The faults of Dalian marine valves generally include valve body bonnet fault, packing fault, gasket fault, etc.

Common faults and cause analysis of valve body and bonnet

The common faults of valve body and bonnet are damage, sand hole and aging or corrosion damage. These faults may be caused by the following aspects.

(1) The main reasons for the damage of the valve body and bonnet are the poor design factors such as low safety factor, unreasonable structure and concentration of internal stress; Or due to poor manufacturing quality, such as uneven thickness and uneven material; Or poor welding quality due to too brittle weld and too large internal stress; Or the position is skewed and distorted due to improper installation; Or the valve is not suitable for the working condition due to improper selection; Or because the water hammer pressure is too high; Or due to poor maintenance, the insulation is not good in winter and it is frozen and cracked; Or due to strong external force.

(2) Sand holes are mainly caused by poor manufacturing quality.

(3) The causes of corrosion or aging are mainly due to poor manufacturing quality, or poor corrosion prevention and maintenance, and untimely replacement and maintenance.

Common faults and cause analysis of packing

The common faults of packing mainly include four types: too small pre tightening force applied on the packing, failure of fasteners, damage of valve stem sealing surface and packing failure. These faults may be caused by the following aspects.

(1) There are several reasons why the preload on the packing is too small: insufficient packing, insufficient filling quantity, or wear, aging and improper filling; Or there is no pre tightening clearance; Or press on the stuffing box due to the deflection of the pressure sleeve and the larger diameter; Or the screw thread is blocked during tightening due to disorderly screwing, rusting and mixing of impurities.

(2) The failure of fasteners is caused by the fracture of gland, gland nut, bolt, ear and other parts; Or relaxation due to vibration; Or damage due to corrosion; Or improper operation of fasteners due to uneven force or excessive force; Or due to poor maintenance.

Why can't the double seal valve in the control valve be used as a shut-off valve?

The advantage of the double seat valve core is the force balance structure and the allowable pressure difference is large. However, its obvious disadvantage is that the two sealing surfaces cannot be in good contact at the same time, which is easy to cause leakage. If it is artificially and forcibly used in cutting-off occasions, it is obviously not good. Even if many improvements have been made (such as double seal sleeve valve), it is not desirable.

Why is the control valve easy to oscillate when the double seat valve works with a small opening?

For single core, when the medium is flow open type, the valve has good stability; When the medium is flow closed, the stability of the valve is poor. The double seat valve has two valve elements, the lower valve element is in the flow closed state and the upper valve element is in the flow open state. In this way, the flow closed valve element is easy to cause the vibration of the valve when working with a small opening. This is the reason why the double seat valve cannot be used for working with a small opening.