What should be kept in mind during valve installation

What should be kept in mind during valve installation

 

 

Taboo 1

Hydrostatic test shall be conducted under negative temperature during winter construction.

 

Measures: the hydrostatic test shall be carried out as far as possible before the construction in winter, and the water shall be blown out after the pressure test, especially the water in the valve must be cleaned, otherwise the valve will rust or freeze crack.

 

 

Taboo 2

Consequence: if the water quality fails to meet the operation requirements of the pipeline system, the pipeline section will often be reduced or blocked.

 

 

 

Taboo 3

Consequence: it may cause water leakage and cause user losses.

 

 

Taboo 4

Consequence: leakage occurs after the operation of the pipeline system, affecting the normal use.

 

Taboo 5

Consequence: the size of butterfly valve flange plate is different from that of ordinary valve flange plate. The inner diameter of some flanges is small, while the valve disc of butterfly valve is large, resulting in failure to open or hard open and damage to the valve.

 

 

Taboo 6

Consequence: during the construction of heating and sanitation project, the building structure is chiseled, and even the stressed reinforcement is cut off, which affects the safety performance of the building.

 

Taboo 7

Consequence: the staggered joint of the pipe is not on the same center line, which directly affects the welding quality and appearance quality. There is no gap for butt joint, no groove for thick wall pipe, and the welding cannot meet the strength requirements when the width and height of the weld do not meet the requirements.

 

Taboo 8

Consequence: the pipeline is damaged during backfill compaction due to unstable support, resulting in rework and repair.

 

 

Taboo 9

Consequence: the pipe support is loose, and the pipe is deformed or even falls off.

 

 

Taboo 10

The strength of flange plate and gasket for pipeline connection is not enough, and the connecting bolt is short or the diameter is fine.

 

Taboo 11

Rubber gasket is used for heat pipe, double-layer gasket or inclined gasket is used for cold water pipe, and flange gasket protrudes into the pipe.

 

Measures: the flange plate and gasket of the pipeline must meet the requirements of the design working pressure of the pipeline.

 

The flange gasket shall not protrude into the pipe, and its outer circle shall be appropriate to the flange bolt hole. Inclined gasket or several gaskets shall not be placed in the middle of the flange. The bolt diameter of the connecting flange shall be less than 2mm than the flange plate hole diameter, and the length of the bolt rod protruding from the nut shall be 1 / 2 of the nut thickness.

 

Wrong valve installation method.

 

Consequences: Valve failure, switch maintenance is difficult, and the valve stem is downward, which often leads to water leakage..

 

 

Taboo 12

For example, the nominal pressure of the valve is less than the system test pressure; When the diameter of water supply branch pipe is less than or equal to 50mm, gate valve shall be adopted; The main and vertical pipes of hot water heating adopt globe valves; The suction pipe of fire pump adopts butterfly valve.

 

Measures: be familiar with the application scope of various valves, and select the specification and model of valves according to the design requirements. The nominal pressure of the valve shall meet the requirements of system test pressure. According to the requirements of construction specifications: the globe valve shall be used when the diameter of water supply branch pipe is less than or equal to 50mm; When the pipe diameter is greater than 50mm, gate valve shall be used. The dry and vertical control valves for hot water heating shall be gate valves, and the suction pipes of fire pumps shall not be butterfly valves.

 

 

Taboo 13

The necessary quality inspection is not carried out as required before valve installation.

 

Measures: pressure strength and tightness test shall be conducted before valve installation. In the test, 10% of the quantity of each batch (same brand, same specification and same model) shall be randomly selected, and not less than one.

 

Taboo 14

Consequence: the project quality is unqualified, there are potential accidents, it cannot be delivered on time, and it must be reworked and repaired; The construction period is delayed and the input of labor and materials is increased.

 

 

Taboo 15

Valve inversion

 

Measures: for general valves, there are direction signs on the valve body; If not, it shall be correctly identified according to the working principle of the valve. The valve cavity of the globe 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 globe valve cannot be revers ed.

 

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

 

For swing check valve, ensure that its pin shaft is horizontal during installation, so as to rotate flexibly.

 

 

Taboo 16

Manual valve opening and closing, excessive force

 

Measures: the hand wheel or handle of the manual valve is designed according to ordinary manpower, taking into account the strength of the sealing surface and the necessary closing force. Therefore, it is not allowed to use a long lever or wrench to move the plate. Some people are used to using wrenches. They should pay strict attention not to use too much force, otherwise it is easy to damage the sealing surface or break the hand wheel and handle. When opening and closing the valve, the force should be stable without impact. The components of some high-pressure valves with impact opening and closing have considered this impact force, which is different from that of general valves. For the steam valve, before opening, it shall be heated in advance and condensate shall be removed. When opening, it shall be as slow as possible to avoid water hammer. When the valve is fully opened, the hand wheel shall be reversed a little to tighten the threads to avoid loosening and damage. For rising stem valves, remember the valve stem position when fully open and fully closed to avoid hitting the top dead center when fully open. And it is convenient to check whether it is normal when fully closed. If the valve disc falls off, or large sundries are embedded between the valve core seals, the valve stem position will change when it is fully closed. When the pipeline is initially used, there is a lot of dirt inside. The valve can be slightly opened, washed away by the high-speed flow of the medium, and then gently closed (it can not be quickly closed or sharply closed to prevent residual impurities from damaging the sealing surface), and opened again. Repeat this for many times to flush the dirt, and then put into normal operation. If the valve is normally open, dirt may stick to the sealing surface. When closing, flush it with the above method, and then officially close it. If the hand wheel and handle are damaged or lost, they shall be equipped immediately and can not be replaced by a flexible wrench, so as to avoid damaging the four sides of the valve stem and ineffective opening and closing, resulting in accidents in production. Some media are cooled after the valve is closed to shrink the valve. The operator should close it again at an appropriate time to keep the sealing surface free of fine cracks. Otherwise, the media will flow through the fine cracks at high speed and it is easy to erode the sealing surface. During operation, if it is found that the operation is too laborious, the reason shall be analyzed. If the packing is too tight, it can be loosened properly. If the valve stem is skewed, notify the personnel to repair it. When some valves are in the closed state, the closing parts are heated and expanded, resulting in difficulty in opening; If it must be opened at this time, loosen the bonnet thread by half a turn to one turn to eliminate the valve stem stress, and then turn the hand wheel.

 

 

Taboo 17

Improper installation of valves in high temperature environment

 

Measures: high temperature valves above 200 ℃ must be tightened again, called "hot tightening", because they are installed at normal temperature, but after normal use, the temperature rises, the bolt expands and the gap increases, so the operators should pay attention to this work, otherwise it is easy to leak.

 

Taboo 18

Measures: when the weather is cold, the water valve shall be closed for a long time, and the ponding behind the valve shall be removed. After the steam valve stops, the condensate shall also be discharged. The valve bottom is like a screw plug, which can be opened for drainage.

 

Taboo 19

Measures: some non-metallic valves are hard and brittle, and some have low strength. During operation, the opening and closing force shall not be too large, especially not strong. Also pay attention to avoid object collision.

 

Taboo 20

Measures: when a new valve is used, the packing shall not be pressed too tightly to avoid leakage, so as to avoid too much pressure on the valve stem, accelerated wear and laborious opening and closing. The quality of valve installation directly affects the use, so we must pay careful attention to the direction and position of the valve, valve construction operation, valve protection facilities, bypass and instrument, and replacement of valve packing.

 

Taboo 21

Measures: the installation position of the valve must be convenient for operation; Even if the installation is temporarily difficult, the long-term work of the operator should be considered. It is best to align the valve hand wheel with the chest (generally 1.2m away from the operating floor), so as to save effort in opening and closing the valve. The hand wheel of the landing valve shall be upward and not inclined to avoid awkward operation. For the valves near the wall machine and equipment, the room for the operator to stand shall also be reserved. Avoid upward operation, especially acid-base and toxic media, otherwise it is very unsafe.

 

Taboo 22

Measures: be careful in installation and construction, and avoid hitting valves made of brittle materials. Before installation, check the valve, check the specifications and models, and identify whether there is damage, especially for the valve stem. Also turn a few times to see if it is skewed, because the valve rod is most likely to be skewed during transportation. Also remove the sundries in the valve. When lifting the valve, the rope shall not be tied to the hand wheel or valve stem to avoid damaging these parts, but shall be tied to the flange. The pipeline connected to the valve must be cleaned. Compressed air can be used to blow away iron oxide chips, sediment, welding slag and other sundries. These sundries are not only easy to scratch the sealing surface of the valve, but also large particle sundries (such as welding slag) can block the small valve and make it invalid. When installing the screw valve, the sealing packing (hemp plus lead oil or PTFE raw material belt) shall be wrapped on the pipe thread and shall not be put into the valve to avoid accumulation in the valve and affect the medium flow. When installing the flange valve, pay attention to tighten the bolts symmetrically and evenly. The valve flange and pipe flange must be parallel with reasonable clearance to avoid excessive pressure and even cracking of the valve. Pay special attention to brittle materials and valves with low strength. For the valve to be welded with the pipe, spot welding shall be carried out first, then the closing parts shall be fully opened, and then welded.

 

Taboo 23

Measures: some valves must also have external protection facilities, which are thermal insulation and cold insulation. Heat tracing steam pipeline is sometimes added in the insulation layer. What kind of valve should be insulated or cold should be determined according to the production requirements. In principle, if the medium in the valve reduces the temperature too much, which will affect the production efficiency or freeze the valve, it needs thermal insulation or even heat tracing; Where the valve is exposed, which is unfavorable to production or causes frosting and other adverse phenomena, it is necessary to keep cold. Thermal insulation materials include asbestos, slag wool, glass wool, perlite, diatomite, vermiculite, etc; Cold insulation materials include cork, perlite, foam, plastic and so on.

 

Taboo 24

 

The drain valve is not installed with bypass

 

Taboo 25

Packing is not replaced regularly

 

The valve faces thousands of different medium, and the stuffing box is always filled with ordinary packing, but when in use, the packing must adapt to the medium.

 

For valves with high requirements, the joint angle is 30 degrees. The joints between rings are staggered by 120 degrees.

 

When compressing the packing, rotate the valve rod at the same time to keep the surrounding uniform and prevent too dead. Tighten the gland evenly without tilting.