Excess pressure valve · Diaphragm actuator
PRV55 excess pressure valve
From 10 mbar
Self-regulating, direct-acting excess pressure valve with a diaphragm actuator and body and internals in 316L stainless steel. It discharges the excess when the upstream pressure exceeds the set pressure, adjustable from 0.01 barg, on gases, liquids, and steam up to 150 °C.
- SizesDN15 to DN25
- Pressure ratingPN25
- Set pressure range0.01 to 8 barg depending on actuator
- Inlet pressureup to 16 barg
- Temperature−10 to 150 °C with Viton gaskets
- Kv2 to 3.5 m³/h
Questions about set pressure or sizing? Call 933 720 888 or email valfonta@valfonta.com.
- In-house design and manufacturing in Badalona
- ATEX II 2 GD marking for zones 1 and 21
- All valves are supplied degreased
- Genuine spare parts available
What the PRV55 is used for
The PRV55 is a self-regulating excess pressure valve: it needs no auxiliary power. The upstream pressure reaches a diaphragm, and when it exceeds the set value, the valve opens proportionally and relieves the excess.
The diaphragm allows set pressures from 10 mbar; the rest of the range starts at 0.5 barg. It is especially designed for gases, although it also works with liquids and steam. More detail in our article on excess pressure valves.
- Low-pressure gasesCompressed air, nitrogen, and inert gases with set pressures from 0.01 barg.
- Steam plantsSteam networks and heat exchangers, with condensate pot.
- Chemical laboratoriesStable pressure in gas and liquid circuits.
- Fuel oil and sprinklersGroup 1 and 2 liquids, such as fuel oil or water.
- Mining slurry linesRelief for abrasive concentrate and tailings pipelines: pressure relief in mining slurry lines.
PRV55 technical specifications
| Type | Self-regulating, direct-acting, piston-balanced excess pressure valve with diaphragm actuator |
|---|---|
| Sizes | DN15 (½″), DN20 (¾″), and DN25 (1″) |
| Connections | BSP or NPT thread · EN flanges · ANSI CL150 flanges · Clamp on request |
| Pressure rating | PN25 |
| Maximum inlet pressure | 16 barg |
| Set pressure range | 0.01 to 8 barg, depending on actuator size and spring |
| Kv coefficient | 2 m³/h (DN15) · 2.5 m³/h (DN20) · 3.5 m³/h (DN25). Special Kv on request |
| Temperature | −10 to +150 °C (with Viton gaskets) |
| Fluids | Group 1 and 2 liquids and gases: steam, compressed air, fuel oil, water, nitrogen, inert gases |
| Materials | Body and internals in AISI 316L stainless steel. EPDM or EPDM+PTFE diaphragm. Steel sheet actuator with epoxy paint |
| Pressure sensing point | Internal or external. External required with steam and with liquids above 125 °C |
| Mounting position | Horizontal pipe. Actuator facing down with any fluid and always with steam; facing up only with gases and liquids up to 80 °C |
| Pressure Equipment Directive | PED 2014/68/EU, Article 4.3: CE marking not required (Group 1 and 2 fluids) |
| ATEX | II 2 GD c IIC Tx / c IIIC TxºC · certificate LOM 14.034 U |
| On request | RG10 bronze body · stainless steel actuator · special gaskets · special Kv |
Dimensions and weight
| ½″ threaded | ¾″ threaded | 1″ threaded | DN15 EN | DN20 EN | DN25 EN | DN15 ANSI | DN20 ANSI | DN25 ANSI | |
|---|---|---|---|---|---|---|---|---|---|
| Kv (m³/h) | 2 | 2,5 | 3,5 | 2 | 2,5 | 3,5 | 2 | 2,5 | 3,5 |
| Length A / AA | 108 | 108 | 108 | 130 | 150 | 160 | 184 | 184 | 184 |
| Height H1 | 258 | 258 | 258 | 258 | 258 | 258 | 258 | 258 | 258 |
| Height H2 | 320 | 320 | 320 | 320 | 320 | 320 | 320 | 320 | 320 |
| Flange Ø D1 | – | – | – | 95 | 105 | 115 | 89 | 98 | 108 |
| Weight (kg) | 2,5 | 2,5 | 2,5 | 5 | 5 | 5 | 5 | 5 | 5 |
Dimensions in millimeters. The actuator diameter (D) depends on the set pressure range. The dimensioned drawings are in the PDF datasheet.
Set pressure range by actuator
| Actuator Ø D (mm) | Set pressure range |
|---|---|
| 295 | 10 – 200 mbar |
| 230 | 100 – 1,000 mbar |
| 230 | 0.5 – 2 barg |
| 175 | 1 – 4 barg |
| 175 | 3 – 8 barg |
| 350 | On request |
Exploded view and materials (33 parts)
| No. | Part | Material |
|---|---|---|
| 1 | Body | Stainless steel AISI 316L |
| 2 | Sealing screw | Stainless steel 316L |
| 3 | Seat | Graphite-filled PTFE |
| 4 | Gasket | PTFE |
| 5 | Seat | Stainless steel 316L |
| 6 | Gasket | PTFE |
| 7 | Valve cover | Steel 1.1141 |
| 8 | Gasket | PTFE |
| 9 | Upper actuator | Steel sheet 1.0035 with epoxy paint |
| 10 | Lower actuator | Steel sheet 1.0035 with epoxy paint |
| 11 | Stem | Stainless steel 316L |
| 12 | Bushing guide | Stainless steel 316L |
| 13 | Stem guide | Stainless steel 316L |
| 14 | Allen screw | Stainless steel A2-70 |
| 15 | Gasket | Graphite-filled PTFE |
| 17 | Seat holder | Stainless steel 316L |
| 18 | Seat guide | Stainless steel 316L |
| 21 | Bottom cover | Stainless steel 316L |
| 22 | Gasket | Viton |
| 23 | Nut | Stainless steel A2 |
| 24 | M8 screw | Stainless steel A2 |
| 25 | KM-6 nut | Steel |
| 26 | O-ring | NBR / Viton |
| 27 | Spring support | Galvanized steel sheet 1.0035 |
| 28 | Adjusting spring | Steel 52SiCrNi5 |
| 29 | Spring cap | Steel 1.1191 with epoxy paint |
| 30 | Adjusting screw | Galvanized steel 1.1191 |
| 31 | Adjusting nut | Galvanized steel 1.1191 |
| 32 | Spring guide | Galvanized steel 1.1191 |
| 33 | Screw | Stainless steel A2-70 |
| 34 | Nut | Stainless steel A2-70 |
| 35 | Lower diaphragm support | Stainless steel 316L |
| 36 | Diaphragm | EPDM / EPDM+PTFE |
Recommended spare parts
| Reference | Description | Parts |
|---|---|---|
| PRV55.SP1 | Seat and balancing system kit | 2, 3, 11, 12, 15, and 17 |
| PRV55.SP2 | Gaskets | 6 and 22 |
| PRV55.SP3 | Springs | See the manual |
| PRV55.SP4 | EPDM diaphragm and O-rings | 26 and 36 |
| PRV55.SP4 | EPDM diaphragm, PTFE diaphragm, and O-rings | 26, 36, and 36b |
How the PRV55 works
The PRV55 works on a balance between the adjusting spring and the inlet pressure acting on the diaphragm, with no air or electricity.
- Closed without pressure. As long as the inlet pressure has not reached the set pressure, the adjusting spring (28) keeps the valve closed. The piston balances the pressure acting on the seat.
- Sensing at the diaphragm. The upstream pressure reaches the diaphragm through the external control line or, optionally, through internal sensing.
- Proportional opening. When that pressure exceeds the set point, the valve opens in proportion to the pressure rise and discharges the excess. If it drops, the spring closes the valve again.
PRV55 installation
The typical installation of the PRV55 is on a branch of the main line, discharging to recirculation.
- Pump or equipment that generates the pressure
- Inlet pressure gauge
- PRV55 excess pressure valve, with isolation valve and strainer upstream
- Discharge to recirculation or tank
- Point of use or protected equipment
Installation and start-up
- Clean the pipe before installing the valve: any particle can damage the seat.
- Install a strainer upstream to protect the seat and the diaphragm, with room to clean it.
- Install the valve in a horizontal pipe, following the arrow on the body. The actuator faces down (always with steam) or, with gases and liquids up to 80 °C, up; never horizontal.
- Connect the external control line with steam and with liquids above 125 °C (also recommended below that; not needed with gases): 10 × 1 mm tubing to the main pipe, at least 1 m from the valve. If the pressure fluctuates, add a needle valve.
- Install the condensate pot with steam and with liquids above 120 °C, at the highest point of the pipe, and fill it with water until it overflows before start-up.
- Support the pipe, not the valve: supports close to the flanges, never on the valve or the actuator. With steam, slope the pipe to drain the condensate.
- Start up slowly: open the isolation valves gradually to avoid water hammer.
- Adjust the set pressure with the adjusting screw. Compressing the spring raises the set pressure; releasing it lowers it. Check the value on the inlet pressure gauge.
The valve must be installed by qualified personnel and must never exceed the operating temperature for which it was sized. In ATEX zones, the valve must be equipotentially bonded to the installation. See also our guide on relief valve set pressure.
PRV55 technical documentation
PRV55 datasheet (in English)PDF · 5 pages · features, exploded view, installation, and dimensions
Do you need an order certificate or the ATEX documentation? See our quality certificates or request it from our technical team.
PRV55 vs. other excess pressure valves
The range covers DN15 to DN150 and set pressures from 0.01 to 20 barg. Check whether the PRV55 is the right model or whether another one suits you better.
| Model | DN | PN | Set pressure (barg) | Max. T (°C) | Steam | Body |
|---|---|---|---|---|---|---|
| PRV53 | 15 – 25 | 25 | 0,5 – 15 | 150 | No | CF3M stainless |
| PRV54 | 15 – 25 | 25 | 0,5 – 12 | 210 | Yes | CF3M stainless |
| PRV55 | 15 – 25 | 25 | 0,01 – 8 | 150 | Yes | CF3M stainless |
| S1 | 15 – 150 | 40 | 0,5 – 15 | 220 | Yes | WCB steel or CF3M stainless |
| S2 | 15 – 100 | 40 | 0,02 – 10 | 180 | Yes | WCB steel or CF3M stainless |
| S3 | 15 – 150 | 40 | 0,5 – 20 | 220 | Yes | WCB steel or CF3M stainless |
| S4 | 15 – 100 | 40 | 0,5 – 20 | 220 | Yes | WCB steel or CF3M stainless |
Data from the Valfonta excess pressure valve summary catalog (2025), except the S2 set pressure, which comes from its datasheet. All models accept liquids, oil, air, and non-flammable gases. If you are unsure whether you need an excess pressure valve or a safety valve, read the difference between a safety valve and a relief valve.
Frequently asked questions about the PRV55
What set pressure can be adjusted with the PRV55?
From 0.01 to 8 barg, depending on actuator size and spring (see the specifications table). The maximum inlet pressure is 16 barg.
Can it be used with steam?
Yes, up to 150 °C. With steam, it is installed in a horizontal pipe with the actuator facing down, with an external control line and a condensate pot filled with water, which protects the diaphragm from heat.
What is the difference between the PRV55 and the PRV54?
Both are DN15 to DN25, PN25, and suitable for steam. The PRV55 has a diaphragm actuator and set pressures from 0.01 to 8 barg, up to 150 °C. The PRV54 is bellows-balanced, has set pressures from 0.5 to 12 barg, and handles up to 210 °C.
What maintenance does it need?
It requires no periodic maintenance, but the wear parts should be checked according to the service conditions. In ATEX zones, the manual specifies replacing the gaskets every 25,000 hours or whenever inspections recommend it. This can be done with the body installed, depressurized, and isolated.
Can it be installed in an ATEX zone?
Yes. The PRV55 carries ATEX II 2 GD marking (certificate LOM 14.034 U) and can be used in zones 1 and 2 (flammable gases, vapors, and liquids) and 21 and 22 (combustible dust), according to the temperature class that corresponds to the fluid temperature. See our article on ATEX valves.
Other excess pressure valve models
PRV54 excess pressure valveWith bellows: set pressure from 0.5 to 12 barg and steam up to 210 °C.- PRV53 excess pressure valve316L stainless, set pressure up to 15 barg and up to 150 °C, no steam.
S1 excess pressure valveFrom DN15 to DN150 and PN40, for steam up to 220 °C.
S2 excess pressure valveFrom DN15 to DN100, PN40, and set pressure from 0.02 barg.
S3 pressure relief valveFrom DN15 to DN150, PN40, set pressure up to 20 barg and 220 °C.
Request a quote for the PRV55
Give us your installation details and we will recommend the size, actuator, and spring range for your set pressure, and the diaphragm and gaskets suited to the fluid.
- Fluid and operating temperature
- Set pressure and normal operating pressure
- Flow rate the valve must discharge
- Connection type (threaded or flanged)
You can also call 933 720 888.
