Plastic valves are made from plastic materials and are used in applications that require corrosion resistance and/or chemical handling.

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Materials

Acetal polymers offer excellent lubricity, fatigue resistance, and chemical resistance.

Polyvinyl Chloride (PVC) provides good flexibility, smooth surfaces, and nontoxic qualities.

Chlorinated PVC (CPVC) is suitable for high temperature applications and is used in hot water distribution.

Polytetrafluoroethylene (PTFE) exhibits a high degree of chemical resistance and a low coefficient of friction.

Polyethylene (PE) is a soft, flexible and tough plastic with outstanding electrical properties but poor temperature resistance. It is prone to stress cracking and has poor resistance to ultraviolet (UV) light.

Polyproylene (PP) is similar to PVC, but can be used in exposed applications because of its resistance to UV, weathering and ozone.

Polyvinylidene fluroride (PVDF) has good wear resistance and excellent chemical resistance, but does not perform well at elevated temperatures. 

Types

There are many types of plastic valves.

Ball valves provide tight shut-offs, but are not suitable for sanitary applications.

Butterfly valves permit flow in only one direction.

Check valves are self-actuating and prevent the reversal of process flow.

Diaphragm valves separate the flow of gases from the closure element.

Directional valves steer flow through selected passages.

Diverter valves redirect process flow.

Drain valves reduce surplus media.

Float valves open or close automatically as the level of a fluid changes.

Foot valves are check valves with a built-in strainer.

Gate or Knife valves are linear motion valves in which a closure element slides into the flow to shut off the stream.

Globe and Pinch valves are other types of linear motion devices.

Needle valves have a slender, tapered point at the end of a valve stem.

Poppet valves open and close ports with a sealing device and spring.

Plug or stop-cock valves are designed for both on/off and throttling functions.

Other types of plastic valves include sanitary or hygienic valves, sampling or dispensing valves, shut off valves, solenoid valves, and toggle valves.   

Selection 

Performance Specifications

• Valve size
• Pressure rating
• Number of ports or ways
• Media temperature
• Valve flow coefficient

Suppliers specify valves according to metric or English (imperial) measurements.

Actuation 

• Manually, by a hand wheel or crank
• With mechanical devices such floats and cams.
• Electric
• Pneumatic

• Electro-hydraulic

Connection Types

• Compression fittings
• Bolt flanges
• Clamp flanges
• Union connections
• Tube fittings
• Butt welds
• Socket welds

Plastic valves with internal or external threads for inlet or outlet connections are also available. 

Uses

Plastic valves are used with a variety of media. Examples include:

• Powders
• Rendering wastes
• Sludge
• Slurry
• Ash slurry
• Coolants
• Hazardous materials
• High viscosity fluids
• Hydraulic fluid
• Liquid metal
• Lubricants
• Air and compressed air
• Hot and cold water
• Salt water
• Wastewater
• Gasoline
• Diesel fuel
• Liquefied petroleum gas (LPG)
• Natural gas
• Abrasive materials
• Acids
• Adhesives  

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Related Standards

ASME B16.40 - Manually Operated Thermoplastic Gas Shutoffs And Valves In Gas Distribution Systems

BS 2456 - Specification For Floats (Plastics) For Float Operated Valves For Cold Water Services

BS EN 12100 - Plastics Piping Systems - Polyethylene (Pe) Valves - Test Method For Resistance To Bending Between Supports

References

Image Credit:

Aalborg Instruments | Air Logic | Applied Industrial Technologies | Beswick Engineering Co., Inc.