What are the main features of a pneumatic pressure relief valve?

A pressure relief valve for pneumatic systems protects compressed air and gas lines, automatically releasing excess pressure when it exceeds the set point.

It acts passively (spring–seal), discharging proportionally to stabilize the line, and closes on its own when the pressure normalizes. It prevents damage, reduces downtime, and improves the safety of people and facilities.

It is a protection device that limits pressure in compressors, manifolds, and pneumatic lines. When the system exceeds the setpoint (calibration), the valve opens and evacuates the fluid in a controlled manner, protecting equipment, extending its lifespan, and preserving operational safety.

This type of valve should not be confused with a safety valve (PSV) that opens instantaneously. Excess relief valves (PRV) open progressively and are designed to keep the system within safe margins.

Table of contents

1. Adjustment spring (calibration): regulates the opening pressure using a screw/nut.
2. Sensitive element: diaphragm or piston (depending on the model) that transmits the pressure to the moving assembly.
3. Seal and seat: metallic or soft seal to ensure tightness and stable modulation.
4. Stem and guides: center the movement and reduce wear.
5. Discharge port / silencer: evacuates the excess; consider backpressure and noise control.
6. Body and trim: nodular iron, carbon steel, or AISI 316L stainless steel (recommended for demanding gases/environments).
7. Seals and elastomers: NBR, EPDM, FKM and PTFE depending on temperature/chemical compatibility.

1. Closed in normal service. The spring keeps the seal sealing against the seat.
2. Opening due to overpressure. If the line pressure exceeds the calibration, it overcomes the force of the spring and the valve opens.
3. Modulating discharge. Evacuates the excess to recover the safe range without shocks or oscillations.
4. Automatic closing. When the pressure drops, the spring returns the seal to the seat and the valve closes.

Some of our most requested valves:

Related articles:

Pressure relief valve S3

1. Typical adjustment ranges (depending on the model):
   • S1: 0.1–15 barg · S2: 0.02–10 barg · S3: up to ~20 barg
   • PRV53: 0.5–10 barg (max. inlet 10 bar) · PRV55: 0.01–8 barg (max. inlet 25 bar).
2. Repeatability and controlled hysteresis: consistent opening/closing at the defined value.
3. Service temperature: from standard conditions up to 210–220 °C in specific models (depending on materials).
4. Connections: BSP/NPT thread and/or DIN/ANSI flanges for easy integration.
5. Regulations: PED versions and ATEX configurations upon request when the installation requires it.

• Fluid and cleanliness: dry/filtered air; oil/condensates condition materials and elastomers.
• Setpoint and accumulation: define the trigger pressure and the % of permissible accumulation without compromising equipment.
• Required flow rate (Kv/Cv): the valve must evacuate more flow than the system can generate in the overpressure transient.
• Backpressure/discharge: size the vent line and silencers to avoid backpressures that alter the calibration.
• Environment: ambient temperature, vibrations, and ATEX classification if applicable.
• Maintenance: prioritize designs with top-entry access, original spare parts kits, and ease of adjustment verification.

• Pre-cleaning + upstream strainer. Prevents premature wear on the seat/seal due to particles.
  
• Orientation and flow direction. Respect the arrow on the body; some models (e.g., S1) perform better in a horizontal line; PRV53/PRV55 support any position.
• Start-up. Check calibration/tightness and record values.
• Periodic inspection. Quarterly visual inspection and annual review of seal, seat, gaskets, diaphragm/piston, and spring.
• Original spare parts. Maintain performance, reduce downtime, and preserve warranties.

The final selection depends on the fluid, the pressure/temperature, and the relief flow rate required by the installation. Our team can calculate the appropriate size and setpoint.

A well-sized, installed, and maintained pneumatic relief valve prevents overpressures, protects critical equipment, and increases operational safety, reducing downtime and the total cost of ownership.

If you need to define the calibration, discharge flow rate, permissible backpressure, and appropriate materials/elastomers (chemical compatibility, temperature, ATEX/PED), our technical team can assist you throughout the process.

We can help you with:

• Calculation and model selection (set point, Kv/Cv, vent line).
• Installation audit and on-site verification of real conditions.
• Start-up and calibration tests , plus preventive maintenance plan.
  Supply of original spare parts kits and complete technical documentation.

For more information or personalized advice, you can contact us by calling 93 372 08 88, sending an email to valfonta@valfonta.com, or completing the form available on our website.