PNEUMATIC PUMPING DEVICE

Abstract: A pneumatic pumping device incorporating a movable valve such as bellows (4), diaphragm driven by air back pressure in a cylinder (3) so that a liquid is inhaled and discharged by reciprocating movement of the movable valve, and in which surfaces contacting the liquid on the internal and external parts of the pumping device are formed of either a single substance or a compound of a fluororesin such as PTFE, PFA, CTFE in order to feed strong acid liquid or strong alkaline liquid without corrosion on components of the pumping device.

Description: 1. Field of the Invention: The present invention relates to a pneumatic pumping device in which a movable member performs reciprocating movement by using air back pressure, and pumping operation is carried out by the reciprocating movement. 2. Description of Prior Art: Hitherto, there has been proposed a pneumatic pumping device in which a bellows performing reciprocating movement by back pressure of air is disposed in a cylinder so that a liquid is inhaled and discharged by the reciprocating movement, as is disclosed in Japanese Patent Official Gazette under Publication No. 56-50116 and Japanese Utility Model Laying-Open Official Gazette under Laying-Open No. 61-29078. In such conventional pumping device, two bellows are respectively disposed in both of left and right cylinder chambers, the bellows being connected with each other through a piston rod, so that when one bellow moves either forwardly in one direction or backwardly in the returning direction by the application of air back pressure, such movement is transmitted to the other bellows through the piston rod to make the other bellows move forwardly or backwardly, thus pumping operation takes place by such reciprocating movement of the bellows. In the conventional pneumatic pumping device of aforesaid construction, there are provided on the outer part thereof connecting members such as fittings for connecting pipes with an inhaling port and a discharging port of the cylinder; bolts and nuts for assembling the cylinder, bellows and other components; and metallic members for letting components of the pump have their rigidity. Accordingly, when the conventional pumping device is used being soaked in a liquid of strong acid otherwise strong alkali, the aforesaid connecting members, bolts, nuts, metallic components, etc. come to be corroded, broken down and out of operation. Furthermore, the conventional pumping device is necessarily composed of a pair of horizontally disposed pumps, thereby construction of a small-sized pumping device is substantially impossible. Moreover, when a pressure for feeding chemical liquid and a heat thereof generated by chemical reaction are applied to the components of the pump, there arises a problem of stress relaxation at joining sections of the components. Accordingly, a gap may come out at the joining section between the bellows and the cylinder, otherwise a compressive creep may attack O rings and the like provided to maintain sealing function, resulting in decline of such function. Pneumatically driven diaphragm pumps are generally known. Examples are disclosed in GB-A-20 53 378 and DE-A-34 08 331. In particular, the DE-A-34 08 331 discloses a pump with a welded housing structure, that should be tight enough for pumping corrosive fluid. However, both pumping systems are intended to be used for medical purposes only and will obviously not stand very corrosive fluids or different heat environments. It is not recommended to introduce only corrosive resistent material in the pumps disclosed in the above mentioned references, if one desires a pump for corrosive fluid. In the liquid end parts materials of high corrosive resistance may be used and metallic materials may be used in other parts. Although the resin is excellent in corrosion resistence, it is likely to induce stress relaxation between unlike metals and if the junction is tightened very firmly, it may be loosen in the course of years of use and leaks may occur. Such stress relaxation is accelerated by heat cycles and moving parts of leakage cannot be ignored. A problem of the invention is to generate a pump that does not have the above mentioned drawbacks and is able to pump corrosive fluids. The problem is solved by a pump according to claim 1. In the liquid conveying system the portion having the highest risk of leak is the pump main body that has the most complicated structure but by immersing the pump main body in the fluid to be conveyed as in this application the all-plastic pump is liberated from the risk of fluid leak due to stress relaxation and a much higher safety is obtained as compared with the conventional fluid conveying pump. In addition, since metallic parts are not used at all, and PTFE of extremly high corrosion resistance is used, elution of metal ions does not occur, which makes it possible to build up a conveying system of high purity fluid. Furthermore, by using air pressure for the pump driving system, the driving system will be simplified. The building of the joining portion between said movable member and the housing protects against risk of leackage as discussed above. A feature of the pneumatic pumping device according to the invention consists in that a joining section between the movable valve and a housing by which the movable valve is fixed to the pump body is circumferentially welded, and that a joining section between the housing and an air tube inserted in the housing are also circumferentially welded. In order to accomplish the mentioned objects, the chemical liquid contacting surfaces of inner and outer parts of the pump are formed of a simple substance of fluororesin otherwise a compound thereof such as PTFE (polytetrafluoroethylene), PFA (polymer of tetrafluoroethylene - ethylene), CTFE (chlorotrifluoro - ethylene). In the pneumatic pump of above composition, since the chemical liquid contacting surfaces are all formed of the simple substance or compound of fluororesin, a satisfactory corrosion resistant condition is attained owing to the anti-corrosion property thereof, and therefore the chemical liquid contacting surfaces of the pump are protected from being attacked by chemical liquid not only when some chemical liquid is inhaled and discharged by the pump, but also when using the pump soaking in the chemical liquid. As a result, there is no possibility of inviting inability to the pump due to corrosion even if liquid leakage out of the pump should occur. Another feature of the pneumatic pumping device according to the invention consists in that the movable valve is operated by change-over between air for application of pressure and vacuum. That is, in the pneumatic pumping device according to the invention , since a single movable valve can be reciprocatingly moved by both the air for application of pressure and vacuum, it becomes feasible to make up a simple and compact pump. Moreover, since there is no need of any piston rod in the pump to inhale and discharge liquid, it is also possible to attain a simple and small-sized pump by forming into a double pump. A further feature of the pneumatic pumping device according to the invention consists in that the air passage of the pump is provided with a detector for detecting leakage of liquid, and a stopping device for stopping pumping operaion in accordance with a signal detected by the liquid leakage detector. According to the pneumatic pumping device of above construction, when a strong acid otherwise a strong alkaline liquid leaks out to the air passage on the vacuum side due to such accident as break down of the movable valve composed of bellows and diaphragm, the liquid leakage detector detects the leakage and stops the pumping operation. As a result, the pumping device is prevented from continuing its pumping operation with the liquid leaking, and the air passage is also protected from corrosion by the leaking liquid. Thus, various components and accessories connected to the vacuum side are kept from the corrosion due to liquid leakage. A still further feature of the pneumatic pumping device according to the invention consists in that a highly corrosion resisitant filter is disposed in the air passage. The filter is gas-permeable but not liquid-permeable. According to such pneumatic pumping device, even if a leaking liquid of strong acid or strong alkali should be inhaled into the air passage on the vacuum side, the liquid is shut off by the filter, and the components and accessories located downstream the filter are prevented from corrosion. According to such pneumatic pumping device, the back pressure chamber is perfectly closed and exactly prevented from entrance of liquid. Moreover, when the pumping device is used being soaked into a liquid, the back pressure chamber is securely kept from entrance of the liquid surrounding the pump. Accordingly, a certain quantity of liquid flow can be continuously delivered at a specified transfer speed resulting in smooth and stable pumping operation. Moreover, since the components and accessories are joined by welding, the pump structure is so strong as to endure under high pressure necessary when transfering a liquid of high viscosity, thus durability and transfer performance of the pumping device being improved. Other objects and features of the invention will become apparent in the course of the following description together with the accompanying drawings. Brief Description of the Drawings In the drawings forming a part of the present application, Fig. 1 is a sectional view of a pneumatic pumping device according to an embodiment of the invention; Fig. 2 is an enlarged sectional view showing a welding section of an air tube; Fig. 3 is an enlarged sectional view showing a welding section of a bellows; Fig. 4 is a diagram of an air change-over control circuit; Fig. 5 is a diagram of a modified air change-over control circuit; and Fig. 6 is a diagram of a further modified air change-over control circuit. Description of the Preferred Embodiments A pneumatic pumping device shown in Figs. 1, 2 and 3 is a vertical pumping device provided with pumps 1, 1 of the same structure on both left and right sides. Referring to one pump 1, a cylinder chamber 3 having a bottom extends from the upper side to the inner part of the cylinder 2 whose external appearance is like a square pillar. A bellows 4 is disposed in the cylinder chamber 3, and a flange 5 formed at the base portion of the bellows 4 is in contact with a step portion 6 of the cylinder chamber 3. A top end of a housing 7 is inserted inside the bellows 4, and a male screw 9 formed on the base portion of the housing 7 is engaged with a female screw 8 formed on the upper end portion of the cylinder chamber 3, thereby the bellows 4 being fixed to the cylinder chamber 3. An air passage 10 for applying back pressure to the bellows 4 is formed in the central portion of the housing 7. An outer end of the air passage 10 is connected to an air supply source by way of a pipe. An inhaling passage 11 is formed on the central bottom portion of the cylinder chamber 3, and a check valve 12 permitting inhalation of liquid is disposed in the passage 11. A valve seat 13 is mounted on the outside of the valve 12 by screwing. A discharging passage 14 is open on one side of the bottom of the cylinder chamber 3, and a check valve 15 permitting discharge of liquid is disposed in the passage 14. In the pumping device of above construction, an air source for application of pressure is connected to one air passage 10, while a vacuum source is connected to the other air passage 10. The air source and the vacuum source are subject to change-over control. That is, referring to Fig. 1, the vacuum source is connected to the air passage 10 of the pump 1 on the left side, while the air source for application of pressure is connected to the air passage 10 of the pump 1 on the right side. Then, under such arrangement, the air source is changed over to the vacuum source and vice versa, so that the bellows 4, 4 repeat alternately contraction and expansion, thereby pumping operation being carried out. For example, when using the pumping device being soaked in a liquid, the liquid is inhaled through the inhaling passage 11 and check valve 12 when the bellows 4 contracts, while the liquid is discharged out through the discharging passage 14, check valve 15 and pipe when the bellows 4 expand. Fig. 1 shows a pump according to the invention. In the pump 1, an air tube 35 is inserted through the central portion of the housing 7. A ferrule 36 being mounted on the outside of the air tube 35 engages with a screwed portion of the housing 7, and the screwed portion is tightened with a union nut 37 to secure the ferrule 36 to the conical face of the screwed portion. The components of the pump 1 are all made of fluororesin, an air source for application of pressure is connected to one air passage 10 while a vacuum source to the other air passage 10, and the air source and the vacuum source are subject to change-over control. As shown in Fig. 3, the flange 5 of the bellows 4 and an annular projection 38 formed on the housing 7 are joined by welding circumferentially. As shown in Fig. 2, a cylindrical part 39 of the housing 7 and a peripheral edge of the top end portion of the air tube 35 are joined by welding circumferentially. In the pneumatic pumping device of above construction, since the bellows 4 and the housing 7 as well as the housing 7 and the air tube 35 are circumferentially joined by welding, the joined portions are perfectly closed and the entrance of liquid thereinto is exactly prevented. When operating the pumping device in a liquid, there is no possibility of entrance of the liquid from outside. The air change-over control circuit shown in Fig. 4 is provided with an electromagnetic five-port-two-position change-over valve 70. In the change-over valve 70, the air source for application of pressure is connected to a port C, and the vacuum source to ports V1 and V2. Ports A and B are connected to each air passage by way of filters 72, 72. The electromagnetic coils on both sides of the change-over valve 70 are alternately switched through change-over control by a timer circuit 73. Accordingly, in the pumps 1,1, each air passage is alternately changed over to the air side and the vacuum side according to the change-over control of the change-over valve 70 by the timer circuit 73, thereby pumping operation being continuously carried out. Fig. 5 shows an embodiment in which the air change-over control circuit is provided with liquid leakage detectors. In a pilot operated five-port two-position change-over valve 70 of the air change-over control circuit, the air source for application of pressure is connected to the port C, while the vacuum source to the ports V1 and V2. Further, a pressure gauge 74 for measuring and indicating the air pressure, a pressure regulator 75 for regulating the air pressure to a setup pressure, and a filter 76 for eliminating dust contained in the air are respectively connected with an air pressure application line to the port C. Each port A, B is connected to each air passage of the pumps 1, 1 by way of the liquid leakage detectors 78 ..., and the pilot port is also connected to the pumps 1, 1 by way of the liquid leakage detectors 78 .... The liquid leakage detectors 78 output liquid leakage detection signals when occurring any liquid leakage in the air passage. A solenoid operated five-port-two-position change-over valve 79 is provided upstream the filter 76. Line from the filter 76 is connected to the port A of the change-over valve 79, and each port V1, V2 of the change-over valve 70 located downstream is connected to the port B. The air source is connected to the port C of the changeover valve 79 located upstream, and the vacuum source is connected to each port V1, V2. Signal of the liquid leakage detector 78 is amplified by the amplifier 80, and the electromagnetic solenoid of the change-over valve 79 is operated by the amplified signal to change over the valve. Once the valve is changed over, line for air and the vacuum is closed, and the pumps 1, 1 stop their operation. Air and vacuum are alternately fed to each air passage of the pumps 1, 1 with the change-over operation of the pilot port in the change-over valve 70. In the control circuit of above construction, if a strong acid liquid or strong alkaline liquid should leak out and come entering such parts as the air passages 19, 19 or pilot ports Pa, Pb situated on the vacuum side due to break down of bellows of the pump for example, the liquid is detected by the liquid leakage detector 78 and operation of the pumps 1, 1 stop. Accordingly, when the pumps are provided with some other air devices, those devices are exactly protected from deterioration caused by the liquid. Fig. 6 shows an embodiment with filters 81 of a porous tetrafluoroetylene resin formed by drawing, which is mounted on the air change-over control circuit. The filters 81 are of highly corrosion resistant material and perform a function of permitting gas to get therethrough while inhibiting liquid from passing therethrough, i.e., gas-permeable but not liquid-permeable. In the pilot operated five-port-two-position change-over valve 70, the pilot ports are changed over to each other so that the air source and the vacuum cource are alternately communicated with each air passage of the pumps 1, 1, thereby the pumps 1, 1 performing their pumping operation. According to this embodiment, even if a strong acid or a strong alkaline liquid should enter the air passage or the pilot port being in the vacuum state, the liquid is shut off by the filters 81 ..., and the air passsage portions downstream the filters 81 ... are protected from corrosion. It should be understood by those skilled in the art that the foregoing relates to only preferred embodiments of the invention, and that various changes and modifications may be made in the invention without departing from the spirit and scope thereof.

Claims: A pneumatic pump for conveying a corrosive fluid by immersing the pump main body in the corrosive fluid to be conveyed, incorporating a movable member, in the form of a bellows (4) driven by back pressure of air in a cylinder (2) so that a liquid is inhaled and discharged by reciprocating movement of the movable member (4), characterized in, that all surfaces, which are in contact with the liquid, of object members are formed either out of a single substance or compound of a fluororesin such as PTFE, PFA or CTFE and that a joining portion between said movable member (4) and a housing part (7) for fixing the movable member (4) into the pump main body is circumferentially welded, and a joining portion between said housing part (7) and an air tube (35) inserted in the housing part (7) is circumferentially welded. A pneumatic pump according to claim 1, wherein the cylinder (2) is formed in a plurality, and the movable members (4) are installed individually in the cylinders (2). A pneumatic pump according to the claims 1 or 2, wherein a leakage detector (78) is provided in an air passage of the pumping device and means (80) for stopping pumping operation based on signals detected by said liquid leakage detector (78) is provided. A pneumatic pump according to the claims 1 to 3, wherein a highly corrosion resistant filter (81), which is gas permeable but not liquid permeable is disposed in the air passage of the pumping device.

Inventors: FUKUMOTO, TOSHIYUKI
Applicants: NIPPON PILLAR PACKING CO. LTD.
Application year: 1987
Main classification: F04B43
IPC codes: F04B43