Principles and requirements for installing valves

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 These regulations apply to the installation of gate valves, globe valves, ball valves, butterfly valves, and pressure relief valves in petrochemical plants. The installation of check valves, safety valves, control valves, and steam traps is subject to the relevant regulations. These regulations do not apply to the installation of valves on underground water supply and drainage pipes. 1. Principles for valve layout 1.1 Valves should be installed according to the types and quantities specified in the Piping and Instrumentation Diagram (PID). When the PID has specific requirements for the installation location of certain valves, they should be set in accordance with the process requirements.     1.2 Valves should be installed in locations that are easily accessible and convenient for operation and maintenance. Valves on rows of pipes should be arranged centrally, with consideration given to providing an operating platform or ladder.     2. Requirements for the installation location of valves 2.1 Cutting valves must be installed at the points where the pipes in the inlet and outlet ductwork connect to the main pipes in the plant’s overall ductwork system. The valve installation locations should be concentrated on one side of the plant area, with necessary operation platforms or maintenance platforms provided.     2.2 Valves that require frequent operation, maintenance, and replacement should be located at a height where they are easily accessible from the ground, platform, or ladder. Pneumatic and electric valves should also be placed in easily accessible locations.     2.3 Valves that do not need to be operated frequently (used only during startup and shutdown) should also be placed in locations where temporary ladders can be set up, if it is not possible to operate them from the ground.     2.4 The height of the center distance between the valve handwheel and the operating surface should be between 750 and 1500 mm, with 1200 mm being the most suitable value. For valves that do not need to be operated frequently, the installation height can range from 1500 to 1800 mm. When the installation height cannot be reduced and frequent operation is required, an operating platform or steps should be provided during design. Valves on pipelines and equipment carrying hazardous materials must not be installed at a height within reach of a person’s head.     2.5 When the height of the center distance between the valve handwheel and the operating surface exceeds 1800 mm, it is advisable to use sprocket operation; the chain length from the sprockets to the ground should be around 800 mm. Sprocket hooks should be installed so that the lower end of the chain can be hung on a nearby wall or pillar, in order to avoid hindering passage. 2.6 For valves located in ducts, if the valves can be operated once the cover plate of the duct is removed, the valve handwheel should not be more than 300 mm below the cover plate. If it is below 300 mm, an extension rod for the valve should be used to keep the handwheel within 100 mm below the cover plate.     2.7 For valves installed in ducts that need to be operated from the ground, or for valves located below an upper floor level (platform), a valve extension rod can be used to extend them above the duct cover, floor, or platform so that they can be operated from there; it is advisable that the handwheel of the extension rod be located at a distance of 1200 mm from the operating surface. Valves with a nominal diameter of 40 DN or less and those connected by threads should not be operated using sprockets or extension rods to avoid damaging the valves. Generally, effort should be made to use sprockets or extension rods as little as possible to operate the valve.     2.8 The distance from the edge of the platform to the valve handwheels located around it should not be greater than 450 mm. When the valve stem and handwheel extend above the platform with a height of less than 2000 mm, they should not interfere with the operator’s operations or movement to avoid potential injury.     3. Requirements for the installation of large valves 3.1 The operation of large valves should utilize gear-driven mechanisms, and when installing them, consideration must be given to the space required by such mechanisms. Generally, for valves whose size is larger than that of the grades listed below, it is advisable to use valves equipped with a gear drive mechanism.     3.2 Large valves shall be provided with supports on one or both sides of the valve; such supports shall not be located on short pipes that need to be removed during maintenance, and it shall be ensured that removing the valve does not affect the support of the pipeline. The distance between the general support and the valve flange should be greater than 300 mm.     3.3 The installation location of large valves should have space for using a crane, or consideration should be given to installing lifting columns or beams. 4. Requirements for the installation of valves on horizontal pipelines 4.1 Unless otherwise specified by the process requirements, the handwheels of valves installed on horizontal pipelines should not face downward; in particular, it is strictly prohibited for the handwheels of valves on pipelines carrying hazardous materials to face downward. The orientation of the valve handwheel is determined in the following order: vertically upward ； Horizontal ； 45° tilt left and right vertically upward ； 45° left and right tilt vertically downward ； It must not be directed vertically downward.     4.2 For horizontally mounted straight-stem valves, when the valve is open, the stem must not obstruct passage; this is especially important when the stem is located at the level of the operator’s head or knees. 5. Other requirements for valve installation 5.1 For valves installed on pipes arranged in parallel, their centerlines should be aligned as much as possible; when valves are placed next to each other, the clear distance between their handwheels should not be less than 100 mm ； Valves can also be arranged offset from each other to reduce the pipe spacing.     5.2 Valves that are required to be connected to the equipment nozzles in terms of manufacturing requirements shall be directly connected to those nozzles when their nominal diameter, nominal pressure, seal face type, etc., are the same as or compatible with those of the equipment nozzle flanges. When the valve is equipped with a concave flange, it is necessary to request the equipment specialists to install a convex flange at the corresponding pipe end.     5.3 Unless the process has special requirements, valves on the bottom pipes of equipment such as towers, reactors, and vertical vessels shall not be installed within the skirt.     5.4 When a branch pipe is led off from the main pipe, its isolation valve should be installed on the horizontal section of the branch pipe near the root of the main pipe, so that the fluid can flow out completely on both sides of the valve.     5.5 The branch isolation valves on the pipe gallery are not operated frequently (only used during shutdown for maintenance); if no permanent ladder is available, space should be reserved for using a temporary ladder.     5.6 High-pressure valves require significant force to open; therefore, supports must be installed to hold the valve in place and reduce the starting stress. The appropriate installation height is between 500 and 1200 mm.     5.7 Fire water valves, fire steam valves, etc. within the device area should be distributed evenly and located in safe areas that are easily accessible to operators in the event of an accident.     5.8 The valve assembly for the fire-extinguishing steam distribution pipe in the heating furnace should be easy to operate, and the distance between the distribution pipe and the furnace body should not be less than 7.5 m.     5.9 When installing threaded valves on pipelines, a union must be installed near the valve to facilitate disassembly.     5.10 Wafer valves or butterfly valves shall not be directly connected to the flanges of other valves and pipe fittings; a short pipe with flanges at both ends must be used as an intermediate connection.     5.11 Valves should not be subjected to external loads to avoid damage due to excessive stress.