Cost-effective actuation concepts

February 2009 Valves, Actuators & Pump Control

Control valves are gaining ground.

Cost pressure, the need to save limited raw materials, regulations, environmental protection and customer demands means that operating parameters are getting ever tighter. In piping systems this means the pressures, temperatures, volume flows and ph-values must be controlled more precisely. With increasing automation the data is recorded automatically, stored and passed on to superior control systems. For these reasons simple open/closed controls are being increasingly replaced by automatic control systems. At the same time pneumatically operated valves are being replaced with motorised valves. The reason for this is often the increasing cost of providing compressed air or the wasteful vending of exhaust air in the unit.

GEMÜ takes these demands into account when developing new products. For globe and other types of valves a range of manual, pneumatic and motorised operators are available for control and regulation applications.

Selection for positioning and control tasks

Control valves have a direct effect on the flow (indirectly on pressure, temperature, concentration etc). In globe valves the appropriate flow characteristics are achieved by means of a defined seat contour (eg, regulating cone).

GEMÜ globe valves for control tasks are optimised in the following areas:

* Inner geometry favourable to the flow even in a partially open state.

* Long stroke distance at low cross sectional increase at the valve seat.

* Jolt-free actuation.

* Long life with regard to actuating frequency.

By using regulating needles, regulating cones and regulating cages they can be optimally designed for the flow range to be controlled and the different characteristics required. They are used preferably for clean media, especially steam and gases. Diaphragm valves are preferred for sterile applications or media contaminated by particles. Usually only ball valves can be considered at high pressures and butterfly valves for large nominal sizes.

Electro-pneumatic positioners

Electro-pneumatic positioners are most frequently used with actuators for control functions, because of the more favourable costs in comparison with motorised actuators, these positioners are used wherever compressed air is readily available.

In addition to the process parameters and the system for which the positioner must be suitable, a few other technical properties play a part in the selection of the right positioner. GEMÜ has a complete range of positioners for performing various control tasks.

For more information contact Keith Hedges, GEMU Valves Africa, +27 (0)11 708 6299, [email protected], www.gemue.de

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Cost-effective actuation concepts

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