Slide valves are one of the many variations of the gate-type valve and were originally designed for use in the pulp and paper industry to overcome the problems in handling wet and dry fluidized solids in pipelines.
The opening or closing was achieved by pushing or pulling the plate to give a crude shut-off. The logical advancement from this design was the fitting of resilient seals and an operating screw and handwheel to open and close the slide. With the improvement in sealing that this gives, the slide valve is suitable for a much wider range of services and can handle solids suspended in liquids or gases.
Design:
Above shows the typical design of slide valves. The seal is housed in the body of the valve and shrouded by the body to avoid damage from solids in the line. In this design, the seal seats on the edges of the slide, which means that the valve will seal equally well with the flow in either direction and the slide have a chamfered leading edge which enables it to slice through any obstruction and seat effectively against the body seal. These features ensure bubble-tight shut-off against pressure or vacuum.
During assembly, the diamond-shaped opening is filled with an oiled-fibre packing which is forced in and pushes the lips of the transverse seals into contact with the body and the slide. Also. by removing the screws on the sides of the body, more packing can be inserted at a later date to maintain a tight seal even if the valve is on-stream and under pressure or vacuum.
Also. by removing the screws on the sides of the body, more packing can be inserted at a later date to maintain a tight seal even if the valve is on-stream and under pressure or vacuum.
During the opening phase, this enables the slide faces to be scraped clean over their whole width before they are drawn through the transverse seals, and damage to the seals is thereby prevented.
Advantages:
- short overall length
- no wedging action
- thin closing member to cut through solids in the line
- substantially full-round bore
- lightweight
- easy to power-operate
- stem/slide connection not in contact with line fluid
- slide exposed for visual inspection when a valve is open
- good regulating characteristics when fitted with specially-shaped slide and/or body bore
