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Valve Setup/Steam How Valve Setup Helps to Reduce the Cost for Steam Systems

| Author / Editor: Dr. Reiner Lange, Peter Stein / Wolfgang Ernhofer

The level of quality attainable in controlling a steam plant is heavily dependent on the dynamic characteristics of the total system comprising the control element, actuator and controller. The control parameters for sliding gate valves relating to dynamic behaviour are clearly superior to those for conventional control valves...

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The sliding gate valve reins in costs for steam systems.
The sliding gate valve reins in costs for steam systems.
(Picture: Schubert & Salzer)

As a result, the highly responsive dynamics not only improve the control quality but also form the basis for control circuits with very short reaction times. This has proved to be the key factor in steam savings of up to 30 %. Current comparisons of steam plant operators show that savings of this magnitude are attainable only by installing a sliding gate valve in place of a traditional control valve.

Reducing Actuator Reaction Time Saves Steam

The most important prerequisites for short reaction times in a control element are short strokes, small actuators and low actuation forces resulting from these. All of these characteristics come together in the sliding gate valve. As it operates, two slotted plates slide against each other transversely to the direction of flow. Thus, the sliding gate valve seals itself without the need for a metallic seat.

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The typical stroke between opened and closed is a mere 6 to 9 mm. One of the most noteworthy advantages stemming from this operating principle is the low actuation force required for the positioning movements.

Sliding Gate Valves Need Reduce Actuation Force by a Factor of Ten

This actuation force F can be determined for the sliding gate valve by the coefficient of friction µ of the sliding pair, the slot area ASlot facing the flow and the differential pressure Δp with F1 = µ ASlot Δp. The force requirement for an equivalent globe style valve is obtained from F2 = ASlot Δp. Comparing these two forces mathematically results in F1 / F2 = µASlot/ASeat = 0.1 for valves with the same Kvs value and the same differential pressure. Therefore, the sliding gate valve needs only one tenth of the actuation force required by a globe style valve under the same process conditions. Also as a direct result of this, the valve actuator for sliding gate valves is naturally correspondingly lighter and smaller...

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