The Common Maintenance Methods In Use Of Regulating Valve

 I. development direction of regulating valve

The development direction of regulating valve is intelligence, standardization, refinement, rotary transformation and safety.

1, intelligent and standardized: intelligent and standardized control valve has come to the agenda, intelligent is the first choice of intelligent valve locator.Intelligent valve positioning device has the function of self-diagnosis and long-distance communication, which makes the control valve convenient and the fault diagnosis simple.The selection of intelligent valve positioner not only facilitates the change of the flow characteristics of the control valve, but also provides the control quality of the control system, thus simplifying and standardizing the flow characteristics of the control valve.In addition, the intelligent valve locator is based on HART communication protocol, so that the control function is completed at the field level, so that the risk is dispersed, so that the control is more timely and agile.The first embodiment of the valve in the modularization of each component, and then in the demand for repair and replacement of the valve, only to replace part of the accessories on the line, greatly save the protection cost and time.

2, fine small: fine small first reflected in: select fine small actuator, reduce the volume and weight of the valve;Change the flow path structure, the linear displacement into angular displacement.

3, rotary conversion: because the rotating type of regulating valve such as ball valve, butterfly valve has a relatively small volume, small flow resistance, adjustable ratio, good sealing, large flow capacity and other advantages, so in the new variety of regulating valve, the proportion of rotary valve is increasing, especially in the large diameter pipeline, throughout the selection of ball valve, butterfly valve to do the adjustment.

4. Safety: the safety of the surface control system has been paid attention to by all aspects, and the safety surface system (SIS) has higher and higher requirements on the regulating valve.Put forward the requirements of timely, reliable and safe action for regulating valves used in emergency shutdown system or safety interlock system to ensure that these regulating valves can respond sensitively and accurately;Certification procedures should be simplified for regulating valves used in risk sites;Similar to the safety of other site appearance, for the safety of the regulating valve, flameproof skills, fire prevention skills, safety skills, safety skills, no spark skills and so on can be selected.

5, energy saving: reduce energy consumption, improve energy efficiency is a development direction of the valve, the primary way: choose the low pressure drop ratio of the valve;Choose self-operated regulating valve;Choose electric control valve;Select piezoelectric positioner;Select the spool structure with balanced structure, and then lower the thrust or torque of the actuator;Choose frequency conversion skill to replace.

6, environmental protection: environmental pollution has become a public hazard, the first pollution of the control valve on the environment is the noise and leakage of the control valve, noise pollution is more serious.

Ii. Importance of regulating valve

A regulating valve is used to regulate the flow of operating variables and is therefore called a regulating valve.From the perspective of the whole control system, a control system that is well or poorly controlled should be completed through the controlvalve, which becomes very important for the following reasons.

1. The regulating valve is a saving device, which belongs to the moving part. Compared with the detection element, transmitter and controller, during the control process, the regulating valve needs to constantly change the flow area of the saving part, making the operating variable change to adapt to the change of load or operating conditions.Therefore, higher requirements are put forward for sealing, pressure resisting and corrosion of regulating valve components.For example, the sealing will increase the conflict force of the control valve, the dead zone of the control valve will increase, and the control quality of the control system will become worse.

2, the moving parts of the control valve is the formation of running, running, dripping, leakage of the primary reason, it not only form a waste of resources or materials, but also pollution of the environment, causing trouble.

The touch medium of the data of the control valve may be different from the touch medium of the detection element. Therefore, higher requirements are put forward for the corrosion resistance function, strength and stiffness of the control valve.

3, the saving of the valve so that the energy in the valve internal consumption, therefore, reduce energy consumption, reduce the pressure of the valve lost, and ensure better control quality between the choice and coordination.

4, the control valve on the fluid to save at the same time also form noise, for example, when the control valve outlet pressure is lower than the liquid steam pressure, the formation of flash steam;Cavitation occurs when the pressure down the regulator is higher than the vapor pressure of the liquid.The noise caused by regulating valve is related to the design of regulating valve flow path, operating pressure and the characteristics of controlled medium.Therefore, the reduction of noise, drop pressure loss and other requirements on the valve.

5, the adaptability of the regulating valve.It is equipment in a variety of different production process, the production process of high temperature, low temperature, high pressure, large flow, small flow and other operating conditions demand regulator has a varietyof different functions, the regulator can adapt to different application requirements.

6. The development of detection components, transmitters and manipulators is fast, and more manpower and material resources are invested.Relatively speaking, it is generally considered that the structure of the valve is brief, so the research and development of the valve input manpower and material resources are relatively lacking.

Iii. Repair methods commonly used in the operation of regulating valve:

Control valve is divided into electric control valve and pneumatic control valve, a small number of occasions and hydraulic control valve.There are generally two types of valve repair:

1, is the preventive repair, primarily refers to the control valve in order to ensure reliable operation, and in the absence of defects on the adoption of preventive maintenance methods, including the control valve in the field of equipment used by the adoption of a series of preventive measures.

2, is the fault repair, that is, the regulator in the fault condition can not meet the operating requirements of a series of maintenance operations, generally completed in the production workshop, special conditions may also be directly repaired in the pipeline.

1. Preventive repair: preventive repair is the program maintenance before the break out of the control valve, which can be reduced to daily repair and generally includes the following operations.

1.1 stress relief;Due to the improper combination or equipment of the pipeline, various forces will occur, such as the thermal stress caused by the high-temperature medium, the stress caused by the unbalanced tightening force during installation, and the stress caused by some man-made collision to the valve and its pipeline.These stresses on the valve and its pipeline is very simple on the valve function attack effect, severe will affect the valve system itself, resulting in stem and guide parts deformation and not seat alignment;Governing valves of split body may cause the valve body flange to be removed;Stress may also cause seat leakage, etc. Therefore, it is necessary to ensure that the stress is avoided or eliminated at all times and directed away from the regulator.

1.2 check the support status;A good orientation of the device regulator is such that the travel direction of the stem is in a straight plane with the actuator above the body.If the regulator is necessary in the direction of horizontal movement of the stem or the direction of movement of the stem has a certain inclination with the horizontal plane, the actuator should be supported so that the various components of the regulator are in natural condition.If do not add support may support erecting improper may form the different center of the valve stem and valve seat, simply lead to the difference or make packing leakage and other problems even if the valve has fixed and support methods, it is necessary to regularly check, generally 2~3 months to check once.

1.3 to eliminate or prevent foreign matters from entering, check whether there is rust, welding slag and dirt in the connecting pipe of the regulating valve.If there is a simple accumulation of foreign matter in the regulating valve and pipeline, it is necessary to consider the simple filtration equipment in the regulating valve swimming side equipment.In the process medium into the hard sundries simply occasions, must be the filter equipment equipment.Because the valve is closed, a small piece of rust or welding slag is enough to destroy the well-ground sealing surface, and these dirt also on the valve core and seat formation wear, affect its normal operation.

1.4 check air source and power supply regularly;Gas source is one of the key energy sources that drives regulating valve.Although the film chamber of the drive control valve does not consume air, but if the air source system contains water, oil and other impurities, it will make the valve locator, follow-up device and other accessories block and attack trouble.Therefore, it is necessary to check the air source and power supply regularly to ensure that the air source is clean, boring and reliable.

1.5 regular maintenance and refueling;Stuffing and filling requirements are adjusted from scratch after short-term use.For dusty conditions, use a plastic or rubber cover around the stem to protect the stuffing box and guide parts. For corrosive gases or droplets, use special protection methods.In the case of fire resistance requirements, can choose special fire-resistant coating, set fire bag and other methods, fire bag information contains multilayer ceramic fiber or glass fiber.

1.6 delivery and storage;Regulating valve in assembly and painting and installed according to the requirement, the handwheel actuator, locator and other accessories, to avoid foreign matter into the regulating valve, regulator all air interface cohesion to plug, connecting flange mount shield, should pay attention to the various parts, such as valve positioner inlet pipe, the status of the interface.Any outstanding accessories that are susceptible to damage, such as pressure gauges for oilers and potentiometers, should be removed from the connection, packed separately with the regulator and shipped together.The regulating valve shall be fixed with a special bracket to avoid looseness.In case of long-distance shipment, use strong wooden cases.When keeping the regulator, do not support the regulator in sensitive places, such as valve positioner, stem, etc.The environmental conditions for transportation and storage shall be satisfactory to the requirements of the product specification.Do not carry out other operations in the storage area, when unavoidable, it is necessary not to touch the regulator.The place avoids to be affected by the bad condition such as wind sand, dust, rain even, if do not have appropriate place, before storing up, it is necessary to put regulating valve in moistureproof bag, or in the container that put.

1.7 view of safe operation;Check the safe operation status of the regulating valve and related accessories used in explosive places, such as whether the sealing cover is tightened, the operation status of the safety grid, power supply status, etc., to ensure the safe operation of the regulating valve and related accessories.

2. Defect repair:

When the regulator can not operate or can not meet the operating requirements, it is indicated that there is a fault, it is necessary to repair the fault.Under the condition that the cause of the problem cannot be determined, the following procedure can be generally followed.

2.1 cleaning;After the defective regulator is removed from the line, the first step in repair is to thoroughly clean the regulator.Regulating valve is polluted by process fluid place simply, if process medium has caustic, explosive, radioactive, have damage to human body, it is necessary to use special method to wash the part that has been soaked by process clean.Cleaning method with the process of different media and different.Under normal conditions, only water or steam can be blown, to some pollution, such as alkaline medium to use pickling method, the pollution of heavy metals to high temperature, long time for special section.Cleaning should avoid repeated contamination and should be done in a safe place.All cleaning tools containers, heating equipment, steam hoses, washing equipment, etc. should be prepared in advance.

2.2 disassemble the regulating valve;When disassembling the regulator, mark the connection direction of the actuator corresponding to the valve body, separate the actuator from the upper cover, separate the upper cover from the valve body, disassemble the valve core, stem and other parts from the valve body after disassembling the upper cover and stuffing box parts.It is necessary to take a close look at all the parts and components that have been taken apart in order to resolve the need to repair and replace the parts.General control valve after the end of the disassembly, in view of the points to pay attention to the following parts:

1) inner wall of valve body.Check its pressure and corrosion resistance;

2) the seats.Due to the entry of the medium, fixed valve seat with the appearance of the thread is easy to be corroded and make the valve seat loose, on the occasion of high pressure, should also check the seat sealing surface of corrosion or damage, of course now some structure temporary, valve seat and valve body is not selected thread connection, but with the sealing parts are necessary points to view;

3) the valve core.To carefully check whether the spool parts are corroded or worn, especially in the case of high pressure difference spool wear is more serious, in addition to the stem should also check whether there is a similar situation, and whether the spool and loose connection;

4) sealing packing and gasket.Check whether the sealing packing and gasket are aged, cracked, etc., and whether the matching surface is intact.

2.3 disassemble the actuator;After disassembling the actuator, carefully check the bracket, diaphragm, tension spring, push rod and thread connection, etc., in which the bracket is a member under stress and cannot have cracks;Diaphragm is the key component, can not damage or aging;There should be no cracks in the spring. For multi-spring actuators, only one of the springs is damaged, and the function of the whole actuator will be severely affected.Whenever any part is corroded or corroded, it is necessary to replace it.

2.4 assembling from scratch;After all the parts and components have been repaired, they must be assembled from scratch.In the process of temporary assembly from the beginning, pay attention to the appropriate gasket and bolt connection, accurate alignment, even tightening, avoid flange leakage.The torque load of a bolt or stud is related to its size and is not allowed to be screwed too tight.The type, quantity and method of packing directly affect the sealing function.After the abutment actuators, appropriate lubricants are applied to the conflicting parts of the valve stem and guide, actuator push rod and guide, bearings, drive parts, adjusting nuts, etc.

2.5 test;After being assembled from scratch, it is necessary for the regulator to be tested, such as fundamental function test, air tightness test, leakage test and so on. Only after passing the test can the regulator be sent to the site for equipment.

3. Conclusion;Defective repair, also known as passive repair, is the fault of the valve when a repair method, because the 

equipment attack fault to repair, often form the production process stop, severe even appear equipment damage or casualties.Defective repair is not expected in the production process.Preventive repair is based on the past work experience, in the process of equipment and use, in regulator hasn't presented under the condition of trouble, a preventive repair way of regulating valve on time, its intent is to nip in the bud, people generally according to the operation conditions of regulator is different corresponding fault prevention, because something wrong with no attack, repair, can be dramatically reduced the probability of fault attack.In the regulator to use temporary, preventive repair and fault repair generally combined use, give priority to with the former which is complementary to maximize the extension of the regulator using useful life, only such, ability of progress control valve using power, drop rate of system fault, the process technology of producing power and economic benefits of progress and quality of the adjustment of the energy system, and ensure the long term production equipment, safe and efficient operation.

Iv. Equipment measures for regulating valve:

Electric regulating valve and pneumatic control valve is fine appearance, it is a good thing, if do not according to the requirements of the equipment, also can't get the correct use, especially the new pipelines, valves, in the process of delivery, the equipment can attack many problems, the right equipment, to ensure that the regulator normal functioning, and the protection of the late, maintenance, use is also important.

1, at the beginning of the new equipment regulator is put into operation and overhaul, to pay more attention to process piping topurge of blocking or dismantled, in order to avoid because the pipe welding slag, rust and other body parts in savings, orientation and the medium circulation by blocking, or packing too tight in the regulating valve repair, the formation of conflict force increases, lead to the phenomenon of small signal action large signal action not overdo.

2, in the equipment pneumatic control valve, to pay attention to the control valve gas opening and closing, in order to avoid the length of the control valve stem discomfort, the formation of valve leakage.

3. To avoid cavitation, the following points should be noted in the original selection and equipment selection:

1) try to place the regulating valve equipment in the lowest position of the system, so as to relatively improve the regulating valve inlet pressure and outlet pressure;

2) in the upstream or downstream of the regulator a globe valve may save orifice plate, to change the regulator original device pressure drop characteristics;

3) special anti-cavitation internals can also be used to effectively avoid flash or cavitation, which can change the flow rate of thefluid in the regulating valve, and then increase the internal pressure;

4) as far as possible choose material harder regulator, because in the onset of cavitation, on such a regulator, surely it has the functions of erosion wear resistance, can under the condition of must let the cavitation existence without damage to control valve internal parts, on the contrary, on the soft material control valve, when the onset of cavitation, the regulator of the internal parts will soon wear.

4, the regulator should generally be upright equipment, if tilt should be supported.

5. The flow direction of medium is necessary to be consistent with the arrow of valve body.

6. The equipment orientation of the regulating valve shall be convenient for observation, operation and protection.

7, the signal tube of the actuator should meet the flexibility, should not hinder the action of the actuator.