Gate valve common faults and preventive measures Feb 09 , 2023

Gate valve common faults and preventive measures

1. Leakage at the connection between the gate valve
First of all, check whether the connecting bolts between the gate valve and the gate valve are tightened. If they are not tightened, the gasket ring inside and the flange sealing groove surface are not fully combined, which often leads to leakage. The bolts and nuts should be checked in sequence, and all the bolts should be tightened until the gasket ring is compressed. Secondly, check the size and accuracy of the sealing gasket ring and flange sealing groove surface. If the sealing contact surface size is wrong or too rough, the gasket ring should be repaired or renewed. Furthermore, check whether there are pitting, sand holes, sand holes or impurities in the contact surface of the gasket ring and the flange sealing groove. If there are such defects, they must be repaired, repaired or cleaned accordingly.

2. Bonnet leakage
Valve cover leakage, this failure phenomenon is mainly manifested in the leakage of packing seals. First check whether the seal is selected correctly and matches the seal groove. If there is such a problem, replace the seal ring or repair the seal groove. Secondly, check whether the seal has burrs, fracturing, twisting, etc. In this case, the seal should be replaced. Again, check whether the sealing surface of each sealing groove is rough or has other defects. If there are defects, eliminate the defects or replace the damaged parts.
There are packings that are compressed to seal in the bonnet or bracket. Check the installation of these packings. If you find that the upper and lower packings are installed upside down, remove them and reinstall them in the correct way. Pay special attention to the joint surface of packing seals. cooperation. Furthermore, check whether the accuracy of each contact surface of the seal meets the specified requirements.

3. Valve body cavity body surface leakage
During the casting process of the valve body, casting defects such as sand holes and sand holes sometimes appear, which are difficult to be found during machining. Once pressure is applied, the hidden casting defects will be exposed. If this happens, it needs to be repaired, repaired or updated.

4. Leakage at the valve seat and plate
Leakage at the seat plate is the most common phenomenon in the installation or maintenance of gate valves. Generally, it can be divided into two categories: one is the leakage of the sealing surface, and the other is the leakage of the root of the sealing ring.

First of all, check the accuracy of the contact sealing surface between the valve seat and the valve plate. The sealing surface should be ground at least. If the surface accuracy is found to be too rough, it should be removed and re-ground. Secondly, check whether there are defects such as pitting corrosion, indentation, sand holes, cracks, etc. on the sealing surface. In this case, the valve plate or valve seat should be replaced. For valve seats with compression springs, the elasticity of the compression springs should be checked to meet the requirements. If the elasticity is weakened, the compression springs should be replaced. Furthermore, check whether the T-shaped connection between the valve plate and the valve stem is too loose, causing the valve plate to have a slope during the compression process. In this case, the valve plate must be removed and adjusted to the optimal size.

In the open position inside the valve body, it is easy to enter foreign matter such as welding, iron filings, and impurities during the installation process. Such debris should be cleaned before installation. If you forget to clean or do not clean thoroughly, the valve plate will not close to the expected depth and cause leakage. In this case, the valve body needs to be removed and cleaned again.

When installing the valve seat, use a special installation tool to install it, and check whether the valve seat is installed in place. If the thread is not screwed to the expected depth, there will be leakage at the valve seat, then need to use special tool installation again.

5. The rotation of the hand wheel is not flexible
(1) The main reason. ①The valve stem is bent and twisted. ②The surface precision is not enough. ③Excessive operation will damage the thread. ④ lack of lubrication or lubricant failure. ⑤The stem nut is tilted. ⑥ The matching tolerance is not allowed, and the bite is too tight. ⑦ The open-air gate valve lacks protection, and the valve stem thread is covered with dust and sand, or is corroded by rain, dew, frost and snow. ⑧The thread is corroded by the medium (referring to the hidden stem gate valve or the gate valve with the stem nut at the bottom). ⑨ Improper material selection, for example, the valve stem and stem nut are made of the same material, which is easy to bite.

(2) Preventive measures and solutions. ① Strictly control the force and measure, and do not twist it rigidly (referring to the gate valve directly connected with the hand wheel and the valve stem). ② Improve the processing quality and meet the specification requirements. ③Operate carefully, do not use force when closing, and do not reach the top dead center when opening. After reaching the dead point, turn the handwheel one or two turns to make the upper side of the thread close, so as to prevent the medium from pushing the valve stem upwards. ④ Frequently check the lubrication condition and maintain a normal lubrication condition. ⑤ Straighten or correct the stem nut. ⑥Revise or update the stem nut to meet the standard specifications. ⑦ Frequently clean the dust and sand on the stem nut to prevent corrosion. ⑧The open-air gate valve should be equipped with a stem protection sleeve. ⑨It is better to use copper material for the valve stem nut, do not use the same material as the valve stem.

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