Daily Maintenance and Problem-Solving of Lubricated Plug Valve

Precautions for Construction & Installation of Lubricated Plug Valve

1. Being gentle with the package case. Keep its top up and don’t invert.
2. The package case can not be stored outdoors. If so, there should have measures for rainproof & dustproof, and ensure that no part in the case is soaked by water.
3. Valves and all parts cannot be stored outdoors, which will make them rusted, even losing their useful function.
4. Take good care of easily lost accessories such as gaskets, bolts and nuts, and store them at designated locations. The flange surfaces are easily damaged, especially when moving and storing. They cannot be placed facing the ground, but should be placed upwards and not under heavy pressure.
5. Make sure the installation part is clean and free of impurities before installation.
6. When lifting the valve, you can hoist with the lifting lugs or neck parts at both ends of the body, do not damage other parts on the surface of the valve.
7. Don’t open & close valves at random when installing. Generally, Plug Valve is in full open position on arrival, so keep the full position unchanged when installing.
8. Please check if the packing & sealing grease valves of the body side are in good condition when installing.
9. The bottom flange of the plug valve is a pressure-bearing seal part, and it is equipped with an adjustment screw, so that it cannot be directly grounded or externally squeezed.

Precautions for Pressure Test of Lubricated Plug Valve

1. For valves that are re-pressure tested on-site by the user, due to water solubility and multiple switches, the sealant will be partially lost during and after the pressure test, which will lead to internal leakage or difficult switch operations. Should perform grease injection maintenance after that.
2. When doing the pressure test for the shell, the plug valve should be in the fully open position, please do not open it halfway. The half-open pressure test will accelerate the loss of sealant. During the sealing pressure test, it should be in the fully closed position.
3. Do not use the plug valve as a blind plate during the pressure test, that is, do not close the plug valve during the shell pressure test. According to API6D, when the valve is closed, the maximum pressure-bearing capacity cannot exceed 1.15 times the design pressure, and the valve cannot be closed under higher pressure.
4. Do not easily loosen or tighten the adjusting screw at the bottom middle of the valve, and do not easily disassemble the valve parts. (The valve generally does not require replacement parts.) Before adjustment, please consult the manufacturer for consent, and make sure to record after adjusting the screw.
5. If there is no natural gas or compressed air on-site for using the grease injection pump when doing pressure test, nitrogen or argon gas can be used.
6. When there is a problem during the pressure test, please refer to the following part of “All kinds of phenomena, handling ways & precautions of lubricated plug valves that may encounter at the site.”

All Kinds of Phenomena, Handling Ways & Precautions of Lubricated Plug Valves May Encounter At The Site

The following phenomena are not valve assembling or technology quality, which could be solved quickly by debugging and maintenance.

Based on the operation principle of lubricated plug valves, one should have full knowledge of the importance of sealing grease, without auxiliary lubrication of sealant, the valves can not operate at all, also can not seal completely. This kind of plug valve utilizes the structure of completely metal sealed and the advantage of supplying sealant at any time to overcome the demanding applications of natural gas, such as high-pressure difference, throttling, unloading and blowdown, etc. Other types of valves cannot fully meet these requirements.

Switch Difficult Operation of The Lubricated Plug Valve

Difficult to open or close the lubricated plug valve not because the plug and body combined too tight, but serious lack of sealing oil on the plug surface, which leads to losing lubrication of the plug surface. Now should refill the sealant and open/close the valve at the same time, and will find the open angle becomes larger and larger, after 2-3 times, normally could gradually open 90 angles. After perfectly normal operation, continue filling some sealant to consolidate and ensure enough lubrication of the plug surface. This kind of problem will not occur again by injecting the sealant in time during daily maintenance.

Different Leakage Problems of Lubricated Plug Valve

Sealing leakage

1. Lack of sealing grease. Only need to fill enough sealant to ensure it fully covers the plug surface can solve this problem.
2. Sometimes, the plug needs to adjust itself about 2 minutes after the pressure boosting to voltage regulation. By translating to the low-pressure side, the whole plug could tightly close to the internal surface of the body, and finally, it seals completely. Such leakage is actually not sealing leakage.
3. If the valve still leaks after injection, please check if the adjustment screw is loose in the bottom middle. For example, the torque of a 12″ 600LB valve is about 475NM after adjusting the screw. The adjustment screw loosen is caused by the plug hitting the bonnet when the fastening screws around the bonnet loosed during a strong jolt. It could restore good performance by tightening the adjustment screw with a 1/4 to 2/3 circle. This situation is more common for valves over 10″.

Please do not easily loosen or tighten the adjustment screw at the bottom of the valve unless it is fully greased and the valve has been used for years. Before adjustment, please consult the manufacturer for consent, and make sure to record after adjusting the screw.

Slight leakage between the bonnet and body bottom

The same reason that the fastening screws around the bonnet are loosed by the plug hitting the bonnet during a strong jolt. It could restore good performance after tightening the screws, especially the screws near the leak point. Also, this situation is more common for valves over 10″.

Slight leakage of the stem or its above parts

This indicates stem lack of packing, the problem could solve by adding packing. Firstly put little bits of packing into the packing check valve, and then tighten the packing screw slowly, pushing the packing inward. Adding the packing several times as far as possible slowly could help the packing to flow around the stem. This process could repeat until the packing is enough. Clamp the packing check valve with a wrench when tightening the screws to avoid being wrung because of uneven force, leaving 3 circles of screws outside.

If the packing cannot continue to be added, but the medium is still leaking through the stem. At this time, please turn the valve, the rotation of the valve stem will make the surrounding packing more fully distributed, which is conducive to complete sealing. At this point, you will find that more packing can be added.

Daily Maintenance Frequency of Lubricated Plug Valve

Daily maintenance means injecting sealants. For natural gas/oil medium with low sand content and room temperature, the general suggested frequency of injection grease is (whichever comes first):

1. Open/close about 10 times
2. Interval about 6 months
3. When the operation is difficult
4. When occurring seal leakage
5. More than 12 months after leaving the factory

Daily maintenance should be completed by users themselves.

Supplementary Instructions on The Frequency and Method of Sealant Injection

Please see it in the previous part and detailed maintenance directions. However, during the water pressure test, almost every operation needs to inject grease. Because the 733 sealing grease is not suitable for water medium, like Serck Audco Plug Valve, it is only suitable for gas medium in the normal working environment. But the 731 sealing grease is suitable for water medium, not natural gas. So for natural gas medium,733 sealing grease is the only sealing grease.

In the working state of natural gas after normal purification, each full grease injection can be effectively opened or closed about 10 times.

During grease injection, the valve should be opened or closed 1-3 times if possible to ensure sufficient distribution of the sealing grease on the surface of the plug. The pressure of the grease gun/pump is generally between 4000psi-8000psi (280Bar-560Bar), and each valve is different.

When the grease is injected with the pump, the pressure is increased and finally reduced, which means that the sealing grease is opened up, which is very sufficient. The grease gun is manually operated discontinuously, so it is not easy to see this phenomenon, but it can be roughly judged according to the amount of grease injected, for example, 2″ half gun, 4″ one gun, 6″ one and a half, 8″-12″ half a barrel.

If the grease injection pressure is as high as 8000psi, the operation should be suspended, wait a moment for the grease inside to fully flow to the surface of the plug, and then continue the injection. The pressure action should not be too fast, otherwise, it will not be conducive to the full flow of the grease to the surface of the plug.

Must inject grease enough every time! Long-term injection of grease inadequately could lead to an unrecovered problem.

Do not use cleaning agents to clean the plug valve!!! This has caused irreversible serious problems in individual projects. Please be noted!