Pressure reducing valves: when to choose the M1 and M2 models
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A practical guide to choosing between these two pressure reducing valve models
A self-operated pressure reducing valve is an essential device in any fluid system.
Its function is simple but critical: to reduce a high inlet pressure, which may vary, to a lower and, above all, constant outlet pressure. It does all this automatically, without the need for external power sources such as electricity or compressed air.
Choosing the right valve is vital to protect sensitive equipment “downstream,” optimize process efficiency, and ensure operational safety. At Valfonta, two of our most reliable models for this task are the M1 and the M2.
Although both are pressure reducing valves, they are designed with different characteristics to cover a wide range of industrial applications, from controlling high-purity gases to handling high-temperature steam.
In this guide, we analyze their differences to help you select the right model for your installation.
What is a self-operated pressure reducing valve?
The term “self-operated” (or “no auxiliary power”) means that the valve uses the energy of the fluid itself to operate its internal mechanism. It requires no electrical wiring or instrument air lines, which makes these valves incredibly reliable, easy to install, and free of any maintenance cost in that respect.
Using a quality pressure reducing valve offers direct benefits for any system:
Equipment protection: This is the most common application. They prevent pressure gauges, heat exchangers, reactors, delicate instrumentation, and other equipment operating “downstream” from being damaged by excessive pressure.
Process stability: Many industrial processes (chemical, pharmaceutical, food) require an exact and constant pressure to work properly. The pressure reducing valve ensures that, even if the inlet pressure fluctuates, the process always receives a stable pressure.
Efficiency and savings: In steam applications, reducing the pressure also reduces the temperature, optimizing energy use. Since it consumes no external energy to operate, its operating cost is zero.
Improved safety: By keeping the pressure within the design limits of the line, they reduce the risk of system failures. However, it is essential to understand that a pressure reducing valve is not a safety valve. Overpressure protection (such as a relief valve) must always be installed when the installation requires it.
The M1 model: robustness and high performance for steam and gases
When the application calls for greater robustness, a higher pressure range, or continuous operation at high temperatures, the M1 model is the right solution.
Unlike the M2, the M1 is a self-operated diaphragm and spring valve, designed specifically for more demanding duties with steam, compressed air, non-hazardous gases, and liquids.
Its internal design is built for maximum durability and minimal maintenance in severe conditions. Its most distinctive feature is the stem seal by means of a double-ply stainless steel bellows. This bellows completely isolates the fluid from the rest of the upper components, preventing leaks and wear on the stem, a critical point in high-temperature steam applications.
How does the M1 work?
The outlet (downstream) pressure is transmitted through an external control line (L) to the diaphragm chamber (H).
This pressure exerts a force on the diaphragm that opposes the force set on the springs (K) by means of the adjusting nut (F).
This balance of forces moves the plug (C), opening or closing the passage to keep the outlet pressure stable.
In large sizes (from DN65), it includes a balancing plunger (D) that cancels the effect of inlet pressure variations.
Key features of the M1 model
Robustness: Designed for high performance and fast response to changes in demand.
Bellows seal: Maximum reliability and durability, especially on steam.
High temperature: Rated for operation up to 220 °C (with EPDM+PTFE diaphragm and condensate pot).
Wide pressure range: Able to regulate the outlet pressure in ranges from 0.1 to 15 barg.
The M2 model: precision and direct action for multiple fluids
The M2 valve is one of the most versatile and popular models in our catalog. It is a direct-acting pressure reducing valve, which means that the outlet pressure acts directly on the internal diaphragm for fast, sensitive control.
Its design is optimized to work with a wide range of fluids, including gases (such as air, nitrogen, and others), liquids, and steam. Thanks to its high sensitivity, it is an ideal valve for applications that require very precise control, even at very low pressures, offering regulation ranges from 20 mbar to 10 bar.
How does the M2 work?
The inlet (upstream) pressure reaches the valve and pushes the piston-plunger assembly, closing the passage automatically.
Turning the adjusting screw compresses a spring that acts on the diaphragm.
The diaphragm opens the valve plug (seat), allowing the fluid to pass until the outlet (downstream) pressure reaches the desired value.
Any variation in the inlet pressure is absorbed by the balancing plunger, and any variation in the outlet pressure is detected by the diaphragm, which readjusts the plug to keep the set point pressure stable.
H4: Key features of the M2 model
Direct-acting: Fast response and high sensitivity.
Materials: AISI 316 internals and PTFE seat, with options for a stainless steel actuator and gaskets made of a food-grade compound.
Diaphragm: It has a diaphragm reinforced with an intermediate fabric layer.
Pressure sensing point: The pressure sensing point is internal as standard, which greatly simplifies installation because no external control line is required (except in steam applications).
This precision makes it ideal for chemical laboratories, water distribution networks, plumbing installations, compressed air lines, fire protection systems, and inert gas control (tank inerting).
| Features | M1 Model Valve | M2 Model Valve |
|---|---|---|
| Operating Principle | Self-operated by diaphragm | Direct-acting, diaphragm |
| Compatible fluids | Steam, compressed air, non-hazardous gases, liquids | Gases (air, nitrogen…), liquids, steam |
| Outlet Pressure Range (P.out) | 0.1 – 15 barg (Wide range) | 0.02 – 10 barg (High precision) |
| Maximum Temperature | Up to 220°C (with EPDM+PTFE diaphragm) | Up to 180°C (with EPDM+PTFE diaphragm) |
| Stem Seal (Plug) | Stainless Steel Bellows | Gaskets (NBR, EPDM, PTFE+GR, etc.) |
| Pressure Sensing Point | External (Control line required) | Internal (Standard) / External (For steam or optional) |
| Inlet P. Compensation | Yes (Plunger from DN65) | Yes (Plunger-balanced) |
Industrial applications: where to install each model?
The choice between one model and the other will depend on the specific pressure and temperature conditions and the fluid in your installation.
When to choose the M1 valve
The M1 model is the ideal choice for more severe processes, where robustness, high temperatures, and a higher outlet pressure capacity are decisive factors.
Its design is intended for:
Steam circuits: This is its flagship application. The stainless steel bellows seal ensures a much longer service life and virtually zero maintenance compared with traditional gaskets on high-temperature steam (up to 220 °C).
High outlet pressures: When a higher regulation range is needed, the M1 reaches up to 15 barg.
High-demand lines: Ideal for main compressed air or gas lines with large variations in demand, where its response is fast and effective.
When to choose the M2 valve
The M2 model is the perfect choice for most general service applications and installations that require very fine control at low or medium pressures.
Its high sensitivity makes it the preferred option in:
Chemical and pharmaceutical laboratories.
Water distribution networks and plumbing installations.
Compressed air lines for instrumentation.
Fire protection systems.
Inert gas control, such as nitrogen tank blanketing, where the pressure must be reduced to very low values (millibars) with great precision.
Installation guide and best practices (M1 and M2)
Correct installation is the best guarantee of optimal performance and a long service life. Although the M1 and M2 have differences, both share fundamental installation principles that must be followed.
Step No. 1: cleaning and filtering
Before mounting the valve, it is essential to clean the inside of the pipe very carefully to prevent any impurities or installation debris from impairing the correct operation of the seat.
For this reason, it is practically essential (and highly recommended) to install a strainer (Y-type) just upstream of the pressure reducing valve. This protects the seat and the plug from erosion and clogging, avoiding excessive maintenance and extending the service life of the equipment.
Mounting position and flow direction
Both models must be installed according to the arrow on the valve body; this arrow must always match the direction of fluid flow.
The standard and preferred mounting position is in a horizontal pipe.
- For most fluids (gases and liquids above 0°C), the actuator (the upper part with the diaphragm and spring) must be installed in a vertical position, facing up.
- For gases and liquids up to 80°C, mounting in a horizontal pipe with the actuator in a vertical position, facing down is also possible.
Important! Mounting the valve “on its side” (that is, with the actuator stem in a horizontal position) is not permitted, as the valve would not behave correctly.
The water seal pot (condensate pot): mandatory for steam
This is one of the most important considerations for high-temperature applications.
The condensate water seal pot is mandatory whenever the fluid is steam or for liquids at temperatures above 125 °C.
Its function is to protect the diaphragm (the most heat-sensitive component) from overheating. The water seal pot creates a “water seal” (condensate) between the hot fluid in the main line and the diaphragm, ensuring that the diaphragm always works at a safe temperature. Before start-up, this pot must be filled with water until it overflows.
The control line (pressure sensing point)
Here we find the main installation difference between the two models:
- M2 model: It is supplied as standard with an internal pressure sensing point. This means that, for most liquid and gas applications, there is no need to install an external line, which greatly simplifies mounting.
- M1 model: It always requires an external control line.
- Exception (M2 on Steam): When the M2 valve is used for steam, the external pressure sensing point is mandatory, and it is connected to the condensate water seal pot.
When an external control line is used (either on the M1 or on the M2 for steam), it must be connected in the reduced-pressure (downstream) zone. To avoid incorrect readings due to turbulence, it must be located at a minimum distance of 1 meter from the valve outlet (or approximately 6-10 times the nominal diameter, DN).
Valfonta: your expert partner in fluid control
The M1 and M2 models are just one part of our specialty in pressure reducing valves. At Valfonta we have an exceptional technical team that will help you from the very first moment to choose the exact valve that your system or installation requires.
Our catalog also includes a complete range of fluid control solutions, such as pressure relief valves, control valves, injectors, and ejectors for liquids and steam.
If you would like us to contact you to discuss which type of valve and which model suit you, just take a few seconds to fill out this form. You can also call us at 93 37 208 88.
Frequently asked questions
What is the main difference between the M1 and the M2?
The main difference is the application. The M1 model is designed for more robust and demanding applications, especially high-temperature steam (up to 220 °C) and higher outlet pressures (up to 15 barg). It uses a stainless steel bellows seal for maximum durability. The M2 model is ideal for general services and applications that require high precision at lower outlet pressures, and it can regulate from 20 mbar.
Do I need a safety valve if I install an M1 or M2 pressure reducing valve?
Yes. This is a critical safety point. A pressure reducing valve controls the pressure, but it is not a safety valve. If there is a chance that the valve may fail (for example, due to dirt on the seat) and the inlet pressure passes “downstream,” it could damage the equipment. Therefore, whenever necessary, overpressure protection, such as a Valfonta pressure relief valve, must be installed downstream of the pressure reducing valve.
What maintenance do these models require?
The most important maintenance is preventive: installing a strainer at the inlet. Apart from this, the gaskets and parts subject to normal wear must be checked periodically and replaced if necessary, depending on the severity of the operating conditions. It is essential to always use genuine spare parts recommended by Valfonta.
What does it mean for a valve to be direct-acting?
It is the operating principle of the M2 model. It means that the outlet (downstream) pressure acts directly on the valve diaphragm. This force, in balance with the adjusting spring, moves the plug to open or close the fluid passage. This design provides a very fast and sensitive response to pressure changes.
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Can we help with your installation?
Tell us the fluid, the inlet and outlet pressures, the temperature, and the flow rate, and we will recommend the right valve.
You can also call 933 720 888 or email valfonta@valfonta.com.
