Overhaul: Clean nozzles and oil cups, replace stuffing, disinfect stem and screw threads, remove debris from valves, tighten and replace bolts, complete handwheels.

Middle repair: including minor repair items, parts disassembly and disinfection, valve body repair, thick seal grinding, stem straightening, etc

Major repair: including repair items, valve stem replacement, support repair, spring and seal replacement.

For valves that are serviced indoors, medium and minor repairs are usually carried out, but they should also be removed for inspection and replacement of gaskets.

Valve maintenance under pressure is a simple, dangerous and low technical task. In addition to being serious, careful and calm, the valve pressure maintenance should also have a strict scientific attitude. In particular, the sealing work of explosive, highly toxic, high temperature, high pressure, radioactive and other media should be strictly carried out in accordance with the scheduled plan and relevant safety regulations

When maintaining valves with pressure, pay attention to the following matters during the maintenance process: strictly abide by the relevant safety operating procedures such as fire, gas and explosion-proof.

After dealing with the pressure valve defect, the treatment plan should be proposed, and obtain the consent of the safety technician and the cooperation of the operator. The treatment of key parts should be jointly studied, and according to the provisions of the fire ticket, poison ticket and other procedures, before the valve defects can be dealt with, the work of dealing with defects should be carried out by experienced maintenance personnel, on-site personnel should not be too much, and there should be 1 to 2 specific guardians should have careful safety measures to be able to deal with serious situations. Maintenance personnel and on-site personnel should wear protective work clothes, shoes, hats, gloves and glasses in accordance with the provisions of protective measures against combustible, explosive, high temperature and high pressure, toxic, highly toxic, weak corrosion and other media. The maintenance of toxic and highly toxic valves should also wear a gas mask. In the process of dealing with valve defects, safety baffles should be set up, and the safety baffles should be carefully observed while drying, and carried out according to the specified program

After tightening the thread, clean the rusty thread with kerosene and penetrate it to check whether the bolt and nut are complete; A tight anti-rust solution or a layer of graphite powder should also be added to lubricate the threads. When tightening nuts, do not tighten them to prevent bolts and screws from breaking. When welding valves, follow the welding specifications. The metal should be prevented from being supercooled and deformed, leading to brand new cracks. If there is a brand new leak in the caulking part, it is not suitable to caulk again to avoid leakage defects to expand the assembly and removal of the valve.

 

1. Locking method of thread connection

Nuts, spring washers, stop washers, cotter pins and other joints are usually used on the valve to prevent the nut from loosening. The connection structure between the valve stem and the closing part usually adopts the locking method of the stop washer and the locking method of the wing washer, and the effect is good

In addition, the methods to prevent the valve from loosening are slotted screws (riding screws) fixing method and point riveting method, both of which are used for occasions that are not often removed. The point riveting method uses a punch to rivet two or more points at the thread where the nut and bolt are joined, thereby squeezing and deforming the thread to achieve the purpose of locking. If the above method is difficult to solve the nut softening problem, you can use the bonding method

Accurate identification of left or right hand threads is fundamental to valve assembly and disassembly. So, how do we know if this line is left-handed or right-handed? It can be determined by the internal or external thread above the valve. Usually, they form a positive thread and negative thread structure to prevent thread loosening. For example, the threaded connection between the stem and the stem nut: the tightening ring above the stem nut is on the right, the thread above the handwheel is on the left, and the trapezoid thread of the stem nut is on the right. In addition, the rise Angle of the thread is to the right, and the thread that rises to the right is called left-handed; Instead, it's the right hand

The method of removing and assembling bolts is usually related to factors such as connection form, damage and corrosion. The following highlights the removal and assembly of studs; Remove rusty bolts and nuts; Method for removing broken bolts

① Disassembly and assembly method of stud

Method for removing and assembling double nuts screwed together. When removing the stud, the upper wrench will tighten the upper nut over the upper nut, the upper wrench will turn the nut counterclockwise and then unscrew the bolt. If the stud is reversed (left), tighten the nut with the upper wrench, and remove the nut clockwise with the upper wrench; When the stud is assembled over the valve, the upper wrench compresses the upper nut, and the upper wrench turns the upper nut clockwise to tighten the stud over the valve body. If the stud is counter-threaded, the lower wrench compresses the lower nut, and the upper wrench turns the upper nut counterclockwise to tighten the stud

Another way to tighten the stud is to tighten the stud using a specific nut with a screw. The internal thread specification of the nut is similar to that of the stud. To use, screw the stud into the nut and tighten the screw, then screw the nut to tighten the stud.

② Disassembling method of rusty bolts and nuts

Before removing rusty and corroded bolts and nuts, soak and clarify the screw orientation with kerosene, then slowly loosen about 14 and return to the earlier position; In this way, the bolt can be gradually unscrewed by repeatedly moving forward and backward several times. You can also tap bolts and nuts with a hammer to loosen the threads, and then loosen the bolts and nuts (but do not damage the threads during the tapping process). Nuts that are difficult to remove can be heated with a blowtorch or oxy-acetylene flame by tapping them to expand the nut and quickly screw it out. For bolts that are difficult to remove, soak them in kerosene, then use pipe tongs to clamp them on top of the smooth rod below and screw them out

③ Disassembly method of broken bolt.

The bolt breaks in the hole, which is a problem during disassembly.