What should you do when a valve in use leaks? What is the main reason?
1. The closing piece falls off and causes leakage
Reason:
① Poor operation causes the closing parts to get stuck or exceed the top dead center, and the connections are damaged and broken;
② The closing piece is not firmly connected, loose and falls off;
③ The wrong material is selected for the connecting parts, which cannot withstand the corrosion of the medium and mechanical wear.
Maintenance method:
① Correct operation. When closing the valve, do not use excessive force. When opening the valve, do not exceed the top dead center. After the valve is fully opened, the handwheel should be reversed slightly;
② The connection between the closing piece and the valve stem should be firm, and there should be a backstop piece at the threaded connection;
③ The fasteners used to connect the closing parts and the valve stem should withstand the corrosion of the medium and have certain mechanical strength and wear resistance.
2. Leakage at the packing (the packing accounts for the largest proportion of valve leakage)
Reason:
① The packing is incorrectly selected and is not resistant to the corrosion of the medium and the valve is not resistant to high pressure or vacuum, high temperature or low temperature;
② The packing is installed incorrectly, with defects such as replacing large ones with small ones, poor spiral coiled joints, tightening up and loosening down;
③ The filler has expired, has aged, and lost elasticity.
④ The valve stem has low accuracy and has defects such as bending, corrosion, and wear.
⑤ The number of packing rings is insufficient and the gland is not pressed tightly;
⑥ The gland, bolts, and other parts are damaged, making it impossible to tighten the gland;
⑦ Improper operation, excessive force, etc.;
⑧ The gland is skewed, and the gap between the gland and the valve stem is too small or too large, causing the valve stem to wear and the packing to be damaged.
Maintenance method:
① The material and type of filler should be selected according to the working conditions;
② Install the packing correctly according to relevant regulations. The packing should be placed and tightened one by one, and the joints should be at 30°C or 45°C;
③ Packing that has been used for a long time, is aged, or is damaged should be replaced in time;
④ The valve stem should be straightened and repaired after bending or wear, and if the damage is serious, it should be replaced in time;
⑤ The packing should be installed according to the specified number of turns, the gland should be tightened symmetrically and evenly, and the gland should have a pre-tightening gap of more than 5mm;
⑥ Damaged glands, bolts and other parts should be repaired or replaced in time;
⑦ The operating procedures should be followed. Except for the impact handwheel, operate it with normal force at a constant speed;
⑧ The gland bolts should be tightened evenly and symmetrically. If the gap between the gland and the valve stem is too small, the gap should be appropriately increased; if the gap between the gland and the valve stem is too large, it should be replaced.
Leakage of sealing surface
Reason:
① The sealing surface is unevenly ground and cannot form a tight line;
② The top center of the connection between the valve stem and the closing member is suspended, incorrect or worn;
③ The valve stem is bent or incorrectly assembled, causing the closing member to be skewed or misaligned;
④ The sealing surface material quality is improperly selected or the valve is not selected according to the working conditions.
Maintenance method:
① Correctly select the material and type of bumper gasket according to the working conditions;
② Careful adjustment and smooth operation;
③ Bolts should be tightened evenly and symmetrically, and a torque wrench should be used if necessary. The pretightening force should meet the requirements and should not be too large or small. There should be a certain preload gap between the flange and the threaded connection;
④ The gasket assembly should be aligned in the center and the force should be even. Overlapping of gaskets and the use of double gaskets are not allowed;
⑤ The static sealing surface is corroded, damaged, and the processing quality is not high. Repair, grinding, and coloring inspection should be carried out to make the static sealing surface meet the relevant requirements;
⑥ Pay attention to cleanliness when installing the gasket. The sealing surface should be cleaned with kerosene, and the gasket should not fall to the ground.
Leakage at the sealing ring connection
Reason:
① The sealing ring is not rolled tightly
② The sealing ring is welded to the body, and the surfacing quality is poor;
③ The connecting threads, screws and pressure rings of the sealing ring are loose;
④ The sealing ring is corroded due to the connection.
Maintenance method:
① If the seal is leaking at the rolling point, adhesive should be injected and then rolled to fix it;
② The sealing ring should be re-welded according to the welding specifications. When the surfacing cannot be repaired, the original surfacing and processing should be removed;
③ Remove the screws, clean the pressure ring, replace the damaged parts, grind the sealing surface of the seal and the connecting seat, and reassemble. For parts that are severely damaged by corrosion, welding, bonding and other methods can be used to repair them;
④ If the connecting surface of the sealing ring is corroded, it can be repaired by grinding, bonding and other methods. If it cannot be repaired, the sealing ring should be replaced.
Leakage of valve body and valve cover:
Reason:
① The casting quality of the cast iron parts is not high, and there are defects such as blisters, loose tissue, and slag inclusions on the valve body and valve cover body.
② Cracked by freezing;
③ Poor welding, with defects such as slag inclusions, lack of welding, and stress cracks;
④ The cast iron valve was damaged after being hit by a heavy object.
Maintenance method:
① Improve casting quality and conduct strength tests strictly in accordance with regulations before installation;
② Valves with temperatures below 0° should be kept warm or heated, and valves out of use should be drained of accumulated water.
③ The welds of the valve body and valve cover composed of welding should be carried out in accordance with the relevant welding operating procedures, and flaw detection and strength tests should be carried out after welding;
