In industrial steam systems and building utility systems, steam pressure needs to be controlled appropriately according to the operating conditions of each piece of equipment. Steam from the supply source may have a higher pressure than the level that downstream equipment can handle; therefore, a device is required to reduce and maintain the downstream pressure at a stable level.

The VENN RP-6 steam pressure reducing valve is a pilot-operated pressure reducing valve designed for steam systems requiring high flow capacity. The product is suitable for various applications in buildings, industrial facilities, and steam distribution systems.

According to the technical documentation, the VENN RP-6 features a compact design, continuous pressure control through a pilot mechanism, an adjustable secondary pressure range of 0.03–0.8 MPa, and multiple sizes from 15A to 200A.

1. What Is the VENN RP-6 Steam Pressure Reducing Valve?

A steam pressure reducing valve is a device installed in a piping system to reduce the steam pressure from the inlet side (primary pressure) to the required pressure at the outlet side (secondary pressure).

In a steam system, the inlet pressure may vary depending on the operating condition of the steam source and the consumption flow rate. If it is not properly controlled, excessive pressure may affect downstream steam-using equipment.

The VENN RP-6 uses a pilot-operated pressure reducing valve mechanism, in which the pilot controls the pressure and regulates the operation of the main valve.

The RP-6 series is designed for:

• Steam systems in buildings.
• Steam systems in industrial facilities.
• Steam distribution piping.
• Steam-using equipment requiring a lower pressure than the supply pressure.
• Systems requiring high flow capacity.

The valve has two main code versions:

• RP-6B
• RP-6G

The two versions use different materials for certain components, particularly the piston & cylinder.

2. Key Features of the VENN RP-6 Pressure Reducing Valve

2.1. Pilot-Operated Type

The VENN RP-6 uses a pilot-operated control mechanism, allowing the valve to continuously control secondary pressure according to downstream pressure conditions.

This design is suitable for systems requiring stable pressure control under varying flow conditions.

2.2. High Flow Capacity

The RP-6 is designed by VENN as a multipurpose pilot-operated type (High capacity), making it suitable for systems with relatively high steam flow requirements.

The product series is available in sizes from 15A to 200A, allowing valve selection according to different piping and flow conditions.

2.3. Wide Secondary Pressure Adjustment Range

The secondary pressure of the VENN RP-6 can be adjusted within the range of:

0.03–0.8 MPa

The outlet pressure is adjusted through the pressure adjusting mechanism of the valve.

2.4. Manual Pressure Adjustment

According to VENN’s technical documentation, the pressure can be easily adjusted manually through the adjustment mechanism.

This allows the operator to set the secondary pressure according to the requirements of the system without changing the valve configuration.

2.5. Compact Design

The RP-6 features a relatively compact design, making it convenient for installation on steam piping systems.

However, sufficient space should be provided during installation for inspection, adjustment, and valve maintenance.

3. Construction of the VENN RP-6 Pressure Reducing Valve

The VENN RP-6 pressure reducing valve consists of multiple components that work together to reduce and control steam pressure.

The main components shown in the construction drawing include:

3.1. Valve Body

The valve body is the main pressure-containing component and is directly connected to the piping system.

According to the technical specifications:

Body: Cast iron

The RP-6 uses a JIS 10KFF flanged connection.

The valve body is designed to meet the operating conditions of the steam system within the specified product parameters.

3.2. Disc & Seat

The Disc & Seat assembly performs the function of regulating the steam flow through the valve.

According to the catalogue:

Disc & Seat: Stainless steel

The interaction between the disc and seat allows the flow passage to be controlled while the valve performs the pressure-reducing process.

3.3. Piston & Cylinder

The piston and cylinder are important components in the operating mechanism of a pilot-operated pressure reducing valve.

According to the documentation, the piston & cylinder materials differ according to the model:

Model	Piston & Cylinder
RP-6B	Cast bronze
RP-6G	Stainless steel

Therefore, when selecting the product, the appropriate RP-6B or RP-6G model should be determined according to the system requirements.

3.4. Pilot Mechanism

The pilot mechanism is an important component that enables the VENN RP-6 to control downstream pressure.

The pilot senses the downstream pressure condition and works together with the main valve mechanism to regulate the amount of steam passing through the valve.

As a result, the valve not only reduces pressure but also controls the downstream pressure according to the set value under operating conditions.

3.5. Pressure Adjustment Mechanism

The RP-6 is equipped with a manual pressure adjustment mechanism.

Through the adjusting screw/handle, the operator can change the force acting on the control mechanism to set the secondary pressure according to the system requirements.

4. Operating Principle of the VENN RP-6 Pressure Reducing Valve

The operating principle of the VENN RP-6 is based on the interaction between the main valve and pilot.

High-pressure steam enters the inlet side of the valve. The pilot mechanism monitors the downstream pressure condition and controls the operation of the piston/main valve.

When the secondary pressure is lower than the set value, the control mechanism allows the valve to open as appropriate to increase the amount of steam passing through.

When the secondary pressure increases to the required level, the pilot mechanism changes its control condition, causing the main valve to reduce its opening. In this way, the downstream pressure is controlled.

This process occurs continuously as the steam flow changes.

Important Terms Related to Operation

Primary pressure: The inlet pressure of the pressure reducing valve or the pressure of the piping near the pressure reducing valve.

Secondary pressure: The outlet pressure of the pressure reducing valve or the pressure of the piping downstream of the pressure reducing valve.

Set pressure: The secondary pressure at the minimum adjustable flow condition.

Offset pressure: The difference between the secondary pressure and the set pressure when the primary pressure is maintained at a constant level while the flow increases from the minimum adjustable flow to the rated flow.

Lockup pressure: The increase in pressure above the set pressure when the secondary pressure rises while the pressure reducing valve is locked/closed.

Minimum adjustable flow: The minimum flow rate at which the pressure reducing valve can maintain stable operation during adjustment.

Rated flow: The maximum flow rate at which the valve can operate when the primary pressure is maintained at a constant level.

5. Technical Specifications of the VENN RP-6 Pressure Reducing Valve

The following are the main specifications shown in VENN’s technical documentation:

Specification	VENN RP-6
Model name	RP-6
Code	RP-6B / RP-6G
Applicable fluid	Steam
Applicable primary pressure	Max. 1.0 MPa
Adjustable secondary pressure	0.03–0.8 MPa
Maximum reducing rate	20:1
Lock up pressure	Max. 0.02 MPa
Leakage allowance	Less than 0.05% of rated flow
Applicable temperature	Max. 184°C*
End connection	Flanged JIS 10KFF
Body	Cast iron
Disc & Seat	Stainless steel
Piston & Cylinder – RP-6B	Cast bronze
Piston & Cylinder – RP-6G	Stainless steel
Valve body pressure test	Hydraulic 1.5 MPa

* The documentation notes that a maximum applicable temperature of 220°C can be supplied upon request.

Size Range

The VENN RP-6 is available in the following sizes:

15A, 20A, 25A, 32A, 40A, 50A, 65A, 80A, 100A, 125A, 150A and 200A.

The Cv value varies according to valve size, ranging from approximately 1 to 256 according to the specification table in the catalogue.

6. Pressure and Flow Characteristics of the VENN RP-6

When selecting a pressure reducing valve, considering only the pipe diameter is not sufficient. The following factors should be considered simultaneously:

• Primary pressure.
• Secondary pressure.
• Steam temperature.
• Steam flow rate.
• Minimum adjustable flow.
• Rated flow.
• Offset pressure.
• Lockup pressure.

According to VENN’s characteristic curves, as the flow increases from the minimum adjustable flow to the rated flow, the secondary pressure may change from the set pressure. This variation is represented by the offset pressure characteristic.

In addition, the primary pressure also affects the secondary pressure.

For example, in VENN’s documentation, when the secondary pressure is set at 0.2 MPa at a primary pressure of 0.3 MPa, the chart shows the change in secondary pressure when the primary pressure varies from 0.3–1.0 MPa.

Therefore, when designing the system, the flow characteristics and pressure characteristics should be considered rather than selecting the valve based only on nominal pipe size.

7. Guide to Selecting the VENN RP-6 Valve Size

Selecting the nominal diameter is one of the important steps when using a steam pressure reducing valve.

VENN provides a Nominal Diameter Selection Chart for the RP-6, 6K, 6BD and 8 series.

Step 1: Determine the Primary Pressure

First, determine the steam pressure at the valve inlet.

Example:

Primary pressure = 0.45 MPa

Step 2: Determine the Secondary Pressure

Determine the required pressure downstream of the valve.

Example:

Secondary pressure = 0.2 MPa

Step 3: Determine the Steam Flow Rate

Determine the steam flow rate required by the system.

Example in the catalogue:

Saturated steam flow = 700 kg/h

Step 4: Use the Diameter Selection Chart

On the chart, identify the intersection between the primary pressure and secondary pressure conditions, then combine this with the temperature and flow rate conditions to determine the appropriate size range.

In VENN’s example, after determining the operating conditions, the result may fall between two nominal sizes. In this case, the catalogue instructs selecting the larger nominal size when determining the valve size.

8. Important Considerations When Selecting Valve Size

8.1. Do Not Select a Valve That Is Too Small

A valve that is too small may not provide the required flow capacity.

In particular, when the valve diameter is too small, the flow velocity may become excessive and cause operating-related issues.

8.2. Do Not Select an Oversized Valve

An oversized valve is not always better.

According to VENN’s documentation, an excessively large valve may cause “hunting”, in which the valve continuously changes its regulating condition and may result in abnormal wear.

The catalogue also notes that the minimum adjustable flow may be approximately 5% of the rated flow. Therefore, if the actual flow frequently falls below the minimum adjustable flow, the valve may not operate under appropriate conditions.

8.3. When the Flow Rate Varies Significantly

If the system flow rate varies significantly over time, the catalogue recommends considering the use of two pressure reducing valves with different sizes and switching between the two valves according to changes in flow rate.

9. Installation Guide for the VENN RP-6 Pressure Reducing Valve

Proper installation has a direct effect on the valve’s operating and maintenance performance.

Step 1: Install the Valve in the Correct Flow Direction

The valve must be installed according to the flow direction indicated on the valve body.

The piping should be arranged appropriately according to the valve construction and flow direction.

Step 2: Install a Strainer on the Primary Side

VENN’s documentation specifies:

Install strainer at the primary side of pressure reducing valve.

The strainer helps prevent contaminants from entering the valve and protects the internal mechanism.

Step 3: Install Pressure Gauges

Pressure gauges should be provided before and after the valve to monitor:

• Primary pressure.
• Secondary pressure.

Monitoring these two values facilitates pressure adjustment and inspection of the operating condition.

Step 4: Provide Bypass Piping When Required

For equipment that cannot be stopped during maintenance, the catalogue recommends installing bypass piping from the primary side to the secondary side.

The bypass should be equipped with an appropriate stop valve so that the pressure reducing valve can be isolated during maintenance.

Step 5: Install Straight Piping Before and After the Valve

Appropriate straight pipe sections should be provided upstream and downstream of the valve.

If threaded connections are used, union joints can be installed to facilitate removal during maintenance.

The diameter of the piping before and after the valve should be determined based on the standard flow velocity and operating conditions.

Step 6: Install a Solenoid Valve or Control Valve

If a solenoid valve or control valve is installed on the secondary side, an appropriate distance should be maintained between the pressure reducing valve and the control valve.

According to the documentation:

• For a solenoid valve, the distance should be L > 2 m.
• For a control valve, the distance depends on the nominal diameter: if the nominal diameter is less than 125 mm, L > 1 m; if it is 125 mm or larger, L > 1.5 m.

Step 7: For Two-Step Pressure Reduction Systems

When performing 2-step pressure reduction, the distance between the two pressure reducing valves should be:

1–2 m

This arrangement allows the two-stage pressure reduction system to be configured according to the manufacturer’s guidelines.

10. Condensate Management and “Hunting”

In steam systems, condensate accumulation can affect pressure reducing valve operation.

According to VENN’s guidelines, “hunting” or vibration may occur if condensate accumulates.

To minimize this condition:

• Provide appropriate drainage to remove condensate from the piping.
• A steam trap may be installed on the primary side.
• When steam consumption is close to zero, a steam trap should be considered on the secondary side because the pressure reducing valve cannot completely close.

This is one of the important points to consider when designing a steam system equipped with a pressure reducing valve.

11. Secondary Pressure Adjustment of the VENN RP-6 Valve

According to the documentation, the secondary pressure of the valve is not adjusted before delivery. Therefore, after installation, the secondary pressure must be adjusted according to the system requirements.

The adjustment procedure is as follows:

Step 1

Close the stop valves on the primary and secondary sides.

Step 2

Open the blowing stop valve or the stop valve on the bypass to remove condensate and contaminants from the piping.

The flushing process should be carried out for a sufficient period of time.

Step 3

Completely close the bypass stop valve or blowing stop valve.

Step 4

Adjust the adjusting screw to eliminate an inappropriate spring load condition.

Step 5

Slowly open the stop valve.

Step 6

Make sure that the pressure has been adjusted appropriately, then slowly open the stop valve on the secondary side.

Step 7

Apply a small spring load through the handle or adjusting screw.

Step 8

Slowly open the stop valve on the secondary side.

Observe the pressure gauge and adjust:

• Turn clockwise: increase pressure.
• Turn counterclockwise: decrease pressure.

Continue adjusting until the secondary pressure reaches the required value.

Step 9

After reaching the desired pressure, use the lock nut to secure the adjusting screw and prevent unintended adjustment.

12. Piping Diameter Before and After the Pressure Reducing Valve

The piping diameter should not be selected solely based on the nominal diameter of the valve.

VENN’s catalogue notes that the piping diameter before and after the pressure reducing valve should be determined based on the standard velocity of the fluid.

If the piping diameter is too small, the flow velocity may become excessive, resulting in:

• Increased pressure loss.
• Increased noise.
• Increased risk of pipe erosion.
• Greater influence of vibration.

For steam, the catalogue provides the following standard velocity reference values:

Condition	Standard velocity
Saturated steam (0.2–0.5 MPa)	15–20 m/s
Saturated steam (0.5–1.5 MPa)	20–30 m/s
Saturated steam	20–30 m/s
Superheated steam	30–40 m/s

These values are provided as references for determining the piping diameter according to the system operating conditions.

13. Safety Valve in a System Using the VENN RP-6

The VENN catalogue also provides guidelines for installing a safety valve or safety relief valve on the secondary side of the pressure reducing valve.

A safety valve is used to protect the downstream system in the event that the secondary pressure increases beyond the required level due to a failure of the pressure reducing valve.

The documentation provides a safety valve set-pressure table based on the pressure setting of the pressure reducing valve.

For example:

Set pressure of pressure reducing valve	Set pressure of safety valve
0.1 MPa or less	+0.05 MPa
Over 0.1 to 0.4 MPa	+0.08 MPa
0.4 to 0.6 MPa	+0.12 MPa
0.6 to 0.8 MPa	+0.15 MPa
0.8 to 1.0 MPa	+0.19 MPa
1.0 to less than 1.2 MPa	+0.23 MPa

For actual system design, the complete operating conditions and safety requirements of the entire system should be fully considered.

14. Applications of the VENN RP-6 Steam Pressure Reducing Valve

With its pilot-operated design and high flow capacity, the VENN RP-6 is intended for various steam system applications.

14.1. Building Steam Systems

The RP-6 can be used in steam systems within building facilities, where steam pressure needs to be reduced before being supplied to downstream equipment.

14.2. Industrial Facilities

In factories and industrial facilities, steam systems often supply multiple pieces of equipment with different pressure requirements.

Pressure reducing valves can be installed on branch piping to reduce the steam pressure to a suitable level for each area of use.

14.3. Steam Distribution Systems

The RP-6 can be installed on steam distribution lines where downstream pressure needs to be controlled.

14.4. Systems Requiring High Flow Capacity

The RP-6 series is classified as High Capacity, and therefore it can be considered for systems requiring high steam flow within the specified product parameters.

15. Why Choose the VENN RP-6 Steam Pressure Reducing Valve?

15.1. Pilot-Operated Mechanism

The pilot-operated design controls the pressure-reducing process according to downstream pressure conditions.

15.2. Wide Pressure Adjustment Range

The secondary pressure can be adjusted within:

0.03–0.8 MPa

This allows the valve to accommodate various steam operating conditions.

15.3. Wide Size Range

The RP-6 is available from:

15A to 200A

This allows selection according to different pipe diameters and flow rates.

15.4. Multiple Piston & Cylinder Material Options

VENN provides two codes:

• RP-6B – Cast bronze piston & cylinder
• RP-6G – Stainless steel piston & cylinder

15.5. JIS 10KFF Flanged Connection

The JIS 10KFF connection is suitable for piping systems designed with the corresponding connection standard.

15.6. Compact Design and Easy Adjustment

The valve features a compact design and a manual adjustment mechanism, making it convenient to set the secondary pressure according to system requirements.

16. Important Notes for Operation and Maintenance of the VENN RP-6

To ensure stable operation of the pressure reducing valve, several points should be considered during use.

Check the Inlet and Outlet Pressure

Regularly monitor the primary pressure and secondary pressure to detect abnormal changes.

Check the Strainer

The strainer on the primary side should be inspected and cleaned periodically to minimize blockage caused by contaminants.

Check for Condensate

Accumulated condensate can cause vibration or affect pressure control. Therefore, the drainage and steam trap systems should be properly maintained and operated.

Check the Adjustment Mechanism

If the secondary pressure changes unexpectedly, the adjusting screw, lock nut, and related components should be inspected.

Ensure Adequate Maintenance Space

VENN’s catalogue requires sufficient space to be provided for pressure reducing valve maintenance.

Provide Proper Piping Support

The piping system should be properly supported so that the weight of the piping, bending forces, or vibration does not act directly on the valve.

17. Conclusion

The VENN RP-6 steam pressure reducing valve is a pilot-operated pressure reducing valve designed for steam media and intended for building facilities and industrial facilities requiring steam pressure reduction and control.

The product provides an adjustable secondary pressure range of 0.03–0.8 MPa, a maximum primary pressure of 1.0 MPa, a size range of 15A–200A, and a JIS 10KFF flanged connection, with a High Capacity design.

The VENN RP-6 is available in two main codes, RP-6B and RP-6G, with piston & cylinder materials of cast bronze and stainless steel, respectively. When selecting the product, the inlet pressure, outlet pressure, steam flow rate, temperature, pressure characteristics, and piping diameter should all be considered.

In particular, correct sizing and proper installation are important for the operating performance of the valve. Factors such as the strainer, pressure gauges, bypass, steam trap, safety valve, and spacing between valves should be considered according to the actual system configuration.

With its pilot-operated design, wide size range, and suitability for industrial and building steam systems, the VENN RP-6 is an option worth considering for systems requiring steam pressure control within the manufacturer’s specified operating parameters.