Safety Valves & Pressure Relief Valves

The last line of defence against catastrophic overpressure. PED-certified safety and relief valves for steam, gas, compressed air and liquid service in boilers, pressure vessels and process pipelines.

The role of safety valves in industrial plants

Safety and relief valves are automatic protection devices — they require no external power, control signal or operator intervention. They are the final layer of overpressure protection for pressure vessels, boilers, steam generators, pipelines, heat exchangers and process reactors. If all other control and protective systems fail and pressure in the protected equipment rises above the set pressure, the safety valve opens automatically to discharge fluid and reduce pressure to a safe level.

In Italy and throughout the EU, the installation of appropriate safety valves on pressure equipment is a legal requirement under the Pressure Equipment Directive PED 2014/68/EU, the successor to the ISPESL regulations. Equipment covered includes: steam boilers and hot-water generators, pressure vessels (autoclaves, compressor tanks, reactors), steam and compressed air distribution networks, hydraulic and pneumatic systems above 0.5 bar, and cryogenic and LPG storage.

Roffia carries a comprehensive range of spring-loaded safety valves (threaded DN 15–50 and flanged DN 25–200) and pilot-operated valves, all PED-certified with CE marking and full documentation. We also offer sizing and selection as a free technical service.

Safety valves and pressure relief valves — Roffia srl

Spring-loaded safety valves

  • Direct-acting, no external power
  • Fluids: steam, gas, air, liquid
  • Set pressure range: 0.5 to 250 bar
  • Connections: threaded BSP/NPT, flanged EN/ANSI
  • Body: cast iron, SS, bronze, carbon steel
  • Certified to EN ISO 4126-1, PED CE marked

Pilot-operated safety valves

  • Tight shut-off up to 98% of set pressure
  • Large capacities in compact body
  • Very low simmer / leakage before set point
  • For steam, gas and vapour service
  • Used on large boilers and steam headers
  • Modulating or snap-action pilot

Thermal and hydraulic relief

  • Thermal relief: liquid expansion in blocked pipe sections, closed loop circuits
  • Hydraulic relief: pump discharge protection, hydraulic power units
  • Body: brass, SS, carbon steel
  • Very compact, direct-acting
  • Set pressures from 4 to 400 bar

Applications by sector

Steam boilers and generators

Every steam boiler in Italy must be equipped with at least one certified safety valve sized to relieve the full boiler output at set pressure. Roffia supplies spring-loaded safety valves from DN 15 (threaded, for small package boilers) to DN 200 (flanged, for large industrial steam generators), all CE-marked to PED Category III or IV as required by INAIL/ISPESL registration. Set pressure range: 0.5 to 40 bar saturated steam.

Compressed air systems

Compressed air receivers, ring mains and downstream equipment require relief valves set at or below the MAWP of the weakest component in the system. Typical set pressures for industrial compressed air are 7–16 bar(g). Roffia stocks compact, direct-acting safety valves in bronze and stainless steel for this service, with certified capacity data for air and nitrogen.

Process vessels and reactors

Chemical reactors, autoclaves, distillation columns and pressure vessels in the chemical and pharmaceutical industry require carefully engineered safety valve installations, including proper inlet and outlet piping, rupture discs upstream and tail-pipe calculations to limit back pressure. Roffia supplies full documentation packages for these applications including sizing calculations, certificates and MTRs.

Hot water and thermal circuits

Expansion vessels and boilers generating hot water above 110 °C (pressure hot water) must be protected by safety valves capable of preventing dangerous flashing. Thermal relief valves are also installed on every section of pipework that can be isolated while hot, preventing catastrophic failure of pipe flanges and fittings due to liquid expansion (thermal relief). See also: our page on steam trap maintenance.

Frequently asked questions

What is the difference between a safety valve and a relief valve?
Although the terms are often used interchangeably informally, there is a precise technical distinction. A safety valve opens rapidly (pops open) to its full flow capacity when the set pressure is reached — it is designed for compressible fluids (steam, gas, air) where full instantaneous flow is needed to rapidly reduce pressure. Once pressure drops to the reseating pressure (blowdown), the valve closes sharply. A relief valve opens proportionally as pressure rises above set point — it is designed for liquid service (water, oil, hydraulic systems) where a proportional, modulating release is acceptable and desirable to avoid pressure spikes. Safety relief valves are designed to handle both compressible and incompressible fluids. In EU and Italian industrial practice, all three types must meet the requirements of PED 2014/68/EU and the relevant standards (EN ISO 4126 series).
What does PED certification mean for safety valves, and is it mandatory?
The Pressure Equipment Directive (PED 2014/68/EU) is the European regulation governing the design, manufacture and conformity assessment of pressure equipment and assemblies. Safety valves protecting pressure vessels and piping systems are classified as safety accessories under the PED and must carry the CE marking in categories I through IV depending on the hazard level of the fluid and the equipment parameters. For Category III and IV equipment (highest risk), the valve manufacturer must have their design assessed by a Notified Body (NB). For steam boilers, pressure vessels, autoclaves and chemical reactors operating in Italy and the EU, CE-marked, PED-certified safety valves are mandatory — using non-certified valves invalidates the equipment certification and creates serious legal and insurance liability. Roffia stocks PED-certified safety valves with full documentation, material test reports (MTRs) and, where required, NB certificates.
How do you correctly size a safety valve?
Safety valve sizing is governed by EN ISO 4126-1 (for steam) and EN ISO 4126-3/-4 (for gases and liquids). The key steps are: (1) Determine the relieving scenario — what causes the overpressure (blocked outlet, fire case, external heat source, etc.). (2) Calculate the required relieving rate (mass or volumetric flow) for the worst-case scenario. (3) Select the set pressure — must be at or below the Maximum Allowable Working Pressure (MAWP) of the protected equipment. The valve must achieve full opening (overpressure) at no more than 10% above set pressure. (4) Determine the back pressure — if the valve discharges to atmosphere, back pressure is zero; if it discharges to a header, back pressure must be factored. (5) Calculate the required effective discharge area (A, in mm²) using the ISO formula for the specific fluid state (steam, gas, or liquid). (6) Select the nearest standard orifice size (orifice lettering system: G, H, J, K, L, M, N, P, Q, R, T). Roffia's technical team performs safety valve sizing as a free service — provide us with your equipment data sheet and we will select the correct valve.
What is a pilot-operated safety valve and when is it used?
A pilot-operated safety valve (POSV) uses the system pressure itself to keep the main valve tightly closed below set pressure, rather than relying entirely on a spring. A small pilot valve (a simple spring-loaded valve) senses the system pressure. Below set pressure, the pilot directs system pressure onto the top of the main valve's piston, adding to the closing force and ensuring a very tight seat seal even when the working pressure is close to the set pressure (high back-pressure ratio). When pressure reaches the set point, the pilot opens, venting the top of the main piston to atmosphere — the unbalanced pressure from below snaps the main valve open. POSVs offer several advantages over conventional spring-loaded valves: very low simmer (no premature leakage at 98–99% of set pressure), full-lift capability at very low overpressure (1–3% instead of 10%), and suitability for very large orifice sizes and high pressures. They are used on large steam boilers, high-pressure steam headers, long pipelines and applications where conventional spring-loaded valves would leak excessively close to set pressure.

Safety valve sizing and supply

Provide your equipment data (design pressure, MAWP, fluid, temperature, relieving capacity required) and we perform the sizing calculation at no cost. We then supply the correct PED-certified valve with full documentation.

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