During use, the control assembly may call for a valve closed state. In this regard, the control assembly creates a pressure above the diaphragm to position the diaphragm in a sealed arrangement with the valve seat.Bellows Seal Valves In particular, the pressure above the diaphragm is equalized with the pressure below the diaphragm, allowing the diaphragm to position and seal against the valve seat. Once sealed, the diaphragm prevents fluid flow to the fluid outlet. Conversely, when the control assembly calls for a valve open state, the control assembly creates a pressure differential across the diaphragm by reducing the pressure above the diaphragm (in the control chamber). In response to this reduction in pressure, the diaphragm extends away from the valve seat, or "inflates". In other words, the control assembly reduces pressure above the diaphragm to a level less than the pressure in the working chamber. The pressure in the working chamber forces the diaphragm to extend away from the valve seat, allowing fluid to flow to the fluid outlet.

A variety of modifications can be made to the above-described design for improved performance.Plug Valves For example, a weight and/or a spring mechanism may be associated with the diaphragm to assist in forcing the diaphragm into engagement with the valve seat. Generally speaking, however, operation of the diaphragm valve remains the same. Namely, positioning of the diaphragm determines whether the valve is open or closed. The diaphragm seals against the valve seat in the valve closed state. Conversely, the diaphragm extends (or inflates) away from the valve seat to open the valve.

While this approach is widely accepted, a potential design constraint does exist. The diaphragm is normally made of a flexible, non-metallic material, such as rubber. In the valve open state, pressure within the working chamber imparts a force on the diaphragm, developing a stress and strain across the diaphragm material as the diaphragm extends. At relatively low working chamber pressures, this internal stress and strain has virtually no effect on diaphragm integrity, as the elasticity of the diaphragm material provides for complete recovery once the pressure is equalized.FILTER SERIES The diaphragm will continue to extend without failure in response to the working chamber pressure to a maximum working extension, which is defined as the maximum extension at which the diaphragm will reliably function over a long period of time. If the diaphragm is subject to further extension beyond this critical force or extension value, the stress and strain across the diaphragm material increases exponentially. The pressure acting on the diaphragm overcomes the inherent strength of the material used for the diaphragm, causing permanent structural damage or even rupture. Thus, the pressure rating of a diaphragm valve is limited by the strength of the diaphragm material itself. While the diaphragm material can be reinforced with a fabric weave, the same rupture problems will occur, albeit at somewhat higher working chamber gas pressures. As a result, failure of the diaphragm beyond the maximum working extension limits the operating pressure rating of most diaphragm gas valves to approximately 5 psi (34.5 kPa).

Diaphragm valves, and in particular diaphragm gas valves, are relatively inexpensive devices used for a wide variety of industrial control applications. Unfortunately, however, diaphragm valves are normally limited to relatively low pressure applications due to inherent constraints associated with the diaphragm material. Therefore, a need exists for a diaphragm valve able to consistently perform in high pressure

MORE NEWS