Tips on daily maintenance of the hottest valve ins

2022-08-08
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Little knowledge about valve installation, use and daily maintenance

stop valves, throttle valves, pressure reducing valves, check valves and other valves are directional. If they are installed upside down, the throttle valve will affect the service effect and life; The pressure reducing valve does not work at all, and the check valve may even cause danger

general valves, with direction marks on the valve body; In case there is no one, it should be correctly identified according to the working principle of the valve

the valve cavity of the stop valve is asymmetric from left to right. The fluid should pass through the valve port from bottom to top, so that the fluid resistance is small (determined by the shape), the opening is labor-saving (due to the upward pressure of the medium), and the medium does not press the packing after closing, which is convenient for maintenance. This is why the stop valve cannot be reversed. Other valves also have their own characteristics

it is estimated that the total market demand in the future is expected to reach 13.26 million tons

the installation position of the valve must be convenient for operation; Even if the installation is temporarily difficult, we should also consider the long-term work of the operators

it is best to align the valve handwheel with the chest (generally 1.2m away from the operating floor), so that it is easier to open and close the valve. The handwheel of the landing valve should be upward and not inclined to avoid awkward operation. For valves close to the wall and equipment, there should also be room for operators to stand. Avoid upward operation, especially acid and alkali, toxic media, etc., otherwise it is very unsafe

do not install the gate valve upside down (i.e. the handwheel is downward), otherwise the medium will remain in the bonnet space for a long time, which is easy to corrode the valve stem, and it is contraindicated by some process requirements. It is extremely inconvenient to replace the packing at the same time

1. The pressure reducing valve should be installed vertically on the horizontal pipeline and should not be tilted in all directions

2. When installing the lift check valve, ensure that its disc is vertical so that it can be lifted and lowered flexibly

3. When installing swing check valve, ensure that its pin shaft is horizontal, so as to rotate flexibly

4. Do not install the rising stem gate valve underground, otherwise the exposed valve stem will be corroded due to humidity

valve use

1. Before installing the valve, carefully check whether the model and specification of the valve used are consistent with the design

2. Check whether the valve can be used under the required conditions according to the valve model and factory instructions

3. When hoisting the valve, the rope should be tied to the flange connection between the valve body and the bonnet, and should not be tied to the handwheel or valve stem, so as not to damage the valve stem and handwheel

4. When installing the valve on the horizontal pipe, the valve rod should be vertical upward, and it is not allowed to install the valve rod downward

5. When installing the valve, it is not allowed to use the forced mouth to mouth connection method of dragging, so as to avoid damage due to uneven stress

6. The rising stem gate valve should not be installed in a wet place underground to avoid stem corrosion

supporting electric actuators

electric actuators are mostly matched with valves and are used in automatic control systems. There are many kinds of electric actuators with different action modes. For example, the angular stroke electric actuator outputs angular torque, while the straight stroke electric actuator outputs displacement thrust. The type of electric actuator used in the system should be selected according to the working needs of the valve

connection mode

I. flange connection:

this is the most used connection form in valves. According to the shape of the joint surface, it can be divided into the following types:

1. Smooth type: used for valves with low pressure. Processing is more convenient

2. Concave convex type: the working pressure is high, and medium hard washers can be used

3. Tenon groove type: washers with large plastic deformation can be used, which are widely used in corrosive media, and the sealing effect is good

4. Trapezoidal groove type: oval metal ring is used as gasket, which is used for valves with working pressure ≥ 64 kg/cm2, or high-temperature valves

5. Lens type: the washer is in the shape of a lens and is made of metal. It is used for high-pressure valves with working pressure ≥ 100 kg/cm2, or high-temperature valves

6. O-ring type: This is a relatively new form of flange connection. It developed with the emergence of various rubber O-rings. It is a sealing effect connection form

II. Clamp connection:

the connection form of directly clamping the valve and the two pipes together with bolts

III. butt welding connection:

directly welded with the pipeline

IV. threaded connection:

this is a simple connection method, which is commonly used in small valves. There are two cases:

1. Direct sealing: internal and external threads directly play a sealing role. In order to ensure no leakage at the joint, lead oil, twine and PTFE raw material belt are often used to fill it; Among them, PTFE raw material belt is widely used; This material has good corrosion resistance, excellent sealing effect and convenient use and storage. When disassembling, it can be completely removed, because it is a layer of non sticky film, which is much superior to lead oil and twine

2. Indirect sealing: the tightening force of the thread is transmitted to the gasket between the two planes, so that the gasket plays a sealing role

v. ferrule connection:

ferrule connection. Its connection and sealing principle is that when the nut is tightened, the ferrule is under pressure, making its edge bite into the outer wall of the pipe, and the outer conical surface of the ferrule is closely connected with the conical surface of the connector body under pressure, so it can reliably prevent leakage

the advantages of this connection form are:

1, small size, light weight, simple structure, easy disassembly and assembly

2. Strong connection force, wide application range, high pressure resistance (1000 kg/cm2), high temperature (650 ℃) and impact vibration

3. A variety of materials can be selected, suitable for corrosion prevention

4. The requirement of machining accuracy is not high; Convenient for high-altitude installation

ferrule connection has been adopted in some small-diameter valve products in China

VI. clamp connection:

this is a quick connection method, which requires only two bolts, and is suitable for low-pressure valves that are often disassembled

VII. Internal self tightening connection:

all the above connection forms use external forces to offset the medium pressure and realize sealing. The following describes the connection form of self tightening by using medium pressure. Its sealing ring is installed at the inner cone at a certain angle with the side opposite to the medium. The medium pressure is transmitted to the inner cone and then to the sealing ring. On the cone at a certain angle, two components are generated, one is parallel to the centerline of the valve body outward, and the other is pressed towards the inner wall of the valve body. The latter component is self tightening force. The greater the medium pressure, the greater the self tightening force. Therefore, this connection form is suitable for high-pressure valves. Compared with flange connection, it saves a lot of materials and manpower, but it also requires a certain preload, so that it can be used reliably when the pressure in the valve is not high. Valves made of self tightening sealing principle are generally high-pressure valves

there are many forms of valve connection, for example, some small valves that do not need to be removed are welded with pipes; Some non-metallic valves adopt socket connection, etc. Valve users should be treated according to specific conditions

sealing requirements

the sealing performance of the valve refers to the ability of each sealing part of the valve to prevent medium leakage, which is the most important technical performance index of the valve. There are three sealing parts of the valve: the contact between the two sealing surfaces of the hoist and the valve seat; The fitting of packing with valve rod and stuffing box; The connection between valve body and bonnet. The leakage in the former part is called internal leakage, which is usually said that if it is not closed tightly, it will affect the ability of the valve to cut off the medium. For block valves, internal leakage is not allowed. The leakage at the last two places is called external leakage, that is, the medium leaks from inside the valve to outside the valve. Leakage will cause material loss, pollute the environment, and even cause accidents in serious cases. For flammable, explosive, toxic or radioactive media, leakage is not allowed, so the valve must have reliable sealing performance

daily maintenance of valves

1. Attention should be paid to the storage environment of valves, which should be stored in a dry and ventilated room and blocked at both ends of the passage

2. The valve should be checked regularly, the dirt on it should be removed, and the antirust oil should be applied on its surface

3. After installation and application, the valve should be regularly overhauled to ensure its normal operation

4. Do not tighten the anchor nut and start the testing machine. Check whether the sealing surface of the valve is worn, and repair or replace it according to the situation

5. Check the wear of the trapezoidal thread of the valve rod and the valve rod nut, and whether the packing is out of date and invalid, and replace it if necessary

6. The sealing performance of the valve should be tested to ensure its performance

7. The valve in operation shall be intact, the bolts on the flange and bracket shall be complete, and the threads shall be intact without looseness

8. If the hand wheel is lost, it should be equipped in time, and cannot be replaced by a monkey wrench

9. The packing gland shall not be skewed or have no pre tightening clearance

10. If the valve is used in a harsh environment and is prone to be contaminated by rain, snow, dust, sand and other dirt, the valve rod should be installed with a protective cover with different elongation

11. The scale on the valve should be complete, accurate and clear, and the lead seal and cap of the valve should be

12. The insulation jacket should be free of dents and cracks

13. For valves in operation, avoid beating them or supporting heavy objects

common problems in valve application

why can't the double seal valve be used as a shut-off valve to further accelerate the integration and development of new material technology with nanotechnology, biotechnology and information technology

the advantage of the double seat valve core is the force balance structure, which allows a large differential pressure, while its prominent disadvantage is that the two sealing surfaces cannot be in good contact at the same time, resulting in large leakage. If it is artificially and forcibly used in cutting off occasions, the effect is obviously not good. Even if many improvements have been made for it (such as double seal sleeve valve), it is not desirable

why is the double seat valve easy to oscillate when working with a small opening

for single core, when the medium is flow open, the valve has good stability; When the medium is flow closed, the stability of the valve is poor. The double seat valve has two valve cores, the lower valve core is in flow closed and the upper valve core is in flow open. In this way, when working with a small opening, the flow closed valve core is easy to cause the vibration of the valve, which is the reason why the double seat valve cannot be used for working with a small opening

what is the poor anti blocking performance of the straight stroke regulating valve and the good anti blocking performance of the angular stroke valve

the valve core of the straight stroke valve is vertical throttling, and the medium flows in and out horizontally. The flow channel in the valve cavity must turn upside down, making the flow path of the valve quite complex (such as the inverted s shape). In this way, there are many dead zones, which provide space for the sedimentation of the medium. In the long run, it will cause blockage. The throttling direction of the angle travel valve is the horizontal direction. The medium flows in and out horizontally, which is easy to take away the dirty medium. At the same time, the flow path is simple, and there is little space for medium sedimentation, so the angle travel valve has good anti blocking performance

why is the cut-off pressure difference of angle stroke valves large

the cut-off pressure difference of angle stroke valve is large because the resultant force produced by the medium on the valve core or valve plate has a very small torque on the rotating shaft, so it can withstand a large pressure difference

why is the stem of the straight stroke regulating valve thinner

it involves a simple mechanical principle: large sliding friction and small rolling friction. When the valve rod of the straight stroke valve moves up and down, and the packing is slightly compressed, it will wrap the valve rod tightly, resulting in a large return difference. For this reason, the valve rod is designed to be very small, and the PTFE packing with small friction coefficient is often used as the packing, so as to reduce the return difference, but this is not the case

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