Common causes of gate valve leakage gate valve leakage of the main reasons: one is the valve body, the valve body in the open surface, packing, bottom drain wire, flange sealing surface caused by leakage, two is the valve leakage.
I. leakage caused by substandard valve quality
Valve itself defect is mainly external defects, external defects are due to valve itself casting welding when the joint is not sealed, the casting body itself quality is not up to standard, at the same time the valve plus often in rapid corrosion, high pressure and temperature changes of the environment, the passage of time will make protective layer on the surface of the valve body is corrosion, thus in the joint, weak body gradually formed on the surface of sand holes, resulting in leakage of forming pores.If the valve in the production process there are a lot of defects such as stomata, slag inclusion, crack, shrinkage and porosity, then under the multiple effects of pressure, corrosion and operating force, these defects will be exposed at any time in the operation of the valve, accompanied by the valve body fracture, support fracture and other more serious damage problems.
II. Leakage caused by sealing of stuffing box
1. Valve stem sealing principle is the use of packing and the squeeze between the stem, make the packing clamping stem, so as to narrow the gap between the packing and stem to achieve. Stem seal leakage reason:
2. The corrosive, temperature and pressure of the packing and the fluid medium are not compatible;
3. The packing gland is not tightened, and the radial deformation is not enough, resulting in a loose seal;
4. The packing used is too thin, resulting in a loose seal;
5. The number of winding of packing installation is too small to meet the requirements;
6. Packing method of packing packing is not right, especially when the whole packing is put in, it is easy to cause leakage;
7. Improper lubrication of packing material, friction with stem;
8. Aging and failure of packing;
9. Stem machining precision or surface finish is not enough, or there are ellipticity, Nick and stem bending, etc., will cause leakage at the stem.
III. Valve leakage caused by non-standard installation
Flange connected valve installation is improper, will also cause leakage after valve installation, leakage is mainly flange sealing surface and valve open.The main cause of flange sealing surface and open surface leakage is the installation of dirt or sand in the sealing surface adhesion, fastening bolts when the force is uneven, resulting in sealing gasket damage.With the extension of valve service time, fastening bolts creep, yield, seal gasket aging, corrosion, then the valve will appear in the flange surface and open surface leakage.
IV. Internal leakage of valve
Causes of valve leakage are many, the new valve soon after the operation of internal leakage and closed not in place, should be the sealing surface with foreign bodies.In addition, the phase transformation of the material of the inner sealing surface produces deformation, which makes the sealing surface with high grinding accuracy warp and deform, and makes the gate and the base not completely close together and cause internal leakage.
V. leakage caused by corrosion of the drain wire at the bottom of the valve
To prevent impurities accumulated at the bottom of the valve cause the closing of the valve gate is lax, equipped with a drain plug at the bottom of the valve, can facilitate periodic blowdown valve, but in the actual production, because of the crude oil containing water, often and long-term accumulation of the water in the valve discharge will drain plug, plus often affected by the impact of the fluid and pressure valve, easy to cause the valve plug at the bottom of the corrosion damage, serious can cause oil spill accidents.