Pressure reducing valve · Direct-acting diaphragm
M2 diaphragm pressure reducing valve
From 0.02 barg
Direct-acting, single-seat, diaphragm-compensated reducing valve that maintains the outlet pressure even when the inlet pressure fluctuates, with no auxiliary power. It regulates from 0.02 to 10 barg on gases, liquids, and steam, from DN15 to DN100.
- SizesDN15 to DN100
- Pressure ratingPN16 to PN40 · Class 150/300
- Inlet pressureup to 40 barg 25 barg from DN65
- Outlet pressure0.02 to 10 barg
- Temperature−40 to 180 °C depending on diaphragm
- Kv3.5 to 115 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
- Internal pressure sensing as standard
- Recommended spare parts marked in the exploded view
What the M2 is used for
The M2 is a direct-acting pressure reducing valve: the inlet pressure tends to close it, the adjusting spring opens it, and the diaphragm, reinforced with an intermediate fabric layer, compensates for the outlet pressure. The valve closes when the downstream pressure rises.
By changing the actuator and spring, it covers outlet pressures from 0.02 barg, the lowest in the range after the PRV45. It is supplied with internal pressure sensing, with no external tubing; with steam, it needs a control line and a condensate pot.
- Chemical laboratoriesStable pressure in laboratory installations.
- Water networksWater distribution and sanitary and industrial installations.
- Compressed airReducing line pressure to the working value.
- Fire protectionPressure stabilization in the network.
- Inert gasInert gas control and protection of tank contents against oxidation.
- SteamUp to 180 °C, with a control line and a water seal pot.
M2 technical specifications
| Type | Direct-acting, single-seat reducing valve, compensated by diaphragm and plunger |
|---|---|
| Sizes | DN15 to DN100 |
| Connections | EN PN16, PN25, or PN40 flanges · ANSI 150/300 flanges · BSP or NPT thread up to 2″ |
| Pressure rating | PN16 to PN40 · Class 150 or 300 |
| Maximum inlet pressure | 40 barg (DN15 to DN50) · 25 barg (DN65 to DN100) |
| Maximum differential pressure | 25 bar from DN15 to DN50; from DN65 to DN100, on request |
| Outlet pressure | 0.02 to 10 barg in several ranges, depending on size and actuator |
| Kv coefficient | 3.5 to 115 m³/h depending on DN. Reduced Kv on request |
| Temperature depending on diaphragm and gaskets | NBR: −20 to 80 °C · EPDM: −40 to 125 °C · FKM: up to 150 °C, on request · PTFE: −40 to 180 °C, with condensate pot |
| Fluids | Gases (air, nitrogen…), liquids, and steam |
| Materials | Body in WCB carbon steel (PN40), CF3M stainless steel (PN40), or RG10 bronze. Internals in AISI 316L stainless steel |
| Pressure sensing point | Internal as standard. External with 10 × 1 mm tubing on request, mandatory with steam |
| Mounting position | Horizontal pipe, actuator facing down (facing up only with gases and liquids up to 80 °C) |
| Pressure Equipment Directive | PED 2014/68/EU: the nameplate indicates whether CE marking is required |
| ATEX | II 2 GD c IIC Tx / c IIIC TxºC · certificate LOM 14.034 U |
| On request | Stainless steel actuator · protective cap for the adjusting stem · duplex or super duplex body · weld ends |
Dimensions and weight
| DN15 | DN20 | DN25 | DN32 | DN40 | DN50 | DN65 | DN80 | DN100 | |
|---|---|---|---|---|---|---|---|---|---|
| Kv (m³/h) | 3,5 | 5 | 9 | 13,5 | 22 | 32 | 57 | 82 | 115 |
| Length A (EN) | 130 | 150 | 160 | 180 | 200 | 230 | 290 | On request | 350 |
| Length A (ANSI 150) | – | – | 184 | – | 222 | 254 | 276 | 298,5 | 352,5 |
| Length A (ANSI 300) | – | – | 197 | – | 235 | 267 | 292 | 317,5 | – |
Dimensions in millimeters. Height and weight: contact us.
Outlet ranges and actuator diameter (mm)
| Range (barg) | DN15–20 | DN25–32 | DN40–50 | DN65 | DN80 | DN100 |
|---|---|---|---|---|---|---|
| 0,02 – 0,05 | 350 | 350 | – | – | – | – |
| 0,03 – 0,1 | 295 | 295 | 350 | 350 | – | – |
| 0,1 – 1 | 295 | 295 | 295 | 295 | 295 | 295 |
| 0,2 – 1,5 | – | – | – | – | 295 | 295 |
| 0,2 – 2 | 230 | 230 | 230 | 230 | – | – |
| 0,5 – 2 | – | – | – | – | – | 230 |
| 1 – 4 | – | – | – | – | 230 | 230 |
| 1 – 6 | 175 | 175 | 175 | 175 | – | – |
| 3 – 8 | – | – | – | – | 230 | 230 |
| 3 – 10 | 175 | 175 | 175 | 175 | – | – |
Exploded view and materials (34 parts)
| No. | Part | Material |
|---|---|---|
| 1 | Body | RG10, 1.0619 (GS-C25N), or 1.4408 (CF3M) |
| 2 | Seat | 1.4404 (316L) |
| 4 | Screws | Steel 8.8 or A2-70 |
| 5 | Gasket (spare part) | PTFE |
| 6 | Screws | A2-70 stainless |
| 7 | Nut | A2-70 stainless |
| 8 | Upper actuator | Steel sheet 1.0335, epoxy-coated, or 316L stainless |
| 9 | Spring support | Galvanized steel sheet 1.0035 |
| 10 | Adjusting spring | Steel 52SiCrNi5 (epoxy) |
| 11 | Adjusting nut | Galvanized steel 8.8 |
| 12 | Bearing (spare part) | PTFE+GR |
| 13 | Adjusting stem | 1.4404 (316L) |
| 14 | Lock washer | A2-70 stainless |
| 15 | O-ring (spare part) | NBR, FKM, or EPDM |
| 16 | Nut | A2-70 stainless |
| 17 | O-ring (spare part) | NBR, FKM, or EPDM |
| 18 | Stem | 1.4404 (316L) |
| 19 | Diaphragm (spare part) | NBR, EPDM, or FKM (PTFE optional) |
| 20 | M8 screw | A2-70 stainless |
| 21 | Lower actuator | Steel sheet 1.0335, epoxy-coated, or 316L stainless |
| 22 | Lower diaphragm plate | 1.4404 (316L) |
| 23 | Plunger guide | 1.4404 (316L) |
| 24 | Cover | Galvanized steel 1.1141 |
| 25 | Gasket (spare part) | Graphite |
| 26 | Compensation plunger (spare part) | NBR, FKM, EPDM, or PTFE+GR |
| 27 | Bushing guide | 1.4404 (316L) |
| 28 | Seat (spare part) | NBR, FKM, EPDM, or PTFE+GR |
| 29 | Seat screw | A2-70 stainless |
| 31 | Seat holder | 1.4404 (316L) |
| 51 | Bushing base | 1.4404 (316L) |
| 41 | Lower bushing stem (DN100) | 316L stainless |
| 42 | O-ring (DN100) (spare part) | NBR, FKM, or EPDM |
| 43 | Spring washer (DN100) | 316L stainless |
| 44 | Screws (DN100) | A2-70 stainless |
How the M2 works
Direct-acting: balance between the adjusting spring and the outlet pressure on the diaphragm.
- Closing by inlet pressure. The fluid pushes the stem–piston–plunger assembly and the valve closes.
- Opening by the spring. Turning the adjusting screw clockwise compresses the spring, which acts on the diaphragm and the seat and opens the passage.
- Regulation. The valve opens until the set downstream pressure is reached and closes when that pressure rises.
- Compensation. The plunger absorbs inlet pressure variations, and the diaphragm absorbs outlet pressure variations.
The M2 is not a safety valve: if the installation requires it, add overpressure protection. Piston or diaphragm: see our reducing valve comparison.
M2 installation
Recommended layout: bypass, shutoff valves, strainer, pressure gauges, and safety valve. On water and gases, internal sensing is sufficient; with steam, the M2 also needs a control line and a condensate pot (water seal pot). More detail in how to install a pressure reducing valve.
- Shutoff valves (1, 1a) and bypass valve (1b)
- Strainer
- Inlet pressure gauge
- M2 reducing valve
- Safety valve
- Outlet pressure gauge
Installation and start-up
- Clean the pipe and install a strainer upstream to protect the seat.
- Install the valve in a horizontal pipe, following the arrow on the body. If condensate is present, give the pipe a slight downward slope.
- Point the actuator downward, the standard position and the one required for steam. Upward only with gases and liquids up to 80 °C; never horizontal.
- Support the pipe close to the flanges, never the valve or the actuator.
- With steam, connect the control line (10 × 1 mm tubing) in the reduced-pressure zone, at least 1 m from the outlet, or to the manifold if there is one. If the valve oscillates, add a needle valve.
- With steam or above 125 °C, install the water seal pot at the highest point, connected from the side and with a slight slope toward the pipe. Fill it with water until it overflows.
- Connect the bypass beyond the pressure sensing point and open the shutoff valves slowly to avoid water hammer.
- Adjust the pressure on site, because the valve does not come with a fixed set point: compressing the spring (turning clockwise) raises the outlet pressure; releasing it lowers it.
Installation must be carried out by specialized personnel. In ATEX zones, ensure electrical conductivity between the valve and the installation. If the pressure is unstable, review the most common problems with reducing valves.
M2 technical documentation
Order and ATEX documentation: see our quality certificates.
M2 vs. other Valfonta reducing valves
Check whether the M2 is the right model or whether another reducing valve in the range suits you better.
Temperature in parentheses: with EPDM or Viton gaskets. Data from the Valfonta general reducing valve catalog (2025).
Frequently asked questions about the M2
What is the minimum outlet pressure of the M2?
0.02 barg, with the 350 mm actuator on DN15 to DN32. On DN40 to DN65 the minimum is 0.03 barg, and on DN80 and DN100, 0.1 barg.
Does it need an external control line?
Not on water and gases: it is supplied with internal pressure sensing. With steam, or if requested with the order, it has a 10 × 1 mm control line connected at least 1 m from the outlet.
Can it be used with steam?
Yes, up to 180 °C, with an EPDM+PTFE diaphragm, a control line, a water seal pot filled with water, and the actuator pointing downward. For higher temperatures, see the M1.
Does the M2 replace a safety valve?
No. A reducing valve is not a safety valve; if necessary, install overpressure protection at the outlet.
What spare parts does the manufacturer recommend?
The gaskets (5 and 25), the bearing (12), the O-rings (15, 17, and, on DN100, 42), the diaphragm (19), the compensation plunger (26), and the seat (28). Maintenance is carried out with the valve installed, depressurized, and isolated.
Can it be installed in an ATEX zone?
Yes. It carries ATEX II 2 GD marking (certificate LOM 14.034 U) for zones 1, 2, 21, and 22, depending on the temperature class of the fluid. More in ATEX valves.
Other pressure reducing valve models
M1 reducing valveUp to DN150 and steam at 220 °C.
M2F bellows reducing valveDN15–50 and steam up to 200 °C without a water seal pot.
PRV45 reducing valveOutlet pressures from 0.01 barg; suitable for steam.
PRV44 reducing valveDN15–25, steam up to 210 °C.
VD reducing valveDN15–100, 40 bar, and steam up to 200 °C.
PRV30 reducing valve316L stainless, DN15–25.
PRV20 reducing valve316L stainless, DN8–20 and 40 bar.
Request a quote for the M2
Give us your installation details and we will recommend the size, actuator, and diaphragm, and whether you need external sensing and a water seal pot.
- Fluid and operating temperature
- Inlet pressure and desired outlet pressure
- Maximum and minimum flow rate
- Size, connection, and body material
You can also call 933 720 888.
