Isolation valve is an indispensable core device in industrial pipelines, energy transmission and fluid control systems, and is known as the “last line of defense” for process safety. It completely cuts off the flow path of the fluid to achieve segmented isolation of the pipeline, equipment maintenance and protection, and rapid shutdown in emergency situations. It is widely used in petrochemical, electric power, water treatment, pharmaceutical and other fields.

Isolation valves can be divided into gate valves, ball valves, butterfly valves, stop valves and other types, each type is optimized for different pressures, flows and media characteristics. This article will start from the definition and core functions of isolation valves, explain their key components, mainstream types, working principles and selection criteria, and deeply explore their practical applications and maintenance points in industrial scenarios, providing authoritative reference for engineering design and operation and maintenance personnel.

What is an isolation valve?

Isolation valve, also known as shut-off valve or cut-off valve, is a key device used to completely block the flow of fluid in industrial piping systems. Unlike check valves (which prevent fluid backflow), the core function of isolation valves is to physically block the flow path to achieve segmented isolation of the system, thereby ensuring safety and controllability during equipment maintenance, overhaul or emergency shutdown. The following is a detailed analysis of the definition, function and classification differences.

Common aliases and industry terms for isolation valves

Isolation valves are commonly referred to by the following names across different industries and applications:

• Shut-off Valve: emphasizes its core function of cutting off fluid.
• ​Block Valve: It highlights the blocking effect on pipeline fluid.
• ​Isolation Gate Valve: specifically refers to the isolation valve type with a gate structure.

Industry terminology standardization ​:

• ISO 5208​: International standard for the classification of valve leakage rates (e.g. Class VI is a high sealing level).
• ​API 600​: American Petroleum Institute design and manufacturing standard for steel gate valves.

Isolation valve symbol

​Isolation valve symbol

The symbols of isolation valves in engineering drawings vary according to type and standard system (such as ISO, ANSI, DIN, GB), but all of them use simple graphics to represent their blocking function and operating logic . The following are the key points:

General Rules

• ​Basic symbols​:
  • ​Rectangular frame: represents the valve body, and a line (vertical or oblique) through it indicates the open or closed state of the flow channel.
  • ​Additional markings​: Arrows, letters or icons indicating the mode of operation (manual/automatic) or special design (fireproof, low temperature).

Common Type Notation Examples

Key annotations

• Manual operation​: The symbol is marked with M or a handwheel icon (🔄).
• Automatic operation​: Note A or actuator type (e.g. P = pneumatic, E = electric).
• Flow direction​: The arrow indicates the direction of medium flow (such as ─→─ ).

​Note: For a complete symbol library and standard comparison, please jump to 👉 Valve Symbols (Isolation Valve)​

Main types of isolation valves

Gate Valve

Working Principle :The flow channel is completely blocked by vertically lifting the gate. When fully opened, the flow channel is consistent with the inner diameter of the pipe, achieving zero pressure loss circulation.

Structural Features :

• ​Valve body: Made of cast steel or stainless steel, suitable for temperatures from -29°C to 425°C.
• ​Gate Type:
  • ​Rigid gate: integral casting, high pressure resistant (Class 1500), used in oil pipelines.
  • ​Elastic gate: with flexible compensation groove to prevent high temperature deformation, used in steam system.
  • ​Knife Gate Valve​: A thin blade gate cuts through viscous media (such as pulp, mud).

​Application Scenarios​: Crude oil transportation, water plant main valve, chemical storage tank isolation.

Learn more about Gate valves《Mastering gate valves from scratch: The ultimate guide from structural principles to selection and application》

Ball Valve

​Working Principle: The sphere with the through hole is rotated 90°. It is open when the through hole is aligned with the pipe and closed when it is vertical. The sealing surface is isolated from the medium.

Structural Features :

• ​Valve Seat Design:
  • ​Floating type​: The ball is pressed against the valve seat (applicable to Class 150 and below).
  • ​Fixed type​: Ball bearing support, high pressure resistance (Class 2500).
• ​Special Types​:
  • ​V-type ball valve: V-shaped cut ball, to achieve linear flow regulation (opening 0~90°).
  • ​Fully welded ball valve: no risk of leakage, used for long-distance natural gas pipelines.

​Application Scenarios: LNG storage and transportation, acid-base medium cutoff, nuclear power plant auxiliary system.

Learn more about Ball valves《Complete Guide to Selecting Zero-Leakage Ball Valves: 30+ Types》

Butterfly Valve

​Working Principle: The disc-shaped butterfly plate rotates around the axis, and the rotation angle 0~90° controls the flow channel opening

Structural Features :

• ​Eccentric design:
  • ​Concentric Butterfly Valve​: The valve plate is coaxial with the pipe, universal for low pressure (PN10~16).
  • ​Double eccentricity: the valve plate deviates from the pipe axis to reduce friction (suitable for food grade media).
  • ​Triple eccentricity: metal hard seal, resistant to high temperature of 550℃ (flue duct of thermal power plant).

​Application Scenarios​: Ship ballast water system, urban heating network, food processing plant.

Globe Valve

​Working Principle: The valve stem drives the conical valve core to vertically press the valve seat, and the cutoff is achieved by changing the cross-sectional area of ​​the flow channel.

Structural Features :

• ​Valve body flow channel:
  • ​Straight-through type​: high flow resistance, suitable for small-diameter (DN≤50) high-pressure cut-off.
  • ​Angle type​: The inlet and outlet are 90°, reducing the use of elbows (boiler blowdown).
  • ​Y-type: The flow channel is oblique, reducing pressure loss (PN420 ultra-high pressure system).

​Application Scenarios​: Steam trap, pharmaceutical reactor feed port, cryogenic liquid oxygen pipeline (-196℃).

Plug Valve

Working principle: Cylindrical or conical plug opening, rotating 90° to switch the flow channel on and off, the sealing surface needs to be filled with grease.

Structural Features :

• ​Lubrication design:
  • ​Conventional type​: Regular grease injection maintenance, used for medium containing particles (mining slurry).
  • ​Non-lubricated type: PTFE bushing is self-lubricating and meets FDA food grade standards.

• ​Multi-way design: Three-way and four-way plug valves are used for fluid distribution (chemical reactors).

​Application Scenarios: Asphalt transportation, beer fermentation tanks, oil field water injection systems.

Diaphragm Valve

Working Principle: The elastic diaphragm (rubber or PTFE) deforms under pressure and fits against the valve weir to block the fluid.

Structural Features :

• ​Body Type:
  • ​Weir type: The diaphragm is pressed against the weir, suitable for throttling control (laboratory micro valve).
  • ​Straight-through type: full flow channel design, no dead corner residue (biopharmaceutical pure water system).
• ​No-filler design: No external leakage, suitable for highly toxic media (such as phosgene treatment).

​Application Scenarios: vaccine production pipelines, electroplating liquid transportation, semiconductor ultrapure water.

Parallel Slide Valve

Working Principle: The double gates slide in parallel, and the spring preload compensates for thermal expansion to ensure stable sealing at high temperatures.

Structural Features :

• ​For steam only: Valve body material ASTM A217 WC9, temperature resistance ≤550℃.
• Self-tightening seal​: The higher the medium pressure, the stronger the fit between the gate and the valve seat (Class 900~2500).

​Application Scenarios​: Main steam pipelines in thermal power plants and catalytic cracking units in refineries.

Pinch Valve

Working Principle: External pneumatic/mechanical force squeezes the rubber sleeve to completely close the flow channel.

Structural Features :

• ​Full bore: No obstruction elements, suitable for media containing fibers and crystals (such as pulp and salt slurry).
• ​Wear-resistant bushing: lined with natural rubber or polyurethane, life ≥ 500,000 operations.

​Application Scenarios​: fly ash transportation in cement plants, sludge pipelines in sewage treatment plants.

Plunger Valve

Working Principle: The plunger-shaped valve core cooperates with the metal sealing ring to achieve bidirectional forced sealing.

Structural Features :

• ​Metal hard seal: Stellite alloy surfacing, resistant to particle erosion (mine tailings).
• ​Compact design​: shorter overall length than a globe valve (API 602 standard).

​Application Scenarios​: geothermal well high-pressure water injection, steel plant high-temperature oil circuit.

Needle Valve​

Working Principle: The tapered needle valve core is precisely matched with the valve seat, and the flow rate is fine-tuned through fine-pitch threads (40-60 threads per inch).

Structural Features :

• Ultra-high pressure design: Forged valve body (ASTM A182 F316), pressure resistance ≤1000Bar.
• ​Anti-misoperation​: Handwheel with locking nut or scale indication (nuclear power plant instrument system).

​Application Scenarios​: Hydraulic test bench, spacecraft fuel filling, chromatograph analyzer.

What is the function of an isolation valve?

Isolation valve is a key device for actively controlling the flow of fluid in pipeline systems. Its core functions include:

Core Features

1. ​Safety Isolation:
   When repairing equipment or troubleshooting, completely block the flow of fluid to prevent media leakage or personnel contact with hazardous substances (such as high-temperature steam, toxic chemicals).
2. ​System Segmentation​:
   Divide large pipe systems into independent units to facilitate segmented maintenance, testing or modification (such as zoning maintenance of water supply networks).
3. ​Emergency Shutdown:
   Quickly cut off the medium in case of sudden leakage or fire to prevent the accident from spreading (such as automatic shut-off valve of natural gas pipeline).
4. ​Flow Control:
   Unobstructed flow when fully open, zero leakage when fully closed (high-grade sealing), some types (such as V-type ball valves) can adjust the flow.

Special scene additional functions

• ​Fireproof Design: Remains sealed during fire (API 607 ​​certified).
• ​Low temperature/high temperature tolerance: Stable operation under deep cold (-196℃) or ultra-high temperature (550℃) conditions.

Risks of not installing isolation valves

• Inability to safely maintain equipment, resulting in extended downtime.
• Leakage may cause environmental pollution or safety accidents (such as leakage of chemical raw materials).

How do isolation valves work ?

The isolation valve drives the actuator (gate, ball, butterfly plate, etc.) inside the valve through external force to change the flow channel state and realize the on-off control of the fluid. Its operation logic is different from that of the check valve (which automatically opens and closes depending on the pressure difference) and requires active intervention. The specific process is as follows:

Open valve

1. Drive mode:
   • ​Manual​: Rotate the handwheel/lever to drive the actuator through the valve stem (such as rotating a ball valve 90° to fully open).
   • ​Electric/Pneumatic​: The actuator receives a signal and drives the valve stem to move (such as an electric gate valve motor raising and lowering the gate).
2. ​Flow channel status:
   • The actuator is completely out of the flow path (such as the gate valve is fully open), the medium flows unimpeded, and the pressure loss approaches zero.

Close valve

1. Drive mode:

• Manual​: Rotate the handwheel in the opposite direction to the mechanical stop to ensure complete sealing.
• ​Automatic​: In an emergency, the PLC signal triggers the pneumatic/electric actuator to close quickly (<5 seconds).

1. Sealing mechanism:

• Soft seal​: PTFE/rubber valve seat deforms under pressure to achieve zero leakage (Class VI).
• ​Metal hard seal​: The ball/gate fits tightly with the metal surface of the valve seat, resistant to high temperature and high pressure.

Operation comparison

Key Tips

• The isolation valve must be installed according to the flow direction mark (such as the arrow on the stop valve points to the outlet).
• Lubricate the valve stem regularly and test the sealing to prevent sticking or internal leakage (refer to ISO 5208 standard).

How to choose the right isolation valve? Key considerations

Based on the check valve selection criteria diagram you provided, the isolation valve selection needs to consider the following core factors:

Valve material and fluid compatibility

• ​Corrosion Risks:
  Select corrosion-resistant materials according to the medium (acid, alkali, oil, gas, etc.), such as:
  • Stainless steel (SS316): general purpose and resistant to corrosive media.
  • ​Hastelloy: Strong acids (such as sulfuric acid and hydrochloric acid).
  • ​PTFE: High purity chemicals (e.g. semiconductor industry).
• ​Pollution Control​: Food/pharmaceutical industries require FDA-certified materials (such as EPDM rubber seals).

Fluid properties and operating conditions

Pressure level and sealing requirements

• ​Pressure Matching:
  The PN (European standard) or Class (American standard) of the valve must be ≥ the maximum working pressure of the system (e.g. PN40 corresponds to Class 300).
• ​Leakage level:
  High-risk media (such as natural gas) require ISO 5208 Class VI (zero leakage), and ordinary water systems can choose Class IV.

Pipe size and connection method

• ​Path Matching​:
  Full-bore ball valves (DN50~600) are suitable for large flows, while stop valves are preferred for small-diameter (DN≤50).
• ​Connection Type​:
  • ​Flange connection: high-pressure large-diameter pipelines (such as oil pipelines).
  • ​Threaded/Wafer Connections​: Compact spaces (such as instrument branch lines).

Operation Mode and Frequency

Special requirements and certification

• ​Fireproof design: API 607 ​​certified valves (such as flammable medium pipelines in refineries).
• ​Sanitary standards: The pharmaceutical industry requires 3A certification (such as diaphragm valves).
• ​Low temperature/high temperature​: Extended bonnet for cryogenic valves, graphite packing for steam valves.

Selection process: Determine medium characteristics → Match material/seal → Calculate pressure level → Select valve type → Determine drive mode → Verify special requirements

Installation, maintenance and troubleshooting of isolation valves

Installation specifications and precautions

Core steps :

1. ​Pre-installation checks:
   • Confirm that the valve model, pressure level (such as PN40), and flow direction mark (arrow) match the pipeline.
   • Clean welding slag and impurities inside the pipeline to prevent damage to the sealing surface.
2. ​Connection method:
   • ​Flange connection​: Align the bolt holes and tighten the bolts evenly (in diagonal order) to avoid uneven force on the valve body.
   • ​Threaded connection​: Wrap PTFE raw tape, no excessive amount (to avoid blocking the flow channel).
3. ​Directions and Locations:
   • The stop valve is installed according to the flow direction (the valve seat side is the inlet), and the ball valve and gate valve can be installed in both directions.
   • The valve stem of a horizontal pipeline is vertically upward, and the valve stem of a vertical pipeline is inclined ≤45° (for easy operation).

Common Mistakes ​:

• No operating space is reserved (for example, the distance between the handwheel and the wall is less than 30cm).
• Direct operation without cooling after welding will cause deformation of the seal.

Daily maintenance and care

Maintenance cycle and content :

Special scene maintenance :

• ​Cryogenic valves: Check the valve cover insulation layer regularly to prevent frost from causing packing failure.
• ​Pinch valve​: Replace the rubber sleeve every 2 years (to avoid aging and cracking).

Common faults and troubleshooting methods

Emergency treatment :

• ​Unable to close​: The manual override device forces the valve to close (such as the handle of a pneumatic valve being pulled off).
• ​Fire risk​: Enable fire hood protection and cut off the upstream medium first.

Repair and Replacement Recommendations

• Q​Repairability:
  • Gate valve, stop valve: valve seat and valve stem can be replaced on site.
  • Ball valves and butterfly valves: Most of them are replaced as a whole (precision sealing components are difficult to disassemble).
• ​Scrap standards:
  • Cracks in valve body (confirmed by penetrant testing).

The corrosion depth of the sealing surface is greater than 0.5 mm (cannot be repaired).

Summary: Correct installation, regular maintenance and rapid fault response are the key to extending the life of the isolation valve (usually 15 to 20 years). Combined with the JH valve parameters provided, it is recommended to strictly follow the manufacturer’s maintenance manual to ensure system safety.

Decision guide for purchasing isolation valves

Based on the logic of the check valve selection criteria you provided, the selection of isolation valves needs to focus on safe isolation, media compatibility and working condition adaptability. The following are the key decision factors and steps:

Valve material and media compatibility

• ​Core Principles​: The material must be compatible with the fluid chemistry to avoid corrosion or contamination.
  • ​Corrosive media (acid, alkali): choose stainless steel (SS316), Hastelloy or fluorine-lined valve body (PTFE).
  • ​High-purity media (pharmaceuticals, food): select EPDM rubber seals and 316L polished inner wall.
  • ​High temperature steam​: Choose carbon steel (WCB) or chrome-molybdenum steel (WC6).

Matching fluid properties with valve type

Pressure level and sealing requirements

• ​Pressure matching: Valve PN (European standard) or Class (American standard) must be ≥ the maximum system pressure (e.g. PN40 corresponds to Class 300).
• ​Sealing level:
  • ​Normal scenarios​ (water, air): ISO 5208 Class IV (allows trace leakage).
  • ​High-risk scenarios​ (natural gas, chemicals): Class VI (zero leakage).

Pipe size and connection method

• ​Distance Adaptation:

• • Small diameter (DN≤50): stop valve, needle valve (precision control).
  • Large diameter (DN＞200): butterfly valve, full-bore ball valve (low flow resistance).
• ​Connection Type​:
  • ​Flange connection: high pressure, easy disassembly scenario (oil pipeline).
  • ​Threaded/Wafer Connections​: For tight spaces or instrument branch lines.

Operation mode and automation requirements

Special working conditions and certification requirements

• ​Fire protection design​: API 607 ​​certification (such as flammable medium pipelines in refineries).
• ​Low temperature/high temperature: Extended bonnet for cryogenic valves (-196°C), graphite packing for steam valves.
• ​Sanitary certification: The pharmaceutical industry requires 3A or FDA standards (such as diaphragm valves).

Selection process

1. Confirm the media type (corrosive/clean/containing particles) → 2. Match the valve material and type → 3. Calculate the pressure and sealing level → 4. Determine the pipe size and connection method → ​​5. Select the drive method (manual/electric/pneumatic) → 6. Verify special requirements (fire protection/sanitation)

Pre-purchase verification checklist

• ​Technical parameters​: Check the PN/Class and temperature range in the manufacturer’s manual (e.g. JH PN40/DN32).
• ​Test Report​: ISO 5208 sealing test and pressure shell test certificates are required.
• ​After-sales service​: confirm the warranty period (usually 1 to 3 years) and spare parts supply capabilities.

Summary: The selection of isolation valves must be based on safe isolation, and the media, pressure, operating logic and cost must be considered comprehensively, and industry standards (such as API 600, ISO 5208) must be strictly followed. The standard check valve drawing (fluid compatibility, pipeline size) you provided can be partially referenced, but the unique active control requirements of the isolation valve (such as drive mode, sealing, etc.) must be supplemented. Summary: The selection of isolation valves must be based on safe isolation, and the media, pressure, operating logic and cost must be considered comprehensively, and industry standards (such as API 600, ISO 5208) must be strictly followed. The standard check valve drawing (fluid compatibility, pipeline size) you provided can be partially referenced, but the unique active control requirements of the isolation valve (such as drive mode, sealing level) must be supplemented.

The isolation valves produced by JH valve manufacturing plant have built an invisible Great Wall in life-and-death pipelines such as energy, chemical and pharmaceutical industries with millimeter-level sealing accuracy and millisecond-level response speed. From the radiation barrier of a nuclear power plant to the sterile barrier of a vaccine plant, we use space-grade redundancy design and life-cycle carbon tracking technology to make every cut-off the ultimate promise of absolute physical isolation – because safety does not need to be compromised, and we are the last silent guardian of the process industry’s line of defense.