In industrial systems, regulating flow rate and distributing the medium between pipeline branches are important requirements for maintaining stable operating conditions. For systems that require mixing two medium streams into one outlet stream or diverting one medium stream into two outlet streams, a three-way control valve is one of the suitable configurations.

The Valvole Hofmann M9-3 is a Three-Way Pneumatic Control Valve, designed for fluid control requirements in industrial systems. According to the technical documentation, the M9-3 can be used in either Mixing Valve or Diverting Valve configuration, while offering various options for Plug, materials, sealing types, connections, and pneumatic actuators.

The M9-3 uses a standard Linear Plug, with a Stem made of AISI 316 or 17-4PH stainless steel that is machined and polished, together with pneumatic actuators available in Ø205, Ø275, Ø360, and Ø430 mm depending on the configuration.

1. Overview of the Valvole Hofmann M9-3 Three-Way Globe Control Valve

1.1. What is a Three-Way Globe Control Valve?

A Three-Way Globe Control Valve is a control valve with three connection ports, used to regulate and change the direction of flow within a system.

Unlike a two-way control valve, a three-way valve allows the fluid flow to be controlled according to two basic configurations:

• Mixing: Two inlets and one outlet.
• Diverting: One inlet and two outlets.

The valve does not only perform an open/close function but can also continuously regulate the flow rate through the movement of the Plug.

According to Valvole Hofmann’s documentation, the M9-3 is designed to meet specific fluid control requirements and can continuously adjust the flow rate from very high to very low values.

1.2. Introduction to the Valvole Hofmann M9-3

The Valvole Hofmann M9-3 is a Three-Way Pneumatic Control Valve equipped with a pneumatic actuator.

Its main technical features include:

• Standard Linear Plug.
• AISI 316 or 17-4PH Stem.
• Bottom Guide from DN32 to DN200 for Stem guidance.
• Epoxy-painted steel pneumatic actuator.
• Actuator sizes Ø205, Ø275, Ø360, and Ø430 mm.
• Available in Mixing or Diverting configurations.
• Soft Seal Class VI and Metal Seal Class IV options.
• Multiple Body and internal component material options.

1.3. Role of a Three-Way Valve in Fluid Control Systems

A three-way valve can perform two main functions.

Mixing

Two medium streams enter through two different ports and are combined into one outlet stream.

A + B → AB

This configuration can be used when the ratio between two medium streams needs to be controlled.

Diverting

One medium stream enters the valve and is distributed to two outlet ports.

AB → A + B

This configuration is suitable for systems that require the medium to be redirected or distributed between two branches.

2. Operating Principle of the M9-3 Three-Way Control Valve

2.1. Flow Regulation Principle

The M9-3 uses a Plug that moves according to the Stroke of the Stem to change the flow area.

When the control signal acts on the Pneumatic Actuator, the actuator generates force to move the Stem and Plug.

The change in Plug position changes the flow capacity through the valve ports, thereby regulating the flow rate.

The M9-3 as being capable of continuously regulating flow from very high flow rates down to very low flow rates.

2.2. Mixing Valve Configuration

In the Mixing Valve configuration, two medium streams enter through two ports and are combined into one outlet stream.

According to the documentation, for the Mixing Valve, the inlet pressure at A and B is considered equal under the calculation conditions, thereby balancing the forces acting on the Plug.

This configuration uses the following flow paths:

• A → AB
• B → AB

Depending on the Plug type and valve configuration, the flow through each path can be regulated by the valve Stroke.

2.3. Diverting Valve Configuration

In the Diverting Valve configuration, one medium stream enters the valve and is divided between two outlet ports.

The flow paths shown include:

• AB → A
• AB → B

The M9-3 can use either a Mixing Plug or Diverting Plug, depending on the configuration. The documentation also shows Diverting configurations with the straight path Normally Closed or Normally Open, while some Diverting Plug configurations are applicable from DN65 and above.

2.4. Effect of Fluid Pressure on the Plug

For a control valve, the force acting on the Plug is an important factor when selecting the actuator.

The M9-3 documentation provides tables for maximum operating pressure / allowable differential pressure according to valve size and actuator type.

The values in these tables take actuator force into consideration and are intended for selection with a positioner. However, the manufacturer notes that the actual application capability of the valve remains limited by the Pressure/Temperature Rating of the Body.

Therefore, the actuator force alone should not be used to determine the operating pressure of the entire valve.

2.5. Continuous Flow Regulation Capability

One of the important features of the M9-3 is its ability to continuously regulate flow through Plug Stroke.

The documentation provides KV, CV, and Stroke values for each DN size and flow configuration.

For example, for the Mixing Valve with Mixing Plug, KV values for the straight and angle paths are provided from DN15 to DN200, while the Stroke varies from 20 mm to 50 mm depending on the valve size.

3. Construction of the Valvole Hofmann M9-3 Three-Way Globe Control Valve

According to the M9-3 sectional drawing, the main components are:

1. Servocontrol – Actuator
2. Bridge
3. Stuffing Box
4. Upper Guide Bonnet
5. Valve Stem
6. Valve Body
7. Plug
8. Bottom Guide

3.1. Valve Body

The Body is the main component containing the flow passages and Seats of the valve.

The M9-3 is available with multiple Body material options, including:

• EN-GJS-400-18-LT.
• A216 WCB.
• AISI 316.
• Super Duplex F55 ASTM A890-A995 Grade 6A.

The Body material is selected according to the product configuration and system requirements.

3.2. Bridge

The Bridge is the structural component above the Body that connects the valve Body to the actuator.

According to the documentation, the Bridge is made of EN-GJS-400-15 (EN JS-1030) in the configurations presented.

3.3. Plug and Stem

The Plug is the component that directly changes the flow area.

The M9-3 uses a standard Linear Plug. In addition, Valvole Hofmann states that Plugs with an EQP=% characteristic can be supplied upon request.

The Stem material options include:

• AISI 316 (1.4401)
• 17-4PH (1.4542)

The Stem is machined and polished and is guided to ensure stable movement. From DN32 to DN200, the documentation refers to the presence of a Bottom Guide for Stem guidance.

3.4. Seat and Bottom Guide

The Seat is the sealing and flow-control surface working together with the Plug.

Depending on the configuration, the Seat may be made of:

• AISI 304.
• AISI 316.
• Super Duplex F55.

The Bottom Guide simultaneously provides guidance and may be integrated with the Bottom Seat depending on the configuration.

3.5. Stuffing Box

The Stuffing Box seals the Stem area to limit leakage of the medium to the outside.

The standard M9-3 configuration uses a self-adjusting stuffing box with PTFE or PTFE+FPM materials depending on the configuration.

For the extended PROE/PROS versions, the documentation also shows Stuffing Box configurations using PTFE, PTFE+FPM, and graphite.

3.6. Pneumatic Actuator

The M9-3 uses an epoxy-painted steel Pneumatic Actuator.

The actuator diameters shown include:

• Ø205 mm – SS0
• Ø275 mm – SS1
• Ø360 mm – SS3
• Ø430 mm – SS2
• Ø430 mm Double – SS4
• Ø430 mm Long – SS2L

Depending on the configuration, the nominal control signals may be:

• 3–15 psi
• 6–18 psi
• 6–30 psi
• 1.6–3.2 bar

For SS2L, the documentation shows a 1.6–3.2 bar signal and requires the use of a positioner.

4. Plug Types and Control Characteristics

4.1. Linear Plug

The Linear Plug is the standard configuration of the M9-3.

The Linear Plug characteristic allows the total outlet KV value to remain close to 100% of the published KV value throughout the valve Stroke, according to the manufacturer’s description for the Mixing and Diverting configurations.

This is one of the important technical characteristics of the M9-3 when the valve is used for control applications.

4.2. EQP Plug

In addition to the Linear Plug, Valvole Hofmann states that an EQP Plug can be supplied upon request.

According to the documentation, with an EQP Plug, at approximately 50% Stroke, the outlet KV value can be lower than 50% of the published KV value, whereas the Linear Plug maintains an outlet KV value close to the nominal value throughout the Stroke.

Therefore, the Plug characteristic directly affects the relationship between Valve Stroke and Flow Coefficient.

4.3. Comparison Between Linear Plug and EQP Plug

Plug selection should be based on the required control characteristic of the system, not only on the valve size.

4.4. Effect of the Plug on Flow Characteristic

The Plug determines how the flow area changes according to Stem Stroke.

Therefore, the same valve size fitted with different Plugs can produce different control characteristics.

For the M9-3, the documentation provides separate KV/CV tables for:

• Mixing Valve with Mixing Plug.
• Diverting Valve with Mixing Plug.
• Diverting Valve with Diverting Plug.

This is an important basis for selecting the valve configuration.

4.5. Plug Selection According to Application

Selection can be considered according to the following sequence:

Determine Mixing/Diverting → determine Flow Characteristic → determine KV/CV → select Plug → select Actuator/Positioner.

For applications requiring an EQP characteristic, the availability of the EQP Plug should be confirmed with the manufacturer.

5. Materials and Configuration Options

5.1. Body Materials

The M9-3 documentation presents multiple Body options:

5.2. Plug and Stem Materials

The standard Linear Plug/Stem configurations can use:

• AISI 304 / AISI 316.
• AISI 316 / 17-4PH.
• Super Duplex F55 for special configurations.

Depending on the model, the Plug and Stem materials are combined differently.

5.3. Seat and Bottom Guide Materials

The Seat can be made of AISI 304, AISI 316, or Super Duplex F55 depending on the configuration.

The Bottom Guide and Bottom Seat also have corresponding material options according to each valve version.

5.4. AISI 304, AISI 316 and Other Material Options

The variety of available materials allows the M9-3 to be configured according to the system requirements.

In particular, AISI 316 and Super Duplex F55 versions can be considered when higher material performance is required compared with ductile iron or carbon steel Body configurations.

However, material selection must be based on the medium, temperature, pressure, corrosion resistance, and Body pressure/temperature rating, rather than solely on the material name.

5.5. Material Selection According to the Medium

When selecting the M9-3, the following factors should be determined:

• Medium composition.
• Operating temperature.
• Pressure.
• Corrosiveness.
• Sealing requirements.
• Continuous or cyclic operating conditions.

The appropriate Body and internal component configuration can then be selected.

6. Connection Types of the M9-3 Valve

6.1. Flanged Connection

The M9-3 supports flanged connection configurations.

According to the documentation, the standard flange standards include:

• UNI EN 1092-2 PN25
• Some configurations use UNI EN 1092-1 PN40
• Exceptions according to DN are specified in the documentation.

Other flange drilling configurations can be supplied upon request.

6.2. GAS Threaded Connection

The documentation allows threaded connections:

• GAS
• NPT

upon request.

6.3. Butt-Welding Connection

The M9-3 can be supplied with a Butt-Welding Connection upon request.

The documentation references DIN EN ISO 1127 for this connection type.

6.4. Socket-Welding Connection

In addition to Butt-Weld, the documentation also shows a Socket-Welding Connection according to UNI EN 12760, applicable to DIN EN ISO 1127 piping.

6.5. Connection Selection According to the Piping System

Before ordering, the following should be confirmed:

• Pipeline DN.
• Flange standard.
• Pressure Class.
• Face-to-Face.
• Connection type.
• Piping standard.

The documentation also states that flange drilling configurations such as UNI PN16, PN25, ANSI 150, ANSI 300, JIS 10K, JIS 20K, and JIS 40K can be supplied upon request depending on the configuration.

7. Sealing Characteristics and Operating Temperature

7.1. Soft Seal Class VI

The standard M9-3 configuration features:

Soft Seal Class VI from DN15 to DN100.

This is the seat tightness class specified by the manufacturer for the corresponding soft-sealing configuration.

7.2. Metal-to-Metal Seal Class IV

For sizes:

DN125 to DN200

the documentation shows Metallic Seal Class IV in the standard configuration.

7.3. Temperature Range

For the standard M9-3 version, the documentation indicates:

• Plastic insert: Tmin -15°C, Tmax 210°C in the standard characteristics table.
• The actual pressure and temperature limits also depend on the Body Rating.

For the extended versions, the maximum temperature limits can be higher.

For example, the M9-3/PROE configuration shows:

• Plastic insert: from -20°C to 240°C, -29°C to 240°C, or -60°C to 240°C depending on the configuration.
• Metal-to-metal seal: from -20°C to 350°C, -29°C to 350°C, or -60°C to 350°C depending on the configuration.

The PROS version has different temperature configurations, in which the documentation shows that the Metal-to-Metal Seal can reach up to 400°C depending on the configuration.

7.4. Effect of Pressure/Temperature Rating

A single temperature value should not be considered as the general limit for every M9-3 configuration.

The manufacturer clearly states that the maximum pressure and temperature are limited by the Body rating.

The documentation provides separate Pressure/Temperature Rating tables for:

• AISI 316 – UNI EN 12516-1
• A216 WCB – UNI EN 12516-1
• EN-GJS-400-18-LT – UNI EN 1092-2
• Super Duplex F55 – ASME B16.34

Therefore, when selecting a valve for an actual system, the Body Material + Pressure Class + Temperature must be checked together.

7.5. Seal Type Selection

Soft Seal or Metal Seal selection should be based on:

• Temperature.
• Pressure.
• Medium.
• Leakage requirements.
• DN.
• Valve configuration.

The selection should not be based solely on the tightness class without considering material limitations and the Pressure/Temperature Rating.

8. KV Characteristics and Control Capability

8.1. Meaning of KV in a Control Valve

KV is one of the important parameters when selecting a Control Valve because it is related to the flow capacity of the valve.

For the M9-3, the documentation provides KV and CV tables according to DN and flow configuration.

8.2. KV According to Valve Size

For the Mixing Valve with Mixing Plug, the documentation indicates:

8.3. Straight-Path and Angle-Path KV

For some Diverting Valve configurations, the KV of the straight path and angle path can differ significantly.

In particular, the documentation notes that for a Diverting Valve, the KV of the angle path can be up to 50% lower than the KV of the straight path depending on the configuration.

Therefore, when sizing a Three-Way Control Valve, each flow path should be considered separately rather than using only one KV value.

8.4. KV Selection

KV selection should be based on:

• Flow rate.
• Pressure drop.
• Medium density.
• Temperature.
• Operating conditions.
• Mixing or Diverting configuration.

In addition, it is necessary to determine whether the system requires a Linear Plug or EQP Plug.

8.5. Valve with Reduced KV

Valvole Hofmann states that valves with reduced KV can be manufactured upon request.

This is a useful option when the standard KV of a valve size is higher than the actual system requirement.

9. Dimensions and Selection Range

9.1. DN Range

The M9-3 documentation shows a size range from:

DN15 to DN200

For some Diverting configurations with Diverting Plug, the table also shows sizes from DN65 to DN300, with some values requiring reference to the catalog.

Therefore, the actual size range must be determined according to the correct Plug and valve configuration.

9.2. Stem Stroke

Stroke depends on DN and configuration.

In the Mixing Valve with Mixing Plug table, the Stroke is shown as:

• DN15–DN80: 20 mm
• DN100: 25 mm
• DN125–DN150: 40 mm
• DN200: 50 mm

These values are indicated by the manufacturer as indicative for the choice of the positioner.

9.3. Overall Dimensions

The overall dimensions of the M9-3 depend on:

• DN.
• Actuator type.
• Body configuration.
• Valve configuration.
• Extension.
• Connection.

The documentation provides dimensions A, A1, B, C, D, E, ØF, H, H1, and V according to each configuration.

9.4. Valve Weight

Weight also varies according to:

• DN.
• Actuator.
• Cast Iron Body or Stainless Steel Body.
• Configuration.

For example, the M9-3 version with SS2 actuator has different dimensions and weights for DN65–DN100 depending on the Body material.

9.5. Size Selection According to the System

DN should not be selected based solely on the pipeline diameter.

The following factors should be determined simultaneously:

Flow rate → Pressure drop → Required KV → DN → Plug → Actuator → Positioner

This is a more appropriate approach when selecting a Three-Way Control Valve for an actual system.

10. Applications of the Three-Way Globe Control Valve

10.1. Temperature Control

A three-way valve can be used in systems requiring the ratio between medium streams to be adjusted in order to control outlet conditions.

In particular, the Mixing configuration allows two streams to be combined into one outlet stream.

10.2. Fluid Flow Distribution

With the Diverting configuration, the M9-3 can regulate the distribution of one medium stream toward two different directions.

This is suitable for systems requiring the flow direction or distribution ratio to be changed.

10.3. Mixing Systems

Configuration:

Two Inlets → One Outlet

is suitable when the ratio between two medium sources needs to be controlled.

10.4. Diverting Systems

Configuration:

One Inlet → Two Outlets

is suitable when the medium needs to be distributed between two branches.

10.5. Industrial Systems Requiring Flow Regulation

Based on its flow control function, the M9-3 can be considered for systems requiring:

• Flow regulation.
• Mixing.
• Diverting.
• Flow distribution.
• Control through a positioner signal.

The specific application must be determined based on the medium, pressure/temperature conditions, and system control requirements.

11. Selection of the Valvole Hofmann M9-3 for a System

11.1. Determine Mixing or Diverting Type

This is the first step.

If the system has:

Two Inlets → One Outlet

→ consider a Mixing Valve.

If the system has:

One Inlet → Two Outlets

→ consider a Diverting Valve.

11.2. Determine DN

DN should be determined based on:

• Flow rate.
• Required KV.
• Pressure drop.
• Pipeline diameter.
• Operating conditions.

11.3. Determine KV

KV should be calculated based on the actual operating conditions.

DN should not be selected first and KV simply assumed afterward.

Especially for a three-way valve, the KV of each flow path must be checked because the straight and angle path KV values can be different.

11.4. Select the Plug

The following options can be considered:

• Linear Plug
• EQP Plug

The Linear Plug is the standard configuration, while the EQP Plug can be supplied upon request.

11.5. Select the Material

The following must be determined:

• Body Material.
• Seat Material.
• Plug Material.
• Stem Material.
• Stuffing Box.
• Seal Material.

The M9-3 configurations can use EN-GJS-400-18-LT, A216 WCB, AISI 316, or Super Duplex F55 depending on the model.

11.6. Select the Sealing Type

Determine:

• Soft Seal Class VI.
• Metal Seal Class IV.
• Special Seal configurations.

The actual temperature and pressure must also be checked.

11.7. Select the Connection Type

Finally, determine:

• Flanged.
• GAS/NPT threaded.
• Butt weld.
• Socket weld.

and the corresponding flange drilling standard.

12. Important Notes for Installation and Operation

12.1. Check the Flow Direction

For a three-way valve, flow direction is particularly important because Mixing and Diverting configurations are different.

The fluid entrance/exit diagram for the correct valve configuration should be checked before installation.

12.2. Check the Piping Connection

The following should be confirmed:

• DN.
• Flange drilling.
• Face-to-face.
• Connection standard.
• Pressure Class.

The documentation references EN 558-1 for the Face-to-Face dimensions of flanged connections.

12.3. Check the Pneumatic/Actuator System

Before operation, check:

• Air supply.
• Control signal.
• Actuator type.
• Positioner.
• Stroke.
• Fail position according to the design configuration.

The pneumatic control signals indicated in the documentation include 3–15 psi, 6–18 psi, 6–30 psi, and 1.6–3.2 bar, depending on the actuator.

12.4. Check Tightness

The M9-3 has Seat Tightness Class VI or Class IV configurations depending on DN and sealing type.

The documentation references ANSI FCI 70-2:2013 for Seat Tightness Class and Hydrostatic Pressure Test.

After installation, the following should be checked for leakage:

• Valve Body.
• Flange.
• Stuffing Box.
• Pneumatic connections.

12.5. Periodic Maintenance and Inspection

The following components should be monitored during operation:

• Plug.
• Stem.
• Seat.
• Stuffing Box.
• Actuator.
• Positioner.
• Pneumatic connections.

For systems requiring accurate control, checking the position feedback and condition of the Positioner is also important.

13. Conclusion

The Valvole Hofmann M9-3 is a Three-Way Pneumatic Globe Control Valve designed for fluid regulation and flow distribution requirements in industrial systems.

One of the key features of the M9-3 is its ability to be configured as either a Mixing Valve or a Diverting Valve, allowing it to accommodate two basic flow arrangements:

Two Inlets → One Outlet

or

One Inlet → Two Outlets.

The valve uses a standard Linear Plug and can be supplied with an EQP Plug upon request. The control system uses Pneumatic Actuators in multiple sizes and with different control signals. The documentation also provides KV, CV, Stroke, and Allowable Differential Pressure tables to support configuration selection.

In terms of materials, the M9-3 offers multiple options ranging from EN-GJS-400-18-LT, A216 WCB, AISI 316 to Super Duplex F55, together with various configurations for Seat, Plug, Stem, and Bottom Guide. This allows the valve configuration to be better matched to the medium and operating requirements.

The valve also supports multiple connection options, including Flanged, GAS/NPT Threaded, Butt-Welding, and Socket-Welding, while flange drilling standards such as UNI PN16/PN25, ANSI 150/300, JIS 10K/20K/40K can be supplied upon request depending on the configuration.

In particular, when selecting the Valvole Hofmann M9-3, selection should not be based on DN alone. A complete selection process should consider:

Mixing/Diverting → Flow Rate → Pressure Drop → KV/CV → Plug Characteristic → Body Material → Seal → Actuator → Positioner → Connection Standard.

In addition, the actual operating pressure and temperature must be checked against the Pressure/Temperature Rating of the Body, as the manufacturer identifies this as an important limitation on the valve’s application capability.

With its wide range of configurations and pneumatic control capability, the Valvole Hofmann M9-3 Three-Way Globe Control Valve is a solution worth considering for systems requiring fluid regulation, mixing, or diverting with accurate flow control.

ANCES can support the selection of the Valvole Hofmann M9-3 configuration based on the medium, flow rate, pressure, temperature, DN, KV, Mixing/Diverting configuration, and connection requirements of each system. e6c88724-83ac-4aca-b347-2aa3954…