Wednesday, April 6th, 2011

When fluids or gases are moved through a piping system, some sort of valve or valve arrangement is necessary to control the flow. The choice of valve will depend on several factors:

· The composition of the material is being transported and pressures involved

· What type of control is required, such as on/off or metered flow

· The precision of control necessary

· Whether the control is performed by human intervention or is automatically controlled

Two of the most common valves are ball valves and solenoid valves. Each valve style has characteristics that make it suitable for defined purposes. Additionally, some valves can be manually operated. Others are controlled by electrical, hydraulic or pneumatic methods.

The ball valve gets its name from the ball-shaped actuator in the valve body. The simple ball valve has one hole or port through the ball and provides quick on/off control with a quarter turn. Valves are also available with multiple ports that will provide directional control as well. Electrical control can be provided by the use of a motorized actuator. Compressed air can also be used for faster operation. It is use mainly for fluid control, although some may be designed for gases. The valve materials should be matched with the fluid characteristics and pressures.

Solenoid valves are used mainly for gases. They are diaphragm type valves and are operated by an electrical coil mounted on the top of the valve. When power is applied to the coil, the valve either opens or closes, depending on the configuration. The valve is returned to the original de-energized position by a spring. Electrical control is usually accomplished by a pressure switch that sends a signal to the coil when conditions are met. There is no manual control for a solenoid valve, although on/off switched and control panel relays can be used to operate the valve.

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