There are many operations in the pump industry, which need to control the flow of various fluids in different processes.

For more than 50 years, thermoplastic valves have been increasingly accepted as an effective choice for metal valves in many applications. The advantages of thermoplastic valves include:

Thermoplastic valves have the advantages of light weight, corrosion resistance, chemical resistance and non-toxicity. They also do not scale or rust, and have low thermal conductivity. Thermoplastics are commonly used in municipal and industrial chemical feed systems. When used within the range of material specifications, they are strong and durable, and are well-proven for industrial applications. Thermoplastic valves equipped with electric or pneumatic actuators also allow operators for automatic control and remote access.

Thermoplastic valve materials The most commonly used materials in thermoplastic valve manufacturing are PVC, CPVC, GFPP and PVDF. Under the same operating temperature, pressure, impact, and UV exposure, these two materials inherently behave differently.

The thermoplastic valve body is precision molded from the base material. Thermoplastic valve assemblies also have smaller parts made of different materials that also interact with the liquid process. Due to potential chemical compatibility, all these materials require special attention when selecting valves. Incorrect selection of materials, especially O-rings and linings, may cause premature valve failure.

The ball valve uses an elastomer O-ring made of EPDM or FMP. They are located in the end connection and the valve stem to form a sealing surface between the plastic parts. The PTFE valve seats on both sides of the ball provide a smooth stroke and sealing surface for the ball, so that the ball can lean on it. The thermoplastic butterfly valve has an elastomer lining in which the disc is sealed, and the O-ring is made of EPDM, Viton or nitrile. The thermoplastic butterfly valve also has a stainless steel or titanium shaft to fix the bushing and disc assembly in the valve body.

When specifying valves for potentially corrosive applications, reviewing the chemical resistance chart for the chemical compatibility of thermoplastic and elastomer materials will ensure the correct choice of materials. EPDM is an elastomer recommended for water, steam, dilute acid, dilute alkali and alcohol.

The working pressure of all thermoplastic materials decreases with increasing temperature. The maximum working pressure of a 2-inch ball valve can be 250 psi at 70°F without shock. The pressure and temperature curves of PVC and CPVC are different. The 80 PVC ball valve of the same specification has a maximum pressure of 130 psi at 145°F.

Read: Asahi, a manufacturer of thermoplastic valves, acquires its Southern African distributor

Valve actuators are devices that "drive" or move a valve to open or close. It is connected to and works with two parts: the valve body and the valve guide.

When considering driving thermoplastic valves, the following points need to be determined:

Electric or pneumatic pneumatic actuators require factory-supplied air and adopt double-acting or spring return. Options include solenoid valve (AC or DC), air filter/regulator, positioner (4-20 mA), auxiliary limit switch, visual indicator and detachable manual operation device.

Actuator cycle time is the time required for the actuator to open to close. It is important to prevent the valve from opening or closing too fast to cause water hammer. The cycle time of Hayward's HRSN2 electric actuator for a 4-inch ball valve is approximately 9 to 13 seconds. The cycle time of a 12-inch butterfly valve is approximately 39 seconds. For electric actuators, this speed is fixed.

The speed of the pneumatic actuator is controlled by the solenoid valve assembly, which opens or closes according to instructions and regulates the air flow into and out of the actuator piston cylinder. The double-acting actuator provides air to open and close the cylinder. When the air supply is lost, the double-acting valve will remain in the last position. Fail-safe spring return actuators are used in applications that require the valve to move to the fully open or fully closed position in the event of an interruption in the air supply. The fail-safe position is selected when specifying the actuator, but it can be changed on site if necessary.

Electric actuators-these types of valves are the most common and reliable. They can quickly operate some of the largest valves, and they are powered by single-phase or three-phase motors that drive a combination of horizontal and spur gears. Subsequently, these gears and spur gears drive the valve stem nut, which engages with the valve stem to open or close it. They usually include a separation mechanism and a handwheel, which can be manually operated when the power is off.

Manual actuators-Manual actuators use levers, wheels and/or gears to facilitate movement. Manual actuators are different from automatic actuators because they have an external power source that can provide the force and movement required to operate the valve automatically or remotely. For many valves, manual operation is not an option, either because the application includes valves in remote pipelines, or because of the absolute force required for operation. In addition, manual actuators are not a practical solution for valves located in toxic or harsh environments, and they are not as useful in applications that require safety precautions that allow immediate closure.

Conclusion When selecting a valve actuator, the use factor is an important consideration. For example, electric actuators essentially require electricity to operate. Pneumatic actuators can operate in the temperature range of -4 to 150°F (-20 to 70°C), or in some cases, -40 to 250°F (-40 to 121°C) , The premise is that the seals are correct and the grease and bearings are in place. Electric actuators can operate in a temperature range of -40 to 150°F (-40 to 65°C).

Due to its explosion-proof nature, pneumatic actuators are usually the first choice in hazardous or toxic environments, but if there is a lack of compressed air or pneumatic actuators cannot meet other operating specifications, electric actuators can be used.

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