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Fault Causes and Solutions of Marine Valves

Marine valves are equipment used to control the pressure, flow and flow direction of fluid in ship pipelines in order to meet the environmental conditions of ships. The valve is the control device of the fluid pipeline. Its basic function is to connect or cut off the circulation of the pipeline medium, change the circulation of the medium, change the flow direction of the medium, adjust the pressure and flow of the medium, and protect the normal operation of the pipeline equipment.


Ⅰ. Reasons and solutions for the failure of valve body and bonnet of marine valves


The common faults of valve body and valve cover are nothing more than damage, sand holes and aging or corrosion damage. The causes of these failures may be as follows.


1. Reason


(1) The damage to the valve body and bonnet of valve products is mainly due to poor design factors such as small safety factor, unreasonable structure, and internal stress concentration; or due to poor manufacturing quality, such as uneven thickness and uneven material; Or due to poor welding quality such as brittle welding seam and excessive internal stress; Or due to improper installation, the position is skewed and twisted; Or due to improper valve selection, it is not suitable for the working condition; Or; or due to poor maintenance, poor insulation in winter will be frozen and cracked; or due to strong external forces.


(2) The production of sand holes is mainly caused by poor manufacturing quality.


(3) Corrosion or aging is mainly caused by poor manufacturing quality, or improper replacement and maintenance due to corrosion protection and poor maintenance.


2. Measures


The following repair methods can also be adopted for common faults of valve body and valve cover: when the valve body and valve cover are damaged, sand holes, corrosion and aging faults, plugging shall be carried out according to scientific plugging methods; Repair or replace damaged parts or marine valves according to actual conditions.


Ⅱ. Reasons and solutions for marine valve packing failures


The common faults of packing mainly include the small pre-tightening force applied to the packing, fastener failure, valve stem sealing surface damage and packing failure. The causes of these failures may be as follows.


1. Reason


(1) The pre-tightening force on the filler is too small for the following reasons: insufficient filler, or due to insufficient filling quantity, or due to wear, aging and improper filling; Or because there is no pre-tightening gap; Or because the pressure sleeve is skewed and the diameter is too large to press on the stuffing box; Or because the thread is buckled, rusted or mixed with impurities, the thread is blocked when it is tightened.


(2) The reasons for the failure of fasteners are: gland, gland nut, bolt, ear and other parts are broken; Or due to vibration to relax; Or due to corrosion damage; Or due to uneven force, too much force, damage the improper operation of fasteners; Or due to poor maintenance.


2. Measures


(1) Repair method for too small preload


After closing the marine valve or activating the seal, repair the parts, add packing, adjust the pre-tightening force and pre-tightening clearance; If the valve cannot be closed, if the upper seal fails, the mechanical plugging method or adhesive plugging method or agent plugging method of the valve can be used for plugging. When the pressure sleeve is stranded, find out the reason for the stranding and suit the remedy to the case. If it is caused by burrs or large diameter, apply file force to trim until normal; If the thread is resistant to entry, it can be cleaned with rust remover or kerosene, and then the thread can be trimmed with assorted file until its tightness is appropriate.


(2) Repair method for fastener failure


After closing the valve, when confirming that the packing will not move outward due to internal pressure, repair the fastener according to the normal method; If the valve cannot be closed, the fastener can be repaired by changing the sealing method or bonding with pressure. If the fastener is loose or damaged, the fastener can be repaired and tightened directly.


(3) Repair method for damage to valve stem sealing surface


If it is slightly damaged, it can be eliminated by polishing method. If the sealing surface is damaged to leak, it is necessary to close the valve or activate the upper seal and repair it with grinding or local plating. If the sealing surface is damaged and difficult to repair, it can be solved by replacing the valve with pressure.


(4) Repair method for filler failure


After closing the valve or activating the upper seal, replace the packing or use the appropriate valve plugging method to stop the leakage, or replace the packing or replace the valve with other methods.

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