Gate valve belongs to the class of shut-off valves and is usually installed on pipes with a diameter greater than 100mm to cut off or connect the flow of media inside the pipeline. Due to the gate valve's valve disc being in a gate-shaped form, it is commonly referred to as a china gate valve. Gate valves have the advantages of easy operation, low flow resistance, etc. However, the sealing surface is prone to wear and leakage, the opening stroke is large, and maintenance is relatively difficult. Gate valves cannot be used as regulating valves and must be in the fully open or fully closed position.
The working principle is that when the gate valve is closed, the valve stem moves downward and relies on the smooth and consistent sealing surfaces of the gate valve and valve seat to fit together to prevent the flow of media, and increasing the sealing effect by relying on the wedge at the top. Its closing component moves vertically along the centerline. There are many types of gate valves, which can be divided into wedge type and parallel type according to the type, and each type has single gate and double gate.
The valve body of the industrial gate valve adopts a self-sealing form. The connection between the valve cover and the valve body is to use the pressure of the medium inside the valve to press the sealing filler to achieve the purpose of sealing. The sealing filler of the gate valve adopts a high-pressure asbestos packing root with a copper wire for sealing. The gate valve structure mainly consists of the valve body, valve cover, frame, valve stem, left and right valve discs, packing seal device, etc.
Step 1: Disassembly of the valve
Remove the fixed bolts of the upper frame of the valve cover, and unscrew the nuts of the four bolts on the valve cover. Turn the valve stem nut counterclockwise to make the valve frame separate from the valve body, and then use a hoisting tool to remove the frame and place it in a suitable position. The valve stem nut location is waiting for disassembly and inspection.
Step 2: Repair of valve components
Use a special grinding tool (grinding gun, etc.) to grind the joint surface of the gate valve seat. Grinding can use grinding sand or sand cloth. The method is from coarse to fine, and finally polished. The joint surface of the valve disc can be manually or machined with a grinding machine. If there are deep pitting or grooves on its surface, it can be sent to a lathe or grinding machine for micro-machining, and then polished after all leveling. Clean the gate valve cover and sealing filler, remove the rust and dirt on the inner and outer walls of the pressure ring of the filler, and ensure that the pressure ring can be smoothly inserted into the upper part of the valve cover, which is convenient for compressing the sealing filler.
Step 3: Assembly of the gate valve
Install the qualified left and right valve discs on the valve stem clamp, and fix them with upper and lower clamp plates. The internal should be installed with swivel top and adjusting gasket according to the maintenance situation. Gate valve manufacturers insert the valve stem together with the valve disc into the valve seat for testing and inspection. When all sealing surfaces of the valve disc and the valve seat are in contact, the valve disc sealing surface should be raised above the valve seat sealing surface and meet the quality requirements. Otherwise, adjust the thickness of the gasket at the universal joint until it is suitable, and use the stop pad to seal and prevent loosening.