What is a Plastic Valve?

1. Plastic valves are valves made of lightweight, corrosion-resistant engineering plastics (such as RPP, PVDF, ABS, CPVC, etc.), offering advantages such as light weight, chemical corrosion resistance, no scaling, integrated connection with plastic piping, and long service life.

2. These valves are widely used in industrial fluid control systems in industries such as solar energy, semiconductors, chemicals, pharmaceuticals, environmental protection, and aquaculture water treatment.

3. Jiangsu Leiting Precision New Materials Co., Ltd., as a leading domestic OEM and customized supplier of all-plastic valve series, maintains industry leadership in material research and development, process innovation, and high reliability, thanks to its RMB 11 billion production capacity investment and 81 patents (36 invention patents, 36 utility model patents, and 9 design patents).

What are the main structural components of a plastic valve?

Main structural components of a plastic valve:

1. Valve Body: The valve body is the core pressure-bearing component of the valve, responsible for housing the internal fluid passage and connecting to the piping system. 1. Valve Body: Commonly made of corrosion-resistant engineering plastics such as polypropylene (PP), polyvinyl chloride (PVC), RPP, PVDF, and CPVC to ensure lightweight and chemical resistance.

2. Cover: The valve cover is located on top of the valve body and is used to close the valve and provide a support surface for mounting the handle or actuator. The cover is usually secured to the valve body with threads or snaps to ensure a reliable seal.

3. Stem: The valve stem is the key component that transmits external operating force (handwheel, pneumatic, or electric actuator) to the valve core. It passes through the sealing hole in the valve body and is often made of stainless steel or carbon steel to provide sufficient strength and wear resistance.

4. Disc/Plug: The valve core is the moving part that directly controls the opening and closing of fluid. Depending on the valve type (ball valve, butterfly valve, gate valve, globe valve, etc.), the shape and working principle of the valve core vary, but all are made of media-resistant plastic materials (such as PPH, RPP, and PVDF) to achieve fast and smooth opening and closing.

5. Valve Seat: The valve seat mates with the valve core to form a sealing surface, crucial for achieving zero leakage in the valve. Valves typically use rigid elastomers (EPDM, FPM) or metal inserts to maintain sealing performance under high pressure or high temperature conditions.

6. Sealing Elements: These include O-rings, gaskets, and sealing pads, used to prevent fluid leakage between the valve body and cover, and between the valve stem and seat. Different materials are selected for sealing elements depending on the medium and operating temperature to ensure long-term reliability.

7. Handwheel/Actuator: Handwheels are a common method for manually operating valves; they are brightly colored and easily identifiable. In automated systems, valves can be equipped with pneumatic, hydraulic, or electric actuators for remote or programmed control.

8. Fasteners: Bolts, nuts, clamps, etc., are used to securely assemble components such as the valve body, cover, and seat, ensuring the rigidity and sealing of the overall structure.

Component	Primary Function	Typical Materials (as used by Leiting)
Valve Body	Bears working pressure and forms the fluid passage	RPP, PVDF, CPVC, ABS
Valve Cover / Seat	Works with the body to achieve sealing	Same as body material or metal flange
Disc / Plug	Controls opening or closing of flow	RPP, PVDF, PPH, ABS
Sealing Elements (O‑rings, Seats)	Prevents leakage and provides tight sealing	EPDM, FPM, fluorinated rubber
Stem / Bolts	Transmits manual or actuator force	Stainless steel or carbon steel (bolts)
Handwheel / Actuator	Manual or automatic adjustment of valve position	ABS handwheel, pneumatic/electric actuators

What are the connection methods for plastic valves?

1. Hot Melt (Heat Fusion Connection): This method fuses the plastic pipe to the valve body using heat, commonly used for PPR and PE series pipelines.

2. Electrofusion (Electrofusion Connection): This method uses resistance heating to achieve a fast and reliable connection, suitable for large-diameter plastic pipes.

3. Rubber Ring (Adhesive) Connection: This method uses specialized adhesives or rubber sealing rings to achieve a tight bond between the valve body and the pipeline, commonly found in UPVC and PVC systems.

4. Flange Connection: The valve body is equipped with plastic or metal flanges, and a stable connection is achieved by bolting. Suitable for high-pressure or large pipeline systems.

Connection Method	Description	Typical Applications
Hot Melt	Heat melts the plastic pipe and valve together for a seamless joint	PPR, PE pipe systems
Electrofusion	Uses electrical resistance heating for rapid, reliable bonding, suitable for larger diameters	Large‑diameter plastic pipelines
Rubber‑gasket (adhesive) connection	Employs special adhesives or rubber gaskets to tightly join valve and pipe	UPVC, PVC systems
Flanged connection	Valve equipped with plastic or metal flanges, bolted together for a secure joint, ideal for high‑pressure or large‑scale pipelines	High‑pressure or large‑diameter systems

What are the common fault symptoms of plastic valves, and how can they be diagnosed and repaired on-site?

1. Common Fault Symptoms

1.1 Leakage or Seepage: The medium seeps from the valve seat, valve disc, valve stem packing, or flange bolts, often accompanied by dripping water, dripping oil, or gas escaping.

1.2 Valve Jamming and Malfunction: Difficulty turning the handwheel or valve stem, or even complete jamming, manifests as a heavy feel and increased noise when opening/closing.

1.3 Valve Inability to Fully Close or Open: Maintaining some flow, or experiencing resistance even in the fully open position, often due to wear on the valve disc or seat, or deformation of the valve stem.

1.4 Abnormal Noise or Vibration: Humming, knocking, or severe vibration during operation is often caused by fluid impact, internal impurities in the valve body, or wear on mechanical parts.

1.5 Inaccurate Valve Opening: Slow response of the actuator or unstable control signal leads to a significant deviation between the actual valve opening and the set value.

2. Key Points for On-Site Diagnosis

2.1 Visual Inspection: Observe the exterior of the valve body for signs of leakage, corrosion, or cracks; check for loose flange bolts; confirm whether the sealing rings are aged or cracked.

2.2 Auditory and Tactile Inspection: Listen to the sound of the valve during operation to determine if there is abnormal noise; manually rotate the valve stem to feel for jamming or significant resistance.

2.3 Pressure/Flow Test
Measure the pressure difference across the valve using a pressure gauge or flow meter to determine if the seal has failed. A large pressure difference may indicate wear on the valve seat or valve disc.

2.4 Internal Inspection
After ensuring safety (shutting off the air/water supply and depressurizing), disassemble the valve body and inspect the valve disc, valve seat, valve stem, packing, and other components for wear, corrosion, or deposits.

2.5 Lubrication and Cleaning Inspection
Check the valve stem, gears, bearings, and other transmission parts for insufficient lubrication or blockage by impurities, as these are common causes of jamming.

3. Repair and Handling Measures

3.1 Leakage Handling
Replace Seals: Replace aged O-rings, packing, or valve seat gaskets; if necessary, use media-resistant fluororubber or polytetrafluoroethylene (PTFE) seals.

Tighten Bolts: Retighten loose flange bolts and install anti-loosening washers on the threads.

3.2 Jamming and Malfunction

Clean Impurities: Clean the valve body of deposited minerals, dust, or corrosion products using a soft brush or compressed air.

Relubricate: Apply suitable grease or lubricating oil to moving parts such as the valve stem, gears, and bearings; for valves that have not been used for a long time, perform several opening and closing cycles to restore lubrication.

Replace Damaged Parts: If the valve stem is broken, the valve disc is deformed, or the gears are severely worn, replace the corresponding parts directly, ensuring that the size and material match.

3.3 Inability to Fully Close/Open

Adjust Valve Seat: If the valve seat is worn, causing poor sealing, the seal can be restored by fine-tuning the valve seat screw or replacing the valve seat.

Replace Valve Disc or Valve Stem: If the valve disc is worn or the valve stem is bent, replace it with a new one to restore the full open/full close function.

3.4 Noise and Vibration

Install Silencing Device: Install a silencer at the valve inlet or outlet to reduce fluid impact noise.

Check Support and Fixation: Ensure that the valve body and pipeline are securely supported to prevent noise caused by resonance.

3.5 Inaccurate Opening

Actuator Calibration: Perform zero-point calibration on the electric or pneumatic actuator and check for poor contact in the control signal lines.

Sensor Replacement or Repair: If the position sensor is faulty, it needs to be replaced or readjusted.

How to Match Materials Based on Pipeline Media?

1. Acidic Media (e.g., hydrochloric acid, sulfuric acid)

Recommended Materials: Non-metallic materials such as polypropylene (PP) and fluoroplastics (PVDF, F4, F46) due to their excellent corrosion resistance to strong acids.

Temperature/Pressure Limitations: Plastic valves may fail when the temperature is >150℃ or the pressure is >1.6MPa, requiring the use of ceramic or metal valves.

2. Alkaline Media (e.g., sodium hydroxide)

Recommended Materials: Polypropylene and ordinary stainless steel (304) are acceptable below 80℃ and within a 30% concentration range; titanium alloy or high-alloy stainless steel is recommended for high temperatures and high concentrations. 3. Oils (Petroleum, Lubricating Oils)
Recommended Materials: Polypropylene, polyvinyl fluoride (PVDF), and specialty engineering plastics (PEEK, PPS) offer good oil resistance; fluoroplastic-lined valves can be used under high temperature and pressure conditions.

4. Steam (High-Temperature Steam)
Recommended Materials: PP and PVDF can be used below 150℃; for temperatures exceeding this or under high pressure, metal valve bodies or ceramic valves are recommended to prevent plastic softening or leakage.