Pneumatic control valve

Product Overview

The Pneumatic Single Seat Control Valve is a straight‑through control valve driven by a pneumatic diaphragm actuator. It is widely used in automatic control systems across industries such as petrochemical, chemical, power generation, metallurgy, and light industry. The valve receives a standard pneumatic signal (typically 0.02–0.1 MPa) from an industrial instrument or controller – or an electrical signal (4–20 mA) via an I/P converter – and changes the flow area between the plug and seat to precisely regulate flow rate, pressure, temperature, or liquid level.

The single‑seat design offers low leakage (up to ANSI Class IV–VI), high allowable differential pressure, and excellent control characteristics, making it particularly suitable for applications with strict shut‑off requirements and high pressure drops. The valve features flanged connections, with nominal diameters from DN15 to DN300, pressure ratings from PN16 to PN160 (Class 150 to Class 900), and body materials including cast iron, carbon steel, and stainless steel.

Product Structure

The Pneumatic Single Seat Control Valve mainly consists of two major assemblies: the pneumatic actuator and the valve body assembly.

Pneumatic Actuator:

1. Diaphragm Case: Upper and lower casings made of carbon steel or cast iron.

2. Rubber Diaphragm: Oil‑resistant fabric‑reinforced rubber diaphragm that divides the actuator into two chambers.

3. Spring: Multiple stainless steel or spring steel springs providing the return force for the plug.

4. Stem (Actuator Stem): Stainless steel stem connecting the diaphragm to the valve stem, transmitting thrust.

5. Air Connection: Port for connecting the air supply line to receive the control signal.

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Valve Body Assembly:

1. Body: Cast or forged body in carbon steel (WCB), stainless steel (CF8/CF8M), alloy steel, etc. Flanged ends conforming to GB/T 9113, ANSI B16.5, EN 1092‑1. Flow path is straight‑through.

2. Plug (Disc): Single‑seat plunger‑type plug. The sealing face can be hardfaced with Stellite or covered with PTFE/PEEK. The plug profile determines the flow characteristic (linear, equal percentage, quick opening).

3. Seat: Removable seat forming the sealing pair with the plug, made of matching material.

4. Valve Stem: Stainless steel stem, connected to the actuator stem at the top and the plug at the bottom.

5. Packing Box: Contains PTFE or flexible graphite packing, compressed by a packing gland to prevent external leakage.

6. Bonnet: Connected to the body, housing the packing and stem. Available in standard, extension (for high/low temperature), bellows seal, etc.

7. Cage (Guide Bushing): Optional cage for guiding the plug and reducing noise.

Compact construction, with the actuator connected to the body via a yoke. Optional accessories include a valve positioner, air filter regulator, solenoid valve, limit switches, etc.

Function

1. Flow Regulation: By varying the plug stroke, the flow area is continuously changed, enabling precise flow control.

2. Pressure / Temperature / Liquid Level Control: Combined with sensors and controllers, the valve forms a closed‑loop control system for automatic regulation of process parameters.

3. High Shut‑Off Performance: The single‑seat design provides very low leakage. Soft sealing achieves ANSI Class VI (bubble‑tight), and metal sealing achieves Class IV.

4. High Allowable Differential Pressure: The single‑seat design withstands higher pressure drops than double‑seat valves, making it suitable for high‑pressure‑drop applications.

5. Multiple Flow Characteristics: Plugs can be profiled for linear, equal percentage, or quick opening characteristics to meet different control requirements.

6. Fail‑Safe Action: Depending on the spring action (air‑to‑open or air‑to‑close), the valve will automatically go to fully open or fully closed position on loss of air supply.

7. Accessory Options: Can be equipped with a valve positioner (improves control accuracy), solenoid valve (on‑off control), limit switches (position feedback), air filter regulator (clean air supply), etc.

Working Conditions

1. Applicable Media: Water, oil, gas, steam, chemical media, corrosive liquids, etc.

2. Temperature Range: –29°C to +200°C (standard PTFE packing); –29°C to +400°C (graphite packing); –196°C to +450°C (bellows seal + extension bonnet).

3. Pressure Rating: PN16, PN25, PN40, PN63, PN100, PN160 (Class 150, 300, 600, 900).

4. Nominal Diameter: DN15 – DN300 (1/2″ – 12″).

5. Air Supply Pressure: 0.14 MPa – 0.6 MPa (standard 0.4 MPa).

6. Signal Range: Standard pneumatic signal 0.02–0.1 MPa (20–100 kPa); can be equipped with an I/P converter for 4–20 mA electrical signal.

7. Typical Applications:

   1. Feed flow control for chemical reactors

   2. Pressure/temperature regulation in steam pipelines

   3. Boiler feedwater flow control

   4. Heating medium flow regulation for heat exchangers

   5. Air flow regulation in wastewater treatment plants (aeration)

   6. Pressure control in oil pipelines

   7. Chilled/hot water regulation in HVAC systems

Summary

The Pneumatic Single Seat Control Valve, with its advantages of low leakage, high control accuracy, high allowable differential pressure, and robust construction, is one of the most widely used control valves in process control systems. It is suitable for a wide range of media from water and steam to corrosive chemicals, covering temperatures from –196°C to +450°C and pressure ratings up to Class 900.

The single‑seat design ensures tight shut‑off, while the multiple flow characteristics and accessory options provide flexibility to meet different control requirements. Compared with electric control valves, pneumatic control valves offer faster response, better explosion‑proof performance, and lower cost. For automated systems that require precise control of flow, pressure, temperature, or liquid level, the Pneumatic Single Seat Control Valve is a reliable and economical choice.