Vacuum pumps commonly used in pharmaceutical equipment
In the pharmaceutical equipment industry, vacuum equipment such as vacuum evaporation, vacuum concentration, vacuum transfer, vacuum sterilization, vacuum drying, vacuum packaging, and vacuum emulsification are frequently used. These equipments must all be equipped with vacuum pumps. Commonly used vacuum pumps include liquid ring vacuum pumps, water jet pumps, and steam jet pumps. These types of vacuum pumps can directly extract water vapor. There are several commonly used rotary vane pumps, reciprocating pumps, and slides. Valve pumps, Roots pumps, etc. Although they cannot directly extract water vapor, they can be used in conjunction with condensing. If the space to be pumped and the surrounding environment are clean and free from pollution, dry pumps of various types can be used. , but it is the direction of future development. 1 liquid ring vacuum pump 1.1 working principle Liquid ring vacuum pump is a positive displacement pump whose working medium is liquid, if the liquid is water, it is called water ring vacuum pump. Its working principle is shown in Fig. 1. The impeller (rotor) is eccentrically installed in the column shell a. When the impeller rotates, the water in the pump shell is thrown around to form an equal thickness water ring b ice ring due to the centrifugal force. The impeller tangentially forms a crescent-shaped space d, which is divided into several chambers and gradually changes as the impeller rotates. When the space becomes small, the suction chamber is formed to evacuate the pump. When the crescent-shaped space is formed by a large change, the exhaust chamber f pump discharges gas to achieve the pumping action of the pump. 1.2 Method of use It is not possible to obtain an inlet pressure below the working fluid vapor pressure using a liquid ring pump. If the liquid vapor pressure approaches the inlet pressure, cavitation will cause damage to the pump. For example, the vapor pressure of ice at 15C is 103Pa. In order to avoid cavitation, the minimum inlet pressure of the water ring pump is allowed to be 3.3×10 3 Pa. If the inlet pressure is lower than this value, a medium with lower vapor pressure such as kerosene, benzene should be connected. Ethylene, ethylene glycol and other extreme pressures are 6.7X. The gas and liquid mixture flowing from the pump outlet side flows into the separator and is separated in the separator. The non-exhausted gas contains the steam content corresponding to the vapor pressure of the liquid at the same temperature. The liquid ring pump operation mode is considered from the aspects of working fluid price and environmental protection. The main feature of this mode of operation is that the amount of new liquid used is greatly reduced. Most of the liquid is returned from the separator to the pump and the cold liquid is added before the pump inlet, so that the inlet temperature of the pump is basically kept constant. Liquid ring pump operation principle diagram If the liquid ring pump removes poisonous and harmful gas, or must use high-priced working liquid because of the working requirement, the gas separated in the separator can not be vented and should be recycled, and the separated liquid must be After the heat exchanger is cooled to the normal operating temperature of the pump fluid, it is returned to the pump. The main types of domestic water ring pumps are SZ, SZB, SZH, SZZ, SZL, SK and ZBE1. Among them, Z-type water ring pump can be used to extract non-corrosive, insoluble or no solid particles of gas and air; ZB type is cantilever type, the use of characteristics and SZ-type is basically the same; SZH type water ring vacuum pump For air extraction, it can also be used in vacuum filtration devices: SZZ type and SZL type are direct-coupled pumps, and use with ZS type pumps; SK-type water ring type vacuum pumps are a kind of high-efficiency double-acting water ring vacuum pumps Gas temperature is widely used in vacuum drying, vacuum dehydration, vacuum filtration, etc. ZBZ1 water ring pump with a large number of water vapor overflow devices is the introduction of German technology development of energy-saving products with the SK-type water ring vacuum pump. 1.3 Operating characteristics Normally, the operating condition of the water ring vacuum pump is that the air temperature at which the pump draws gas is 20 CI and the relative humidity is 70%. The air inlet gas pressure is 101.325 kPa. The pump working liquid is 15C water. The temperature of the working fluid and its vapor pressure seriously affect the pumping speed. The partial pressure of the working fluid in the pumping chamber and the impeller chamber increases as the temperature increases. As a result, the transport gas volume becomes smaller and the pumping speed decreases.圄 3 gives 20C dry air to be pumped out. When pump working fluid is water, the pumping speed at different temperatures is SU2. and the pumping speed is at a pressure p at 15C. The working temperature of the single-stage pump is relative to the pumping speed. Affecting the pumped gas also has an effect on pump performance. If the gas to be pumped is composed of a mixture of air and steam, condensation may occur when the extracted steam is brought into contact with the cold working liquid. At this time, the pumping speed increases.圄4 is the pumping speed of a certain amount of air and steam mixture at different temperatures when 15C water is used as the working fluid. (The ratio of pumping speed Su,20 of 35.5 and 20C dry air. Of course, the ratio of air to water vapor. Different effects on pumping speed are also different. If dry air is transported, due to the small heat capacity of the drying air, the temperature of the steam saturated gas sent by the single-stage pump is quickly cooled to the temperature of the working fluid, and the large temperature difference between the pumped gas and the working fluid is caused. The volume of the gas decreases, as a result of which the liquid ring pumping speed increases. If the pumped gas is dissolved in the working fluid, it will be released as the working fluid enters the pump inlet side, and as a result, the pumping speed will decrease. The power required by the liquid ring vacuum pump must be concerned when it is affected by the working fluid viscosity, density, flow, and outlet pressure. 2 water jet vacuum pump 2.1 Working principle Water jet pump working principle as shown in 圄 5, with a certain pressure of the working medium water through the nozzle to the suction chamber at high speed; the water pressure energy into kinetic energy to form high-speed jet suction chamber The gas is forced to be mixed with a high-speed jet to form a gas-liquid mixed flow and enter the diffuser, so that the pressure in the suction chamber is reduced to form a vacuum. During the expansion of the diffuser, the kinetic energy of the mixed jet is converted into pressure energy and velocity. To reduce the pressure increase, the gas is further compressed and discharged out of the pump together with the water. The gas and water are separated in the water tank. The gas is released into the atmosphere and the ice is recycled by the water pump. The nozzle of a single-stage water jet pump may be a single nozzle structure consisting of one tapered nozzle, or it may be a multi-nozzle structure in which a plurality of orifices are formed in one orifice plate. ZSW type water squirting pumping characteristic curve 2.2 Operating characteristics Water jet pump working system consists of water pump, water jet pump, pipeline, valve, water vapor separator and test instrument, etc. The common system has two vertical and horizontal installation methods Shown is a vertical installation. The pumping volume of the domestic water jet pump is between 5800m3/h and the ultimate vacuum of the single-stage pump is up to about 300023 Torr.圄7 shows the ZSW water jet pump single stage rotary vane pump produced by Shanghai Hugang Vacuum Equipment Co., Ltd. As shown in 圄8, this pump has only one working chamber, and the pump is mainly composed of a stator, a rotary vane, and a rotor. Rotor eccentrically mounted in the stator cavity The rotor rotor is equipped with two rotors that are in close contact with the cavity wall due to the spring force and the centrifugal force of the rotor. The intake and exhaust ports on the stator and the crescent-shaped pump chamber are divided into two parts, the suction chamber and the exhaust chamber by the rotor and the rotary vane. As the rotor rotates within the stator chamber, the volume of the inlet port is gradually expanded to draw in gas, while the volume of the outlet port is gradually reduced to discharge the sucked gas from the exhaust valve. The exhaust valve is immersed in oil to prevent air from flowing into the pump. The oil enters the pump chamber through the gap, the oil hole and the exhaust valve on the pump body so that all the moving surfaces in the pump chamber are covered with oil to form a seal between the suction chamber and the exhaust chamber. At the same time, the oil is also filled with all the harmful cavities inside the pump chamber to eliminate their effect on ultimate vacuum or residual pressure. (Injection ordinate vacuum degree mmHg is determined to be non-statistical units shall be converted into Pa, in order to improve the vacuum degree can be used in the soda series operation if the use of a water jet pump and three-stage steam jet pump to form a four-stage soda jet pump unit limit The pressure can reach 20 (0.15mmHg).In order to prevent the pumped medium from corroding, the vacuum pump can be used in conjunction with anti-corrosion jet pump. The centrifugal pump can be made of reinforced polypropylene (RPP) stainless steel, fluorine alloy, fiberglass; the jet pump can be used together with stainless steel, cast iron roller Polyethylene (PE) or poly (trifluorochloroethylene) steel lined ceramics, nozzles such as PTFE or ceramics. 3 rotary vane vacuum pump 3.1 Structure and working principle Rotary vane vacuum pump, divided into two single-stage and two-stage structure. The working principle of the two-stage rotary vane pump is shown in Fig. 9. The two-stage rotary vane vacuum pump is composed of two working chambers. The two chambers are connected in series and rotate in the same direction at the same speed. Room I is the front room of the room, the room is a low vacuum, and the room is a high vacuum. The gas to be pumped first enters the chamber from the inlet. When the gas pressure is high, the pressure of the gas increases after the chamber is compressed. The compressed gas passes through the inter-stage channel 2 and enters the I outdoor, and the intermediate exhaust valve can be pushed open. Exhausted from it to achieve pump exhaust. When the gas pressure entering the chamber is low, the exhaust valve 1 is not pushed through the compression of the chamber, and the gas passes through the inter-stage passage 2 into the chamber I and continues to be compressed by the chamber and is exhausted by the exhaust valve 3 . Therefore, a two-stage rotary vane vacuum pump has a higher ultimate vacuum than a single-stage rotary vane vacuum pump. 3.2 High speed direct pump Direct high speed rotary vane vacuum pump is referred to as direct pump. The motor does not use an intermediate exhaust valve 2 - channel 3 - exhaust valve belt, directly driving the mechanical pump has the characteristics of small vibration, low sound, small size, light weight, etc., and with gas-town device, when pumping condensable gas When the valve is opened, a small amount of air is added to allow the condensable gas to escape without congealing in the pump and affecting the ultimate vacuum. The structure of the direct pump is shown as 0. 3.3 Gas-fired units Difficulties in pumping out large amounts of water vapor have always been a problem in rotary-plate type mechanical pumps. The reason is that when the gas to be pumped contains more water vapor, the gas is compressed in the pump until it reaches the exhaust pressure, in which the partial pressure of the water vapor has reached the saturated vapor pressure at the corresponding temperature, and the water vapor condenses into The liquid water remains in the pump chamber and mixes with the pump oil and emulsifies it; when the water circulates with the pump oil to the suction chamber, it is re-evaporated into water vapor due to the reduced pressure, resulting in the repeated circulation of the water vapor in the pump chamber. It also greatly reduces the pump performance and pumping capacity. The gas ballast device is a one-way checkback trim valve specially designed to reduce and prevent the condensation of water vapor in the mechanical pump. The ballast valve is connected to the exhaust chamber at the exhaust port of the low vacuum stage of the rotary vane pump. When the ballast valve is fully closed, it does not affect the operation of the pump. If the content of water vapor in the pumped gas is large, the valve cap of the gas ballast valve can be rotated; open it. Whenever the pump rotor drives the rotary vane into a compressed air exhaust, and the gas sealed and isolated by the other side of the rotary vane communicates with the exhaust port, the gas pressure in the exhaust chamber is still far less than the external atmospheric pressure, and the outside air is pushed open. The check valve in the ballast valve flows into the pump's exhaust chamber. Due to the introduction of the outside air and the continuous reduction of the volume of the exhaust chamber, the pressure in the chamber rapidly rises. When the pressure in the exhaust chamber is equal to the outside atmospheric pressure, the one-way valve in the gas ballast valve closes and stops inflating into the pump. It also prevents the gas in the pump from being discharged through the ballast valve. The introduction of outside air causes an increase in the content of ice vapor in the permanent gas component of the gas in the exhaust chamber to relatively decrease, and the partial pressure of water vapor can be controlled during the process in which the mixed gas is compressed until the exhaust pressure is discharged from the exhaust port. Saturation vapor pressure below, thereby preventing condensation in the pump chamber to eliminate water vapor. For each revolution of the rotor of the rotary vane pump, the two rotary vanes are compressed into a single compression and exhaust process, respectively, and the gas ballast valve is also inflated into the pump twice. Since the air filled in the exhaust chamber leaks into the suction chamber through the gap in the pump, when the ballast valve is opened, the ultimate vacuum degree of the rotary vane pump is reduced by about one order of magnitude. Adjusting the degree of rotation of the pressure ball valve cap of the gas ballast valve valve can adjust the amount of air pumped into the pump chamber to accommodate different amounts of steam extraction. When the gas ballast valve is opened, the discharge volume of the rotary vane pump increases, the exhaust sound increases, and sometimes the pump exhaust port is injected. Another use of the gas ballast valve is to close the inlet valve of the pump and not to pump the air from the vacuum system. Open the ballast valve and start the rotary vane pump to run at no load. This effectively eliminates condensation in the pump chamber and pump oil. Moisture, appropriate to reduce the degree of emulsification pump oil to improve the pump performance. 4 Spool type vacuum pump 4.1 Structure and working principle Spool type vacuum pump is called as a slide valve pump. It is a kind of vacuum pump with simple operation, sturdy and durable, and safe and reliable. Its application range is roughly the same as rotary vane pump, and it can be used alone as a high vacuum system. The foreline pump can also be used in series with the Roots pump to make rough pumping of large systems. It can also be used for operations such as vacuum impregnation, vacuum distillation, and vacuum drying. However, it is not suitable for gases that are too high in oxygen, explosive, and corrosive to ferrous metals. The structure of the slide valve pump is shown in Fig. 1. The pump consists of a pump body, a slide valve, a motor and a base. A cylindrical spool ring 3 is provided in the pump body. The spool ring is driven by the eccentric wheel 5 mounted on the shaft 4 and can roll along the inner surface of the pump cylinder. The upper part of the slide valve ring is provided with a valve stem 2; The rod is held in two half-shaped rams 6 and is free to slide up and down. Therefore, the pump cylinder is divided into two chambers by the slide valve ring and the valve rod. When the motor drives the shaft to rotate counterclockwise, if the chamber gradually expands, the gas will expand. It is inhaled while the other chamber is gradually reduced. The final gas is discharged from the exhaust valve, so that the circulation of the pump is effected endlessly. The exhaust valve 11 is mainly composed of a spring and a valve piece pressed by a spring. When the gas and the pump oil in the pump are compressed and the exhaust valve plate is opened, the exhaust valve 11 passes through the base to separate the oil and gas. Air outlet. The lubrication of this pump is performed automatically. The oil is pumped from the base of the pump to the bearing cover through the tubing at the atmospheric pressure, and then enters the slide valve part and the pump cylinder via the bearing. In this way, the vacuum oil can both lubricate and seal, and finally the oil is discharged to the base together with the exhaust valve and the gas. The slide valve pump is the same as the rotary vane pump. There are also single-stage and double-stage pumps. The former's ultimate vacuum can only reach 7X10-1Pa left rock, while the latter can reach 7X10-2Pa. 5 Reciprocating vacuum pump 5.1 Structure and working principle The structure and working principle of the reciprocating pump are shown in Fig. 2, in which a) is a single-acting pump. (,b) is a double acting pump. The main components in the figure are a cylinder 1 and a piston 2 in which a reciprocating linear motion is performed. The piston is driven by the crank linkage 3 including a crosshead. In addition to the above main components, there are important components such as the exhaust valve 4 and the suction valve 5 as well as auxiliary components such as a seat, a crankcase, a dynamic seal, and a static seal. During operation, the piston in the cylinder reciprocates through the action of the crank linkage mechanism driven by the motor. When the piston moves from the left end to the stone end in the cylinder, due to the continuous increase in the volume of the left chamber of the cylinder, the density of the gas in the cylinder is reduced to form a pumping process. At this time, the gas in the pumped container enters through the intake valve 5 . Pump left chamber. When the piston reaches the topmost position, the gas in the left chamber of the cylinder is full of gas. The piston then moves from the stone end to the left end (in this case, the suction valve 5 is closed. The gas in the cylinder is gradually compressed as the piston moves leftward from the stone, and exhausts when the pressure in the cylinder reaches or exceeds one atmosphere. The valve 4 is opened (the gas is discharged into the atmosphere into a working cycle. When the piston again moves from the left direction to the stone, the previous cycle is repeated, and so on, the final equilibrium pressure is eventually reached in the pumped vessel. Double-acting pumps have suction and exhaust valves at both ends of the cylinder. When the piston moves downwards, the upper suction valve inhales and the exhaust valve closes; the lower exhaust valve exhaust suction valve closes. When the piston moves upwards, the suction valve on the bottom suctions (the non-valve closes the exhaust valve on the upper side and the suction valve closes. The piston reciprocates twice to achieve a suction and exhaust process. In the case of the same pump chamber volume, 5.2 use a reciprocating pump as shown in Fig. 3. When starting, check that the direction of rotation is correct. The working environment of the reciprocating pump should be kept clean and dry with little temperature change. If the ambient temperature in winter is lower than 5C, the water in the cooling water jacket should be discharged after stopping to avoid freezing the pump body when the temperature drops to zero. After the reciprocating pump can only pump clean and dry air for 1 hour, check the wearing parts of the friction parts such as the piston, piston ring, guide rail, air valve, bearing, crosshead, and sealing ring. If there is any wear, it shall be promptly repaired or replaced. 6 Roots vacuum pump 6.1 Working principle The Roots vacuum pump is a volumetric vacuum pump that uses the volume change of the working chamber in the pump chamber to produce a pumping action. The change in volume of the pump chamber is caused by a pair of rotors with special profiles, which are caused by the rotation in opposite directions in the pump chamber at a synchronous angular velocity. The rotor starts from a) and rotates to position b) is the suction process of the pump. The pumped gas enters the rotor from the suction port, the pump body, and the space formed by the end cap rotates to the position c) When the suction is completed, the suction gas is The area of ​​the hatched area A. The volume formed by the product of the length of the pump chamber V., rotates to the position d), V. The volume communicates with the exhaust port. When the rotor rotates again, the gas is discharged from the pump. At this time, the other side of the rotor and the intake port Connect again and start inhaling to repeat the above process. A rotor removes two V. volumes of gas per rotation of the rotor. The two rotors draw away 4 V. volumes of gas. 6.2 Operation characteristics From the operating principle of the Roots pump, it can be known that no gas compression occurs in the pump chamber, so that condensable gases such as water vapor can be extracted. Except for the vertical roots pump, the Roots pump can not directly discharge the atmosphere. It is necessary to configure the fore pump to work normally. Roots water ring pump units, Roots rotary vane pump units and Roots slide valve pump units are commonly used in pharmaceutical equipment. During operation, its characteristics are: To make the unit as small as possible, can try to condense the steam to be pumped before entering the pump unit, leaving the non-condensable gas and trace residual steam, the gas cooling at the same pressure after the volume is reduced small. The amount of pumping required after condensation is small and the pump can be connected even smaller. Because there is a gap between the rotor and the pump between the rotor and the rotor of the Roots pump, there is a backflow, and this backflow is affected by the inlet pressure and the outlet pressure. Even if the same Roots pump is used, different levels are used. When pumping, the pumping speed will not be the same. The ultimate vacuum degree will also be different. When the extreme pump vacuum is high, the ultimate vacuum of the Roots pump unit will also be high. 7 Conclusion This article describes the operating characteristics of several types of vacuum pumps that are commonly used in pharmaceutical equipment. The purpose is to make the personnel working on these vacuum equipment more systematically aware of them so that they can be applied more beautifully and targetedly. Vacuum equipment. Yang Naiheng, chief editor. Vacuum gets tone 2nd edition. Beijing: Metallurgical Industry Press, 2001.6 Xu Chenghai. Vacuum drying. Vtol. Xu Chenghai et al. Vacuum drying. Chemical Industry Press, 2004.4 4 Working principle of Roots vacuum pump Fig. A. Suction pressure of PV - Pressure of outlet PV V2 - Committee member of pump chamber volume, member of the drying science group of Institute of Chemical Industry Research direction Vacuum drying theory.
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