Shut-off pipeline valves are installed on pipelines of steam, hot water, as well as other liquid and gaseous media. It is mainly used for pipelines with a nominal diameter from DN6 to DN300. Available with stuffing box or bellows seal.
Stop valves with stuffing box or bellows stem seal can be supplied complete with gearbox, pneumatic or electric actuator.
In stuffing box valves, the tightness of the connection between the cover and the movable part of the shutter is ensured by a stuffing box device. In the place where the stem or spindle passes, the stuffing box is laid. With the help of special devices, the packing is pressed along the axis of the spindle (rod), resting against the walls of the stuffing box and compacted. Thus, ALMOST tightness is created and the working medium does not penetrate outside the case. In shut-off valves of small diameters, the packing is pressed with a union nut, for large ones - with a special part using two hinged or anchor bolts with nuts.
Glands simplify the design as much as possible and reduce the cost of fittings, it has many advantages that make it preferable in most cases:
the ability to manufacture stuffing box packing from various materials to ensure good sealing in a wide range of operating pressures and temperatures;
simplicity of design;
the possibility of stuffing the stuffing box or changing the stuffing during operation.
But the stuffing box does not guarantee absolute tightness - therefore, such fittings cannot be used for toxic and hazardous environments.
Bellows shut-off valves.
The bellows piping assembly as a seal is essentially “a kind of diaphragm valve”: a corrugated tube is used as a force transfer assembly, which is stretched and compressed. Naturally, the working medium is physically separated from the control rod - it is on one side of the tube, and the rod is on the other. Thus, bellows shut-off pipeline valves are airtight, but limited by the number of movements and almost unrepairable. The bellows seal of the rod ensures FULL TIGHTNESS of the connection and eliminates the need for maintenance during operation, but at the same time, the bellows seal is structurally more complicated, more expensive and has a limited resource of rod movements.
