Pressure reducing valve · Low outlet pressure
PRV45 pressure reducing valve
Low pressure
Self-regulating, direct-acting reducing valve with diaphragm actuator, designed especially for gases at low outlet pressure: it regulates from 10 mbar to 8 barg. The body and internals are made of AISI 316L stainless steel, and it handles steam up to 150 °C.
- SizesDN15 to DN25
- Pressure ratingPN25
- Inlet pressureup to 16 barg
- Outlet pressure0.01 to 8 barg
- Temperature−10 to 150 °C with Viton gaskets
- Kv2 to 3.5 m³/h
Questions about 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
- Regulation from 10 mbar
- Internal pressure sensing as standard
What the PRV45 is used for
The PRV45 is the Valfonta pressure reducing valve for very low outlet pressures. It is direct-acting, with no auxiliary power: the outlet pressure acts on a diaphragm and opposes the adjusting spring. The actuator diameter is chosen according to the range: the larger it is, the lower the pressure it can regulate, down to 10 mbar.
It is designed mainly for low-pressure gases, but it also works with steam, water, fuel oil, and other Group 1 and 2 liquids and gases. It comes with internal pressure sensing as standard, so with liquids and gases it needs no control line. If you are unsure whether to choose a piston or a diaphragm reducing valve, see our piston vs. diaphragm comparison.
- Low-pressure gasesCompressed air, nitrogen, and inert gases with outlet pressures in millibars.
- SteamUp to 150 °C, with an external control line and, above 120 °C, a condensate pot.
- Chemical laboratoriesSupplying equipment with low, stable pressure.
- Sanitary plantsLines where 316L stainless steel is required.
- Sprinkler systemsStabilizing the supply pressure.
- LiquidsWater and fuel oil, from −10 to 150 °C.
PRV45 technical specifications
| Type | Self-regulating, direct-acting pressure reducing valve with diaphragm actuator |
|---|---|
| Sizes | DN15 (½″), DN20 (¾″), and DN25 (1″) |
| Connections | BSP or NPT thread · EN PN16/25 flanges · ANSI CL150 flanges · Clamp, SW, or BW on request |
| Pressure rating | PN25 |
| Maximum inlet pressure | 16 barg |
| Outlet pressure range | 0.01 to 8 barg, depending on the actuator: 10 – 200 mbar · 0.1 – 2 barg · 1 – 8 barg |
| 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, nitrogen, fuel oil, water, inert gases |
| Materials | Body and internals in AISI 316L stainless steel. Super duplex body on request |
| Diaphragm | NBR, EPDM, or EPDM+PTFE |
| Gaskets and seat | NBR, EPDM, Viton, or graphite-filled PTFE |
| Pressure sensing point | Internal as standard; external optional, required for steam |
| Pressure Equipment Directive | PED 2014/68/EU, Article 4.3: CE marking not required |
| ATEX | II 2 GD c IIC Tx / c IIIC TxºC · certificate LOM 14.034 U |
Dimensions
| 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 |
| Flange Ø D1 | – | – | – | 95 | 105 | 115 | 89 | 98 | 108 |
Dimensions in millimeters. Height and weight depend on the selected actuator: see the PDF datasheet or ask our technical team.
Outlet range by actuator
| Actuator Ø D (mm) | Outlet pressure range |
|---|---|
| 175 | 1 – 8 bar |
| 230 | 0.1 – 2 bar |
| 295 | 10 – 200 mbar |
| 350 | Millibars, on request |
How the PRV45 works
The PRV45 regulates by balancing the forces between the adjusting spring and the outlet pressure acting on the actuator diaphragm. The large-diameter diaphragm allows it to work in millibars.
- Closing by inlet pressure. The fluid enters the valve and, due to the difference in areas, the inlet pressure tends to close it.
- Opening with the spring. When the adjusting spring (28) is compressed with the screw (30), the closing assembly opens the valve and allows regulation.
- Regulation. The outlet pressure reaches the diaphragm through the internal sensing port and opposes the spring. When it exceeds the set value, the valve closes.
- Zero flow. If the downstream valves are closed, the PRV45 absorbs the fluctuations and holds the outlet pressure at the set value.
PRV45 installation
This is the recommended layout, with a bypass so that maintenance can be carried out without interrupting service. With steam, the installation is different: we explain it below the steps. More detail in our guide on how to install a pressure reducing valve.
- Shutoff valves (1, 1a) and bypass valve (1b)
- Strainer
- Inlet pressure gauge
- PRV45 reducing valve
- Safety valve, 0.5–1 m from the reducing valve
- Outlet pressure gauge
Installation and start-up
- Clean the pipe before installing the valve: any impurity can impair the operation of the reducing valve.
- Install a strainer upstream to protect the seat and the diaphragm, and leave room to remove and clean it.
- Install the valve in a horizontal pipe and follow the arrow on the body. There is one mounting position that is not permitted, in which the valve would not perform well: check it in the manual.
- Support the pipe, not the valve: supports should be as close as possible to the reducing valve, but never attached to it or to the actuator.
- Leave 0.5 to 1 m of pipe up to the safety valve for better compensation.
- Start up slowly: open the shutoff valves gradually to avoid water hammer.
- Adjust the outlet pressure with an 8 mm Allen key on the adjusting screw (30). Compressing the spring raises the outlet pressure; releasing it lowers it.
Installation with steam and an external control line
With steam, or if requested with the order, the valve works with an external control line. Connect it to the main pipe in the reduced-pressure zone, at least 1 m from the valve outlet, using 10 × 1 mm tubing. If there is a manifold downstream of the reducing valve, connect the control line to the manifold, even if it is several meters away. If the valve tends to hunt, install a needle valve in the control line.
With steam, the actuator is mounted in the low position and, above 120 °C, a condensate pot is essential to protect the diaphragm from overheating. Also read our article on the pressure reducing valve for steam.
The valve must be installed by qualified personnel and must never exceed the operating pressure and temperature for which it was sized. In ATEX zones, the valve must be equipotentially bonded to the installation.
PRV45 technical documentation
Do you need an order certificate or the ATEX documentation? See our quality certificates or request it from our technical team.
PRV45 vs. other Valfonta reducing valves
The PRV45 is the reducing valve with the lowest minimum outlet pressure in the range. This table helps you check whether it is the right model or whether another one suits you better.
Temperature in parentheses: with EPDM or Viton gaskets. Data from the Valfonta general pressure reducing valve catalog (2025). More information on diaphragm reducing and stabilizing valves.
Frequently asked questions about the PRV45
What is the minimum outlet pressure of the PRV45?
10 mbar (0.01 barg). With the 295 mm actuator it regulates from 10 to 200 mbar; with the 230 mm one, from 0.1 to 2 bar; and with the 175 mm one, from 1 to 8 bar. For special millibar ranges, a 350 mm actuator is available on request.
Can it be used with steam?
Yes, up to 150 °C. With steam, the valve works with an external control line, the actuator is mounted in the low position, and above 120 °C a condensate pot must be installed to protect the diaphragm.
Does it need a control line?
With liquids and gases, no: it is supplied with internal pressure sensing. With steam, or if requested with the order, a 10 × 1 mm control line is connected to the reduced-pressure zone, at least 1 m from the valve outlet.
How do you adjust the outlet pressure?
With an 8 mm Allen key on the adjusting screw. Compressing the spring raises the outlet pressure; releasing it lowers it. We explain it in how to adjust a pressure reducing valve.
What maintenance does it need?
Very little. Check the gaskets, diaphragm, and wear parts according to the operating conditions; this can be done with the valve installed, depressurized, and isolated. Gasket, spring, and diaphragm spare parts kits are available: give us the serial number on the nameplate when ordering them.
Can it be installed in an ATEX zone?
Yes. The PRV45 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), within the temperature class corresponding to the fluid temperature.
Other pressure reducing valve models
PRV30 reducing valvePiston-type, DN15–25, and up to 25 bar inlet pressure.
PRV44 reducing valveBellows-balanced, steam up to 210 °C, and 25 bar inlet pressure.
PRV20 reducing valve316L stainless, from ¼″ to ¾″ and up to 40 bar inlet.
VD reducing valveFrom DN15 to DN100, up to 40 bar, and steam up to 200 °C.
M1 reducing valveUp to DN150 and 220 °C, for steam.
M2 diaphragm reducing valveDN15–100, outlet pressures from 0.02 barg, and up to 40 bar inlet pressure.
M2 bellows reducing valveVersion with sealing bellows.
Request a quote for the PRV45
Give us your installation details and we will recommend the right size, actuator, and gaskets.
- Fluid and operating temperature (state whether it is steam)
- Inlet pressure and desired outlet pressure, in mbar if very low
- Maximum and minimum flow rate
- Connection type (threaded or flanged)
You can also call 933 720 888.
