Common valve installation knowledge

Valve inspection and installation

Check the valve before installation
① Carefully check whether the valve model and specification meet the requirements of the drawing.
② Check whether the stem and disc are open flexibly, and whether they are stuck and skewed.
③ Check whether the valve is damaged, and whether the thread of the threaded valve is correct and intact.
④ Check whether the combination of 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.
The old or shelved pressure reducing valve should be removed, dust, sand and other debris must be cleaned with water.
⑦ Clear the orifice cover, check the degree of sealing, the valve disc must be closed tightly.

Pressure test of valve
Low pressure, medium pressure and high pressure valves should carry out strength test and tightness test, alloy steel valves should also carry out spectral analysis of the shell one by one, and review the material.
1. Strength test of valve
The strength test of the valve is tested in the open state of the valve to check the leakage of the outer surface of the valve. PN≤32MPa valve, the test pressure is 1.5 times the nominal pressure, the test time is not less than 5min, the shell, packing gland no leakage is qualified.
2. Tightness test of valve
In the valve completely closed state of the test, check whether the valve sealing surface leakage, the test pressure, in addition to the butterfly valve, check valve, bottom valve, throttle valve outside the valve, generally should be carried out with nominal pressure, when the working pressure can be determined, can also be 1.25 times the working pressure test, to the valve flap sealing surface is not leaking as qualified.

General requirements for valve installation
1. The position of the valve installation should not hinder the operation, disassembly and maintenance of the equipment, pipes and valve body itself, while taking into account the beautiful appearance of the assembly.
2. The valve on the horizontal pipeline, the valve stem is installed upward, or the valve is installed at a certain Angle, and the hand wheel cannot be installed downward. The valve, stem and handwheel on the high-altitude pipe can be installed horizontally, and the valve is opened and closed remotely by a low vertical chain.
3. Symmetrical arrangement, neat and beautiful; The valve on the riser, under the premise of the process permits, the valve handwheel is most suitable for operation at chest height, generally 1.0-1.2m from the ground, and the valve stem must be installed along the direction of the operator.
4. The valve on the side-by-side riser, its center line elevation is best consistent, and the net distance between the handwheels is not less than 100mm; Valves on side-by-side horizontal pipes should be staggered to reduce pipe spacing.
5. When installing heavy valves on pumps, heat exchangers and other equipment, valve brackets should be set up; When the valve is frequently operated and installed more than 1.8m away from the operating surface, a fixed operating platform should be set up.
6. The valve body is marked with an arrow, and the arrow points to the direction of the flow of the medium. When installing the valve, be careful to make the arrow point the same as the medium flow in the pipeline.
7. When installing flange valves, ensure that the end faces of the two flanges are parallel and concentric, and double gaskets shall not be used.
8. When installing the threaded valve, for easy disassembly, a threaded valve should be equipped with a loose joint. The setup of the connector should consider the convenience of maintenance, usually the water flow first through the valve and then through the connector.

Valve installation precautions
1. The valve body material of the valve body is made of cast iron, which is brittle, so it can not be hit by heavy objects.
2. When handling the valve, it is not allowed to throw; When lifting and hoisting the valve, the rope should be tied to the valve body, and it is strictly prohibited to tie to the handwheel, valve stem and flange bolt holes.
3. The valve should be installed in the most convenient place for operation, maintenance and overhaul, and it is strictly prohibited to be buried underground. The valve on the pipeline in the direct burial and trench should be equipped with a check well chamber to facilitate the opening and closing of the valve and adjustment.
4. Ensure that the thread is intact, and wrap hemp, lead oil or polytetrafluoroethylene raw material belt on the thread. When screwing, use a wrench to clamp the hexagonal valve body at one end of the pipe.
5. When installing the flange valve, pay attention to tighten the connection bolts along the diagonal direction, and the force should be uniform when screwing, to prevent the gasket from running off or causing deformation and damage to the valve body.
6. The valve should be kept closed during installation. For threaded valves close to the wall, the installation often needs to remove the stem valve disc and handwheel in order to turn. Disassembly should be carried out after twisting the hand wheel to keep the valve open.

Installation of common valves

Gate valve installation
Gate valve, also known as gate valve, is the use of gate plate to control the opening and closing of the valve, by changing the cross section to adjust the pipeline flow and opening and closing pipeline. Gate valves are mostly used for pipelines that are fully open or fully closed for fluid media. Gate valve installation generally has no directional requirements, but can not be inverted.

Installation of globe valve
The globe valve is a valve that uses the disc to control the opening and closing. By changing the gap between the disc and the seat, that is, changing the size of the channel section, the medium flow rate is adjusted or the medium path is truncated. When installing a globe valve, pay attention to the flow of fluid.
The principle that the globe valve must be installed is that the fluid in the pipeline passes through the valve hole from bottom to top, commonly known as "low into high", and is not allowed to install the reverse.

Installation of check valve
Check valve, also known as check valve, check valve, is a valve that automatically opens and closes under the pressure difference before and after the valve, and its role is to make the medium flow in only one direction, and prevent the medium from flowing backward. Check valve according to its different structure, there are lift, swing and butterfly type. The lift check valve is divided into horizontal and vertical. When installing the check valve, you should also pay attention to the flow direction of the medium and cannot install the reverse.

Installation of pressure reducing valve
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 keep the outlet pressure stable automatically.
From the fluid mechanics point of view, the pressure reducing valve is a local resistance can change the throttling element, that is, by changing the throttling area, the flow rate and the kinetic energy of the fluid change, resulting in different pressure losses, so as to achieve the purpose of decompression. Then rely on the adjustment of the control and adjustment system, so that the fluctuation of the pressure after the valve is balanced with the spring force, so that the pressure after the valve is kept constant within a certain error range.

Installation of pressure reducing valve
1. The vertically installed pressure reducing valve group is generally arranged along the wall at a suitable height from the ground; The horizontally mounted pressure reducing valve group is generally installed on a permanent operating platform.
2. The application steel is loaded into the wall on the outside of the two control valves (often used for globe valves) to form a bracket, and the by-pass pipe is also stuck on the bracket to level and align.
3. The 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 the medium flow, not installed reverse.
4. Both sides should be installed with globe valves and high and low pressure gauges in order 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 in front of the valve, and install a by-pass pipe for maintenance.
5. The equalizing tube of the film pressure reducing valve should be connected to the low-pressure pipeline. For low-pressure pipelines, safety valves should be set to ensure the safe operation of the system.
6. When used for steam decompression, the 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, washed 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 flushing valve for flushing.

Installation of trap
The basic function of the steam trap is to discharge condensate, air and carbon dioxide gas in the steam system as soon as possible; At the same time, it automatically prevents steam leakage to the maximum extent. There are many varieties of traps, each with different performance.
According to the different working principles of the trap, it can be converted into the following three types:
Mechanical type: depends on the change in the height of 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 bucket type with an open upward float.
Open downward float type: The float is the open downward bucket type.
Thermostatic: depends on the temperature of the liquid to change the action, including:
Bimetal plate: The sensitive element is a bimetal plate.
Steam pressure type: The sensitive element is a bellows or ink cartridge, which is filled with volatile liquid.
Thermodynamic type: The action 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 to drive the disc valve plate action.
Pulse type: Because the condensate of different temperatures is connected through the two poles of the orifice plate, different pressures will be formed between the two poles of the orifice plate to drive the valve disc action.

Installation of trap
1. The cut-off valve (stop valve) should be set before and after, and the filter should be set between the trap and the front cut-off valve to prevent the dirt in the condensate water from blocking the trap.
2. An inspection pipe should be set between the trap and the rear cut-off valve to check whether the trap is working normally. If a large amount of steam is generated when the inspection pipe is opened, it indicates that the trap is broken and needs to be repaired.
3. The by-pass pipe is set up to discharge a large amount of condensate when starting and reduce the displacement load of the trap.
4. When the trap is used for condensate removal of the hot equipment, it should be installed at the lower part of the hot equipment, so that the condensate pipe is connected to the trap vertically to prevent water storage by the hot equipment.
5. The installation position should be as close as possible to the drainage point, if the distance is too far, the thin pipe in front of the trap will accumulate air or steam.
6. The problem of drainage should be considered when the horizontal pipe of the steam main pipe is too long.

Installation of safety valve
The safety valve is a special valve that is normally closed under the action of external force, and when the medium pressure in the equipment or pipeline rises beyond the specified value, the medium is discharged outside the system to prevent the medium pressure in the pipeline or equipment from exceeding the specified value.
Safety valve is an automatic valve, mainly used in boilers, pressure vessels and pipelines, control pressure does not exceed the specified value, personal safety and equipment operation plays an important role in protecting. The injection safety valve must be tested before it can be used.
1. Before installation, the product must be carefully checked to verify whether there is a certificate and product manual to clarify the constant pressure situation at the factory.
2. The safety valve should be arranged near the platform as far as possible for inspection and maintenance.
3. The safety valve should be installed vertically, 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 cut-off valve can not be set before and after the safety valve to ensure safety and reliability.
5. Relief 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 relief valve should be 3m higher than the surrounding highest structure, but the following circumstances should be closed system to ensure safety.
7. Population pipe diameter, the minimum should be equal to the inlet pipe 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 outdoors and installed with a bent pipe so that the pipe outlet faces the safety zone.
8. When the safety valve is installed, when the safety valve is connected with the equipment and the pipeline for opening welding, the diameter of the opening hole should be the same as the nominal diameter of the safety valve.