Definition
A pneumatic diaphragm valve is a specialized valve that uses a flexible diaphragm made of soft materials to isolate the valve stem and other moving parts from the process media. This design prevents media from coming into contact with the valve stem and eliminates the need for traditional packing seals, thereby avoiding potential leakage.
Classification
According to the structural form, diaphragm valves can be divided into six types: house type, direct flow type, cut-off type, direct flow type, gate type and right angle type; The connection form is usually flange connection, which can be divided into three types according to the driving mode: manual, electric and pneumatic, among which pneumatic driving is divided into three types: normally open, normally closed and reciprocating.
Pneumatic diaphragm valves are categorized into three main types:
– Normally Closed: The valve is closed until actuated by air pressure.
– Normally Open: The valve remains open until air pressure is applied to close it.
– Reciprocating: The valve can be actuated to open or close with air pressure.
Structural Features
The key feature of a pneumatic diaphragm valve is the diaphragm, which acts as a barrier between the valve stem and the fluid. The valve closure is achieved when the stem tip and the diaphragm press the valve disc against the seat. The valve opens when an internal spring lifts the disc as the stem rises. The valve’s lift is limited by the diaphragm’s movement, resulting in a smaller lift compared to conventional valves. To compensate for this, the seat and flow area are enlarged to ensure adequate flow capacity.
Advantages
Pneumatic diaphragm valves offer several advantages:
– No stem packing is required, which eliminates a common source of leakage.
– The diaphragm provides a reliable seal even for dirty liquids.
– Suitable for sterile and sanitary applications due to the separation of the media from the valve mechanism.
– Can handle abrasive media effectively.
Selection Principle
When selecting a pneumatic diaphragm valve, consider the following:
– Suitable for low-pressure applications and low-differential pressure scenarios.
– Ideal for applications requiring tight shut-off, especially with abrasive or corrosive media.
– Not recommended for high-pressure or high-temperature applications unless a metal diaphragm is used.
– Can be used in two-position control, throttling, and low-noise applications.
Summary
Pneumatic diaphragm valves are widely used in semiconductor and electronic special gas industries, etc. When selecting them, we should choose according to the actual application requirements and the characteristics of applicable media.
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