Knowledge

Common faults and preventive measures for gate valves



The gate valve is the main component of the oil (gas) wellhead device. The common faults of several gate valves in use are as follows. 1. Leakage between the gate valve and the gate valve First check whether the gate valve and the gate valve coupling bolt are tightened. If it is not tightened, the gasket ring and the flange sealing groove surface in the joint are not fully combined, which may cause leakage.
The gate valve is the main component of the oil (gas) wellhead device. The common faults of several gate valves in use are as follows.
1. Leakage between gate valve and gate valve

First, check whether the gate valve and the gate valve coupling bolt are tightened. If it is not tightened, the gasket ring and the flange sealing groove surface are not fully combined, which may cause leakage. The bolts and nuts should be inspected in order, and all bolts should be tightened until the gasket ring is pressed. Next, check the size and accuracy of the gasket ring and flange seal groove surface. If the seal contact surface is not the right size or too rough, the gasket ring should be repaired or updated. In addition, check whether there are some corrosion, sand holes, sand holes or impurities in the contact surface of the gasket ring and the flange seal groove. If such defects exist, repair, repair or clean them accordingly.

2. Bonnet leakage

The bonnet leaks, and this failure phenomenon is mainly manifested in the leakage of the packing seal. First check that the seal is selected correctly and that it matches the seal groove. If there is such a problem, replace the seal or repair the seal groove. Next, check the seal for burrs, fracturing, twisting, etc. In this case, replace the seal. Again, check the seal faces of each seal groove for rough or other defects. If there are defects, eliminate the defects or update the damaged parts.

The bonnet or bracket has packings that are sealed by compression. The installation of these packings should be checked. If the upper and lower packings are found to be upside down, they should be removed and reinstalled according to the correct method. Pay special attention to the packing seal joint surface. Cooperation. Furthermore, it is checked whether the accuracy of the contact surfaces of the seals meets the specified requirements.

3. Body cavity leakage

During the casting process, casting defects such as sand holes and sand holes sometimes occur, which are difficult to be found during machining. Once pressure is applied, hidden casting defects are exposed. If this happens, repair, repair or update it.

4. Leakage at the seat plate

Leakage at the seat plate is the most common phenomenon in installing or repairing 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, the accuracy of the sealing surface of the valve seat and the valve plate should be checked. The sealing surface should be at least ground. If the surface accuracy is too rough, it should be removed and re-grinded. Next, check the sealing surface for defects such as pitting, indentation, blisters, cracks, etc. In this case, replace the valve plate or valve seat. For a valve seat with a compression spring, it should be checked that the elasticity of the compression spring is in accordance with the requirements. If the elasticity is weakened, the compression spring is updated. In addition, check whether the T-shaped joint between the valve plate and the valve stem is too loose, so that the valve plate is inclined during the pressing process. In this case, the valve plate should be removed and adjusted to the optimal size.

The internal opening of the valve body is easy to enter foreign objects such as welding, iron filings and impurities during the installation process, and such debris should be cleaned before installation. If you forget to clean or clean it thoroughly, it will cause the valve plate to close less than the expected depth and cause leakage. In this case, remove the valve body and clean it again.

When installing the valve seat, it should be installed with a special installation tool, and the valve seat should be inspected for installation. If the thread is not screwed to the expected depth, the valve seat will leak. In this case, the special tool should be used again. The seat is installed.

5. Handwheel rotation is not flexible

 (1) The main reason. 1 The stem is bent. 2 surface accuracy is not enough. 3 The operation is too strong to damage the thread. 4 Lack of lubrication or lubricant failure. 5 The stem nut is tilted. 6 The tolerance is not allowed, and the bite is too tight. 7 The open-air gate valve lacks protection, the stem thread is covered with dust sand, or it is rusted by rain, frost and snow. The 8 thread is corroded by the medium (refer to the dark gate valve or the stem valve at the lower part of the stem nut). 9 improper material selection, such as the stem and stem nut are the same material, easy to bite.

 (2) Preventive measures and solutions. 1 Strictly control the force measurement, not rigid torsion (refer to the gate valve directly connected to the hand wheel and the valve stem). 2 Improve processing quality and meet regulatory requirements. 3 Careful operation, do not make it violent when closing, do not go to the top dead center when opening, after the stop point, the hand wheel should be inverted one or two times, so that the upper side of the thread is tightly closed, so as to prevent the medium from pushing the valve stem upward. 4 Always check the lubrication and maintain normal lubrication. 5Spread or correct the stem nut. 6 Correct or update the stem nut to meet the standard specifications. 7 Always clean the stem nut dust to prevent rust. 8 open gate valve should be added with a stem protector. 9 The stem nut is made of copper. Do not use the same material as the stem.