Gate valve common failures and preventive measures

Gate valve common failures and preventive measures

Gate valve is the main component of the oil production (gas) wellhead device, several gate valve in the use of common failures are as follows.

1. Gate valve and gate valve joint leakage

First of all, we should check whether the gate valve and gate valve coupling bolts are tightened, such as not tightened, the sealing gasket ring and flange sealing groove surface is not sufficiently combined often lead to leakage. The bolts and nuts should be checked in order, and all the bolts should be tightened until the gasket ring is pressed. Secondly, the size and accuracy of the gasket ring and flange sealing groove surface should be checked. If the sealing contact surface size is not correct or too rough, the gasket ring should be repaired or renewed. Further check the gasket ring and flange sealing groove contact surface whether pitting, sand holes, sand holes or impurities, if there are such defects, it is necessary to carry out the corresponding patch welding, repair or cleanup.

2. Bonnet leakage

Bonnet leakage, this failure phenomenon is mainly manifested in the packing seal leakage. First of all, check whether the seal is selected correctly, whether with the sealing groove, if there is such a problem to replace the seal or repair the sealing groove. Secondly, check whether the seals have burrs, cracks, twisted and other phenomena, this situation is to replace the seals. Again, check whether the sealing surface of each sealing groove is rough or has other defects, if there are defects, then eliminate the defects or renew the damaged parts.

Bonnet or bracket inside the packing through the compression to seal, should check the installation of these fillers, if the upper and lower filler installation is found to be reversed, it is necessary to remove, in accordance with the correct method of re-installation, especially pay attention to the filler seals with the surface of the seal with. Furthermore, check whether the precision of each contact surface of the seal meets the specified requirements.

3. Valve body cavity decent leakage

Valve body in the casting process, sometimes there will be sand holes, sand holes and other casting defects in the machining process is difficult to be found, once the pressure is applied, the hidden casting defects will be exposed. In this case, it is necessary to patch welding, repair or update.

4. Valve seat valve plate leakage

Valve seat valve plate leakage, in the installation or repair of gate valve is the most common phenomenon. Generally can be divided into two categories: one is the sealing surface leakage, the other is the sealing ring root leakage.

First of all, you should check the valve seat and valve plate contact sealing surface accuracy, this sealing surface should be at least grinding, such as found that the surface accuracy is too rough, it should be removed to re-grind. Secondly, the sealing surface should be checked to see if there are defects such as pitting, indentation, sand eyes, cracks, etc. If this happens, the valve plate or seat should be replaced. For the valve seat with pressure spring, the elasticity of the pressure spring should be checked to meet the requirements, and if the elasticity is weakened, the pressure spring should be renewed. Furthermore, check whether the valve plate and valve stem T-shaped joint is too loose, resulting in the valve plate in the process of compression of the tilt of the situation, in this case, the valve plate should be removed and adjusted to the optimal size.

Valve body internal open file, in the installation process is easy to enter the welding, iron filings, impurities and other foreign objects, should be cleaned up before installation of such debris. If you forget to clean up or clean up is not complete, it will cause the valve plate to close the expected depth and produce leakage, in this case, the valve body should be removed to clean up.

Installation of the valve seat should be installed with a special installation tool, and should check whether the valve seat is installed in place, if the threads screwed less than the expected depth, the valve seat will leakage phenomenon, this situation should be re-installed with a special tool for the valve seat.

5. Handwheel rotation is not flexible

(1) The main reason. (1) Valve stem bending and twisting. ② surface precision is not enough. ③The operation is too violent to make the thread damage. Lack of lubrication or lubricant failure. ⑤ Stem nut tilt. ⑥ Matching tolerance is not allowed, bite too tight. (7) lack of protection of open-air gate valve, stem threads covered with dust and sand, or rusted by rain, frost and snow. (8) Thread corrosion by the medium (refers to the dark stem gate valve or stem nut in the lower part of the gate valve). ⑨ Improper selection of materials, such as valve stem and stem nut for the same material, easy to bite.

(2) Preventive measures and solutions. ① To strictly control the force of the proportion, not hard twisting (refers to the handwheel and valve stem directly coupled gate valve). ② Improve the processing quality to meet the specification requirements. ③ careful operation, do not make a hard closing, do not open to the upper dead center, to the stop point should be the handwheel inverted one or two turns, so that the upper side of the threads close, so as to avoid the medium to promote the upward impact of the valve stem. ④Check the lubrication condition frequently and keep normal lubrication condition. ⑤ Square or correct the valve stem nut. ⑥Correct or update the stem nut to meet the standard specification. ⑦ often clean up the stem nut dust sand, to prevent corrosion. (8) open gate valve to add a protective sleeve of the valve stem. Valve stem nut using copper material is better, do not use the same material with the valve stem.