Inspection of the valve before installation
(1) Carefully check whether the valve model and specifications meet the requirements of the drawings.
(2) Check whether the valve stem and disc are opened flexibly, and whether there is any jamming and skewness.
(3) Check whether the valve is damaged, and whether the thread of the threaded valve is correct and intact.
(4) Check whether the connection between the valve seat and the valve body is firm, the connection 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 gasket, packing and fasteners (bolts) are suitable for the requirements of the nature of the working medium.
(6) The old or long-standing pressure reducing valve should be disassembled, and dust, sand and other debris should be cleaned with water.
(7) Remove the opening cap, check the degree of sealing, and the valve disc must be closed tightly.
Pressure test of the valve
Low-pressure, medium-pressure and high-pressure valves should be tested for strength and tightness, and alloy steel valves should also be spectrally analyzed for the shell one by one and the material should be reviewed.
1. Strength test of valve
The strength test of the valve is to test the valve in the open state to check the leakage on the outer surface of the valve. The test pressure of PN≤32MPa valve is 1.5 times of the nominal pressure, the test time is not less than 5min, and the shell and packing gland are qualified if there is no leakage.
2. Tightness test of valve
The test is carried out in the state of complete closure of the valve, check whether there is leakage on the sealing surface of the valve, and the test pressure, except for the butterfly valve, check valve, bottom valve, throttle valve, should generally be carried out at nominal pressure, and when the working pressure can be determined, it can also be tested with 1.25 times the working pressure, and the sealing surface of the valve disc is not leaking.
General provisions for valve installation
1. The position of the valve installation should not hinder the operation, disassembly and maintenance of the equipment, pipeline and valve body itself, and the aesthetics of the assembled appearance should be taken into account.
2. The valve on the horizontal pipeline should be installed with the stem facing upwards or at an angle, and the handwheel should not be installed downward. The valves, stems and handwheels on the high-altitude pipeline can be installed horizontally to remotely control the opening and closing of the valve with a chain that is vertically low.
3. Symmetrical arrangement, neat and beautiful; The valve on the riser, under the premise that the process allows, the valve handwheel is suitable for operation with chest height, generally 1.0-1.2m from the ground, and the valve stem must be installed in the direction of the operator.
4. The valves on the side-by-side riser should have the same elevation of the center line, and the net distance between the handwheels should not be less than 100mm; Valves on side-by-side horizontal pipes should be staggered to reduce pipe spacing.
5. When installing heavier valves on water pumps, heat exchangers and other equipment, valve brackets should be installed; When the valve is frequently operated and installed more than 1.8m away from the operating surface, a fixed operating platform should be provided.
6. If there is an arrow mark on the valve body of the valve, the direction of the arrow is the flow direction of the medium. When installing the valve, care should be taken to make the arrow point in the same direction as the medium flow in the pipeline.
7. When installing the flange valve, it should be ensured that the end faces of the two flanges are parallel and concentric to each other, and double gaskets should not be used.
8. When installing the threaded valve, in order to facilitate disassembly, one threaded valve should be equipped with a union joint. The setting of the union should consider the convenience of maintenance, usually the water flow through the valve first and then through the union.
Precautions for valve installation
1. The valve body material of the valve is mostly made of cast iron, which is brittle, so it should not be hit by heavy objects.
2. When handling the valve, it is not allowed to throw it with your hands; When lifting and hoisting valves, the rope should be tied to the valve body, and it is strictly forbidden to tie it to the handwheel, valve stem and flange bolt hole.
3. The valve should be installed in a convenient place for operation, maintenance and overhaul, and it is strictly forbidden to bury it underground. The valves on the pipelines in the directly buried and trenches should be equipped with an inspection well chamber to facilitate the opening and closing of the valves.
4. The thread should be guaranteed to be intact, and the thread should be wrapped with hemp, lead oil or PTFE raw meal tape, and the hexagonal valve body screwed into one end of the pipe should be clamped with a wrench when the buckle is turned.
5. When installing the flange valve, pay attention to tighten the connecting bolts along the diagonal direction, and the force should be uniform when screwing, so as to prevent the gasket from deviating or causing deformation and damage to the valve body.
6. The valve should remain closed when installed. For threaded valves that are close to the wall, the valve stem disc and handwheel often need to be removed for installation, and the valve wheel can be twisted. When dismantling, the handwheel should be twisted to keep the valve open, and then disassembled.
Installation of commonly used valves
Installation of gate valves
Gate valve, also known as gate valve, is a valve that uses the gate to control the opening and closing, and adjusts the pipeline flow and opening and closing the pipeline by changing the cross section. Gate valves are mostly used for pipelines that operate fully open or closed on fluid media. There is generally no directional requirement for gate valve installation, but it cannot be installed upside down.
Installation of shut-off valves
A globe valve is a valve that uses a disc to control opening and closing. By changing the gap between the disc and the seat, i.e. changing the size of the channel cross-section, the medium flow is regulated or the medium path is cut off. When installing a shut-off valve, attention must be paid to the flow direction of the fluid.
The principle that must be adhered to in the installation of the globe valve is that the fluid in the pipeline passes through the valve hole from the bottom up, commonly known as "low in and high out", and it is not allowed to be installed.
Installation of check valves
Check valve, also known as check valve and check valve, is a valve that automatically opens and closes under the action of the pressure difference between the front and back of the valve, and its function is to make the medium flow in only one direction, and prevent the medium from flowing backwards and forth. According to its different structures, check valves have lifting type, swing type and butterfly clamp type. Lifting check valves are divided into horizontal and vertical types. When installing the check valve, attention should also be paid to the flow direction of the medium, and it should not be reversed.
Installation of pressure reducing valves
The pressure reducing valve is a valve that reduces the inlet pressure to a certain required outlet pressure by adjusting it, and relies on the energy of the medium itself to automatically maintain a stable outlet pressure.
From the point of view of fluid mechanics, the pressure reducing valve is a throttling element whose local resistance can change, that is, by changing the throttling area, the flow rate and the kinetic energy of the fluid are changed, resulting in different pressure losses, so as to achieve the purpose of pressure reduction. Then, relying on the adjustment of the control and regulation system, the fluctuation of the pressure behind the valve is balanced with the spring force, so that the pressure behind the valve is kept constant within a certain error range.
Installation of pressure reducing valves
1. The vertically installed pressure reducing valve group is generally set at a suitable height from the ground along the wall; Horizontally installed pressure reducing valve manifolds are generally installed on a permanent operating platform.
2. The application section steel is loaded into the wall on the outside of the two control valves (often used for the globe valve) respectively to form a bracket, and the bypass pipe is also stuck on the bracket for leveling and alignment.
3. The pressure reducing valve should be installed upright on the horizontal pipeline, not tilted, and the arrow on the valve body should point to the direction of medium flow, and should not be reversed.
4. Globe valves and high and low pressure pressure gauges should be installed on both sides to observe the pressure changes before and after the valve. The diameter of the pipe behind the pressure reducing valve should be 2#-3# larger than the diameter of the inlet pipe before the valve, and the bypass pipe should be installed for maintenance.
5. The pressure equalizing pipe of the diaphragm pressure reducing valve should be connected to the low-pressure pipeline. For low-pressure pipelines, safety valves should be set up to ensure the safe operation of the system.
6. When used for steam decompression, a drain pipe should be set. For piping systems that require a high degree of purification, a filter is set in front of the pressure reducing valve.
7. After the installation of the pressure reducing valve group, the pressure reducing valve and safety valve should be tested, flushed and adjusted according to the design requirements, and the adjusted mark should be made.
8. When flushing the pressure reducing valve, close the inlet valve of the pressure reducer and open the flushometer for flushing.
Installation of traps
The basic function of the steam trap is to exhaust the condensate, air and carbon dioxide gas in the steam system; At the same time, it automatically prevents steam leakage to the greatest extent. There are many types of traps, each with different properties.
Depending on how the trap works, it can be divided into the following three types:
Mechanical: Operates by changes in the condensate level in the steam trap, including:
Float type: The float is a closed hollow sphere.
Open upward float type: The float is a barrel type with an open upward direction.
Open downward float type: The float is a barrel type with an opening downward.
Thermostatic: Operates on changes in the temperature of a liquid, including:
Bimetal: The sensitive element is a bimetal.
Vapor pressure type: The sensitive element is a bellows or ink cartridge, and the inside is filled with volatile liquid.
Thermodynamic: Depends on the change of the thermodynamic properties of the liquid.
Disc type: due to the different flow rates of liquid and gas under the same pressure, different dynamic and static pressures are generated, which drives the disc valve plate to act.
Pulsed type: When condensate of different temperatures passes through the two poles in series with the orifice plate, different pressures will be formed between the two pole orifice plates, which will drive the valve disc to act.
Installation of traps
1. A shut-off valve (shut-off valve) should be set before and after, and a filter should be set between the steam trap and the front shut-off valve to prevent the dirt in the condensate from blocking the steam trap.
2. There should be an inspection pipe between the trap and the rear cut-off valve, which is used to check whether the trap is working normally, if the inspection tube is opened and a large amount of steam is emitted, it means that the trap is broken and needs to be overhauled.
3. The bypass pipe is set up to discharge a large amount of condensate at start-up and reduce the discharge load of the trap.
4. When the trap is used for the condensate removal of the heating equipment, it should be installed in the lower part of the heating equipment, so that the condensate pipe is vertically returned to the trap to prevent the water storage of the heating equipment.
5. The installation position should be as close to the drainage point as possible, if the distance is too far, air or steam will accumulate in the slender pipe in front of the trap.
6. When the horizontal pipeline of the steam main pipe is too long, the hydrophobic problem should be considered.
Installation of safety valves
The safety valve is a special valve that is normally closed under the action of external force of the opening and closing parts, and when the medium pressure in the equipment or pipeline rises to exceed the specified value, the medium in the pipeline or equipment is discharged to the outside of the system to prevent the medium pressure from exceeding the specified value.
Safety valves belong to the automatic valve category, which are mainly used in boilers, pressure vessels and pipelines, and the control pressure does not exceed the specified value, which plays an important role in protecting personal safety and equipment operation. Note: Safety valves must be pressure-tested before they can be used.
1. Before installation, the product must be carefully inspected to verify whether there is a certificate and product manual, so as to clarify the constant pressure at the factory.
2. The safety valve should be arranged near the platform as much as possible for inspection and maintenance.
3. The safety valve should be installed vertically, and the medium should flow out from the bottom to the top, and the verticality of the valve stem should be checked.
4. Under normal circumstances, the shut-off valve cannot be set before and after the safety valve to ensure safety and reliability.
5. Safety valve pressure relief: when the medium is liquid, it is generally discharged into the pipeline or closed system; When the medium is gas, it is generally discharged to the outdoor atmosphere;
6. The oil and gas medium can generally be discharged into the atmosphere, and the outlet of the vent pipe of the safety valve should be 3m higher than the surrounding high-rise structures, but the following situations should be discharged into the closed system to ensure safety.
7. The diameter of the population pipe, which is as small as the inlet diameter of the valve; The diameter of the discharge pipe shall not be less than the diameter of the outlet of the valve, and the discharge pipe shall be led to the outside and installed with a bent pipe so that the outlet of the pipe is facing a safe zone.
8. When the safety valve is installed, when the connection between the safety valve and the equipment and the pipeline is open welding, the opening diameter should be the same as the nominal diameter of the safety valve.
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