1. Gate valve and valve leakage at the junction of the first check valve and gate valve bolts are tightened, if not tightened, the gasket ring and the flange seal groove surface is not fully integrated often lead to leakage. The bolts and nuts should be checked in sequence, tighten all bolts until the packing ring is tightened. Second, check the dimensions and accuracy of the gasket ring and the flange seal groove surface, and repair or renew the gasket ring if the seal contact surface is incorrect or too rough. Also check the gasket ring and the flange seal groove contact surface pitting, sand hole, trachoma or impurities, if there is such defects, they should be the appropriate welding, repair or cleaning. 2. Leakage valve cover leakage, the failure phenomenon mainly in the packing seal leakage. First check whether the correct choice of seal, seal groove match, if there is such a problem will need to replace the seal or repair seal groove. Second, check whether the seal flash, fracturing, twisting and so on, in which case you want to replace the seal. Again, check each sealing groove sealing surface is rough or have other defects, if there is a defect, to eliminate defects or update damaged parts. The valve cover or bracket with the packing sealed by compression should be checked for the installation of these packing, if you find the upper and lower packing installed upside down, remove and follow the correct method to re-install, with particular attention to packing seal surface With the cooperation. Again, check the accuracy of the contact surfaces of the seals to meet the specified requirements. 3. Body cavity leakage in the valve body In the casting process, and sometimes there will be trachoma, sand holes and other casting defects in the machining process is difficult to find, once the pressure, the hidden casting defects will be exposed. If this happens, repair it or renew it. 4. Leakage valve seat valve plate at the valve plate leak, which is the most common phenomenon in the installation or maintenance of the valve. Generally can be divided into two categories: one is the sealing surface leakage, the other is the root seal leakage. First of all should check the valve seat and valve plate seal surface accuracy, the seal surface at least grinding, found that the surface roughness is too rough, you should remove and re-ground. Second check the sealing surface pitting, indentation, trachoma, cracks and other defects, this situation occurs, the valve plate or valve seat to be replaced. For pressure spring seat, you should check the elasticity of the compression spring is to meet the requirements, if the elasticity weakened, we must update the compression spring. Also check the valve plate and the valve stem T-junction is too loose, resulting in the valve plate in the process of pressing the emergence of the slope, in which case you have to remove the valve plate, adjust it to the best size. Internal body open file at the installation process is easy to enter the welding, iron filings, foreign matter and other foreign matter, should be cleaned before installation of such debris. If you forget to clean or cleaning is not complete, it will cause the valve plate closed less than the expected depth of the leak, in which case you have to remove the body to clean. Install the valve seat should be installed with a dedicated installation tool, and should check the valve seat is installed in place, if the thread is less than the expected depth of the screw, there will be leakage at the valve seat, this situation will have to re-use of special tools on the valve Block for installation. 5 hand wheel rotation is not flexible (1) the main reason. ①stem bending and torsion. ② surface accuracy is not enough. ③ too much operation to thread damage. ④ lack of lubrication or lubricant failure. ⑤ stem nut tilt. ⑥ with the tolerance is not allowed, bite too tight. ⑦ open gate valve lacks protection, stem thread covered with dust, or rain and snow by the rust. ⑧ thread corrosion by the medium (refers to the dark bar valve stem or stem nut in the lower gate valve). ⑨ improper choice of materials, such as stem and stem nut for the same material, easy to bite. (2) preventive measures and solutions. ①To strictly control the force level, not rigid torsion (refer to hand wheel and stem directly connected to the gate valve). ② improve the quality of processing, to meet regulatory requirements. ③ careful operation, do not turn off when Meng, open Do not go to the top dead center, to the point after the hand wheel should be reversed one or two rings, the thread close to the top, so as to avoid the medium to promote the impact of the valve stem. ④ often check the lubrication, maintain normal lubrication. ⑤ square or correct stem nut. ⑥ Modify or renew the stem nut so that it meets the standard specifications. ⑦ clean the stem nut dust often to prevent corrosion. ⑧ open gate valve to add stem protection sleeve. ⑨ stem nut copper material is better, do not use the same material with the stem.