A pressure regulating valve (PRV), also called a pressure reducing valve, maintains a steady downstream outlet pressure regardless of fluctuations in upstream supply pressure or flow demand. A spring acts against a diaphragm or piston to open and close the valve, keeping outlet pressure at a set value. There is no external power supply, no control signal, and no electronics involved.
That mechanical simplicity translates into reliable, low-maintenance service across a wide range of duties and operating pressures. Browse the full range of pressure reducing valves from Measure Monitor Control, from mbar gas regulation through to 400 bar.
Step 1: Define Your Pressure Requirements
Inlet pressure is the supply pressure upstream of the valve. It may be stable or variable depending on the source. A supply fed directly from a vessel or cylinder will see inlet pressure fall as contents are consumed. These variations matter because of a characteristic called Supply Pressure Effect (SPE): as inlet pressure drops, outlet pressure tends to creep up slightly, due to the internal force balance within the valve. Where outlet pressure must be held within tight limits, the standard approaches are a two-stage regulator arrangement or a pressure relief valve installed downstream.
Outlet pressure is determined by the range spring. Lighter springs cover lower pressure ranges and allow finer adjustment; heavier springs handle higher outlet pressures. It is important to select a valve whose outlet range sits close to your target setpoint. A spring significantly oversized for the duty produces poor sensitivity and coarse control.
For high-pressure duties, Measure Monitor Control stock regulators to 400 bar for air, gas, and liquids and 50 bar regulators from 1/8" to 4". For instrument and analyser supply requiring very low pressures, mbar regulators for gases are available from 1/4" to 2".
Step 2: Understand Your Flow Requirements
An undersized valve creates excessive pressure drop at peak demand. An oversized valve can hunt or chatter at low flow rates, accelerating wear on internal components and destabilising system pressure. Both outcomes are avoidable with accurate flow data at the specification stage.
Establish the full operating range: minimum, normal, and peak flow. Check the Cv (flow coefficient) values in the manufacturer's data sheets against the actual pressure differential across the valve at each condition. Where flow demand is highly variable, turndown ratio requires particular attention.
For high-flow duties on large bore pipework, a pilot-operated design gives better capacity and tighter regulation than a direct-acting type. The P02 pilot-operated valve covers 2" to 12" and is suited to demanding flow duties.
Step 3: Direct-Acting or Pilot-Operated?
Direct-acting valves apply outlet pressure directly against the control spring and diaphragm. Compact, cost-effective, and straightforward to maintain, they are well suited to the majority of duties where flow demand is moderate and relatively stable. The P08 direct-acting valve handles liquids and gases from 1/2" to 6". The P15 series covers low-pressure duties from 0.2 bar.
Pilot-operated valves use a separate pilot valve to sense outlet pressure and control a larger main valve. The result is tighter regulation across a wider flow range, making them the preferred choice where demand is highly variable, pipe sizes are large, or consistent outlet pressure is critical to downstream equipment or process performance. The P02UL is UL-approved for water duties and available from 3" to 8".
Step 4: Consider the Media
The fluid or gas passing through the valve determines which body materials, seal compounds, and diaphragm materials are appropriate. Every wetted component needs to be checked, not just the valve body.
Brass and bronze are suitable for many water and air applications. Corrosive media, aggressive chemicals, and high-purity duties generally require 316 stainless steel throughout. Incompatible elastomers degrade in service, contaminate the downstream system, and cause premature valve failure. Always verify seal material compatibility against the process fluid, including any cleaning agents if the line undergoes periodic washdown or sterilisation.
Potable water applications in the UK require WRAS (Water Regulations Advisory Scheme) approval. This is a regulatory requirement. The P48 WRAS-approved direct-acting valve is designed for this duty in sizes 1/2" to 6".
Steam duties require materials rated for the operating temperature across every wetted component, together with attention to condensate management on the downstream side.
Step 5: Temperature and Connections
Temperature affects both material suitability and regulation accuracy. Elevated temperatures reduce the effective life of elastomeric seals; sustained operation above rated limits is a common cause of premature PRV failure. Check the valve's rated temperature limits against the full operating range, including transient peaks during start-up or process upsets.
End connections must match the pipe size and piping standard in use. Threaded BSP or NPT connections are standard for smaller bore pipework up to around 2". Flanged connections, available in ANSI and PN-rated standards, are appropriate for larger bore pipework and higher pressure duties. Socket-weld and butt-weld connections are specified where leak integrity requirements are particularly stringent. For compact or instrument-scale installations, the P39 micro direct-acting valve handles liquids and gases from 1/2" to 2".
Step 6: Certifications and Compliance
Approval requirements should be confirmed at the specification stage, not identified during commissioning or inspection.
WRAS is a legal requirement for any valve in contact with drinking water in the UK. UL approval is required for fire suppression system components in many markets. CE / PED (Pressure Equipment Directive) applies to valves above certain pressure-volume thresholds in European markets. ATEX certification is required for equipment installed in hazardous areas where flammable atmospheres may be present.
Quick Selection Summary
| Factor | Key questions |
|---|---|
| Inlet pressure | Stable or variable? What is the maximum? |
| Outlet pressure | What setpoint is required, and how tight is the tolerance? |
| Flow | Minimum, normal, and peak flow rates? |
| Valve type | Direct-acting or pilot-operated? |
| Media | Liquid, gas, or steam? Corrosive or purity requirements? |
| Temperature | Full operating range including transient peaks? |
| Connection | Pipe size, BSP/NPT/flanged, piping standard? |
| Certifications | WRAS, UL, PED, ATEX? |
Specifying the Right Valve
Measure Monitor Control stock a comprehensive range of pressure reducing valves to cover the full spectrum of commercial and industrial duties. Browse the complete range of pressure reducing valves, or contact the team to discuss your specification requirements.