can gate valves fail

- Apr 19, 2020-

Can gate valves fail

The gate valve's opening and closing parts are the gate. The movement direction of the gate is perpendicular to the direction of the fluid. The gate valve can only be fully opened and fully closed. The parameters of the unsuitable gate are different, usually 5 ° and 2 ° 52 'when the medium temperature is not high. To improve its processability and make up for the deviation of sealing surface angle in the process of processing, this kind of ram is called elastic ram.

Main categories: there are many domestic gate valve manufacturers, and most of the connection sizes are not uniform. It is mainly divided into the following categories: general class mainly based on JB / t2203-1999 structural length of gate valve. At present, most domestic safety valve manufacturers are designed and manufactured according to this standard. According to different classification methods, gate valve can be divided into parallel gate valve, wedge gate valve, lifting gate valve, rotary rod gate valve, quick opening and closing gate valve, necking gate valve, flat gate valve, etc.

1. Leakage at the joint of gate valve and gate valve

First, check whether the connecting bolts of gate valve and gate valve are tightened. If they are not tightened, the insufficient combination of the gasket ring and the flange sealing groove surface will often lead to leakage. The bolts and nuts shall be inspected in sequence, and all bolts shall be tightened until the gasket ring is compressed. Secondly, check the size and accuracy of the gasket ring and flange sealing groove surface. If the size of the sealing contact surface is not correct or too rough, repair or update the gasket ring. Moreover, check whether there is pitting, sand hole, sand hole or impurity in the contact surface between the gasket ring and the flange sealing groove. If there is such defect, repair, repair or clean it accordingly.

2. Valve cover leakage

The leakage of valve cover is mainly manifested in the leakage of packing seal. First, check whether the seal is selected correctly and whether it 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 burr, fracturing, twisting and other phenomena. In this case, replace the seal. Again, check whether the sealing surface of each sealing groove is rough or has other defects. If there are defects, eliminate the defects or update the damaged parts.

There are packings sealed by compression in the bonnet or bracket. The installation of these packings shall be checked. If it is found that the upper and lower packings are installed upside down, they shall be removed and reinstalled according to the correct method. Pay special attention to the fit of the joint surface of the packing seal. Moreover, check whether the accuracy of each contact surface of the seal meets the specified requirements.

3. Body cavity face leakage

In the casting process of valve body, sometimes there are sand holes, sand holes and other casting defects, which are difficult to be found in the machining process. Once the pressure is applied, the hidden casting defects will be exposed. In this case, repair welding, repair or renewal shall be carried out.

4. Leakage at valve seat plate

Zui is a common phenomenon in the installation or maintenance of gate valves. Generally, it can be divided into two categories: one is the leakage of sealing surface, the other is the leakage at the root of sealing ring.

First, check the accuracy of the sealing surface between the valve seat and the valve plate, and grind the sealing surface at least. If it is found that the surface accuracy is too rough, it should be removed and grinded again. Secondly, check whether there are pitting, indentation, sand hole, crack and other defects on the sealing surface. If this happens, replace the valve plate or valve seat. For the valve seat with compression spring, the elasticity of the compression spring shall be checked to meet the requirements. If the elasticity is weakened, the compression spring shall be renewed. Furthermore, check whether the T-joint between the valve plate and the valve stem is too loose, resulting in the inclination of the valve plate in the process of compression. In this case, remove the valve plate and adjust it to the Zui preferred size.

In the opening position inside the valve body, it is easy to enter foreign matters such as welding inspection, iron scraps and impurities during the installation process. Such foreign matters shall be cleaned before installation. If you forget to clean or do not clean thoroughly, the valve plate will not close to the expected depth, resulting in leakage. In this case, remove the valve body and clean again.

When installing the valve seat, special installation tools shall be used for installation, and check whether the valve seat is installed in place. If the thread cannot be screwed to the expected depth, leakage will occur at the valve seat. In this case, special tools shall be used again for installation of the valve seat.

5. Inflexible rotation of hand wheel

(1) Main reasons. ① Bent stem. ② Insufficient surface accuracy. ③ Thread damage due to excessive operation. ④ Lack of lubrication or lubricant failure. ⑤ Stem nut tilt. ⑥ The fit tolerance is not allowed, and the bite is too tight. ⑦ The outdoor gate valve lacks protection, the valve rod thread is covered with dust and sand, or rusted by rain, dew, frost and snow. ⑧ The thread is corroded by the medium (refers to the gate valve with concealed stem or stem nut at the lower part). ⑨ Improper material selection, such as stem and stem nut are the same material, easy to bite.

(2) Preventive measures and solutions. ① Strictly control the force and size, and do not twist hard (referring to the gate valve directly connected with handwheel and stem). ② Improve the processing quality and meet the specification requirements. ③ Operate carefully, do not make strong force when closing and do not reach the top dead center when opening. After reaching the dead center, turn the hand wheel one or two times to make the upper side of the thread close, so as to avoid the upward impact of the medium pushing the valve rod. ④ Check the lubrication condition frequently and keep it in normal lubrication condition. ⑤ Straighten or correct the stem nut. ⑥ Correct or update stem nuts to standard specifications. ⑦ Clean the dust and sand of valve rod nut frequently to prevent rust. ⑧ Open gate valve shall be equipped with valve rod protection sleeve. ⑨ It is better to use copper material for the stem nut instead of the same material as the stem.

flanged gate valve