Inspection and installation of valves

Valve installation before the check

　　①Check carefully whether the valve model and specification meet the requirements of the drawings.

　　②Check whether the valve stem and valve flap opening is flexible, there is no jamming and skewed phenomenon.

　　③Check whether the valve is damaged and whether the thread of the threaded valve is correct and intact.

　　④Check whether the combination of the valve seat and the valve body is firm, the valve flap and the valve seat, the valve cover and the valve body, the valve stem and the valve flap linkage.

　　⑤ check whether the valve bedding, packing and fasteners (bolts) are suitable for the requirements of the nature of the working medium.

　　⑥The old or long-shelved pressure reducing valve should be disassembled, and the dust, sand and other debris should be cleaned with water.

　　⑦ Clear the through-port capping, check the sealing degree, the valve must be closed tightly.

　　Pressure test of the valve

　　Low-pressure, medium-pressure and high-pressure valves should be strength test and tightness test, alloy steel valves should also be one by one spectral analysis of the shell, review the material.

　　1. 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.

　　2. Tightness test of the valve

　　Test in the valve completely closed state, 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 the test, to the valve sealing surface does not leak as qualified.

　　General provisions of the valve installation

　　1. The location of the valve installation should not interfere with the operation, disassembly and maintenance of the equipment, piping and the valve itself, taking into account the aesthetic appearance of the assembly.

　　2. Horizontal pipeline on the valve, valve stem upward installation, or tilt a certain angle installation, not handwheel downward installation. The valve, stem and handwheel on the overhead pipeline can be installed horizontally, and the valve can be operated from a distance with a chain that hangs low.

　　3. 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.

　　4. Side by side on the riser valve, the 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.

　　5. 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.

　　6. 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.

　　7. When installing flange valves, ensure that the two flange faces are parallel and concentric to each other, and do not use double gaskets.

　　8. When installing a threaded valve, a threaded valve should be equipped with a live connection for easy disassembly. The setting of the connection should consider the convenience of maintenance, usually the water flow through the valve first after the connection.

　　Valve installation precautions

　　1. The valve body material is mostly made of cast iron, brittle, so it should not be hit by heavy objects.

　　2. 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.

　　3. The valve should be installed in the most convenient place for operation, maintenance and maintenance, and 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 as to facilitate the opening and closing of the valve and adjustment.

　　4. It should ensure that the threads are intact, and wrap hemp, lead oil or PTFE raw material around the threads, and when screwing the buckle, it is necessary to use a wrench to catch the hexagonal valve body screwed into one end of the pipe.

　　5. 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.

　　6. The valve should be kept closed during installation. For the threaded valve near the wall, it is often necessary to remove the stem flap and handwheel to unscrew the valve during installation. When disassembling, the valve should be disassembled after the handwheel is unscrewed to keep the valve open.

　　Installation of commonly used valves

　　Installation of gate valve

　　Gate valve, also known as gate valve, is a valve that uses a gate to control the opening and closing of the valve by changing the cross-section to regulate the flow of pipeline and open and close the pipeline. Gate valve is mostly used for the fluid medium to do fully open or fully closed operation of the pipeline. Gate valve installation generally no directional requirements, but can not be installed backwards.

　　Installation of stop valve

　　The shut-off valve is a valve that uses the valve flap to control opening and closing. By changing the gap between the valve flap and the valve seat, that is, to change the size of the channel cross-section to regulate the flow of media or cut off the media path. Installation of the shut-off valve must pay attention to the flow direction of the fluid.

　　Installation of globe valves must comply with the principle that the fluid in the pipeline from the bottom up through the valve hole, commonly known as "low into high", not allowed to install the reverse.

　　Installation of check valves

　　Check valve, also known as check valve, one-way valve, is a kind of valve before and after the valve pressure difference under the action of automatic opening and closing of the valve, its role is to make the medium only do a direction of flow, and to prevent the flow of the medium backwards and forwards. Check valve according to its structure is different, there are lift type, swing type and butterfly butt type. Lifting check valve and horizontal and vertical. When installing the check valve, you should also pay attention to the flow direction of the media, not installed in reverse.

　　Installation of pressure reducing valve

　　Pressure reducing valve is to adjust the inlet pressure to a certain required outlet pressure, and rely on the energy of the medium itself, so that the outlet pressure automatically maintain a stable valve.

　　From the viewpoint of fluid mechanics, pressure reducing valve is a throttling element whose local resistance can be changed, that is, by changing the throttling area, the flow rate and the kinetic energy of the fluid can be changed, resulting in different pressure loss, thus achieving the purpose of pressure reduction. Then it relies on the adjustment of the control and regulation system to balance the fluctuation of the pressure after the valve 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 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.

　　2. 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.

　　3. 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.

　　4. 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.

　　5. 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.

　　6. 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.

　　7. 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.

　　8. When flushing the pressure reducing valve, close the inlet valve of the pressure reducing valve and open the flushing valve for flushing.

　　Installation of Trap

　　The basic function of steam traps is to discharge condensate, air and carbon dioxide gas from the steam system as soon as possible; and to prevent steam leakage automatically to the maximum extent possible. There are many varieties of traps, each with different properties.

　　Depending on the operating principle of traps, they can be divided into the following three types.

　　Mechanical: Actions that rely on the change in condensate level within the steam trap, including

　　Float type: The float is a closed hollow sphere.

　　Open Top Float Type: The float is a bucket type with an open top.

　　Open mouth downward float type: float for the opening downward barrel type.

　　Thermostatic type: Relies on the change of liquid temperature to act, including

　　Bimetal: The sensitive element is a bimetal.

　　Vapor pressure type: The sensitive element is bellows or cartridge, filled with volatile liquid inside.

　　Thermodynamic type: relying on changes in the thermodynamic properties of the liquid and the action.

　　Disc type: Due to the different flow rates of liquid and gas at the same pressure, the different dynamic and static pressures generated drive the disc valve blade to act.

　　Impulse type: As condensate of different temperatures passes through the two poles in series with the throttle plate, different pressures are created between the two throttle plates, driving the valve flap to act.

　　Installation of trap

　　1. A shut-off valve (stop valve) should be installed before and after the trap, and a strainer should be installed between the trap and the front shut-off valve to prevent dirt in the condensate from clogging the trap.

　　2. An inspection tube should be installed between the trap and the rear shut-off valve to check if the trap is working properly. If a large amount of steam comes out when the inspection tube is opened, it means that the trap is bad and needs to be serviced.

　　3. A bypass tube is provided to discharge a large amount of condensate during startup to reduce the trap's drainage load.

　　4. When the trap is used for condensate removal from heat-using equipment, it should be installed in the lower part of the heat-using equipment so that the condensate pipe returns vertically down to the water trap to prevent water storage in the heat-using equipment.

　　5. The installation location should be as close as possible to the drainage point, if the distance is too far, air or steam will accumulate in the slender piping in front of the trap.

　　6. Trapping should be considered when the horizontal piping of the steam main is too long.

　　Installation of Safety Valve

　　Safety valve is a special valve in which the opening and closing parts are normally closed under the action of external force, and when the pressure of the medium in the equipment or pipeline rises above the specified value, it prevents the pressure of the medium in the pipeline or equipment from exceeding the specified value by discharging the medium to the outside of the system.

　　Safety valve belongs to the automatic valve category, 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 the protection. Note safety valves must be pressure tested before use.

　　1. Before installation, the product must be carefully checked to verify whether there is a certificate of compliance and product specifications to clarify the factory pressure setting.

　　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, so that the medium flows from the bottom up, and to check the verticality of the valve stem.

　　4. In general, the safety valve can not be set before and after the cut-off 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. Oil and gas media can generally be discharged to the atmosphere, safety valve venting pipe outlet should be 3m above the highest surrounding structures, but the following cases should be discharged to the closed system to ensure safety.

　　7. Population pipe diameter, the minimum should be equal to the valve's inlet diameter; discharge pipe diameter shall not be less than the valve's outlet diameter, the discharge pipe should be led to the outdoors and installed with a bend, so that the pipe outlet towards the safety zone.

　　8. Safety valve installation, when the safety valve and equipment and piping connection for the opening welding, the opening diameter should be the same as the nominal diameter of the safety valve.