Sliding gate control valves are easy to handle, compact, light and extremely precise. They provide accurate, fast and economic control of liquid, steam and gaseous media. At the heart of all sliding gate valves are two slotted discs, sliding across and against each other and forming a seal. One of them, the sealing plate, is permanently fixed in the valve body perpendicular to the direction of flow and has a certain number of transverse slots. The second disc, aligned so that it cannot rotate, has the same slot arrangement and moves perpendicularly to the sealing plate, thus changing the cross section of the flow. The pressure difference acts on the moving disc, forcing it against the stationary disc. This provides the seal in the sliding gate valve without the need for a metallic seat.
This superior structural principle forms the basis of an extremely short and compact construction with very low weight inherent in its design. As a result, the newly developed DN250 sliding gate valve weighs a mere 50 kg, including its actuator, whereas a globe valve of the same nominal size tips the scale at about 500 kg. This significant weight advantage not only reduces the space needed to install it, but also minimises the cost and effort to fit it. Because of the weight advantage of sliding gate valves, in most cases it is not necessary to provide additional support for the pipeline. As a general rule, the amount of labour needed in installation and maintenance is reduced to one person – without any need for lifting gear. And, of course, the lower material content is reflected in the price, particularly for stainless steel versions.
Furthermore, the sliding gate valve is characterised by other important advantages through its design which play an ever increasing role as size increases. Since the throttling elements are designed to be perpendicular to the flow, it needs very small actuation forces to operate it, so that, in contrast to the traditional globe valve, it needs barely one tenth of the force to position and close it. In the case of a DN250 sliding gate valve, the surface area of the diaphragm in the valve actuator is a mere 500 square centimetres to control a pressure difference of 10 bar. The comparatively low force requirement not only means significantly lower energy consumption, and, therefore, substantially lower operating costs, but is also visually evident, above all, in smaller and therefore much more economical valve actuators which are reflected on the scales and in the budget.
Benefitting additionally from a stroke of only 8,5 mm, switching times for a complete on/off process take less than a second, while in control mode, achievable positioning times of 2-3 seconds are obtained. Furthermore, the sliding gate valve offers favourable flow-related characteristic data, variable Kvs values and excellent rangeability. Added to this are extremely low rates of leakage, both internal as well as external, minimal wear, insensitivity to cavitation and reduced noise emission. The DN250 sliding gate valves from Schubert & Salzer Control Systems are available in PN16 and ANSI150 versions and, in summary, open up not only advantages for the process but also provide a tremendous savings potential through low operating costs during their service lives.
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