DOUBLE-ACTING PUMP

Abstract: A double-acting pump which includes two rooms that are each divided into an operating chamber (6) and a working chamber (5) by means of a moveable partition wall (4) in the form of a piston or a diaphragm (membrane), wherein each of said operating and working chambers is provided with a valve-controlled inlet and outlet (7, 9; 8, 9) for a gaseous drive medium or operating medium and a liquid working medium transported by the pump respectively, wherewith said partition walls lack all form of mechanical connection therebetween. An outlet conduit (23) includes a cavitation-gene-rating restriction (24). The pump can be operated in a manner such as to maintain cavitation in the restriction (24) when working medium passes through said outlet conduit.

Description: DOUBLE-ACTING PUMP The present invention relates to a double-acting pump of the kind defined in the preamble of Claim 1. The pump may therewith be of the kind that includes two rooms which are each divided into an operating chamber and a working, chamber by means of a respective moveable partition wall in the form of a piston or diaphragm, wherewith each of said operating and working chambers includes valve-controlled inlet and outlet means for a gaseous driving and operating medium and a liquid working medium transported by the pump. Double-acting diaphragm or membrane pumps of this kind are known to the art, cf for instance EP Patent Specifications 0 132 913 and 0 181 756 in this regard. The operating medium is normally air and the working medium is one of the liquids that are normally pumped through piping, primarily in the pharmaceutical, foodstuffs, chemical and paint industries. One drawback with these known double-acting pumps is that the outlet pressure is influenced by the inlet pressure. Another drawback is that the flow of medium pulsates when switching the operating pressure from one operating chamber to the other. Another problem is that the pump outflow is normally dependent on the viscosity and temperature of the pumped liquid, which can also often vary during a pumping operation, and that the pump operating medium, compressed air, is usually only readily available at a pressure of about 7 bar at the highest, which is a typical maximum pressure with respect to commercially available compressors of simple design and also with respect to permanently installed industrial compressed air systems. One object of the present invention is to provide a novel and advantageous double-acting pump with which the aforesaid drawbacks can be eliminated, either completely or partially. The object of the invention is achieved with a pump according to the accompanying Claim 1. Further embodiments of the invention are set forth in the accompanying dependent Claims. One of the advantages afforded by the invention is that the pump can be used to replace pressure vessels in, e.g., filling machines with a time pressure-system. In this case, the pump can be combined conveniently with a venturi-like constriction combined with a diffuser placed downstream of the pump outlet, wherewith the velocity of the liquid is maintained at such a high magnitude as to create cavitation in the constriction. Provided that cavitation is maintained in the constriction, the flow will be precisely constant even if the resistance in the pipe, or conduit, changes downstream of the constriction. Liquid can be sucked into one working chamber without affecting the pumping of liquid from the other working chamber, when displacement movements of the partition walls are mutually independent (for instance when the partition walls have no mechanically fixed coupling relative to one another) , wherewith the pressure in the outlet conduit will be totally independent of the pressure in the inlet conduit. The inflow of liquid to respective working chambers can be effected with a spring that is compressed in pumping liquid and that expands in sucking liquid in. Alternatively, the operating chamber may be connected to a subpressure which is effective to cause liquid to be sucked into the working chamber. A third alternative is to press liquid into the operating chamber. Liquid is pumped from the liquid chamber by pressurising respective operating chambers with preferably compressed air of constant although adjustable pressure. Respective operating chambers are pressurised through the medium of an electrically operated three-path valve. These valves are controlled electronically such as to pressurise one operating chamber at a time, where- with liquid is forced out at the same time as liquid is sucked into the non-pressurised pump chamber. The switch-over is effected at a frequency that is adapted to liquid flow re- quirements. In order to avoid pulsating liquid flows in the pump outlet, the electronic circuitry is adapted to ensure that a given time overlap is achieved each time pressuπsa- tion is switched from one operating chamber to the other. In other words, both operating chambers are pressurised simultaneously for a brief moment in time, e.g. for a duration corresponding to 5-10% of the total cycle time, meaning that the liquid flow from the pump will be completely smooth, i.e. free from pulsations. It must be ensured, however, that the amount of liquid pressed from the pump will not be greater than the amount of liquid that can be sucked into the pump m continuous pumping operations. It has been found highly favourable to provide the cavitational flow generating constriction with a venturi form on the inlet side and with a downstream diffuser having a cone top in the region of 4-20°, preferably about 14°, since this will enable cavitation to be established even in working media that have a viscosity m the region of 5,000-15,000 cP and even when the available compressed air has a highest pressure of 7 bar. Conventional compressors and permanent compressed air systems in production plants are normally designed to deliver a pressure of about 7 bar at the highest; a requirement for higher air pressure would result in problematic cost increases. When only small quantities of liquid shall be pumped at any one time, for instance m conjunction with liquid filling machines, and quantities which are in the order of 2-3 times the displacement of the pump chambers, the instantaneous outflow may be greater than the inflow. Other features characteristic of the invention and advantages afforded thereby will be apparent from tne following description of exemplifying embodiments thereof made with reference to the accompanying drawings, in which Fig. 1 is a sectional view of an inventive double-acting pump; and Figs. 2 and 3 illustrate respectively alternative embodiments of movement transmission devices. Mutually corresponding elements have been identified with the same reference signs in the different Figures. Although the moveable partition walls have been illustrated and described as diaphragms, or membranes, it will be understood that the partition walls may alternatively comprise technically equivalent piston-cylinder devices in which the pistons fit in passageways and slide sealingly therealong. The double-acting pump shown in Fig. 1 is a so-called diaphragm pump that includes a generally cylindrical pump housing 1 which has two rooms or spaces delimited by housing end walls 3. Each of these rooms is, in turn, divided into a working chamber 5 and an operating chamber 6 by means of a respective partition wall or diaphragm (membrane) unit 4, wherewith the working chambers 5 are located proximal to one another and the operating chambers 6 are located outwardly of associated diaphragm units 4. The working chambers 5 are provided with valve-controlled inlets and outlets for liquid working medium transported by the pump. In the case of the Fig. 1 illustration, these inlets and outlets have the form of openings 7, 8 in the working chamber walls 3, said openings coacting with check valves 9. Although these check valves may have the form of ball valves for instance, they are preferably in the form of flap valves as in the illustrated case. The working medium arrives at the pump in the arrowed direction through a conduit 10 which discharges into a space 11 located between the walls 3 and exits in a diametrically opposite space 12 which is also located between the walls 3, and continues out through an outlet conduit 13 in the arrowed direction. The diaphragm units 4 consist of a round, preferably rigid central part 14 and a peripheral part 15 which is preferably made of a soft, pliable material and which is connected to the pump housing 1 at its radially outer edge. Each of the diaphragm units 4 is in contact with its respective resilient spring device 16. Fig. 1 illustrates an embodiment in which this device has the form of a helical spring 16 situated in the liquid between the diaphragm units 4 and the inner working chambers walls 3. As shown at 18, the operating chambers 6 include openings which function as drive medium inlet and outlet means and which are connected to a net 20 ~ for a pressurised drive medium, via two-position three-path valves 21. In turn, the valves 21 are caused to take one or the other of said two positions by an electronic control unit 22. In the functional state shown in Fig. 1, the left-hand diaphragm unit 4 is shown just prior to its turning point at the end of its suction movement. The liquid working medium is sucked from the space 11 through the inlet 7 with the check valve 9 open, and into the left-hand working chamber 5, wherewith the check valve 9 of the outlet 8 of said working chamber is held closed by the pressure exerted by the liquid portion that is pressed by the right-hand diaphragm unit 4 from the right-hand working chamber 5 into the space 12, said right-hand diaphragm unit 4 being close to the end of its pressure stroke at this stage. The right-hand operating chamber 6 is connected to the drive medium net via the right- hand valve 21, whilst the left-hand operating chamber 6 is evacuated via the left-hand valve 21. For instance, when the left-hand operating chamber 6 of the Fig. 1 embodiment is pressurised via its associated three- path valve 21, which is controlled by the electronic control unit 22, liquid is forced out of the working chamber 5 and the spring 16 compressed at the same time. The pressure force from the operating chamber always exceeds the force of the spring. Air is evacuated from the right-hand operating chamber through the right-hand electropneumatic valve 21, which is controlled from the electronic unit 22. The spring 16 therewith expands and liquid is sucked into the right-hand liquid chamber through the check valve 7, 9. After a time lapse adapted with respect to the outflow, the control valves 21 switch over so as to pressurise the right-hand operating chamber and evacuate air from the left-hand operating chamber. The same sequence of events is repeated in the reverse order, and so on. In this way, liquid is forced from the pump continuously, air a pressure that is unaffected by the pressure from the inlet side of the pump. The electronic control unit 22 can be given the function of controlling the valves 21 so that both the left-hand and the right-hand operating chambers will be pressurised simultaneously for a very brief moment of time before the operating pressure is released from the operating chamber next in turn to be air-evacuated. This completely avoids pulsation of the flow at the outlet. It will be obvious that the two three-path valves 21 controll- ing the operating medium can be replaced with a two-position four-path or five-path valve. However, this may result in difficulties in obtaining overlap times of sufficiently long duration to achieve a non-pulsating flow, which is why the embodiment illustrated in Fig. 1 has two three-path valves. Fig. 2 shows an embodiment in which the resilient element 16 has been placed outwardly of the liquid chamber and also outwardly of the operating chamber. The spring abutment means 19 is mounted on the centre part 14 of the diaphragm 4 and extends through an airtight seal in the outer wall of the housing 2. Positioning of the spring 16 in the operating chamber would increase dead space when the operating medium is a gaseous medium. As will readily be understood, the operating medium may be a liquid medium, for instance oil. The function of the spring element may also be achieved with the aid of a piston-cylinder device that is pressurised at the same time as air is evacuated from a corresponding operating chamber. Fig. 3 illustrates the following features: In order to ensure that the pump will deliver a precise constant flow, its outlet conduit may be provided with a venturi-configured constriction 24 which is preferably provided with a diffuseT and in which the velocity of the liquid is maintained at such a high magnitude as to cause cavitation in the constriction. (A sharp-edge constriction will result in much higher energy losses.) Constant flows are achieved even if the resistance downstream of the constriction changes, provided that cavitation prevails. The pump outlet conduit may also be provided with a so-called manifold 23 which distributes the liquid to several, parallel conduits each having a cavitation-generatmg constriction so that a constant flow will be obtained in each conduit. This arrangement can be used in conjunction with metering liquid volumes into packages when valves 25 in each conduit open and close at precise, adjustable times, these opening and closing times being controlled from the electronic control unit 22 which also controls the pump. The discharged volumes can be repeated precisely, since said volume is held constant m this way. The volume will remain constant even if the pressure n the conduits is changed downstream of the cavitation-generatmg restriction, provided that cavitation is maintained in said conduits. The filling volume and the flow will also remain constant in the event of changes in the viscosity of the liquid. Liquid can also be sucked into the pump working chambers without the assistance of resilient elements or like spring means, simply by forcing liquid into the pump at an overpressure which is lower than the pressure imparted to the liquid in said working chambers by the operating chambers of said pump.

Claims: CLAIMS 1. A double-acting pump which includes two rooms that are each divided into an operating chamber (6) and a working chamber (5) by means of a moveable partition wall (4) in the form of a piston or a diaphragm (membrane) , wherein each of— said operating and working chambers is provided with a valve- controlled inlet and outlet (7, 9; 8, 9) for a gaseous drive medium or operating medium and a liquid working medium transported by the pump respectively, wherewith said partition walls lack all form of mechanical connection therebetween, characterised by an outlet conduit (23) which includes a cavitation-generating restriction (24); and further characterised in that the pump can be operated in a manner such as to maintain cavitation in the restriction (24) when working medium passes through said outlet conduit. 2. A pump according to Claim 1, characterised in that the conduit (23) includes a controllable valve (25) downstream of said restriction (24). 3. A pump according to Claim 2, characterised in that the valve (25) can be controlled to precisely repeat outfeed volumes through said conduit by holding the valve open for a selected period of time. 4. A pump according to any one of Claims 1-3, characterised in that the cavitation-generating restriction (24) has the form of a venturi and includes a diffuser. 5. A pump according to any one of Claims 1-4, characterised in that the conduits for feeding gas to the operating chambers have valves (21) which can be independently controlled from a control unit (22) ; and in that the control unit (22) is adapted to enable a selectable time overlap with respect to the open state of the valves of respective operating conduits to be applied, so as to minimise drops in working medium pressure when switching between working chambers. 6. A pump according to any one of Claims 1-5, characterised in that each partition wall (4) is supported by a restoring spring (16) located outwardly of the working chamber and — functioning to return the partition wall such as to draw working medium into the working chamber. 7. A pump according to Claim 6, characterised in that the partition wall (4) can be moved to a position in the close proximity of a fixed chamber wall, so as to minimise the dead space of the working chamber. 8. A pump according to any one of Claims 1-7, comprising at least two parallel outlet conduits each of which includes a cavitation-generating restriction and a controllable valve arranged downstream of said restriction; and in that the control unit (22) is adapted to control all of the valves arranged downstream of said constrictions.

Inventors: BAHRTON SVANTE, BAHRTON, SVANTE
Applicants: BAHRTON SVANTE, BAHRTON, SVANTE
Application year: 1999
Main classification: F04B43
IPC codes: F04B11, F04B43