A
slab gate valve is a sliding valve whose closing member is a parallel wedge and its closing part can be a single wedge or a double wedge with a spreading mechanism in between. The pressing force of the wedge to the valve seat is controlled by the medium pressure acting on the floating wedge or floating valve seat. A
slab gate valve has diameters from DN25 to 1200 and pressure ranges between 0.6MPa and 45MPa or 150LB to 3000LB. A
slab gate valve is applied to natural gas, petroleum, chemical, environmental protection, urban pipelines, gas pipelines and other transportation pipelines, venting systems and steam storage devices, as an opening and closing device.
Structural features and working principles of slab gate valves
1. A floating valve seat is adopted to achieve the purposes of two-way opening and closing, which has reliable sealing, flexible opening and closing.
2. The wedge has a guide bar for precise guidance, and the sealing surface is spray-welded with cemented carbide, which is resistant to erosion.
3. The valve body has a good load-bearing capacity, and the passage is straight-through. When the valve is fully opened, it is similar to a straight pipe through the wedge orifice, and the flow resistance is small. The valve stem adopts composite packing and multiple seals, which makes the seal reliable and has low friction.
4. When closing the slab gate valve, turn the handwheel clockwise, and the wedge moves down to the bottom. Because of the pressure of the medium, the seal seat of the inlet end is pushed toward the wedge to form a great seal specific pressure, thus forming the first sealing. At the same time, the wedge is pressed against the seal seat at the outlet end to form a double seal.
5. The wearing parts can be replaced without affecting the work of the pipeline due to the double seal.
6. When opening the wedge, turn the handwheel counterclockwise to move the wedge up, and the diversion hole and passage hole are connected. As the wedge rises, the through hole is gradually enlarged. When it reaches the limit position, the diversion hole and passage hole overlap, and then the slab gate valve is fully opened.
Maintenance of a slab gate valve
Precautions for the use and maintenance of a slab gate valve after leaving the factory are as follows:
1. When a slab gate valve is stored in the warehouse, both ends of the valve passage must be covered with cover plates and stored in a dry and ventilated room. When it is stored for a long time, it should be checked frequently to remove dirt.
2. A slab gate valve and pipeline should be cleaned before installation to prevent debris from entering the valve passage, and check whether the label on the valve meets the requirements.
3. Turn the hand wheel clockwise to close the slab gate valve until the position is reached (The valve stem is in the lowest position by checking the switch indicator or the observation window. Turn it counterclockwise to open the valve.)
4. For valves with pressure relief devices, when the pressure in the middle valve cavity rises, the pressure can be relieved through the pressure relief device on the valve body or valve bonnet in the using process to ensure safety.
5. The drain device of the valve is located at the bottom of the valve body. If users need to drain frequently, they can remove the screw plug to assemble the drain valve when the valve is closed.
6. For the valve with a grease injection device, when internal leakages are found in the valve during use, inject the sealing grease at each grease injecting part to ensure that the valve is free of leakage and absolutely sealed. The pipeline does not need to be injected with sealing grease during purging and pressure tests.
7. In the daily inspection, check whether the valve has external and internal leakages, and deal with them in time.
8. When the valve is stop for troubleshooting, you must slowly loosen the drain plug or the drain valve to drain the residual pressure in the valve cavity to ensure safety.
Failures and troubleshooting methods that may occur during daily use of the valve are as follows:
