How To Face The Failure Of The Electric Flat Gate Valve

The problem description is as follows:

One of our domestic oil pipelines is more than 540 kilometers long. There are 6 oil transmission stations to download oil products and increase the pipeline's product oil delivery pressure. The pipeline has the characteristics of high pressure and large pipe diameter. Since the delivered oil is flammable and explosive, and it is not easy to handle pipeline leaks and mechanical failures, in valve selection, considering economy and practicability, imported ball valves are often used in oil pipelines and stations. Used in conjunction with domestic electric flat gate valve. The Z9B43WbFPN2.5DN200 electric flat gate valve (parallel gate valve) currently used in the oil station is mainly composed of electric actuator, valve body, bonnet, valve stem, valve plate, floating valve seat, etc. The valve seat and valve plate are Two-way sealing, high requirements for the cleanliness of the pipeline medium. The Z9B43WbFPN2.5DN200 electric flat gate valve has a low pressure level but a high failure rate, which affects the normal execution of the oil delivery plan of the control center. Moreover, if the valve cannot be operated in time during operation, the pipeline pressure may be overpressured and cause other equipment failures and oil leakage, which may pose a greater safety hazard. Among them, the joint surface of the valve seat and the valve plate, and the joint surface of the valve seat and the valve body are the frequent points of failure.

(1) The joint surface of the valve seat and the valve plate is processed with a Φ200mm×8mm sealing groove, and the inlay material is a PTFE (reinforced polytetrafluoroethylene) sealing ring, which can effectively fit the working surface of the valve plate to make the valve seat Sealed with the valve plate, no oil leakage.

(2) The joint surface of the valve seat and the valve body is sealed by an O-shaped rubber ring. A spring is installed in the arc length between the two inlet and outlet valve seats and the valve body. The spring is compressed during assembly to apply a certain pre-tightening force to the valve seat. Make the valve inlet and outlet valve seat and valve plate achieve two-way sealing effect.

For failure and analysis

Generally, for electric flat gate valve failures, after troubleshooting the electrical circuit and the mechanical problems of the electric head, the valve drain plug is usually opened first for sewage treatment. By observing the clogging of impurities in the valve cavity, a preliminary analysis of the internal failure of the valve is carried out. Based on experience, The fault phenomenon is mostly the valve plate being stuck and the valve seat displacement.

Example 1 When the electric flat gate valve with valve position No. 512 (the rear valve of the flowmeter in the oil transmission station) is closed, it cannot continue to descend until the limit stroke is 11%.

Failure analysis observes that the electric head of the valve indicates normal, there is no alarm symbol on the display screen, and the valve can be fully opened when the dispatching room remotely operates the valve. After changing the control switch of the electric head from remote control to local control, it is closed manually, the torque of the handwheel is large, and there is no obvious effect, and it is no longer forced to pull. According to the stuck position of the valve plate, it is preliminarily determined that there is a foreign body stuck in the valve plate at 11% of the valve plate stroke. There is no filter installed in the pipeline before the No. 512 valve. According to the process requirements, the valve must be in an open state during operation. However, the rust and oil sand in the long-running pipeline oil will settle in the valve cavity when it passes through the valve. When the valve needs to be closed, the operator did not perform the sewage timely (the amount of impurities in the valve cavity is not easy to judge on site, and the sewage plug should not be removed frequently) , Resulting in more and more impurities. When the operating valve is closed, the limit block (guide block) at the bottom of the valve plate gradually compresses the impurities, and some of the impurities are compressed into a cake in the valve cavity and no longer flow. When the valve cannot be closed, the electric head stroke indicator indicates that the position of the valve plate is between 1% and 99% (the fully closed state is 00%, and the fully open state is 100%). When the valve cavity space is filled with impurities such as rust, the impurities and dirty oil in the closed valve cavity will expand under the influence of high temperature, and the pressure will increase. During the lifting and lowering process of the valve plate, the spring between the valve seat and the valve body will slightly expand and contract, and impurities will gradually infiltrate between the springs in contact with the valve seat and adhere to the joint surface of the valve body and the valve seat. As the valve seat is affected by the medium pressure, it will be self-sealing adjustment relative to the valve plate. When the valve plate is lifted to the fully open state, the valve plate limit is about 1/2 of the valve seat diameter, and the valve seat sealing spring is affected by the valve plate. Moving, showing an uneven stress state, the gap between the valve seat and the valve body increases. The impurities adhering to the joint surface of the valve seat and the valve body gradually fill up the gap between the valve seat and the joint surface of the valve body during the expansion and contraction movement of the spring, the amount of spring expansion and contraction is reduced, and the valve seat cannot be reset after being ejected. The two valve seats are in a V-shaped state in the valve body, with a large upper side and a small lower side. When the valve plate is closed to the minimum position of the PTFE sealing ring, it is stuck, and the sealing ring inlaid on the valve seat is scratched, causing the valve to close incorrectly.

Example 2 The electric flat gate valve with valve position No. 521 (the front valve of the flowmeter in the oil delivery station) cannot be opened or closed manually or remotely. The electric head indicates the limit stroke is 4% to 6% swimming.

Failure analysis observes that the valve electric head indicates normal, and it is judged that the valve plate is firmly stuck in the slideway. When the electric head is operated, only the worm gear inside the electric head is idling at 4% to 6%, and the actual valve stem does not act. The electric flat gate valve cannot be opened and closed, indicating that the internal damage of the valve has been serious, and the valve must be disassembled for comprehensive inspection and maintenance. When there are many impurities in the valve cavity, the position of the valve seat in the valve body is displaced into a V-shaped state. However, the operator did not know the internal situation and repeatedly operated the valve, causing the large area of the chrome-plated layer of the valve plate to be scratched, the valve plate was scratched and damaged, the PTFE sealing ring of the valve seat was damaged, and the metal surface was rough. Impurities adhere to the valve plate and enter the valve plate slideway, increasing the friction between the slideway and the valve plate. The electric head drives the valve stem and valve plate to move up and down. After the load increases, the worm wheel of the electric head makes a difficult rotating sound. After the friction in the slideways on both sides is out of balance, the side with the lower friction of the valve plate tilts upward slightly, and the valve stem tilts or sways under abnormal force, causing friction with the valve cover and sealing flange, and it is easy to scratch the valve Rod. If the lifting force of the valve stem exceeds the set value, the torque protection of the electric head is turned on and stopped, and the valve plate is stuck in the slideway and does not move.

3. Treatment measures

Drain the faulty electric flat gate valve, clean up the impurities in the valve cavity, remove minor faults, and restore it to normal use. If the valve is not closed properly or cannot be opened or closed, you need to contact the dispatcher to arrange a repair time. If the valve does need to be disassembled for inspection, the maintenance personnel need to contact the manufacturer to prepare spare parts before disassembling, mainly O-rings, springs, PTFE sealing rings and bonnet open face combination pads of floating valve seats, understand the maintenance technical requirements of the same model valve .

The maintenance personnel release the valve circuit and interlock, disassemble the pipeline flange bolts, install the blind plate, and transport the electric flat gate valve to the maintenance area for disassembly inspection. First disassemble and separate the electric head from the valve, place the valve on the operating table, clean the leaking screw part and the sealing surface of the valve stem, spray a little lubricating oil on the valve stem to prevent the stem seal from being scratched when it is taken out. hurt. Loosen the sealing gland bolts so that the seals are no longer under pressure, loosen the middle flange bolts of the bonnet of the electric flat gate valve, use a lifting chain to slowly take out the bonnet and the seal from the top of the stem and open the valve to drain If the wire is blocked, flush the inside of the valve with clean water, and check the cleanliness of the slideway of the valve plate and the tilt of the valve plate.

After cleaning the valve cavity, knock the valve plate with a copper rod and adjust the valve plate to the middle position of the slideway. Prefabricated a pair of Z-shaped brackets welded with steel plates. Install two Z-shaped lifting brackets at the position of the valve plate dovetail groove and the valve stem connection block. Take good protection to prevent scratches), place a 3t jack on each to support the other end of the Z-shaped bracket.

(1) Check the displacement of the floating valve seat, measure the width of the valve seat installation process groove (8mm), and the linear distance from the process groove to the inlet and outlet flanges (240mm). Process the special external nut of M24, the thickness is 6mm, and the M24×400mm lead screw is used to make a set of tensioners. Install 4 stretchers in the inlet and outlet valve seat process grooves to compress the gap between the valve seat and the valve body and reduce the thrust of the valve seat on the valve plate. At this time, two people operate the jack at the same time, push the Z-shaped bracket together with the valve plate and valve stem out of the valve cavity, and then the valve plate can be taken out for inspection.

(2) Loosen the tensioner, remove the valve seat, clean the joint surface impurities, and check the damage of the valve seat part.

(3) Clean the valve seat, valve plate and the inside of the valve cavity.

(4) As long as the four tensioners of the valve seat are evenly tightened during installation, the gap between the two valve seat sealing rings is measured, and the matching tolerance with the thickness of the valve plate is confirmed to be a transitional fit, and lubrication is applied to the sealing surface of the valve plate. The oil can be easily refilled. The order of reassembly is reverse to that of disassembly.

The chrome-plated layer of the electric flat gate valve that was repaired in the field fell off in a large area, and the valve plate was scored with two scratches about 3mm long, extending to the bottom of the valve plate, and there were protruding iron filings, which made the valve unable to open. Due to the presence of impurities between the valve seat and the valve body, the valve seat is displaced. Below the nozzle of the valve seat and the valve body, about 2mm thick sludge is adhered around the spring, and the upper part is relatively clean, indicating the O-shape of the valve seat The sealing ring has been squeezed by impurities to form a leak, and the overall sealing effect has been lost. The valve seat is in a V shape and firmly clamps the valve plate, making the valve unable to close. The sealing ring inlaid on the two valve seats is seriously damaged and cannot be used. The metal surface of the lower part of the valve seat is scratched and can be used after grinding and repairing. The maintenance personnel will repair and grind the scratches on the valve plate with adhesive on site. The protruding part is repaired with a file, and is polished to make it close to the original finish. However, the chrome-plated layer of the valve plate cannot be repaired manually. The cost and conditions of chrome-plating on a small area are not allowed. The enhanced PTFE sealing ring of the valve seat has been worn and scrapped. It needs to be replaced with a new PTFE material. The sealing surface of the machine tool can protrude from the valve seat by 0.25mm. After the processing is completed, the sealing surface is refined and leveled with a grinding table.

After the maintenance treatment, a manual trial operation was performed, and the switch limit of the valve was reset after the switch was smooth. The multiple operations were normal. Make rational improvements, replace the sewage plug with a pair of wires-small ball valve-diversion pipe-plug structure, which meets the pressure level requirements and use conditions, is economical and convenient, and can be drained before the operator operates the valve to avoid serious blockage Deal with it later.