Inspection before installation
There are many types, models and specifications of commonly used valves. The type of valve to use should be selected according to the purpose of the valve, the characteristics of the medium, the maximum working pressure, the maximum temperature, the flow rate and flow rate of the medium or the nominal diameter of the pipe.
Before installation, carefully check whether the models and specifications of all valves meet the design requirements. According to the valve model and factory instructions, check whether they can be used under the required conditions, and conduct water or air pressure tests if necessary. In addition, check whether the packing is in good condition, whether the gland bolts have sufficient adjustment margin, and check whether the valve stem and valve disc are flexible, whether there are jams or distortions. The sealing surface of the valve disc must be tightly closed. For valves connected with threads, the thread quality should be checked. Unqualified valves cannot be installed and should be stacked separately or marked.& nbsp;
Precautions when installing valves
Open stem valves cannot be laid directly underground, to prevent corrosion of the valve stem, it can only be installed in a covered trench, and the valve should be installed in a position convenient for operation, inspection, disassembly, maintenance and operation.
Do not throw the valve casually when handling it to avoid damage and deformation.When stacking, carbon steel valves should be separated from stainless steel valves and non-ferrous metal valves. When lifting the valve, the steel wire rope should be tied to the connecting flange between the valve body and the bonnet. Do not tie it to the handwheel or valve stem to prevent damage to the valve stem and handwheel.& nbsp; The valve installation position should not hinder the disassembly, maintenance and operation of equipment, pipelines and the valve itself.The installation height should be convenient for operation and maintenance. Generally, the valve operating handle should be 1-1.2m away from the ground. For valves with many operations, when they must be installed more than 1.8m away from the operating surface, a fixed operating platform should be installed. When they must be installed above or below the operating surface, an extension rod should be installed or the valve stem should be installed horizontally, and at the same time, a handwheel with a transmission device or a remote operating device should be installed. The included angle between the axis of the valve transmission device should not exceed 30°, and the joint should be flexible to rotate, flexible and easy to use during operation, and accurate instructions. For valves with thermal displacement, the transmission device shall have compensation measures.
In horizontal pipes, it is best to have the valve vertically upwards or the valve stem installed within the upper semicircle, but the valve stem must not be installed downward.Valve stems and handwheels on vertical pipes must be installed in the direction of the operation circuit line. When conditions permit, valves should be installed as centrally as possible for easy operation. Valves on pipelines in the tower area above 4 meters above the ground should not be placed outside the platform for ease of installation and operation.
For directional valves, the installation direction should be determined according to the medium flow direction of the pipeline during installation. For example, when installing a stop valve, the medium should flow from below the cabinet plate to above, commonly known as low inlet and high outlet.When installing cocks and gate valves, allow medium to flow out from either end. When installing a check valve, special attention must be paid to the flow direction of the medium to ensure that the valve disc can automatically open. On important occasions, arrows must be clearly marked outside the valve body to indicate the direction of medium flow. For swing check valves, ensure that the rotating pivot of the insert plate is installed in a horizontal position. For lifting check valves, ensure that the center line of the valve disc is perpendicular to the horizontal plane.
For valves with special requirements, be familiar with installation requirements.For example, when installing lever-type safety valves and pressure reducing valves, the center line of the valve disc must be perpendicular to the horizontal plane, and correction must be made when tilting is found.
When installing threaded valves on pipes, be sure to install a union near the valve for easy disassembly.
Shut-off valves shall be set up for auxiliary system pipes entering the workshop. When the workshop is shut down for maintenance, they can be cut off from the main pipe.These valves are generally installed at a high height and should be arranged together as much as possible to allow for a fixed operating platform.
When installing flanged valves, ensure that the two flange end faces connected to them are parallel and coaxial with the valve flange.Especially when installing valves with brittle materials such as cast iron, valve damage caused by incorrect installation position and uneven stress should be avoided. When tightening the flange bolts, a symmetrical or cross-crossing method should be used and gradually tightened in several times.
Before installing high-pressure valves, the product certificate and test records must be reviewed.Most high-pressure valves are angle valves, and often two are connected in series. When opening, the starting force is large. A valve holder must be set to support the valve and reduce the starting stress. The installation height should be 0.6-1.2m.
Pipe joints on pumps, heat exchangers, towers and containers should not bear the weight of valves and pipes, and brackets should be added to valves with nominal diameter dn 80 mm.
The lining, spraying, and non-metallic materials used in the construction of doors are generally of low quality and strength. In addition to considering manufacturing requirements, it’s important to arrange these components in a concentrated manner, which will facilitate the design of the valve frame.Even a single valve should be fixed to the valve holder. When installing heavy valves on horizontal pipes, consider installing brackets on both sides of the valve.
Valves with threaded connections should be installed in such a way that the threads are intact andPacking should be selected according to working conditions, and the position of the valve stem should meet the installation requirements when tightened in place. When tightening, you must use a wrench to firmly tighten the valve hexagon at one end of the pipe to ensure that the valve body will not be deformed or damaged. Flanged or threaded valves should be installed in a closed state.
Argon arc welding should be used for the back sealing of the connection seam between the valve and the pipeline to ensure that the interior is smooth and smooth.The valve should not be closed during welding to prevent overheating and deformation of the sealing surface. If the sealing material is not resistant to high temperatures, the sealing material must be removed before welding to prevent the welding temperature from damaging the sealing material.
For valves on side-by-side pipelines, the clear distance between handwheels shall not be less than 100mm,In order to reduce pipe spacing, it is best to staggered valves arranged side by side.
Before positioning, the cryogenic valve should be opened and closed as much as possible in cold conditions, and it is required to be flexible and free from jamming.
The connection of the safety valve should have an elbow (or a fitting such as a tee)Avoid fluid directly impacting the valve; in addition, ensure that the safety valve is not frosted during operation to avoid failure during operation.
It is strictly prohibited to use the valve stem as a scaffold to climb during valve installation.
High temperature valves above 200℃Since the valve is installed at room temperature, but after normal use, the temperature rises, the valve bolt expands by heat, and the gap increases, so it must be tightened again, which is called "hot tightening". Operators should pay attention to this work, otherwise valve leaks will easily occur.
In cold winter, if the water valve is closed for a long time, the accumulated water behind the valve should be drained.After the steam valve is stopped, the condensate must also be drained. The bottom of the valve is like a drain switch that can be turned on to drain water.
Non-metallic valves, some are hard and brittle, and some are low in strength. When operating, the opening and closing force should not be too large, especially not violent.Also pay attention to avoid bumping objects.
The flow direction of the stop valve during installation should be consistent with the arrow marked on the valve body (it cannot be installed backwards), so that when the valve is closed, pressure is applied to the cone at the top of the valve, and the packing is not under load. However, for valves (such as heating valves) that are not frequently opened and closed but need to be strictly ensured that there is no leakage in the closed state, they can be consciously reversed according to needs to make them tightly closed with the help of medium pressure.
Large size gate valves (DN200 - 500MM) and pneumatic regulating valves should be installed vertically,In order to avoid being biased to one side due to the large weight of the valve core, increasing the mechanical wear between the valve core and the bushing, causing leakage.
When tightening the hold-down screws, the valve should be slightly open,In order to avoid crushing the sealing surface of the valve top.
After all valves are in place, they should be opened and closed again, and they are qualified if they are flexible and free from jamming.
After naked cooling of a large air separation tower, pre-tighten the connecting valve flange once in the cold state,Prevent the valve from leaking at normal temperature but leaking at low temperature.
When using the new valve, do not press the packing too tightly,The principle of no leakage is to prevent the valve stem from being under too much pressure, causing accelerated wear, and making it difficult to open and close.
