Inspections, tests, and precautions before valve installation

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Inspections before valve installation: ① Carefully check and verify that the valve model and specifications meet the requirements of the drawings. ② Check whether the valve stem and disc move freely, and whether there is any jamming or misalignment. ③ Check whether the valve is damaged, and whether the threads of the threaded valve are straight and intact. ④ Check whether the valve seat is firmly bonded to the valve body, as well as the connections between the valve disc and the valve seat, the valve cover and the valve body, and the valve stem and the valve disc. ⑤ Check whether the valve gaskets, packing, and fasteners (bolts) are suitable for the requirements of the working medium. ⑥ Obsolete or long-idle pressure relief valves should be disassembled, and dirt, sand, and other debris must be thoroughly washed off with water. ⑦ Remove the access cover and check the sealing degree; the valve disc must close tightly. Pressure testing of valves: Low-pressure, medium-pressure, and high-pressure valves must undergo strength tests and leakiness tests. For alloy steel valves, spectral analysis of the casing must be performed on a per-unit basis to verify the material composition. 1. Strength test of the valve The strength test of the valve is conducted with the valve in the open position, to check for any leaks on the outer surface of the valve. For valves with PN≤32 MPa, the test pressure shall be 1.5 times the nominal pressure; the test duration shall be no less than 5 minutes. The valve is considered satisfactory if there is no leakage at the shell or packing gland. 2. Valve tightness test This test is carried out with the valve fully closed, in order to check for any leaks in the valve’s sealing surfaces. For valves other than butterfly valves, check valves, foot valves, and throttle valves, the test pressure should generally be the nominal pressure; however, when the operating pressure is known, a pressure of 1.25 times the operating pressure can also be used. The test is considered successful if there are no leaks in the sealing surfaces of the valve disc. General provisions for valve installation: 1. The location where the valve is installed should not hinder the operation of the equipment, pipelines, and the valve itself, nor should it complicate its disassembly, assembly, and maintenance. At the same time, attention must be paid to the aesthetic appearance of the overall assembly.     2. For valves on horizontal pipes, the valve stem should be installed upright or at an angle; it must not be installed with the handwheel facing downward. The valves, valve stems, and handwheels on high-altitude pipelines can be installed horizontally, with chains positioned at a lower vertical position being used to operate the opening and closing of the valves from a distance.     3. Symmetric arrangement, neat and aesthetically pleasing ； For the valves on the risers, as permitted by the process requirements, it is most convenient to operate the valve handwheel at chest height; generally, a height of 1.0–1.2 meters above the ground is suitable, and the valve stem must be installed in the direction facing the operator.     4. For valves on parallel vertical pipes, it is advisable that their centerlines be at the same elevation, and the clear distance between the handwheels should be no less than 100 mm ； Valves on parallel horizontal pipes should be installed offset from each other to reduce the pipe spacing.     5. When installing heavier valves on equipment such as water pumps and heat exchangers, valve supports should be provided ； For valves that are operated frequently and are installed at a height of more than 1.8 m above the operating surface, a fixed operating platform should be provided.     6. If there are arrow marks on the valve body, the direction indicated by the arrows is the flow direction of the medium. When installing the valve, care should be taken to ensure that the arrow points in the same direction as the flow of the medium within the pipeline.     7. When installing flanged valves, it is necessary to ensure that the end faces of the two flanges are parallel and concentric; double gaskets must not be used.     8. When installing threaded valves, to facilitate disassembly, one threaded valve should be equipped with a union fitting. The installation of the union should take into account ease of maintenance; usually, the water flow passes through the valve first and then through the union. Precautions for valve installation: 1. The valve body is usually made of cast iron, which is brittle; therefore, it should not be subjected to impacts from heavy objects.     2. When moving valves, it is not allowed to throw them around carelessly ； When lifting valves, the rope should be tied to the valve body; it is strictly prohibited to tie it to the handwheel, valve stem, or flange bolt holes.    3. Valves should be installed in locations where operation, maintenance, and repair are easiest; it is strictly prohibited to bury them underground. Valves on pipes buried directly in the ground or in trenches should be equipped with inspection manholes to facilitate the opening, closing, and adjustment of the valves.    4. The threads must remain intact and undamaged; hemp should be wrapped around them, lead grease applied, or Teflon tape used. When tightening, a wrench should be used to hold the hexagonal valve body at one end of the pipe in place.    5. When installing flanged valves, be careful to tighten the connecting bolts in a diagonal direction, applying even force while tightening to prevent the gaskets from shifting or to avoid deformation and damage to the valve body.    6. The valve should be kept closed during installation. For threaded valves located close to a wall, it is often necessary to remove the valve stem, valve disc, and handwheel during installation in order to turn them. When disassembling, the valve should be kept open by turning the handwheel before proceeding with the disassembly. Installation of common valves – Installation of gate valves. A gate valve, also known as a gate plate valve, is a valve that uses a gate plate to control opening and closing; it regulates the flow rate in the pipeline and controls whether the pipeline is open or closed by changing its cross-sectional area. Gate valves are commonly used in pipelines where fluid media need to be fully opened or fully closed. Gate valves generally have no orientation requirements for installation, but they must not be installed upside down. Installation of globe valves A globe valve is a type of valve that uses a valve disc to control opening and closing. The flow rate of the medium is regulated or the medium flow path is blocked by changing the gap between the valve disc and the valve seat, thereby altering the size of the channel cross-section. When installing a stop valve, attention must be paid to the flow direction of the fluid. The principle that must be followed when installing a stop valve is that the fluid in the pipeline flows through the valve orifice from bottom to top, commonly known as \"flow from low to high\"; it must not be installed in the reverse direction. Installation of check valves A check valve, also known as a non-return valve or one-way valve, is a type of valve that opens and closes automatically due to the pressure difference before and after it. Its function is to allow the flow of fluid in only one direction, while preventing the fluid from flowing back in the opposite direction. Depending on their structure, check valves come in lift type, swing type, and butterfly wafer type. Lift-type check valves are further divided into horizontal and vertical types. When installing a check valve, attention should also be paid to the flow direction of the medium; it must not be installed in the reverse direction. Installation of pressure relief valves A pressure relief valve is a valve that reduces the inlet pressure to a desired outlet pressure through regulation, and relies on the energy of the medium itself to maintain the outlet pressure stable automatically.     From a fluid dynamics perspective, a pressure reducing valve is a throttling element whose local resistance can be varied; by changing the throttling area, the flow velocity and the kinetic energy of the fluid are altered, resulting in different pressure losses and thus achieving the purpose of pressure reduction. Then, through the regulation of the control and adjustment system, the fluctuations in pressure behind the valve are balanced with the spring force, allowing the pressure there to remain constant within a certain error range. Installation of pressure relief valves 1. For vertically installed pressure relief valve assemblies, they are generally mounted along the wall at an appropriate height above the ground ； Horizontally installed pressure relief valve assemblies are generally mounted on permanent operation platforms.    2. The profiled steel is inserted into the wall on the outside of the two control valves (commonly used in globe valves) to form brackets, and the bypass pipe is also fixed to these brackets for leveling and alignment.    3. The pressure relief valve should be installed vertically on a horizontal pipe, without any tilt; the arrow on the valve body must point in the direction of fluid flow, and it must not be installed in the reverse direction.    4. Globe valves and high/low pressure gauges should be installed on both sides to monitor the pressure changes before and after the valve. The diameter of the pipe downstream of the pressure relief valve should be 2#-3# larger than that of the inlet pipe upstream of the valve, and a bypass pipe should be installed for maintenance purposes.    5. The pressure equalizing pipe of the diaphragm-type pressure reducing valve should be connected to the low-pressure pipeline. Safety valves should be installed on low-pressure pipelines to ensure the safe operation of the system.    6. When used for steam pressure reduction, a drain pipe must be installed. In piping systems where a high level of purification is required, a filter is installed before the pressure reducing valve.   7. After the installation of the pressure reducing valve assembly is completed, the pressure reducing valves and safety valves shall be pressure-tested, flushed, and adjusted in accordance with the design requirements, and markings indicating the adjustments made shall be applied.   8. When flushing the pressure reducing valve, close the inlet valve of the pressure reducer and open the flushing valve to carry out the flushing. Installation of steam traps The primary function of steam traps is to remove condensate water, air, and carbon dioxide gas from steam systems as quickly as possible ； At the same time, it automatically prevents steam leakage to the greatest extent possible. There are many types of steam traps, each with different properties. Based on the different working principles of steam traps, they can be classified into the following three types: Mechanical type: It operates based on changes in the level of condensed water inside the steam trap; this includes the float-type variant, in which the float is a closed hollow sphere. Upward-opening float type: The float is in the form of a bucket with an opening facing upward. Open-bottom float type: The float is in the form of a bucket with an open bottom. Thermostatic type: Operates based on changes in liquid temperature; includes: bimetallic strip: the sensing element is a bimetallic strip. Steam pressure type: The sensitive element is a diaphragm or cartridge filled with a volatile liquid. Thermodynamic type: Operates based on changes in the thermodynamic properties of the liquid. Disk type: Under the same pressure, the different flow rates of liquid and gas result in varying dynamic and static pressures, which drive the disk valve element to move. Pulse type: As condensate at different temperatures passes through the throttle orifices connected in series at both ends, different pressures are generated between these orifices, which drives the valve disc to move. Installation of the steam trap: 1. Isolation valves (gate valves) should be installed at both the front and back. A filter should be placed between the steam trap and the front isolation valve to prevent dirt in the condensed water from clogging the steam trap.    2. An inspection pipe should be installed between the steam trap and the back shut-off valve, to check whether the steam trap is functioning properly. If a large amount of steam emerges when the inspection pipe is opened, it indicates that the steam trap is damaged and requires repair.    3. The bypass pipe is installed to discharge a large amount of condensate during startup, thereby reducing the drainage load on the steam trap.    4. When a steam trap is used to drain the condensate from heat-using equipment, it should be installed below the equipment, with the condensate pipe running vertically downward to connect to the steam trap, in order to prevent water from accumulating in the heat-using equipment.    5. The installation location should be as close as possible to the drainage point; if the distance is too great, air or steam will accumulate in the long, narrow pipe ahead of the steam trap.    6. When the horizontal length of the steam main is too great, attention should be paid to the issue of water drainage. Installation of safety valves A safety valve is a special type of valve whose closing element remains in a closed position under external forces. When the pressure of the medium inside a device or pipeline rises above the specified value, this valve releases the medium outside the system, thereby preventing the pressure from exceeding that specified level.      Safety valves belong to the category of automatic valves and are primarily used in boilers, pressure vessels, and pipelines to ensure that pressure does not exceed specified levels, thereby playing a crucial role in protecting both human safety and the proper operation of equipment. Note: The safety valve must undergo a pressure test before it can be used.    1. Before installation, the product must be carefully inspected to verify whether it comes with a certificate of conformity and user manual, in order to determine the set pressure at the time of manufacture.    2. The safety valve should be located as close as possible to the platform to facilitate inspection and maintenance.    3. The safety valve should be installed vertically, with the medium flowing from bottom to top, and the verticality of the valve stem should be checked.    4. Under normal circumstances, shut-off valves should not be installed before or after the safety valve to ensure safety and reliability.    5. Pressure relief by safety valve: When the medium is a liquid, it is generally discharged into pipelines or closed systems ； When the medium is gas, it is generally discharged into the outdoor atmosphere ；     6. Oil and gas fluids can generally be discharged into the atmosphere; the outlet of the safety valve vent pipe should be 3 m above the highest surrounding structures. However, in the following situations, they should be discharged into a closed system to ensure safety.     7. The diameter of the population pipe should be at least equal to the diameter of the valve’s inlet pipe ； The diameter of the discharge pipe must not be smaller than the outlet diameter of the valve; it should lead outside and be installed using elbows so that its outlet faces a safe area.    8. When installing a safety valve, if the connection between the safety valve and the equipment or pipes is made through welding of an opening, the diameter of that opening should be the same as the nominal diameter of the safety valve.