1 ACTIVE CHECK VALVES IN DIAPHRAGM PUMP WITH SOLENOID DRIVE Field of the Invention This invention relates generally to diaphragm pumps and more particularly to a diaphragm pump, in particular for use as a detergent dosage pump comprising a pump housing, a working fluid chamber, at least one intake, at least one outlet, at least one diaphragm defining a wall of the working fluid chamber and reciprocatingly moveable, diaphragm driving means reciprocating said diaphragm and at least one check valve including a spring biassed valve body for controlling ingress of the fluid into the working fluid chamber. Background of the Invention Diaphragm and piston pumps are used to supply metered quantities of liquids with various properties. Depending on the field of application, the pump behaviour is subject to various requirements in order to ensure that the delivered quantity of the metered medium is as precise as possible and remains constant for as long as possible. Diaphragm pumps are common industrial pumps that use positive displacement to move liquids. These devices typically include a single diaphragm and chamber, as well as discharge check valves to prevent back-flow. Pistons are either coupled to the diaphragm or used to force hydraulic oil to drive the diaphragm. Diaphragm pumps are normally highly reliable because they do not include internal parts that rub against each other. Diaphragm pumps can handle a range of media that includes abrasive materials, acids, chemicals, or the like since the drive means is normally completely separated from hydraulic part of the pump. Since diaphragm pumps can deliver small volumes of fluid with the maximum discharge, they are especially suitable as dosage pumps. Another reason for using diaphragm pumps as dosage pumps is that these pumps have two strokes, i.e. an aspiration stroke in which the medium is aspirated from a reservoir and a compression stroke or delivery stroke where delivery of the metered medium e.g. into a metered line takes place. Diaphragm pumps known in the art for instance comprise suction check valves as well as discharge check valve to prevent back flow. These check valves are usually spring biassed and are opened and closed by the pressure difference of the medium to be pumped.
2 Especially when pumping highly concentrated detergents, known diaphragm pumps often fail because of crystallization and particles in the check valves. The valve bodies of the check valves are normally held in sealing relationship to the valve seat by means of a compression spring. The check valves are normally only operated by the differential pressure of the fluid. This compression spring exerts a comparatively low spring force in order to ensure that the check valve can easily be opened. This applies in particular to the check valve on the suction side of the pump. The diaphragm pumps known in the art suffer from the disadvantage that sometimes only small amounts of dirt prevent the valve body to be located properly in the valve seat so as to guarantee function of the check valve. This results in complete failure of the pump. Accordingly, it is desirable to provide a diaphragm pump which is unsusceptible to small particles of dirt and crystallization in the metered medium. Object of the Invention It is the object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages or to provide a useful alternative. Summary of the Invention According to one aspect of the invention, there is disclosed herein a diaphragm pump for use as a detergent dosage pump comprising: a pump housing, a working fluid chamber, at least one intake, at least one outlet, one diaphragm defining a wall of the working fluid chamber and reciprocatingly movable, diaphragm driving means for reciprocating said diaphragm and at least one check valve including a spring biassed valve body for controlling ingress of the fluid into the working fluid chamber, comprising additional means for mechanically pushing the valve body into its valve seat, wherein said additional means for pushing the valve body into its associated valve seat is driven by said diaphragm driving means. Preferably, the diaphragm pump comprises first and second check valves, the second check valve opening in the opposite direction than the first check valve.
3 Preferably, the paths of travel of said first and second valve bodies of said first and second check valves, respectively, intersect each other such that the second valve body pushes said first valve body into its associated first valve seat when said second valve body is lifted into its open position. Preferably, said second valve body constantly holds said first valve body in the closed position when the pump is not operated. Preferably, the second valve body is coupled to the diaphragm driving means and is reciprocated synchronously with the stroke of the diaphragm. Preferably, said diaphragm forms part of the second check valve. Preferably, the second valve body is yieldingly held in sealing relationship against the diaphragm, thereby closing an aperture in the diaphragm at least during a first stroke of the diaphragm and establishing fluid communication between said working fluid chamber and said outlet during a second stroke of the diaphragm. Preferably, the second valve body and said diaphragm are spring biassed against each other so that pressure built up during the compression stroke of the diaphragm is determined by the elastic resilience of the spring. Preferably, said diaphragm drive means is a solenoid drive. Brief Description of the Drawings A preferred embodiment of the present invention will now be described, by way of an example only, with reference to the accompanying drawings wherein: Figure 1 shows a cross-sectional view of an exemplary diaphragm pump consistent with an embodiment of the present invention during an aspiration stroke; Figure 2 shows the diaphragm pump according to figure 1 during a compression stroke; and Figure 3 shows the diaphragm pump according to the embodiment of the invention at the end of the compression stroke.
4 Description of Preferred Embodiment With reference now to the drawings, figure 1 shows an exemplary embodiment of the diaphragm pump 1 consistent with the present invention. The diaphragm pump 1 comprises a pump housing 2 with an intake 3 and an outlet 4, the intake 3 being the suction port and the outlet 4 being the pressure port. Within the pump housing 2, a pump chamber 5a, 5b is defined. The pump chamber 5a, 5b houses a main diaphragm 6 which divides the pump chamber into first and second compartments 5a, 5b. The intake 3 communicates with the first compartment 5a of the pump chamber defining the working fluid chamber, the outlet 4 communicating with the second compartment 5b of the working fluid chamber. The diaphragm pump 1 according to the embodiment of the invention comprises first and second check valves 7 and 8, the first check valve 7 controlling the intake 3, the second check valve 8 being arranged in series with the first check valve 7, as will be explained hereinafter in greater detail. The first check valve 7 comprises a mushroom-like first valve body 7a which is spring biassed against the first valve seat 7b, by means of a first compression 5 Page 5 left blank intentionally WO 2008/058558 PCT/EP2006/010969 6 spring 7c. The first valve body 7a is sealed against the first valve seat 7b by means of a sealing ring 7d, preferably by means of a 0-ring sealing. The diaphragm 6 is reciprocatingly driven within the pump housing 2 by a solenoid 5 drive only the armature 9 of which is shown in the drawings. The armature 9 of the solenoid drive is coupled to a stem 10 of a second mushroom-like valve body 8a. The stem 10a of the second valve body 8a penetrates an aperture 11 in the centre of the main diaphragm 6. In the state shown in figure 1, the second valve body 8a is held spring biassed in sealing relationship against the main diaphragm 10 6, thereby sealingly closing the aperture 11. For that purpose, a second compression spring 8c which rests on the base 12 of the stem 10 forces the main diaphragm 6 against the sealing surface 13 of the second valve body 8a. For sealing against the corresponding sealing surface 13 of the second valve body 8a, the surface of the main diaphragm forming the inner wall of the first compartment 1s 5a is provided with an annular sealing rib 14. At this side of the main diaphragm 6 facing the second compartment 5b of the pump chamber, a rigid holding member 15 with a peripheral collar 16 for abutment of the second compression spring 8c is provided. 20 As this can easily be understood from the drawings, the main diaphragm 6 with its central aperture 11 does form part of the second check valve 8. The armature 9 of the solenoid drive is sealed against the second compartment 5b of the pump chamber by an auxiliary diaphragm 17 which has only sealing function as it 25 synchronously reciprocates with the main diaphragm on operation of the diaphragm pump 1 as will be explained hereinafter. As can be taken from the drawings, the stem 10 of the second valve body 8a penetrates the holding member 15 and the aperture 11 of the main diaphragm 6. 30 Between the stem 10 and the aperture 11 and between the stem 10 and an aperture 18 in the holding member 15, the aperture 18 being in alignment with the aperture 11, an annular gap 19 is formed which establishes fluid communication between the first and second compartments 5a and 5b when the second check valve 8 opens.
WO 2008/058558 PCT/EP2006/010969 7 The function of the diaphragm pump 1 will now be explained with reference to the accompanying drawings. 5 As already explained above, figure 1 shows the diaphragm pump according to the invention during the aspiration stroke. During the aspiration stroke, the armature 9 of the solenoid drive is retracted (i.e. moved to the right in figure 1). By a reciprocating movement of the armature 9, which is coupled to the stem 10, also the main diaphragm 6 and the auxiliary diaphragm 17 are moved synchronously io with the armature 9. The volume of the first compartment 5a increases so that suction is applied to the intake 3. This causes the first valve body 7a to lift from its associated first valve seat 7b against the pressure of the first compression spring 7c. The first compartment 5a of the pump chamber is now in fluid communication with the intake 3 allowing ingress of the medium to be pumped into the first 15 compartment 5a. The fluid may enter the first compartment 5a through an annular gap 20 between the first valve body 7a and the first valve seat 7b. The compression force exerted by the first compression spring 7c is comparatively low so that only a little pressure difference between the first 20 compartment 5a and the intake 3 is sufficient to allow the medium to be pumped to flow into the compartment 5a. Turning now to figure 2, the diaphragm pump 1 according to the invention is shown during the compression stroke. 25 As has been explained before, operation of the solenoid drive causes the armature 9 connected to the stem 10 of the second valve body 8b to reciprocate within the pump housing. The pumping action is thereby mainly performed by the main diaphragm 6. During the compression stroke, the volume of the first 30 compartment 5a will be decreased, which causes pressure built up in the compartment 5a. The spring force of the first compression spring 7c causes the first valve body 7a to move into its associated valve seat 7b. This movement is supported by the rising pressure within the compartment 5a. Moreover, the rising pressure within the first compartment 5a acts on the main diaphragm to the effect WO 2008/058558 PCT/EP2006/010969 8 that the main diaphragm 6 is pushed against the spring force of the second compression spring 8c which is compared to the first compression spring 7c relatively strong. This pressure built up within the first compartment 5a causes a relative movement between the second valve body 8a and the main diaphragm 6 5 to the effect that the second valve body 8a is lifted up from its associated second valve seat formed by the main diaphragm 6. The fluid which was trapped in the first compartment 5a is now allowed to enter the second compartment 5b via annular gap 19. io As can be seen more clearly from figure 3, the first and second valve body 7a and 8a are arranged such that their paths of travel intersect. That is to say that the second valve body 8a at the end of the compression stroke pushes the first valve body 7a into its closed position. For instance in the event that the first valve body should be jammed in its open position due to particles or crystals gathering 15 between the sealing ring 7d and the associated sealing surface of the valve body, the second valve body 8a would push the first valve body 7a by force into its closed position. Figure 3 shows the initial situation of the pump when the solenoid drive is not 20 operated. In another words, in this situation the first valve body 7a is constantly held in its closed position by the second valve body 8a, so that the first and second check valves function like a security shut-off valve. It is to be understood that during the subsequent stroke of the diaphragm pump 1, 25 the volume of the second compartment 5b would decrease so that the fluid would move into the outlet 4 (pressure port). It is also clear from the above explanation that the second valve body 8a forms part of the diaphragm drive mechanism as it reciprocates the main diaphragm 6 30 within the pump housing 2. The embodiment that has been described herein has been described by way of illustration but not of limitation. It is obvious that many other embodiments, which WO 2008/058558 PCT/EP2006/010969 9 will be readily apparent to those skilled in the art, may be made without departing materially from the spirit and scope of the invention.
WO 2008/058558 PCT/EP2006/010969 10 Reference numerals: 1 diaphragm pump 5 2 pump housing 3 intake 4 outlet 5a, 5b first and second compartments of the pump chamber 6 main diaphragm 10 7 first check valve 7a first valve body 7b first valve seat 7c first compression spring 7d sealing ring 15 8 second check valve 8a second valve body 8c second compression spring 9 armature 10 stem 20 11 aperture 12 base of stem 13 sealing surface 14 sealing rib 15 holding member 25 16 collar 17 auxiliary diaphragm 18 aperture 19 annular gap 20 annular gap 30