Valves generally have two characteristics: operational characteristics and structural characteristics.

① Operational characteristics. They determine the main operational performance and scope of use of valves. Valve operational characteristics include: valve types (closed-circuit valves, regulating valves, safety valves, etc.); product types (gate valves, globe valves, butterfly valves, ball valves, etc.); materials of main valve components (valve body, valve cover, valve stem, valve disc, sealing surface); valve transmission methods, etc.

② Structural characteristics. They determine some structural features of valve installation, maintenance, and repair methods. Structural characteristics include: valve structural length and overall height, connection type with pipelines (flange connection, threaded connection, clamp connection, external threaded connection, welding end connection, etc.); sealing surface type (inlaid ring, threaded ring, build-up welding, spray welding, machined from the valve body itself); valve stem structural type (rotating stem, lifting stem), etc.

In some cases, the use of features and structural features are interrelated and cannot be strictly separated.

The general steps and criteria for selecting a valve are as follows.

(1) Selection steps

① Clarify the purpose of the valve in the equipment or device, and determine the operating conditions of the valve: applicable medium, working pressure, working temperature, etc.

② Determine the nominal diameter and connection method of the pipeline connected to the valve: flange, thread, welding, etc.

③ Determine the method of valve operation: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage, etc.

.

④ Determine the materials for the valve housing and internals based on the medium being transported, working pressure, and working temperature: gray cast iron, malleable cast iron, ductile cast iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloy, etc.

⑤ Select the type of valve: closed-circuit valve, regulating valve, safety valve, etc.

⑥ Determine the valve type: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap valve, etc.

⑦ Determine the valve parameters: for automatic valves, first determine the allowable flow resistance, discharge capacity, back pressure, etc., based on different needs, and then determine the nominal diameter of the pipeline and the diameter of the valve seat hole.

.

⑧ Determine the geometric parameters of the selected valve: structural length, flange connection type and size, dimensions in the height direction of the valve after opening and closing, size and quantity of bolt holes for connection, overall external dimensions of the valve, etc.

⑨ Use existing information: valve product catalogs, valve product samples, etc., to select appropriate valve products. In addition, it is necessary to check whether the parameters of the selected valve meet the given working conditions.

(2) Basis for selecting valves

While understanding the steps for selecting valves, it is also necessary to further understand the basis for selecting valves.

① The purpose, operating conditions, and control methods of the selected valve.

② The properties of the working medium: working pressure, working temperature, corrosion resistance, presence of solid particles, toxicity of the medium, flammability, explosiveness, viscosity, etc.

③ Requirements for the fluid characteristics of the valve: flow resistance, discharge capacity, flow characteristics, sealing level, etc.

④ Installation and external dimensions requirements: nominal diameter, connection method and size with the pipeline, external dimensions or weight limits, etc.

⑤ Additional requirements for the reliability, service life of the valve product, and explosion-proof performance of the electric actuator.

Based on the above-mentioned criteria and steps for selecting valves, a detailed understanding of the internal structure of various types of valves is also necessary for reasonable and correct valve selection, so as to make the right choice for the preferred valve.

Valves are accessories on equipment and pipelines, and their maintenance should be carried out in conjunction with the maintenance of the equipment and pipelines.

According to the maintenance and repair procedures for refinery equipment stipulated by Sinopec, the repair content for high, medium, and low-pressure valves of oil products, steam, water, and various gases with a nominal pressure lower than PN16 MPa and a medium temperature lower than 550℃ is divided into three major categories: minor repair, medium repair, and major repair.

The repair items included in each category are as follows:

① Minor repair: Cleaning the oil nozzle and oil cup, replacing the packing, cleaning the valve stem and its threads, removing impurities from the valve, tightening and replacing bolts, and completing the handwheel, etc.

③ Major overhaul: includes the items of medium maintenance, such as dismantling and cleaning of parts, valve body repair, grinding of seals, straightening of valve stems, etc.

A static seal refers to a condition where the sealing pair is in a relatively static state without relative motion, and the surface of this seal is called the static sealing surface.

The reasons for damage to the static sealing surface are summarized as follows:

① The surface roughness of the static sealing surface is relatively high, mainly due to prolonged use, erosion by the medium, and poor maintenance.

② There are obvious indentations on the static sealing surface, mainly caused by the selection of gaskets with too high a hardness or the inclusion of sand particles, weld beading, and other objects.

③ There are scratches and gouges on the static sealing surface, mainly caused by disassembly and cleaning processes that violate operating procedures and use improper force.

.

④Severe corrosion of the static sealing surface is mainly caused by the corrosion of the medium and improper selection of valves.

⑤The presence of obvious grooves on the static sealing surface is mainly due to leakage, which has not been repaired in time, resulting from erosion by the medium.

⑥Deformation of the static sealing surface is mainly caused by insufficient rigidity, excessive connecting force, and thermal creep under high temperatures.

⑦The presence of leakage holes on the static sealing surface is mainly due to poor manufacturing quality, resulting in defects such as wrinkles, pores, and slag inclusions.

⑧ Cracks on the static sealing surface are mainly caused by unreasonable design, poor manufacturing quality, improper installation or operation, and long-term exposure to alternating loads.

Damage to the static sealing surface is one of the main causes of valve leakage and should be taken seriously.

The repair items for the static sealing surface include the repair of convex outer circle, too small reserved gap, and screw plug. The specific methods are as follows:

① Repair of convex outer circle. Due to reasons such as too small manufacturing fit gap, collision deformation of convex and concave surfaces, and other factors, it is difficult to fit the convex surface into the concave surface. In addition to turning, a file can be used for repair. The repair method is as follows: Select a flat file to grind off the side teeth, creating a smooth surface. Clamp the workpiece in a vise, place the flat file flat on the convex outer circle, and position the smooth surface against the shoulder. While filing, move the file back and forth, and make circular movements up and down. After filing for a while, change the direction. Continue filing in the above-mentioned manner until the entire circle is filed. For workpieces with large machining amounts, mark out the lines before filing; the filed circular arc should be connected naturally, and keep filing until the required size is achieved. The fit between the convex and concave surfaces is generally H11/d11.

② Repair of too small reserved clearance. First, check the reason for the too small pre-tightening clearance. If the convex surface height is normal but the concave surface depth is too deep, the shoulder surface of the concave surface should be turned or filed; if the convex surface height is insufficient, the convex surface height should be increased. When the thread reserved clearance is too small, the internal thread depth should be appropriately reduced, or the external thread height should be appropriately increased, so that there is a few threads of reserved clearance after the gasket is compressed.

③ Repair of screw plugs. Screw plugs are common static sealing points on valve bodies and valve covers, used for water injection pressure testing and medium discharge. Due to their small size, they are often overlooked, yet leaks are often caused by them. If the screw plug has general leakage, it should be removed, cleaned, the sealing surface ground, and the gasket replaced to repair it; for plugs with severely corroded threads and stripped threads, the screw hole can be enlarged based on the original hole, and a new plug can be matched; for severely damaged plug holes, plug welding can also be used to weld and reprocess the original screw hole. This method is only suitable for steel parts; for severely damaged plug holes on cast iron valves, the plug and plug screw hole can be chemically treated and then glued firmly with appropriate glue. This method is suitable for screw plugs that are not frequently disassembled.

In the structure of the static sealing surface connected by screws, to prevent leakage after the gasket is damaged, a layer of liquid sealant can be applied to the screws or a layer of polytetrafluoroethylene (PTFE) film can be wrapped around them. This will effectively reduce leakage at the static sealing point.

④ Repair of trapezoidal groove static sealing surface. The trapezoidal groove static sealing surface is prone to corrosion and indentation during use. The repair method is as follows: clamp the trapezoidal groove on the lathe, calibrate it with a micrometer, and turn off about 1 mm of thickness on the end face of the trapezoidal groove. Then, cut a new trapezoidal groove on the original one according to the standard size. The surface roughness of the inner and outer sides of the groove should beabove. For trapezoidal grooves with other serious defects that cannot be repaired using the above method, methods such as build-up welding and groove inlaying can be used to solve the problem.

In addition, if the static sealing surface is severely corroded, has serious casting defects, surface cracks, etc., and cannot be repaired, it should be replaced.

Due to the sealing components' functions in the valve passage, such as cutting off and connecting, regulating and distributing, separating and mixing media, the sealing surface is often corroded, eroded, and worn by the medium, making it extremely vulnerable to damage.

The reasons for sealing surface damage can be divided into two categories: human-induced damage and natural damage. Human-induced damage is caused by factors such as poor design, manufacturing precision, improper material selection, incorrect installation, poor usage, and inadequate maintenance. Natural damage, on the other hand, refers to the wear and tear of the valve under normal operating conditions, as well as damage caused by the inevitable corrosion and erosion of the medium on the sealing surface.

The causes of sealing surface damage can be summarized as follows.

① Poor processing quality of the sealing surface. This is mainly manifested as defects such as cracks, pores, and slag inclusions on the sealing surface, which are caused by improper selection of welding and heat treatment specifications, as well as poor operation during welding and heat treatment processes. The hardness of the sealing surface is too high or too low due to incorrect material selection or improper heat treatment.

; The uneven hardness and poor corrosion resistance of the sealing surface are primarily caused by the blowing of the base metal onto the surface during the welding process, diluting the alloy composition of the sealing surface. Of course, there are also design issues involved.

②Damage caused by improper selection and poor operation. This mainly manifests in the failure to select the valve according to the operating conditions, using a block valve as a throttle valve, resulting in excessive closing pressure, rapid closing, or poor sealing, which leads to erosion and wear of the sealing surface.

③Improper installation and inadequate maintenance lead to abnormal operation of the sealing surface, causing the valve to operate with defects and prematurely damage the sealing surface.

④Chemical corrosion of the medium. In the absence of an electric current, the medium surrounding the sealing surface directly reacts chemically with the sealing surface, corroding it.

⑤Electrochemical corrosion. The potential difference generated by the contact between sealing surfaces, the contact between the sealing surface and the closure body and valve body, as well as the concentration difference and oxygen concentration difference of the medium, can lead to electrochemical corrosion, resulting in the corrosion of the sealing surface on the anode side.

⑥ Erosion of the medium. It is the result of wear, scouring, and cavitation of the sealing surface caused by the flow of the medium. At a certain speed, the floating fine particles in the medium collide with the sealing surface, causing local damage; high-speed flowing medium directly scours the sealing surface, causing local damage; when the medium flows in a mixed flow and undergoes local vaporization, bubbles burst and impact the surface of the sealing surface, causing local damage. The alternating effects of medium erosion and chemical corrosion can strongly erode the sealing surface.

⑦ Mechanical damage. The sealing surface may suffer abrasions, bumps, and crushing during the opening and closing process. Under the action of high temperature and high pressure, atoms penetrate each other between the two sealing surfaces, resulting in adhesion. When the two sealing surfaces move relative to each other, the adhered areas are prone to tearing. The higher the surface roughness of the sealing surface, the more likely this phenomenon occurs. During the closing process of the valve, the valve disc may bump and crush the sealing surface, causing local wear or indentation on the sealing surface.

⑧ Fatigue damage.

. Over long-term use, the sealing surface experiences fatigue due to alternating loads, leading to cracks and delamination. Rubber and plastic are prone to aging after prolonged use, resulting in deteriorated performance.

From the analysis of the causes of sealing surface damage mentioned above, it can be seen that to improve the quality and service life of valve sealing surfaces, it is necessary to select appropriate sealing surface materials (see material section), reasonable sealing structures, and processing methods.

The process of operating valves is also the process of inspecting and handling valves.

When operating valves, the following items should be noted.

① High-temperature valves. When the temperature rises above 200°C, the bolts will elongate due to heat, which can easily cause the valve to seal poorly. At this time, it is necessary to perform "hot tightening" on the bolts. It is not advisable to perform hot tightening when the valve is fully closed, as this may cause the valve stem to become stuck and make it difficult to open in the future.

② In seasons when the temperature is below 0°C, it is important to open the valve seat screw plug for valves that have stopped steam or water supply to remove condensate and accumulated water, so as to prevent the valve from freezing and cracking. For valves that cannot remove accumulated water and valves that work intermittently, attention should be paid to insulation.

③ The gland should not be pressed too tightly, and should be based on the flexibility of the valve stem operation (it is wrong to think that the tighter the gland, the better, as it will accelerate the wear of the valve stem and increase the operating torque). Without protective measures, do not casually replace or add packing under pressure.

④ During operation, any abnormal phenomena found through listening, smelling, observing, and touching should be carefully analyzed for causes. If it can be resolved by oneself, it should be promptly eliminated; if it requires a repairman's attention, one should not force it, so as not to delay the repair opportunity.

⑤ Operators should have a dedicated log or notebook to record the operation of various valves, especially important valves, high-temperature and high-pressure valves, and special valves, including their transmission devices. They should record the faults they encounter, the handling methods, and the replacement parts. These materials are important for operators, repair personnel, and manufacturers. Establishing a dedicated log with clear responsibilities is beneficial for strengthening management.

The sliding intermediate bearing is used to support the load of the shafting and adopts splash oil lubrication to ensure the normal operation of the ship's shafting. It is suitable for ships with a shafting linear velocity within the range of 1.5 m/s ~ 8m/s.

Sliding intermediate bearings are divided into three types: Type A, Type B, and Type D (adjustable center with high specific pressure). When the specific pressure is less than or equal to 1.0 MPa, Type A is usually chosen for single oil wedges, while Type B is preferred for multiple oil wedges. If the specific pressure exceeds 1.0 MPa, Type D (adjustable center with high specific pressure) should be selected.

1) Fault phenomenon: Abnormal increase in lubricating oil temperature

Fault causes:

    A. Insufficient cooling water volume;

    B. Blocked cooling water circuit;

    C. Emulsification of lubricating oil.

Solutions:

    A. Adjust the cooling water volume;

    B. Eliminate blockages or leaks in the cooling water circuit;

    C. Check for leaks and replace the lubricating oil;

2) Fault phenomenon: Abnormal temperature of bearing bush

Fault causes:

    A. Too low lubricating oil level;

    B. Loose oil slinger, losing its oil-throwing function.

Solutions:

    A. Top up the lubricating oil level;

    B. Tighten the bolts of the oil slinger, check and adjust the gap between the oil slinger and the oil filler.

.

3) Fault phenomenon: Oil leakage at both ends of the D-type intermediate bearing

Fault cause:

    A. Oil level is higher than the maximum oil level;

    B. Seal ring failure.

Solution:

    A. Adjust the oil level;

    C. Replace the seal ring.

The CB/T3282-2001 planar friction watertight upper rudder bearing (hereinafter referred to as the upper rudder bearing) is used to support the weight of the ship's rudder stock, tiller, and rudder blade, and to withstand the lateral force exerted on the rudder blade by the water pressure during partial ship steering, ensuring the reliable operation of the ship's rudder system.

According to the structural form of the upper rudder bearing: Type A, Type B, and YYDJ; Type A uses hinge bolts to bear lateral forces; Type B uses stop blocks to bear lateral forces; YYDJ is designed according to customer requirements.

According to the requirements for water sealing of the upper rudder bearing: the sealing of the rudder stem is divided into packing seal and "J" ring seal. Packing seal is selected when the upper rudder bearing is above the heavy-load waterline, and "J" ring seal is selected when the upper rudder bearing is below the heavy-load waterline.

1）Fault phenomenon: severe noise

Fault cause: A. The packing gland is too tight;

           B. Grease has not been injected into the friction plate bushing as required.

Solution: A. Replenish lubricating grease;

           B. Adjust the tightening force of the packing gland.

2）Fault phenomenon: Severe water leakage from the rudder shaft seal

Fault cause:A. The upper rudder bearing is below the full load waterline;

          B.The sealing ring has failed.

Solution:A. Replace the sealing structure;

          B.Check the lip of the sealing ring. If the lip is turned up, reinstall it; if the lip is severely worn, replace the sealing ring in time.

3）Fault phenomenon: The amount of sinking of the rudder stock exceeds the scale mark

Fault cause: Severe wear of the friction plate

Solution: Replace the friction plate

4）Fault phenomenon: The clearance between the rudder stock and the rudder bearing is too large

Fault cause: Severe wear of the bushing

Solution: Replace the bushing

The stern shaft sealing device is divided into: oil-lubricated stern shaft sealing device and water-lubricated stern shaft sealing device

The repair content of the oil-lubricated stern shaft sealing device is divided into:

Crew level: including maintenance of the sealing device, routine inspection of the sealing device, and routine basic maintenance.

Dock level: including replacement of seals or bushes, etc.

The repair content of the water-lubricated stern shaft sealing device is divided into:

Crew level: including maintenance of the sealing device, routine inspection of the sealing device, inspection of air seal components, and inspection of fasteners.

Dock level: including replacement of spring components, replacement of dynamic and static rings, and replacement of air tires, etc.

The reasons for damage to the sealing pair include wear failure of the working surface of the sealing pair bushing, severe wear of the working surface of the rotating or stationary ring, and aging or severe wear of the sealing components.

If the wear on the sealing surfaces of the bushing and the dynamic and static rings is not severe, the surfaces can be processed and ground to meet the requirements of the drawings and then continue to be used; if the wear on the surfaces of the bushing and the dynamic and static rings is severe, the bushing or the dynamic and static rings should be replaced directly.

If the sealing ring is damaged, it should be replaced immediately.

No operation for oil-lubricated sealing device.

Precautions for operation of water-lubricated sealing device:

1) Check if all connecting bolts on the stern shaft sealing device are tightened. (Except for the double-headed screw nut on the bow side of the Ω spring boat, which is in a loose state.)

2) Check that the cooling water pipeline and air pipeline are in the correct open and closed state;

3) Check that the cooling water pipeline and air pipeline are in the correct open and closed state;

; font-size: 16px; font-family: Fangzheng Fangsong_GB2312;">Check whether the dynamic and static rings are installed in place;

4) Before operating the shafting, check and ensure that the water and air pipelines, as well as all instruments and valves, are properly connected;

5) Before starting the machine, ensure that there is no compressed air in the pneumatic tire, and the pneumatic tire is in a free state;

6) Before starting the machine, be sure to open the inlet valve first to provide cooling water to the stern shaft sealing device.

Functional characteristics of oil-lubricated sealing devices:

Oil-lubricated sealing devices consist of front and rear sealing devices, which are installed at the front and rear ends of the stern tube bearing, respectively. They rely on the oil film established during operation to reduce bearing wear. The rear sealing device prevents the lubricating oil in the stern tube from leaking out of the ship, while also preventing the intrusion of river water. The front sealing device prevents the lubricating oil in the stern tube from entering the ship's hold.

Functional characteristics of water-lubricated sealing devices:

The stern tube sealing device is a sealing device between the stern shaft and the stern tube end face of the ship's hull. It is used to seal the seawater between the outboard and the stern shaft of the ship's hull. This device is a water-lubricated end face sealing device that automatically compensates and adjusts the pressure balance between the friction pairs caused by changes in draft depth through elastic components, thereby improving the sealing performance of the friction pairs. This device allows for inspection of seal wear at sea, and when maintenance is necessary, the equipment can be repaired or damaged seals can be replaced without the ship entering a dry dock.

（1）Classification based on lubricating medium

If the lubricating medium is oil, an oil-lubricated stern shaft sealing device should be selected; if the lubricating medium is water, a water-lubricated stern shaft sealing device should be used.

（2）Selection based on functional characteristics

For ships with significant axial (0~40mm) and radial (0~10mm) play requirements, CSMB or CSMC type water-lubricated stern shaft sealing devices can be selected.

For ships without axial and radial play requirements, CSM type water-lubricated stern shaft sealing devices can be selected.