Slide valve for closing a large pressurized gas conveying pipe

A slide valve for closing large gas pipes, particularly such pipes carrying dust-containing hot gases, said slide valve comprising:

• a housing having an axial passage therethrough connectable to gas pipes, said housing having therein a housing opening;
• a stationary sealing seat within said housing;
• a movable sealing seat opposed to and axially spaced from said stationary sealing seat within said housing;
• a slide plate mounted to be selectively movable from an open position exterior of said housing, through said housing opening to a closed position within said housing between said sealing seats closing said axial passage;
• means for urging said movable sealing seat, when said slide plate is in said open position, into contact with said stationary sealing seat, and when said slide plate is in said closed position, into contact with said slide plate;
• said slide plate, when in said closed position, being in sealing contact with both said movable sealing seat and said stationary sealing seat;
• a closing element on said housing and selectively movable from a first position closing said housing opening when said slide plate is in said open position to a second position opening said housing opening when said slide plate is in said closed position;
• and
• a chamber within said housing exterior of said passage, said chamber, when said slide plate is in said closed position, being sealed in a gas tight manner from the gas pipe and being open to the atmosphere through said housing opening such that any leakage from a pressurized section of the gas pipe will be vented to the atmosphere, and said chamber when said slide plate is in said open position, being closed by said closing element and thus forming a back-up seal to any leakage from the gas pipe.