The need to maintain the valve is its main disadvantage, but the possibility of repair is one of the main advantages.
Possible malfunctions and methods for their elimination
| Malfunction |
elimination |
|
| Leaky flow shutoff |
Defects in the contact surfaces of the shutter and housing. (scale, shells, scratches) |
Lapping of sealing surfaces on the valve and in the body. As a rule, the contact surfaces are made of bronze. To do this, it is necessary to dismantle the cover, remove the shutter, and, if necessary, the housing. Grinding is performed with diamond pastes of various grain sizes with a gradual transition from coarse to fine. It should be borne in mind that in wedge gate valves after several lappings, the valve sags, which leads to leakage even with polished surfaces of the wedge. |
| Leak from under the stuffing box on the stem |
stem not sealed |
Tighten the glands, and if necessary, replace the gland packing. If, after replacing the stuffing box, the leak could not be eliminated, most likely corrosion shells have formed in the stem and it will have to be welded or replaced. |
| Handwheel cannot be turned |
Shutter jammed |
Occurs in valves devoid of attention from service personnel and opened less than once a year. The reason is scale on the sealing surfaces. Remove the valve top cover and clean the sealing surfaces of the disc and body. If necessary, grind the rubbing surfaces. It is not allowed to knock on the stem, as the guide nut may be torn off. |
| Handwheel turns but valve does not open |
Broken shutter "cheeks fell" |
In rising stem valves, this problem occurs when the "cam" of the stem holding the valve is worn or if the threads on the stem guide nut have been stripped. If there is a problem with the stem, it should be replaced or a worn "cam" welded on. A worn guide nut should be replaced if the design of the valve allows it. In valves with a non-rising stem, the valve may fall when the nut fixed in it is worn. To eliminate the malfunction, it is necessary to replace the shutter, since most likely it will not be possible to replace a nut with a stripped thread. |
It is forbidden to dismantle the valve under pressure.
After installation, it is necessary to remove air from the valve, for this, the bolts pressing the stuffing box are loosened, and after the appearance of water drops from under the stuffing box, the bolts are pressed.
Once a month, perform a full cycle, open / close, to clean the rubbing surfaces from a small layer of accumulated scale or sludge.
Keep the valve stem with rising stem lubricated.
Once a week, check the tightness of the stem packing and, if necessary, tighten or replace it. It is not allowed to replace the stuffing box on the pipeline under pressure.
The gate valve must not be in an intermediate position during operation. Either the fully open or fully closed position of the shutter is allowed.
Gate valves made of cast iron parallel, flanged with rising stem and manual drive
Valve failure
Valve leaks water
Cause
Disks 8 (Fig. 33) did not completely lower, did not press against the sealing rings of the housing
Remedy
Screw the flywheel 2 (Fig. 32) with a special wrench 8 or a pipe lever wrench 1. The ends of the spindle 4 and nuts must be at the same height. Before tightening with a wrench, turn the flywheel a few turns in the opposite direction. This will ensure that the valve closes with less effort, since by extending the spindle, you can lubricate its threads.
Rice. 32. Opening and closing the valve: a, b - correct; c - wrong; 1 - lever pipe wrench; 2 - flywheel: 3 - scrap or pipe cut; 4 - spindle; 5- stuffing box cover; 6 - housing cover; 7 - body; 8 - special key
Valve failure
The handwheel rotates, but the spindle is stationary
Cause
Rounded corners of the convergence of the faces of the square on the spindle under the flywheel
Remedy
Holding the spindle 13 (FIG. 33) with a pipe wrench, unscrew the nut 3 with any wrench and remove the flywheel 1. File the new edges lower than the existing ones, if the length of the spindle allows. You can, holding the pipe wrench by the spindle, open and close the valve
Rice. 33. Gate valve made of cast iron, parallel, flanged with a sliding spindle and a manual drive: 1 - flywheel; 2 - running nut; 3 - nut; 4 - key; 5 - nut; 6 - gland packing; 7 - gasket; 8 - disk; 9 - sealing ring of the disc: 10 - sealing ring of the body: 11 - wedge; 12 - body; 13 - spindle; 14 - housing cover; 15 - bolt; 16 - stuffing box cover
Valve failure
The flywheel rotates, but the running nut is stationary
Cause
Key falling out or shearing
Remedy
Hold flywheel 1 with one pipe lever wrench, and unscrew nut 3 with the other. After removing the flywheel, insert a new key 4 into the keyway, made from a piece of steel wire or a nail filed down. The new key should fill the recess in the travel nut 2 and rest against the bottom of the flywheel keyway. This will eliminate the key drop.
Valve failure
The handwheel rotates with the spindle and the valve cannot be opened for the passage of water
Cause
The rectangular end of the spindle, located inside the valve body, has disengaged from the discs
Remedy
Grasp the top threaded end of the spindle with the jaws of the pipe wrench and, preventing it from spinning, rotate the handwheel, while raising and lowering the rectangular end of the spindle 13 inside the body 12 of the valve until it falls between the disks 8 and pulls them up. Usually this is possible in three or four turns of the spindle 13 with a pipe wrench by 15-90 °. If, with such a movement, the rectangular end of the spindle does not pull up the disks 8, then they have fallen to the bottom of the housing 12 and the valve must be disassembled. Shut off the water supply to the emergency valve with other valves. Remove the nuts from the bolts holding the housing and housing cover together. If the valve has been outdoors with pipelines or in a very humid place, the edges of the bolt heads are damaged by rust, then the only way to disassemble is to cut the bolts with a hacksaw blade. This is possible due to the large gap between covers 14 and 16. During installation, generously lubricate new bolts and nuts with solid oil, technical petroleum jelly, etc. Holding the flywheel 1, try to separate cover 14 from body 12. Lightly hit the lower edge of the cover with a hammer or chisel and a hammer will help remove the cover. Don't worry about gasket 7, cut out a new one. The old rubber gasket is suitable if it has retained its elasticity. If using an old gasket, turn it over. The body 12 of the valve, which has been in operation for a long time, may not separate from the discs 8. Then, by hammering on the chisel, chip off the layers that prevent the discs from separating. After lifting the disks, clean them and the internal cavity of the case from deposits. Place gasket 7 on the housing flange. Put the disks 8 on the rectangular end of the spindle 13 and lower them all together into the housing. To ensure that the discs are firmly installed on the spindle, fix them with steel wire. To do this, use a file or a hacksaw to make grooves on the necks of the discs and wind the wire around them. This winding should not interfere with the contact of the sealing rings 9 and 10 of the disk and the housing. Winding with wire can be replaced by installing a bracket made of sufficiently elastic steel wire.
To lock such a bracket, two opposite recesses are drilled on the neck of one of the disks.
Valve failure
The handwheel rotates with the spindle and the valve cannot be used
Cause
The corners of the spindle rectangle between the discs are rounded
Remedy
The easiest way is to replace the spindle using an old valve that has fallen into disrepair for other reasons. It is also possible to remove the spindle from a new valve, which will take less time than installing another valve.
The worn rectangular end of the spindle is restored by shrinkage, by heating the spindle in a forge, or by surfacing using electric welding. After electric welding, they correct the corners on a grinding machine
Valve failure
Gate valve does not completely close the water despite normal movement of the discs
Cause
Uneven deposits and scratches on O-rings
Remedy
Separate cover 14 and body 12, bringing the disks as close as possible to the body cover. To do this, unscrew the spindle to its extreme position. This will make it easier to remove the discs with the spindle, if layers do not interfere. In this case, the rectangular end of the spindle should not push the discs apart. Discs 8 must not be allowed to sink to the bottom of the case, because wedge 11 will burst them, pressing against the sealing rings of the case and not allowing the discs to be removed. If the valve is disconnected from the pipe, through the hole in the body flange, you can push the discs from below with the fingers of one hand, and pull the spindle with the other hand. After dismantling, clean the adjacent surfaces of the sealing rings 9 and 10 of the discs and the housing with a knife. Moreover, hold the knife blade so that it immediately captures the entire width of the ring. Failure to do so will result in new scratches. In particular, the valve may leak water due to the fact that the contact surfaces of the bronze rings in the body and on the discs are scratched by sand, scale, etc., which accumulate between the internal parts of the valve. After closing and opening the valve, the particles are washed out with a jet of water and enter the taps and mixers. If you unscrew the valve head, a rusty stream will gush. The O-rings of the discs can be cleaned by pickling. Pour half a glass or a glass of washing soda or washing powder into a bucket of water and put the discs in there for a day or two. The same can be done with the body sealing rings. But for this, firstly, the body must be disconnected from the pipelines and, secondly, a suitable container must be used. Sometimes both methods are used to free the surface of the sealing rings from deposits (physical and chemical).
After cleaning, rub one of the surfaces of the rings with chalk or wipe with the working side of an old typewriter carbon paper. Now with the contaminated surface, wipe the corresponding mating surface. Scrub the resulting colored tubercles. Grinding is not forbidden, but it is longer.
For rough grinding, you can use the powder left by the grinder. You can also prepare the powder yourself from a mixture of finely crushed brick and glass. Sprinkle the powder on a flat metal surface, on ceramic tiles, etc. Drive the mixture in different directions with the bronze sealing rings of the discs, sometimes lifting it up. In order for the mixture to better envelop the surface of the rings, add liquid oil to it, the mixture should acquire the consistency of shoe polish in boxes (cream is thinner in tubes). Coarse lapping can also be done with an abrasive skin glued or tied along the edges to the board. The width of the plank should be greater than the diameter of the ring. Rub the entire surface at once, changing the direction of the reciprocating motion and exerting even pressure on the entire surface of the plank. In this way it is convenient to clean the surface of the disk, but it is difficult to clean the inner surface of the case when grinding in, you can use special pastes like GOI.
Valve failure
The flywheel is folded from the running nut
Cause
Nut missing
Remedy
1. Turn a new nut on a lathe by creating edges on a milling machine or with a hacksaw and file. Note that the lead nut almost always has an internal trapezoidal thread and an external metric thread. In valves D = 50mm, often instead of a key on the running nut 2, an external thread is cut. A flywheel is screwed onto it, having a corresponding thread in the inner hole of the hub. The flywheel is locked with nut 3 (see Fig. 33). It should be noted that the threads on the running nut and flywheel are left-handed, i.e. the flywheel will turn off the running nut if it is tightened, wanting to lower the discs and close the valve.
2. Remove the nut from a similar valve not installed in pipelines. Turn the nut clockwise. Reinstall the nut by turning counterclockwise until it locks into the threads of the flywheel hub.
3. Unscrew the flywheel. Putting a rag under the jaws of the pipe wrench, rotate the spindle with the upper threaded end in the desired direction
Valve failure
Flywheel hub cannot be rotated
Cause
Broken wheel and flywheel spokes
Remedy
On the hub, select a pipe wrench of the appropriate number or remove the hubs and work with the existing wrench. To capture cylindrical surfaces, the wrench must have two jaws with sharp teeth
Valve failure
Unable to open and close the valve
Cause
flywheel missing
Remedy
Putting a rag under the jaws of the pipe screw, rotate the spindle with the threaded end
Valve failure
Leakage from under the stuffing box cover
Cause
Weakening of gland packing
Remedy
Tighten nuts 3 evenly and alternately on bolts 15. If the flange of the stuffing box cover 16 abuts against the flange of the cover 14 of the body, then you need to add Packing 6 or remove the remains of the old one and replace it with a new one. The gland can be replaced only by turning the flywheel to the limit and checking how closed the valve is. To do this, open one of the valves or taps located behind the valve. A weak water leak will not be a hindrance, but with a strong stream of water, packing the stuffing box is prohibited, as the water will squeeze it out.
To stuff the stuffing box, unscrew the nuts 3 pressing the stuffing box cover. Remove it from cover 14 of the housing. It is easier to do this if the stuffing box cover is sequentially, and even better at the same time, pry on both sides, for example, with the blade of a large screwdriver and the blade of a nail puller or with the handles of the levers of the pipe wrench. So that the stuffing box cover does not interfere in the future, hang it on a wire to the flywheel spokes. Clean the exposed gland seat from dirt and scraps of old stuffing with a steel hook. After laying the first layer of fresh stuffing, try to compact it well. It is most convenient to do this with the same stuffing box cover, if it freely enters
into the hole. When laying the seal layers, half a tube of a suitable diameter, cut lengthwise, will also help. It will be more convenient to use such a half of the tube if the handle is welded to it at an angle of 90 ° C. It is possible to use as a handle sawn at an angle of 20-30 ° and bent sector: tubes.
Lower the stuffing box cover onto the restored stuffing box and tighten it with nuts. The gap between the flange of this cover and the flange of the housing cover must remain 6-10mm as a reserve. Check the quality of your work by raising and lowering the spindle. Leakage of water will signal the need for further tightening of the nuts.
In the absence of a standard seal, use twisted burlap threads or strips of cotton fabric, lightly oiled with any oil, which prevents them from rotting. Suitable for sealing and natural fiber ropes. The stuffing box can also be made up of specially cut rubber half-rings, but in this case it is necessary to slightly tighten the stuffing box cover. A strong tightening will lead to excessive resistance to the movement of the spindle, and the rubber will crumble
Valve failure
Leakage from under the gasket
Cause
Broken or crushed gasket
Remedy
As in the previous case, close the valve and check how it does not let water through. Then remove the connecting bolts between the cover 14 and the body 12 and after one temporarily replace them with longer ones (longer by 20-25mm). Also remove the remaining bolts, and on long ones, unscrew the nuts 2-5 threads of thread and immediately turn the flywheel in the direction of closing. Cover 14 will rise slightly. Repeat the "procedure" until there is a gap of 1-15mm, sufficient to change the gasket 7. Sometimes the gap is increased in order to clean the surfaces of the remnants of the worn gasket.
Cut the new gasket along the old one or along the cover, reducing the outer dimensions by two bolt diameters. In one place, cut the gasket in a zigzag manner to insert it into the gap between the cover and the body. The zigzag on the section of the gasket should protect against water seepage. For reliability, two spacers can be installed with the cuts offset by 180°. To adjust the position of the gasket when cutting, leave the "horns" on it.
The best material for gaskets is sheet rubber, the worst is ordinary, non-corrugated oiled cardboard
All domestic and imported valves newly installed at the facilities of the main oil pipeline must have certificates of conformity, certifying the compliance of the shut-off valves with the requirements of the State standards and regulatory documents of Russia and the permission of the Gosgortekhnadzor of Russia for the right to manufacture and use these products.
RNU (JSC) should take into account the service life, operating time and the number of “closed - open” operation cycles of the valve.
The fitting is considered to be operational if:
The strength of the materials of parts and welds operating under pressure is ensured;
There is no leakage of the medium and sweating through the metal and welds;
The tightness of stuffing box seals and flanged fittings in relation to the external environment is ensured;
The tightness of the valve gate is ensured in accordance with the passport for the shut-off valves;
Provides smooth movement of all moving parts of the valve without jerking and jamming;
The electric drive ensures smooth movement of the shutter, opening and closing within the time specified in the passport; the electric drive is switched off when the shutter reaches the extreme positions and when the torque exceeds the permissible value on the yoke assembly.
If any of these conditions is not met, the valve is considered inoperable and is taken out of service.
Reinforcement performance is characterized by reliability indicators. Reliability indicators include: the assigned valve service life, the assigned resource - in open-closed cycles, the assigned service life before repair, the probability of failure-free operation during the assigned resource.
Valve inoperability is determined by the criteria of failures and limit states.
The failure criteria for stop valves are:
Loss of tightness in relation to the external environment that cannot be eliminated by an additional tightening;
the passage of the medium in the shutter in excess of the allowable;
impossibility of working movements of the locking body (jamming of moving parts) when opening and closing the valve;
increase in response time in excess of the allowable;
failure of the electric drive.
The criteria for limit states of reinforcement are:
Achievement of the assigned service life;
destruction or loss of density of the base material and welds;
Violation of the geometric dimensions of the mating parts (due to wear or corrosion damage).
Upon reaching the designated service life, the shut-off valves are subject to re-examination in order to determine their technical condition and the possibility of extending their service life.
Reliability indicators, failure criteria and limit states are indicated in the valve certificates.
Control of operability and technical condition of valves is carried out by external inspection, diagnostics and testing
During an external examination, the following are checked:
condition and density of materials and welded joints of reinforcement;
smoothness of movement of all moving parts of valves and electric drives;
the serviceability of the electric drive;
tightness of fittings in relation to the external environment, including:
tightness of gasket seals;
tightness of stuffing box seal.
In the working condition of the stop valves, the passage of the medium through the stuffing box and gasket seals is not allowed.
The technical condition of the valve during operation must be determined by diagnostic control. Acoustic emission (AE), ultrasonic (US) and other non-destructive testing methods are used to determine the technical condition of the valve body and welds.
The diagnostic control of the gate valve is combined in time with a major overhaul, and is also carried out when excessive stresses are detected on the nozzles or when failures occur in the operation of the gate valve according to the criteria for limit states. When diagnosing, devices and AE sensors and ultrasonic testing devices or flaw detectors are used.
Diagnostic control and a conclusion based on its results are carried out by specialized organizations that have the permission of the Gosgortekhnadzor of Russia, or specialists from RNU, TsBPO in the presence of a developed and approved method of diagnostic control.
The results of diagnostic control (conclusion) are entered in the valve form or attached to its passport.
Checking the tightness of the valve gate during operation can be carried out by acoustic emission leak detectors.
On operating main oil pipelines, valves are also tested for strength and density of materials and welds, tightness in relation to the external environment, tightness of the gate and operability. The testing of fittings is combined in time with the testing of oil pipelines or is carried out after the overhaul of oil pipelines.
The test mode and test pressures are established depending on the period and parameters of operation of oil pipelines in accordance with the regulatory documents governing testing on existing oil pipelines.
During the operation of pipelines, one of the main duties of maintenance personnel is the constant and careful monitoring of the condition of the outer surface of pipelines and their parts (welds, flange joints, including fasteners, pipeline fittings), anti-corrosion protection and insulation, drainage devices, compensators, supporting structures, etc. .d.
The main method of monitoring the reliable and safe operation of technological pipelines is a periodic audit, which is carried out by the technical supervision service together with mechanics, supervisors and installations (productions).
The results of the audit serve as the basis for assessing the condition of the pipeline and the possibility of its further operation. As a rule, the revision of pipelines should be timed to the scheduled preventive maintenance of pipeline valves, individual units, installations or workshops. The timing of the inspection of pipelines at pressures up to 10 MPa (100 kgf / cm 2) is established by the administration of the enterprise, depending on the rate of corrosion and erosion wear of pipelines, operating experience, the results of the previous external inspection, revision. The timing should ensure safe, trouble-free operation of the pipeline between revisions.
For high pressure pipelines [over 10 MPa (100 kgf / cm 2)], the following types of revision are established:
selective, general selective and complete. The timing of a selective audit is set by the administration of the enterprise, depending on the operating conditions, but at least once every 4 years.
Process pipeline valves are the most critical element of communications, therefore, the necessary measures must be taken to organize constant and thorough supervision of the serviceability of valves, as well as timely high-quality inspection and repair.
Revision and repair of pipeline fittings, including non-return valves, as well as actuating devices of fittings (electric, pneumatic, hydraulic, mechanical drive), as a rule, are carried out during the revision of the pipeline. Revision and repair of fittings should be carried out in specialized workshops or at repair sites. In some cases, at the discretion of technical supervision, it is allowed to revise the fittings by disassembling and inspecting them directly at the installation site (welded fittings, large-sized, hard-to-reach, etc.). During the revision of the reinforcement, the following work must be performed:
a) external examination;
b) disassembly and inspection of the condition of individual parts;
c) inspection of the inner surface and, if necessary, control by non-destructive methods;
d) lapping of sealing surfaces;
e) assembly, testing and pressure testing for strength and density.
When planning the revision and repair of valves, it is necessary, first of all, to carry out the revision and repair of valves operating in the most difficult conditions, while observing the principle of alternation. The results of repair and testing of fittings are documented in an act.
an important object of attention are the sealing rings, the wear of which leads to a decrease in tightness. For example, in oil wells, valve replacement may be required monthly (especially if the oil contains sand), an aggressive environment causes corrosion of the rings, in thermal power engineering, high-pressure and high-temperature steam leads to erosion of the sealing rings.
Also, depending on the operating medium of the pipeline, resins or sediment can accumulate on the o-rings or in the lower part of the body, which prevents tight closure and the passage of the medium in the closed state. All these moments can cause an emergency, and therefore require measures to prevent them and timely eliminate them.
You should also pay attention to spindle wear. The rising type valve spindle requires thread lubrication, so this procedure should be carried out regularly. Gate valves with a non-rising stem are easier to operate, but do not have the ability to lubricate without interrupting the operation of the pipeline and disassembling the valve. Therefore, it should be noted that valves with a non-rising spindle wear out much faster.
In the case of using electric drives, attention should also be paid to the condition of the motor mechanisms, power cable, and control system. For hydraulic and pneumatic drives, maintenance requires a control system, as well as a stuffing box for the drive rod.
- the use of exclusively high-quality products (for example, valves, which have proven themselves in the market and have a wide range of applications);
- timely maintenance, taking into account the design features and operating conditions;
- quick response to the appearance of uncharacteristic phenomena (leaks, incomplete locking, etc.).
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