Installation of valves

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Installation of valves HG/T 20570.18—95 1 Scope of application 1.0.1 These regulations apply to the field of chemical process systems. The valves mentioned do not include safety valves, steam traps, sampling valves, pressure relief valves, etc.; however, they include the installation of pipe fittings with similar functions to valves, such as orifice plates and blind flanges. The term “shut-off valves” is used as a general term for these valve-like components. The function of a shut-off valve is to stop the flow of a fluid or to change its direction. It should be installed in accordance with the requirements of production (including normal operation, start-up and shutdown, as well as special operating conditions), maintenance, and safety, while also taking economic feasibility into consideration. 1.0.2 Valve setting and selection of appropriate category (not model). Valves are an important aspect of the work carried out by professionals in process systems when preparing PI diagrams, and the provisions outlined herein take into account the general requirements regarding production and safety. When conducting engineering design in accordance with these regulations, system professionals should make decisions based on the specific circumstances of the project, local weather conditions, inter-plant cooperation arrangements, requirements for plant operation, fluid properties, any special requirements of the users, and economic considerations. 1.0.3 These regulations provide a comprehensive overview of the valve installations for the situations listed; detailed requirements for various chemical processing units can be found in the basic unit patterns shown in the PI diagrams for those respective units. 1.0.4 file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image002.gif This regulation also introduces the characteristics of general industrial valves and the factors to consider when selecting valves for engineering design. file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image002.giffile:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image004.jpg 2 Valve Settings 2.0.1 Valve settings at boundaries 2.0.1.1 Shut-off valves shall be installed at the plant boundary for pipelines carrying process materials and utilities (usually on the inner side of the plant perimeter), with the following exceptions: (1) Vent systems. (2) Drain pipe when the emergency discharge tank is located outside the boundary ； In both of these cases, if valves must be installed, they also require to be opened with a lead seal (C.S.O.). (3) A material pipe that does not cause cross-contamination or accidents. (4) Material pipes that do not require measurement. 2.0.1.2 The valve settings at the boundaries are shown in the various methods depicted in Figure 2.0.1. Among them, (1) is applicable to the cutting of general materials ； In areas where the accumulation of materials may lead to safety incidents such as explosions or fires, or to defects in product quality, blind plates as shown in (2), (4), and (5) in Figure 2.0.1 are used to prevent internal leakage of the valves ； In Figure 2.0.1, items (3) and (5) are suitable for situations where line purging upstream or downstream is required after feeding. Valve C can also be used for purging, draining, and leak detection; additionally, monitoring and metering instruments can be installed between two valves connected in series. Item (5) in Figure 2.0.1 is suitable for areas where pressure changes may be significant, as the check valve can provide immediate shut-off. 2.0.2 Settings for root valves file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image010.gif 2.0.2.1 When a medium needs to be delivered to multiple users, for the sake of ease of maintenance, energy conservation, and freeze prevention, in addition to installing a shut-off valve near the equipment, another shut-off valve is installed on the branch pipe right next to the main pipe; this is known as a root valve. It is commonly used in utility material systems (such as steam, compressed air, nitrogen, etc.). When a process material is supplied to multiple users (such as solvents), the same setup is required. The valve shown in Figure 2.O.2 is the root valve. When energy savings and anti-freezing requirements are in place, the distance between the root valve and the main pipe should be as small as possible. 2.0.2.2 file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image002.gif Root valves should be installed on all the branch pipes of the utility pipelines within the chemical plant, to prevent the plant or the entire facility from coming to a stop due to the failure of individual valves. 2.0.2.3 Steam and overhead water pipes. Even if it leads to only one device or apparatus, a foot valve is required when the branch pipe exceeds a certain length in order to reduce the dead zone, lower energy consumption, and prevent freezing. 2.0.2.4 For two or more steam-using devices that serve as backups for one another, it should be determined based on their importance in production whether separate root valves for the branch pipes should be installed. 2.0.2.5 The root valve of the common material branch pipe is installed by the piping discipline during pipeline layout design; the process system discipline shall verify whether the branch is appropriate and indicate the root valve on the common material PI diagram (distribution diagram). 2.0.3 Double valves
2.0.3.1 For storage tanks used for liquefied petroleum gas, other flammable, toxic, valuable liquids, substances with strong corrosiveness (such as concentrated sulfuric acid and caustic soda), and substances with special requirements (such as media with a foul odor that can cause serious environmental pollution), two valves should be installed in series on the pipeline at the bottom of the tank leading to other equipment. Regardless of whether there are valves near such equipment or not, one of these valves must be located right next to the tank’s outlet. When the tank has a large capacity or is located at a considerable distance from other equipment, it is preferable for this valve to be a remotely operated valve. To reduce the number of valves, and where operating conditions permit, several pipes may be combined and connected to a single nozzle as shown in Figure 2.0.3-1. The drain valve of the container containing the aforementioned medium should also be a double-valve, as shown in Figure 2.0.3–1. The sampling valve and drain valve on the aforementioned medium pipeline should have dual valves installed or not, depending on the frequency of operation and other conditions. file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image013.gif 2.0.3.2 file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image014.gif For equipment that needs to be shut down for maintenance, cleaning, or regeneration while the device is in operation, dual valves should be installed, with an inspection valve placed between them. When the device is disconnected from the system, both valves close and the check valve opens. Other measures can be taken to replace the dual valves. For the backup reboiler, due to its larger valve diameter and strict requirements regarding pressure drop, a single valve (usually a rising stem gate valve) can be installed along with an 8-shaped blind plate. A separate drain valve should be provided on each side of the reboiler, as shown in Figure 2.0.5–1. For equipment that needs to switch to regeneration mode, since the regeneration temperature is often much higher than the operating temperature, installing a reversible elbow allows for a safe transition while also preventing significant thermal stress. As shown in Figure 2.0.3–2. file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image016.gif2.0.3.3 Public material pipelines should be connected to process material pipelines as little as possible via fixed connections; instead, they ought to be connected using hose stations and quick connectors. When a direct connection is required for operation, it should be made using two valves, with an inspection valve in between. The inspection valve opens when feeding is stopped, or it can be opened by applying a lead seal (C.S.O). In situations where pressure may fluctuate, add a check valve, as shown in Figure 2.0.3-3. file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image020.gif If the pressure gauge for the common fluid is located far away from this valve assembly, a pressure gauge can be installed between these two valves so that the pressure of that common fluid can be monitored on-site during use. This type of connection is also suitable for situations where auxiliary materials such as oxygen and hydrogen are frequently supplied to the process system. To prevent liquid materials from contaminating the water system, when water needs to be added frequently, the water pipe should be connected to the gas space of the equipment; in this case, it is also possible to omit the dual valves. 2.0.3.4 When designing high-pressure waste heat boilers and steam systems, professionals in the chemical process engineering field may refer to the relevant regulations set forth by the General Administration for Electric Power Construction under the Ministry of Electric Power: as specified in the “Technical Regulations for the Design of Steam and Water Pipelines in Thermal Power Plants” (DLGJ233—81) (provisional version), Articles 7–7.1: For pipelines where Pg > 40*, two stop valves should be installed in series for drainage and water release purposes. Articles 7–8: For pipes with Pg＞40*, two stop valves shall be installed in series as the venting device. The pressure unit is kg/cm2 (table). Please be sure to follow the latest regulations when using it. 2.0.3.5 For materials such as hydrocarbons and toxic or hazardous chemicals, double valves should be installed at the upstream side of the connection points with other process materials, as well as on the vent and drain pipes; refer to Table 2.0.3 for details. Temperature and pressure conditions for reaction double valves. Table: Medium name, Operating temperature (°C), Operating pressure. Heavy hydrocarbons (kerosene, lubricating oil, asphalt, etc.): ≥; Hydrocarbons with a Reid vapor pressure lower than the value specified in the table and a flash point below that value: crude gasoline, etc.: ≥; Hydrocarbons with a Reid vapor pressure higher than the value specified in the table but lower than another specified value: butane, light crude gasoline, etc.: ≥; Hydrocarbons with a Reid vapor pressure higher than the value specified in the table: propane, etc.: ≥; Liquefied petroleum gas: any; Any combustible gas: ≥; Toxic gases and harmful chemical agents: any. 2.0.4 file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image022.gif Utility material stations (utility service stations). 2.0.4.1 Utility material stations within chemical plants (simply referred to as utility stations) can be installed in areas with a radius of approximately 15 meters. Utility stations located outside the plant area are installed according to design requirements. 2.0.4.2 The specifications of the isolation valves for various media range from DN15 to DN50, depending on the characteristics of the device. The model specifications of valves and joints at utility stations can be deliberately made different; however, the order in which various media are arranged at each utility station must remain consistent. This helps prevent accidents from worsening due to incorrect connection of media during emergencies. 2.0.4.3 For water pipes in outdoor public stations in cold regions, the following approach can be adopted: (1) Multi-story framework: Install valves according to standard piping arrangements; cut off the pipes near the ground floor and provide quick connectors, with water being drawn from nearby water valve chambers when in use. If a fixed pipeline with a drain valve is used, the drain valve should be installed in a valve chamber. (2) In areas such as tank farms or loading/unloading platforms, it is possible to negotiate with the water supply and drainage team to adjust the location of the valve chambers appropriately, so that the water supply valves can be placed within those chambers. (3) Insulate together with the steam pipe. 2.0.4.4 To accommodate the use of pneumatic tools during maintenance, the diameter of the compressed air pipes and the shut-off valves at the utility station can be increased appropriately, for example from DN25 to DN50. 2.0.4.5 For small units, the pipe fittings that match the equipment, pipelines, and utility stations can share the drain and vent ports of the equipment pipelines ； For large-scale installations, a dedicated common material connection port (U.C.) can be provided on the equipment; this connection port and the vent valve should be located at the lower and upper parts of vertical equipment, or at both ends of horizontal equipment along its length. 2.0.4.6 When a utility material pipeline may be contaminated due to backflow of process fluids, a check valve is installed downstream of the isolation valve for the utility material pipeline. 2.0.5 Tower 2.0.5.1 The steam pressure condensed in the top condenser of the tower should be kept as close as possible to the pressure at the tower top; the pressure drop in the pipes leading from the tower top to the condenser should be minimized. Unless there are specific requirements for process control, no shut-off valves should be installed in these pipes. 2.0.5.2 For the connecting pipelines between reboilers (including intermediate reboilers) and the tower body, no shut-off valves shall be installed, except where required for process control or for cleaning during plant operation. When valves need to be installed on the connection pipe between the thermosyphon reboiler and the tower, gate valves with the same diameter as the connection pipe should be used. An 8-shaped blind flange shall be installed between the valve and the reboiler; additionally, the reboiler shall be equipped with its own drain valve, as shown in Figure 2.0.5-1. A one-pass thermal siphon reboiler should be equipped with a connecting pipe between the reboiler’s material inlet and the bottom outlet of the tower, along with a shut-off valve, as shown in Figure 2.0.5–2. The diameter of this valve should be at least 1/4” larger than that of the tower’s bottom outlet pipe. file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image028.gif file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image030.jpg In a reboiler with forced circulation, another throttle valve is installed on the pipeline from the reboiler to the tower, near the tower itself. This valve can be replaced by a flow-restricting orifice plate. However, this throttle valve can be omitted when excessive flashing does not reduce the efficiency improved by forced circulation or lower the logarithmic mean temperature difference. As shown in Figure 2.0.5—3. 2.0.5.3 Except as required for process control, no shut-off valves are installed on the side-line discharge and steam return pipes of the distillation column. 2.0.5.4 For towers where the feed composition may vary, additional feed inlets shall be provided according to the extent of the design variations; the shut-off valves for each feed inlet shall be located close to the feed nozzle on the tower shell. Since depressurization generates a two-phase flow of material (liquefied gas or saturated absorbent), the feed cut-off valve should also be placed as close as possible to the tower’s feed inlet. For towers with a large number of trays and an excessively long shell that is divided into two sections connected in series, no shut-off valve shall be installed on the vapor pipeline from the top of one tower to the bottom of the other. The shut-off valve or control valve added to the kettle liquid for process control purposes should be placed as close as possible to the nozzle of the receiving tower, as shown in the figure. 2.0.6 Heat exchangers 2.0.6.1 Except for heat exchangers that need to be controlled or that must (can) be shut off during operation of the unit, no shut-off valves are generally provided on the process fluid side. 2.0.6.2 When process fluids are present on both sides of the heat exchanger, a shut-off valve shall be installed on only one side, depending on the operating and control requirements. 2.0.6.3 When a bypass is required for a heat exchanger due to production or maintenance purposes, shut-off valves shall be installed on both the inlet and outlet pipes as well as on the bypass. Bypasses are typically required in the following situations: (1) During certain processes in the production cycle, heat transfer is not needed; thus, the heat exchanger must be shut off ； (2) Automatic or manual adjustment of process temperature ； (3) The heat exchanger must be temporarily shut down for maintenance. 2.0.6.4 Steam heating equipment (1) The inlet pipe for heating steam shall be equipped with a manually operated control valve or an automatically controlled valve that has good regulating performance. (2) A non-condensable gas discharge valve must be installed in an appropriate location; this valve should be placed at the highest point on the equipment, on the side far from the steam inlet, as shown in Figure 2.0.6. (3) In the case of heating with coiled tubes, a check valve before the steam trap is used to remove non-condensable gases; no separate non-condensable gas removal valve is provided. 2.0.6.5 file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image036.giffile:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image037.gif Water cooling equipment (1) During operation, the cooling water gets heated and releases dissolved gases; therefore, vent valves must be installed at appropriate locations on the heat exchange equipment (as specified in 2.0.6.4). This valve is also used to discharge gas from the equipment at startup, or to introduce air when draining it at shutdown. (2) Each equipment’s water inlet and each cooling circuit inlet of machines and pumps shall be equipped with their own shut-off valves. When it is necessary to adjust the water volume, this valve should be a automatically controlled valve or a manual valve with good regulating performance. (3) Gravity return water: No shut-off valve is provided at the outlet. (4) Pressure return water: A shut-off valve should generally be installed at the outlet. Only several devices that can be shut down simultaneously can share a single isolation valve at the outlet. (5) Typically, a drain valve is installed at the lowest point of the pipeline. A drain valve is installed on the equipment only when the drain valve on the pipeline is unable to remove all the water from it. Multi-pass shell-and-tube heat exchangers and heat exchangers equipped with baffles discharge liquid by creating tear holes in the partitions. (6) For outdoor water coolers in cold regions, if shutdown for maintenance is required during operation, a anti-freezing bypass should be provided. 2.0.6.6 Generally, no isolation valves are installed on the inlet and outlet pipes of air coolers. However, since the feed stream is often a two-phase flow, special attention must be paid to the pressure drop distribution across each set of cooling tubes; in the design, the inlet and outlet pipes should be arranged symmetrically. For air coolers in the process flow that require isolation during operation or need maintenance while in use, isolation valves, drain valves, and vent valves should be installed at their inlet and outlet. 2.0.7 Container 2.0.7.1 includes two main categories: device inner containers and storage tanks. Valves should be installed in the following situations: (1) When there are multiple inlets or outlets that need to be switched, valves should be installed at the pipe ends. (2) Valves are installed at the outlets of containers holding flammable, toxic, or corrosive materials; inner containers are generally equipped with a single valve, while storage tanks in the intermediate or entire plant tank areas are fitted with double valves. Engineering specifications should be established in the engineering design for special circumstances. (3) A drain valve should be installed at the lowest point, and the discharge pipe should be positioned slightly above the drain valve. (4) Except for containers with a small volume (that do not have manholes for maintenance) or those that can be replaced along with the system, a common material inlet/outlet (U, C) equipped with a shut-off valve must be installed at the bottom of the container, and a vent valve must be installed at the top of the container, at a position far from the outlet of the common material pipe. (5) For containers and tanks that require inert gas protection, self-acting control valves should be installed in series with check valves; refer to the industry standard \"Installation of Gas Seals\" (HG/T20570.16—95). (6) Large pressure-vacuum storage tanks with conical or arch-shaped roofs should be equipped with breather valves when storing volatile materials. In areas where the components of the conditioned or vented air exceed environmental protection and health standards, a low-temperature condensation system is used in place of breather valves. 2.0.8 Except for air compressors that draw air from the atmosphere and do not have inlet valves, all compressors must be equipped with shut-off valves at both the inlet and outlet. For compressors that may require maintenance during operation of the unit, letter-shaped blind plates should also be installed on the inside of the inlet and outlet. Parallel air compressors should each have their own independent air intake. There should be a bypass pipe between the inlet and outlet valves of the compressor, equipped with a connecting valve. (1) Reciprocating compressors are equipped with bypass pipes to enable low-load startup during initialization, to allow disconnection from the system during testing after maintenance and thus prevent pressure buildup, and also to maintain positive pressure at the inlet – which is particularly important when the operating medium is a flammable or explosive gas. (2) The bypass pipes of multi-stage reciprocating compressors can be connected stage by stage, which not only saves energy but also allows the load on each stage to be adjusted during commissioning to ensure balanced operation. If required by the process or safety considerations, an additional bypass can be installed between the final stage and the inlet. (3) The air compressor only requires an outlet leading to the atmosphere, equipped with a shut-off valve, upstream of the outlet valve. (4) For centrifugal compressors, the capacity of the bypass should be at least equivalent to the load at the compressor’s surge point. Auxiliary systems of compressors (1) Generally, auxiliary systems include cooling water, lubricating oil, sealing oil, flushing oil, venting, and drainage. To make full use of the cooling water, it can be used in series according to temperature requirements, with the cooling water flowing first to the cooler and then to the cylinder jacket. Each cooling water circuit inlet should be equipped with its own isolation valve, and measures should be taken at the outlet: the normal-pressure return water outlet should be positioned above the upper edge of the return water funnel, and pressure return water systems should be fitted with sight glasses to enable observation of the water flow. A shut-off valve must be installed at the cooling water outlet for pressure return water, to facilitate shutdown and maintenance. The outlet ports of the same device can be combined and equipped with a shut-off valve. (2) When the compressor product documentation does not include lubricating oil, seal oil, and flushing oil systems, pipes and valves shall be installed in accordance with the requirements specified in the documentation. Independent circuits must be available for critical areas (such as lubrication at bearings). (3) Each separation tank between stages of the compressor shall be equipped with its own drain valve. When all liquids are directed to a single main pipe, the pressure drop must be calculated to ensure that the pressure at the main pipe is lower than the pressures at each stage, and check valves should be installed at the outlets where the liquids are separated at various stages. (4) It is absolutely not allowed for liquid droplets to enter the compressor, as this will immediately cause mechanical damage in both reciprocating and centrifugal compressors ； It does not cause significant damage to screw-type liquid ring compressors, but it affects the quality of the seal oil (liquid). Therefore, a separation tank with good performance and sufficient capacity must be installed at the compressor inlet ； The piping design should be reasonable to prevent condensate in the gas from entering the compressor. a. Install a drain valve on the pipeline to remove condensate and droplets from it. b. Limit the vertical straight pipe height above the compressor at the inlet and outlet pipes of the compressor. (5) When the compressor needs to be replaced, common material connections can be added at the inlet and outlet of each compressor, either in the suction separation tank or in parallel compressors; the outlet should be directed to a safe location. 2.0.9 Pumps 2.0.9.1 Pumps can be classified into various types based on their structural design. These regulations divide them into two main categories from the perspective of piping and valve installation: impeller-type pumps (including centrifugal pumps, axial flow pumps, and vortex pumps) and positive-displacement pumps (including reciprocating and rotary types). 2.0.9.2 Inlet and outlet isolation valves (1) Isolation valves shall be provided at the inlet and outlet of each pump. (2) The pump inlet isolation valve should have the same pipe diameter. When the suction pipe is two sizes larger than the pump inlet, a valve that is one size larger than the pipe mouth can be used. At this point, it is necessary to verify the effective net positive suction head under various conditions. (3) The pump outlet shut-off valve should be the same size as the pipeline. When the outlet pipe diameter is two or more sizes larger than that of the pump outlet, the valve can be one size smaller than the pipe diameter. 2.0.9.3 Check valve (1) Positive displacement pumps: Positive displacement pumps, such as reciprocating pumps, usually have a built-in check valve at their inlet, so there is no need to install an additional check valve in the pipeline to prevent backflow of fluid. The system specialist should check the information provided for the selected pump; if the pump manufacturer does not supply a built-in check valve, such a valve should be added. (2) Backflow of liquid in vane pumps can lead to various situations as follows; therefore, a check valve should be installed on the pump outlet pipe: a. When the liquid temperature rises by more than 90°C above the normal conveying temperature. b. The combined temperature and pressure of the output fluid exceed the design specifications of the pump casing. c. The impeller may be damaged due to reversal. d. Various variations that are not permissible in the process operation. (3) The size of the check valve should be the same as that of the pump outlet isolation valve. (4) Check valves should be installed at the outlet of each pump in a parallel setup. 2.0.9.4 Inlet/Outlet Connection Valve (1): Centrifugal pumps generally do not have this valve. (2) Since positive displacement pumps and vortex pumps must not be subjected to pressure buildup during startup or individual testing, a bypass valve must be installed between the inlet and outlet valves of the pump, as shown in Figure 2.0.9(a). (3) For small reciprocating metering pumps, only a safety valve may be provided, without the need for inlet and outlet connection valves. 2.0.9.5 Vent valve (1): Centrifugal pumps must be filled with liquid before startup, and a vent valve should be provided. Large horizontal centrifugal pumps are equipped with an exhaust valve above the pump casing. For ordinary centrifugal pumps, this valve can be installed slightly above the pump body, between the pump outlet check valve and the pump itself. For smaller pumps, the drain valve located between the check valve and the isolation valve can be used as the exhaust valve. Vertical centrifugal pumps (including submersible pumps) should have such a valve installed according to the specifications provided in the product data; see Figure 2.0.9(b). (2) Positive displacement pumps do not require this valve. 2.0.9.6 When the suction level of a bottom-valve centrifugal pump is below the pump inlet, a bottom valve (sometimes accompanied by a filter screen) must be installed at the bottom of the pump inlet pipe to prevent leakage while filling the pump with liquid. 2.0.9.7 Low-flow protection: Centrifugal pumps designed for low flow rates. Operation under such conditions is highly inefficient, or even impossible; a low-flow protection pipeline must be installed. (1) The pump may need to operate in the short term at a flow rate of less than 20% of its rated value; a bypass equipped with a flow-limiting orifice plate should be installed, without any valves. The size of this orifice plate should ensure that the flow rate through the pump remains at least 20% of the rated value (or as determined by the pump’s operating curve). When flashing may occur as the liquid passes through the bypass orifice plate, the bypass pipe should lead back to the liquid suction device upstream of the pump, with the orifice plate placed close to this device, as shown in Figure 2.0.9(c). (2) Since the pump may operate for extended periods at a flow rate below 40% of its rated value, a bypass or manual valve equipped with a orifice control valve should be provided. (3) When the pump operates at low flow rates for an extended period, the bypass pipe should lead back to the suction device upstream of the pump. 2.0.9.8 The venting and drainage valves of the pump can be installed together in accordance with the provisions of 2.0.9.5. For liquefied gas or saturated absorbent liquid, an exhaust line must be installed at the pump inlet. When the released gas is flammable, explosive, or toxic, the exhaust pipeline should be connected as close as possible to the gas space of the storage tank or to the flare pipeline. The vent from the vacuum system pumps should all be returned to the gas phase space of the upstream liquid suction equipment, as shown in Figure 2.0.9(d). This pipeline is also used to remove liquefied gas from the pump before maintenance. When the liquid inside the pump can be drained through a drain valve on the pipeline, or when the liquid being transported is harmless (non-toxic, non-corrosive, and non-polluting), it may not be necessary to install a drain valve on the pump body. Conversely, a drain valve should be installed according to the size specified for the drainage hole in the pump’s technical specifications. 2.0.9.9 Heat pumps and anti-condensation bypasses: Pumps in the following situations shall be equipped with heat pumps and anti-condensation bypasses, as shown in Figure 2.0.9(e). (1) Transport temperature exceeds 200℃ ； (2) The temperature may be below the pour point or freezing point of the material ； The anticoagulation bypass should be insulated using steam tracing or electric tracing. (3) This bypass can be replaced by drilling holes in the check valve disc. 2.0.9.10 For pumps with high pressure bypass and high head, the pressure difference across the outlet isolation valve is significant; the larger valves experience excessive unidirectional pressure, making it difficult to open them. Therefore, a DN20 bypass line must be installed in front of and behind the valve, and this bypass should be opened first to balance the pressures on both sides of the valve before opening the valve itself. As shown in Figure 2.0.9 ( ). 2.0.9.11 Others (1) Cooling water, flushing fluid, and sealant pipelines: Under normal circumstances, several inlet pipes can share one inlet isolation valve; however, in critical applications (such as the bearings of high-temperature or high-speed pumps), an inlet valve should be provided for each circuit. Additionally, measures should be in place to monitor the flow of cooling water and other fluids at the outlets, as specified in 2.0.8.3(l). (2) On the steam pipeline of the steam reciprocating pump, a drain valve should be installed at the lowest point of the pipeline; discharge valves should also be installed on both the inlet valve and outside the waste steam outlet. file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image046.gif file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image042.gif 3 Selection of Valve Types in Engineering Design 3.0.1 Factors to Consider When Making the Selection The selection of valves is based on operational and safety considerations, as well as economic viability, and is the result of a comprehensive comparative analysis. Before selecting a valve, the following initial conditions must be specified: 3.0.1.1 Properties (1) Material state a. The material state of gaseous materials includes relevant property data, such as whether it is a pure gas or a mixture, whether there are liquid droplets or solid particles present, and whether there are components that tend to condense. b. The material state of liquid materials includes: data on physical properties, whether the pure component or mixture contains volatile components or dissolved gases (which can precipitate to form a two-phase flow when pressure decreases), whether it contains solid suspensions, as well as the viscosity, freezing point, or pour point of the liquid. (2) Other properties: including corrosivity, toxicity, solubility in the materials used for valve construction, and whether it is flammable or explosive. These properties sometimes affect not only the material but also give rise to special structural requirements or the need to upgrade the pipe grade. 3.0.1.2 Operating conditions during operation ( ) shall be based on the temperature and pressure under normal operating conditions, taking into account also the conditions during startup, shutdown, or regeneration. a. The pump outlet valve should take into account the pump’s maximum shut-off pressure, etc. b. When the system’s regeneration temperature is much higher than normal while the pressure decreases, for this type of system, the combined effect of temperature and pressure must be taken into account. c. Degree of operation continuity: that is, the frequency at which the valve is opened and closed, which also affects the requirements regarding wear resistance; for systems where the valve is operated frequently, it should be considered whether to install a dual-valve system. (2) Pressure drop allowed by the system: a. If the system permits only a small pressure drop, or if a moderate pressure drop is acceptable without the need for flow regulation, then valve types with a low pressure drop, such as gate valves or straight-through ball valves, should be chosen. b. If flow regulation is required, a valve type with good regulating performance and a certain pressure drop should be selected (the proportion of the pressure drop to the total pressure drop in the pipeline is related to the sensitivity of regulation). (3) Environment in which the valve is located: In outdoor areas with cold climates, especially when dealing with chemical substances, the valve body should not be made of cast iron; instead, cast steel (or stainless steel) should be used. 3.0.1.3 Valve functions (1) Shut-off: Almost all valves have a shut-off function. Gate valves and ball valves can be used when cutting off flow alone without the need for flow regulation; for rapid shutdown, plug valves, ball valves, butterfly valves, etc., are more suitable. A stop valve can both regulate flow and shut it off. Butterfly valves can also be suitable for regulating large flow rates. (2) Changing the flow direction: By using a two-way (L-shaped channel) or three-way (T-shaped channel) ball valve or plug, it is possible to quickly change the direction of the material flow. Since one valve can serve the function of multiple straight-through valves, this simplifies operations, ensures accurate switching, and reduces the space required. (3) Regulation: Globe valves and plunger valves can meet general flow regulation requirements, while needle valves can be used for fine adjustments of very small flow rates ； For stable regulation (pressure, flow rate) over a wide range of flow rates, a throttle valve is the appropriate choice. (4) Check valve: A check valve can be used to prevent the backflow of material. (5) For different production processes, valves with additional functions can be selected, such as valves with jackets, drain ports, and bypasses, as well as valves with air injection ports to prevent the deposition of solid particles. 3.0.1.4 Power for switching valves: For the vast majority of valves that are operated locally, hand wheels are used; for those that need to be operated from a certain distance, sprockets or extended rods can be employed. Some large-diameter valves are equipped with motors at the time of design due to their high starting torque. Appropriate-rated explosion-proof motors must be used in explosion-proof areas. Remote control valves: The power sources used include pneumatic, hydraulic, electric, etc. Among these, electric types can be further divided into solenoid valves and valves driven by motors. It should be chosen based on needs and the available energy source. 3.0.2 Characteristics and application ranges of various types of valves 3.0.2.1 Gate valves (1) The flow direction of the fluid does not change as it passes through a gate valve. When the gate valve is fully open, its resistance coefficient is one of the lowest among all types of valves, and it can be used across a wide range of pipe diameters as well as pressure and temperature conditions. Compared to globe valves of the same size, it has smaller installation dimensions, which is why it is the most commonly used type in chemical processing plants. (2) Gate valve handles come in two types: stem-type and hidden-stem type. Stem-type gate valves are particularly advantageous when it is necessary to alternate between two or more identical sets of equipment, as their stems allow for an obvious indication of whether the valve is open or closed. (3) When the gate valve is partially open, the valve core is prone to vibration; therefore, it is suitable only for fully open or fully closed positions, and not for applications that require flow regulation. (4) The gate valve has grooves inside its body, so it is not suitable for fluids containing solid particles. In recent years, gate valves with air blowing ports have become available for this purpose. 3.0.2.2 Globe Valve (1) The globe valve is a type of valve widely used in chemical plants. It has reliable sealing performance and is also suitable for flow regulation; it is generally installed at locations where flow needs to be controlled, such as at the pump outlet or upstream of the flow meter in the bypass circuit of control valves. (2) When the fluid flows through the valve core, its flow direction changes, resulting in a large pressure drop. Additionally, solid particles tend to deposit on the valve seat; therefore, it is not suitable for suspensions. (3) Compared with gate valves of the same diameter, globe valves are larger in size, which limits their maximum diameter (maximum DN150–200). (4) Compared with ordinary straight-through valves, Y-type and angle-type stop valves have a lower pressure drop, and the angle-type valve also has the function of changing the flow direction. (5) The needle valve is also a type of stop valve; its valve element is conical, and it can be used for fine adjustment of small flow rates or as a sampling valve. 3.0.2.3 Plug valves, piston valves, and ball valves (1) have similar functions; they are all valves that can be opened and closed quickly. The valve core has transverse openings through which the liquid flows in a straight line, resulting in low pressure drop; it is suitable for suspensions or viscous liquids. The valve core can also be designed with L-shaped or T-shaped channels, resulting in three-way or four-way valves. They have a regular shape, making them suitable for use as jacketed valves in applications where heat retention is required. These types of valves can also be easily converted into pneumatic or electric valves for remote control. (2) The difference among the three lies in the plunger valve; the operating pressure of the ball valve is slightly higher. 3.0.2.4 Butterfly valves have a certain regulating function, making them particularly suitable for regulating large flow rates; their operating temperature is limited by the sealing material used. 3.0.2.5 Check Valve (1) A check valve is a valve used to prevent fluid from flowing in the reverse direction. It is generally used to prevent contamination, temperature rise, or mechanical damage caused by fluid backflow. (2) The commonly used types are swing type, lift type, and ball type. The swing-type has a larger diameter compared to the latter two types; it can be installed on either horizontal or vertical pipes. When installed on a vertical pipe, the fluid should flow from bottom to top. The lift-type and ball-type have smaller diameters and can only be installed on horizontal pipes. (3) Check valves can only be used to prevent sudden backflow, but their sealing performance is poor; therefore, for materials whose mixing is strictly prohibited, other measures must also be taken. (4) When the inlet of the centrifugal pump is in suction mode, a bottom valve installed at the inlet pipe is also used to keep the liquid inside the pump in place; it functions as a check valve as well. When the container is open, the bottom valve can be equipped with a filter screen. 3.0.2.6 Diaphragm valves and clamp valves: With these types of valves, the fluid comes into contact only with the diaphragm or hose, and does not touch any other parts of the valve body; they are particularly suitable for use with corrosive fluids, viscous liquids, suspensions, etc. However, its range of use is limited by the material of the diaphragm or hose.