Valves are used in a wide range of applications, from the simplest shut-off valves to various valves used in extremely complex automatic control systems. Valves are closely related to people's daily life, such as the tap for water pipes, the pressure reducing valve for LPG stoves are valves. Valve is also a variety of mechanical equipment such as internal combustion engines, steam engines, compressors, pumps, pneumatic transmission devices, hydraulic transmission devices vehicles, ships and aircraft in indispensable components.
Valve is the most common equipment in chemical enterprises, the installation of valves, seemingly easy, but if not in accordance with the relevant technical implementation, will cause safety accidents.
Valve installation before the check
- Check carefully whether the valve type and specification meet the requirements of the drawings.
- Check whether the valve stem and valve flap opening is flexible, there is no jamming and skewed phenomenon.
- Check whether the valve is damaged and whether the threads of the threaded valve are correct and intact.
- Check whether the combination of the valve seat and the valve body is firm, the connection of the valve flap and the valve seat, the valve cover and the valve body, the valve stem and the valve flap.
- Check whether the valve bedding, packing and fasteners (bolts) are suitable for the requirements of the nature of the working medium.
- The old or long-shelved pressure reducing valve should be disassembled and cleaned with water for dust, sand and other debris.
- Clear the cover of the through-port, check the sealing degree, and the valve must be closed tightly.
Pressure test of the valve
Low-pressure, medium-pressure and high-pressure valves to strength test and tightness test, alloy steel valves should also be carried out on a case-by-case spectral analysis, review the material.
- Strength test of the valve
The strength test of the valve is tested in the valve open state, check the leakage of the external surface of the valve. pn ≤ 32MPa valve, the test pressure of 1.5 times the nominal pressure, the test time of not less than 5min, the shell, packing gland at no leakage for qualified.
- Tightness test of the valve
In the valve completely closed test, check whether the valve sealing surface leakage, the test pressure, in addition to butterfly valves, check valves, bottom valves, throttle valves outside the valve, generally should be nominal pressure, in the ability to determine the working pressure, also available 1.25 times the working pressure for testing, to the valve sealing surface does not leak as qualified.
General provisions of valve installation
- The location of the valve installation should not interfere with the operation, disassembly and maintenance of the equipment, piping and the valve itself, while taking into account the beauty of the assembly shape.
- Horizontal pipeline on the valve, the stem is installed facing up, or tilted at an angle, not handwheel down installation. Valves, stems and handwheels on overhead pipelines can be installed horizontally, with chains hanging low to manipulate the opening and closing of the valve from a distance.
- Symmetrical arrangement, neat and beautiful; the valve on the riser, as long as the process allows, the valve handwheel to flush chest high most suitable for operation, generally 1.0-1.2m from the ground is appropriate, and the valve stem must be installed in the direction of the operator.
- Side by side on the riser valve, its centerline elevation is best consistent, and the net distance between the handwheel is not less than 100mm; side by side on the horizontal pipeline valve should be staggered installation to reduce the pipeline spacing.
- In the pump, heat exchanger and other equipment installed on the heavier valves, should be set up valve bracket; in the operation of frequent and installed in more than 1.8m from the operating surface of the valve, should be set up a fixed operating platform.
- The valve body has an arrow mark, the arrow points to the direction of the flow of the medium. When installing the valve, care should be taken to make the arrow pointing in the same direction as the media flow in the pipeline.
- When installing flange valves, ensure that the two flange ends are parallel to each other and concentric, and do not use double gaskets.
- When installing a threaded valve, a threaded valve should be equipped with a live connection for easy disassembly. The setting of the connection should take into account the convenience of maintenance, usually the water flow through the valve first and then flow through the connection.
Valve installation precautions
- The valve body material is mostly made of cast iron, brittle, so it should not be hit by heavy objects.
- Handling the valve, do not allow hand-throwing; lifting, lifting the valve, the rope should be tied to the valve body, is strictly prohibited in the hand wheel, stem and flange bolt holes.
- Valves should be installed in the operation, maintenance and maintenance of the most convenient place, is strictly prohibited to be buried underground. Directly buried and trench pipeline on the valve, should be set up to check the well room, so that the valve opening and closing and adjustment.
- Should ensure that the threads are intact, and wrap hemp, lead oil or PTFE raw material tape around the threads, when screwing the buckle, it is necessary to use a wrench to catch the hexagonal valve body screwed into one end of the pipe.
- When installing the flange valve, pay attention to tighten the connecting bolts along the diagonal direction, screwing with even force to prevent the gasket from running off or causing deformation and damage to the valve body.
- The valve should be kept closed during installation. For threaded valves near the wall, it is often necessary to remove the stem flap and handwheel to unscrew during installation. When disassembling, the valve should be disassembled after the handwheel is unscrewed to keep the valve open.
Installation of pressure relief valves
- The pressure reducing valve set installed vertically is generally set along the wall at a suitable height from the ground; the pressure reducing valve set installed horizontally is generally installed on a permanent operating platform.
- Application of steel sections are loaded into the wall on the outside of the two control valves (commonly used for shut-off valves) to form a bracket, and the bypass pipe is also stuck on the bracket to level and square.
- Pressure reducing valve should be installed upright on the horizontal pipeline, not tilted, the arrow on the valve body should point to the direction of media flow, not installed in reverse.
- Both sides should be equipped with shut-off valves and high and low pressure gauges to observe the pressure changes before and after the valve. The diameter of the pipe after the pressure reducing valve should be 2#-3# larger than the diameter of the inlet pipe before the valve, and a bypass pipe should be installed for maintenance.
- The equal pressure pipe of membrane pressure reducing valve should be connected to the low pressure pipeline. Low-pressure pipeline should be set up with safety valve to ensure the safe operation of the system.
- When used for steam pressure reduction, a drain pipe should be set. For piping systems with high purification requirements, set up a filter before the pressure reducing valve.
- After the installation of the pressure reducing valve set, the pressure reducing valve and safety valve should be tested, flushed and adjusted according to the design requirements, and make the adjusted mark.
The role of valve installation seat valve
- Protection,which can also be described as a protective measure for the main valve, to prevent the valve due to the front and rear pressure difference is too large, and cause a large opening resistance, the valve is not good to open, especially in some large diameter or high pressure pipeline. High-pressure pipelines open before the pressure relief through the bypass valve, in order to avoid a sudden surge of high pressure, the formation of impact on the pipeline below the valve. Or the pressure difference between the two ends of the valve is too large, the opening torque is too large, in order to avoid torsional damage to the valve, bypass pressure relief before opening the valve.
- Emergency, as a backup pipeline to use, the biggest advantage is that when the main valve failure, or the need for maintenance and repair, you can open the bypass valve circulation, and does not affect normal production.