When a valve is used for corrosive chemicals, choosing the right material for the wetted parts is just as important as selecting the correct size and pressure rating. Acids, alkalis, solvents and other aggressive fluids can attack conventional metallic surfaces if the valve construction is not suitable for the service.
Lined valves are used in such applications by providing a protective lining between the process fluid and the valve body. PTFE, PFA and FEP are commonly considered lining materials, with the choice depending on the chemical, concentration, temperature, pressure and valve design.
In this guide, we will look at the main types of lined valves, how PTFE, PFA and FEP differ, where these valves are used, and what engineers and purchase teams should check before placing an order.
What Is a Lined Valve?
A lined valve has a protective material on the internal surfaces that come into contact with the process fluid. The purpose is to reduce direct contact between the fluid and the metallic valve body.
The lining material is selected according to the process conditions. For corrosive chemical service, fluoropolymer linings such as PTFE, PFA and FEP are commonly considered.
A lined valve is not selected simply because a fluid is called “corrosive.” The actual chemical concentration, temperature, pressure, flow conditions and required valve function all need to be considered.
Why Are Lined Valves Used?
The main reason is chemical compatibility.
For example, a process may contain an aggressive chemical that can cause corrosion of conventional valve body materials. A suitable lining can provide a barrier between that chemical and the body.
Depending on the application, lined construction may offer:
- Protection against corrosive process media
- Better chemical resistance
- Reduced exposure of the metallic body
- Suitable sealing surfaces for specific chemical services
- A practical option for chemical and process piping
The lining itself also has operating limits. Temperature, pressure, vacuum conditions and mechanical stresses must therefore be checked before selecting the valve.
PTFE, PFA and FEP Lined Valves
PTFE, PFA and FEP are fluoropolymer materials, but they are not interchangeable in every application.
PTFE Lined Valves
PTFE (Polytetrafluoroethylene) is widely used in valve lining applications because of its resistance to many chemicals.
PTFE-lined construction can be found in different valve designs used for chemical and process services.
The suitability of PTFE depends on the actual chemical, concentration and operating temperature rather than the chemical name alone.
PFA Lined Valves
PFA (Perfluoroalkoxy) is another fluoropolymer used where chemical resistance and specific process requirements are important.
PFA can be considered for demanding chemical services, particularly where the process requires a different lining construction from conventional PTFE.
FEP Lined Valves
FEP (Fluorinated Ethylene Propylene) is also used for corrosion-resistant lining applications.
It may be considered for selected chemical services where its material properties are compatible with the process conditions.
PTFE vs PFA vs FEP
There is no single lining material that is suitable for every chemical application.
The selection should consider:
- Chemical compatibility
- Concentration
- Operating temperature
- Pressure
- Vacuum conditions
- Permeation requirements
- Required valve construction
- Manufacturer’s design limits
Therefore, the correct approach is to match the lining with the actual process conditions.
Types of Lined Valves
Lining can be used with different valve designs depending on the required function.
Lined Ball Valve
A lined ball valve uses a quarter-turn ball mechanism for flow isolation. The lined construction helps protect the valve’s wetted surfaces when handling compatible corrosive fluids.
It can be considered for applications involving:
- Chemical transfer
- Acid and alkali service
- Solvents
- Process fluids
- Corrosive media
For automated systems, the valve can be combined with a pneumatic or electric actuator where the design permits.
Lined Butterfly Valve
A lined butterfly valve uses a rotating disc for flow isolation, with an internal lining providing protection against the process media.
Its compact construction makes it useful where space and valve weight are important considerations.
Depending on the design, configurations may include:
- Wafer type
- Lug type
- Flanged type
- Manual operation
- Gear operation
- Pneumatic actuation
- Electric actuation
The lining material and disc construction should be checked against the actual chemical service.
Lined Diaphragm Valve
A lined diaphragm valve is used where isolation of corrosive or process fluids is required and the diaphragm provides separation between the operating mechanism and the fluid.
These valves are commonly considered for chemical processing and other applications where contamination and corrosion need to be controlled.
Lined Control Valve
A lined control valve is used when a corrosive fluid needs to be regulated rather than simply isolated.
Selection is more involved than for an ordinary isolation valve. Engineers may need to consider:
- Flow rate
- Inlet and outlet pressure
- Pressure drop
- Cv/Kv
- Temperature
- Fluid properties
- Cavitation
- Flashing
- Trim design
- Actuator requirements
The lining must also remain compatible with the process throughout the operating range.
Lined Plug Valve
A lined plug valve uses a rotating plug for flow isolation. Lining can be provided on wetted surfaces where corrosion resistance is required.
It may be considered for chemical and process applications depending on the valve design and media.
Lined Check Valve
A lined check valve allows flow in one direction and prevents reverse flow.
For corrosive services, the wetted surfaces can be lined with a suitable material selected for the process.
When specifying a check valve, engineers should also consider flow velocity, pressure drop, installation orientation and the possibility of reverse-flow conditions.
Lined Globe Valve
A lined globe valve can be considered for applications requiring a globe-type valve arrangement with corrosion-resistant wetted surfaces.
The body lining, trim and sealing materials must be selected according to the pressure, temperature and chemical service.
Other Lined Valve Types
Depending on the manufacturer and application, lined construction may also be available for special process valve designs.
These can include:
- Lined sampling valves
- Lined flush-bottom valves
- Lined strainers
- Lined foot valves
- Special-purpose process valves
The availability and construction should always be confirmed for the particular valve model.
Where Are Lined Valves Used?
Lined valves are mainly considered where the process fluid can cause corrosion or where compatibility of the wetted surfaces is important.
Chemical Processing
Chemical plants are one of the major applications. Lined valves may be used for:
- Acid handling
- Alkali service
- Chemical transfer
- Dosing systems
- Solvent handling
- Corrosive process lines
The chemical concentration and temperature should always be provided when selecting the valve.
Pharmaceutical Industry
Selected process applications may use lined valves where chemical resistance and process compatibility are required.
Fertilizer Industry
Corrosive chemicals used in fertilizer manufacturing can require carefully selected valve materials and lining systems.
Water & Wastewater Treatment
Lined valves may be used in chemical dosing and other sections where aggressive treatment chemicals are present.
Petrochemical & Process Plants
Selected corrosive process streams may require lined construction depending on the fluid and operating conditions.
How to Select the Right Lined Valve?
This is one of the most important parts of the selection process.
Do not start with the valve material alone. Start with the process.
1. Identify the Fluid
Give the exact name of the process media.
For example:
- Acid
- Alkali
- Solvent
- Chemical solution
- Water treatment chemical
- Hydrocarbon or process fluid
If it is a chemical mixture, provide its composition wherever possible.
2. Specify Concentration
Chemical concentration can affect compatibility.
For this reason, an RFQ should ideally mention:
Chemical + concentration + temperature
rather than only the chemical name.
3. Check Temperature
Provide:
- Minimum operating temperature
- Normal operating temperature
- Maximum operating temperature
- Design temperature
The lining must be suitable for the complete operating range.
4. Check Pressure
Provide both operating and design pressure.
Also mention if the line experiences:
- Vacuum
- Pressure fluctuations
- Pressure surges
Vacuum service can be particularly important for lined valve construction.
5. Select the Lining
PTFE, PFA and FEP should be evaluated according to the process rather than selected simply because one material is commonly used.
6. Select the Valve Type
Ask what the valve needs to do.
Isolation: Ball, Butterfly, Plug
Non-return: Check Valve
Throttling: Control Valve
Diaphragm isolation: Diaphragm Valve
7. Select the Operating Method
Depending on the application, the valve may be:
- Manual
- Gear operated
- Pneumatic
- Electric
For automated valves, actuator sizing should be based on the actual operating torque or thrust required by the valve.
PTFE Lined Valve vs PFA Lined Valve
This is a common question during valve selection.
Both materials are fluoropolymers, but their properties and suitability can differ depending on the application.
Instead of asking which one is universally better, compare the materials based on:
- Chemical compatibility
- Operating temperature
- Chemical concentration
- Permeation requirements
- Purity requirements
- Mechanical conditions
- Valve construction
- Manufacturer’s recommended limits
The final choice should be based on the actual service conditions.
Common Mistakes When Selecting Lined Valves
Selecting only by chemical name
The concentration and temperature can change the material requirement.
Choosing the valve only by pipeline size
For control applications, flow conditions and Cv/Kv are important.
Ignoring vacuum conditions
A valve suitable for positive pressure may not necessarily be suitable for the required vacuum service.
Selecting an actuator without checking torque
Automated valves should be matched with the actual valve operating requirements.
Assuming all PTFE-lined valves have identical limits
The actual temperature, pressure and vacuum limits depend on the valve construction and lining system.
Not providing complete RFQ information
A manufacturer cannot properly evaluate a valve application if important process conditions are missing.
Lined Valves Manufacturer in India
ALIS Valves is a Lined Valves Manufacturer in India, offering lined valve solutions for chemical, process and other industrial applications where corrosion resistance and compatibility with the process media are important.
The suitable valve configuration can be evaluated based on valve type, media, concentration, pressure, temperature, size, lining material, end connection and operating method.
For a lined valve enquiry, providing complete process details helps in selecting the appropriate construction for the application.
Frequently Asked Questions
What is a lined valve?
A lined valve has a protective lining on its wetted surfaces to separate the process fluid from the valve body and provide suitable chemical resistance for the application.
What are the common lining materials?
PTFE, PFA and FEP are commonly used fluoropolymer lining materials. The appropriate material depends on the process conditions.
What is the difference between PTFE, PFA and FEP?
They are different fluoropolymer materials with different properties. Selection depends on chemical compatibility, temperature, concentration and the requirements of the valve construction.
Which valve types can be lined?
Depending on the design, lined construction can be available for ball, butterfly, diaphragm, plug, check, globe and control valves.
Are lined valves suitable for acid service?
They can be used for compatible acid services, but the specific acid concentration, temperature and pressure must be checked before selection.
Can lined valves be automated?
Yes. Depending on the valve design, pneumatic and electric actuators can be used for automated operation.
Can PTFE lined valves be used under vacuum?
Some designs can be suitable for vacuum service, but the specific valve construction must be checked against the required vacuum conditions.
How do I choose between PTFE, PFA and FEP?
Compare the lining materials against the actual chemical, concentration, temperature, pressure, vacuum and process requirements.
What information is required for a lined valve quotation?
Provide the valve type, size, media, concentration, operating/design pressure, temperature, lining requirement, body material, end connection, operation and quantity.
Who is a Lined Valves Manufacturer in India?
ALIS Valves is a Lined Valves Manufacturer in India, offering lined valve solutions for chemical and industrial process applications.
Conclusion
As an Lined Valves Manufacturer in India Lined valves are considered when the process fluid requires more attention to chemical compatibility and corrosion resistance than a conventional valve construction can provide. PTFE, PFA and FEP offer different options, but the lining should always be selected according to the actual chemical, concentration, temperature and pressure.
The valve type is equally important. A ball valve may be selected for isolation, a check valve for preventing reverse flow, and a control valve where continuous flow regulation is required.
For engineers and purchase teams, the best starting point is the process data. Once the media, concentration, pressure, temperature, valve size, lining and operating method are known, the appropriate valve construction can be evaluated.
ALIS Valves provides lined valve solutions for industrial and process applications, with configurations selected according to the requirements of the service.