Piston diaphragm pump for the delivery of liquids in doses

A piston diaphragm pump operable for delivering doses of liquids such as surfactants, or wetting agents, for example, includes a pump piston that is reciprocally moveable within a pump tube that encloses a pump pressure chamber. The pump piston is electromagnetically driven against the force of a return spring by a magnetic coil that surrounds the pump tube. In addition, a pump diaphragm is rigidly clamped about an inner circumference to a portion of an upper end of the pump piston. The outer circumference of the pump diaphragm is rigidly clamped about its periphery between upper and middle housing sections. One side of the diaphragm faces a suction chamber, and the other side faces a pressure chamber. A longitudinal bore, that encloses a pump piston provided with a piston valve, extends centrally through the pump diaphragm and links the pressure chamber to the suction chamber. In order to obtain the same pump capacity with reduced pump lifts, without requiring a specially sealed guidance of the pump piston in the pump tube, a pressure chamber located on the side of the pump diaphragm opposite to the suction chamber is designed as an additional pump pressure chamber that is constantly connected to the piston longitudinal bore that leads to the pump tube pressure chamber by cross-channels arranged in the pump piston behind the piston valve.

BACKGROUND 
1. Field of the Invention 
This invention relates generally to a piston diaphragm pump for the 
delivery of liquids, and more particularly surfactants, wetting agents or 
the like, in doses. 
2. Discussion of Related Art 
A piston diaphragm pump of the above type is known from DE-OS 28 31 437. In 
this known piston diaphragm pump, the particular liquid is drawn into the 
suction chamber through the flexible diaphragm. The liquid to be dosed is 
displaced from the pressure chamber solely by the pump piston which is 
fixedly connected to the diaphragm and which, to this end, is sealingly 
guided in the pump tube surrounding the pressure chamber. Not only does 
this require corresponding sealing, it can also lead to seizing of the 
pump piston after prolonged breaks in operation through drying of the 
liquid to be dosed. Since, in addition, the pump piston has a much smaller 
effective cross-section than the pump diaphragm and since both operate 
with the same lift because they are fixedly connected at both ends, less 
liquid is always displaced from the pump pressure chamber during the 
particular delivery stroke of the pump than is taken into the suction 
chamber through the diaphragm. The result of this is that the suction 
chamber has to be connected to the liquid reservoir by a special liquid 
line designed to be shut off by a non-return valve to enable the quantity 
of liquid delivered in excess into the suction chamber to be returned to 
the reservoir during the return stroke of the pump membrane. Another 
disadvantage of the known pump is that, because of its comparatively small 
delivery cross-section, the pump piston and, hence, the diaphragm have to 
complete comparatively large strokes to enable a certain volume of liquid 
to be delivered in dosed form. 
3. Summary of the Invention 
Accordingly, the problem addressed by the present invention is to improve 
and complete a piston diaphragm pump of the type mentioned above so that 
it does not have any of the disadvantages mentioned above and, instead, 
operates with shorter pump strokes for delivering comparable quantities of 
liquid, without requiring sealed guiding of the pump piston in the pump 
tube, thereby preventing seizing of the piston after prolonged breaks in 
operation. The modified piston diaphragm pump of the invention includes a 
working chamber lying on the side of the pump diaphragm remote from the 
suction chamber serving as an additional pump pressure chamber which is 
permanently connected to a longitudinal bore through a piston leading to 
the pump tube pressure chamber by transverse channels present in the pump 
piston behind the piston valve. This ensures that the pumping movements of 
the diaphragm also become fully effective on the pressure chamber side 
with the pump piston serving as a drive element for the pump diaphragm 
designed to be actuated by an electromagnetic coil with a return spring 
acting thereon. Accordingly, the piston does not have to be specially 
sealed in the pump tube as in the prior art, but instead may be guided 
therein with greater tolerances, so that there is virtually no danger of 
seizing through liquid which has dried out after prolonged breaks in 
operation. Since, in addition, the liquid to be displaced from the 
pressure chamber via the pump diaphragm corresponds in volume to the 
particular quantity of liquid drawn into the suction chamber, there is no 
need for a special return pipe from the suction chamber to the liquid 
reservoir, as in the prior art. Comparable delivery volumes of liquid can 
be obtained with relatively small delivery strokes of the diaphragm and, 
hence, the pump piston which in turn leads--in the same way as its 
unsealed guiding in the pump tube--to less heating and to reduced friction 
losses relative to the prior pump. 
The piston valve is preferably provided in the immediate vicinity of that 
end of the pump piston which passes through the pump diaphragm, while the 
transverse channels are preferably provided immediately behind that end of 
the pump piston. This provides for a particularly compact construction of 
that part of the pump situated on the pressure chamber side, particularly 
if, in addition, the pump housing is tapered in the manner of a funnel 
towards the pump tube in its region surrounding the transverse channels 
and the diaphragm pressure chamber. 
In another embodiment of the invention, a pump piston stop provided with a 
seal is advantageously provided in that part of the housing which 
surrounds the pump suction chamber, acting as a safety valve separating 
the pressure chamber from the suction chamber in the stop position of the 
pump piston brought about by the return spring. In this manner, unwanted 
flow of the delivery medium from the pressure chamber into the suction 
chamber and vice versa is effectively prevented, even after prolonged 
periods of stoppage of the pump when the piston valve may possibly be 
prevented from closing by dry, crystallized liquid residues. 
Finally, in another embodiment of the invention, a rectifier which converts 
the current supplying the magnetic coil into pulsating direct current is 
built into the current lead and is preferably integrated into that part of 
the pump housing which surrounds the electromagnetic coil. This provides 
for quiet, current-saving driving of the diaphragm pump through the pump 
piston acting as an armature. The switching on and off of the 
electromagnetic diaphragm drive is generally controlled by a pulse 
generator which is installed in the consumer pipe or container to be 
charged with the liquid to be dosed, and which responds to the particular 
demand for that liquid.

The piston diaphragm pump illustrated comprises a multi-compartment pump 
housing 1 which is divided by the pump diaphragm 2 peripherally clamped in 
the housing into an upper intake zone 1' and a lower pressure zone 1" 
which also accommodates the pump drive. 
In the suction zone 1', the suction chamber 4 is situated between the upper 
part 3 of the housing and the diaphragm 2. The suction chamber 4 is 
designed to be connected to a reservoir (not shown) for the liquid to be 
dosed via the suction valve--consisting of the spring 5, the valve ball 6 
and the associated seal 7--and the connecting socket 8 and a feed line to 
be mounted thereon. In addition, the upper part 3 of the housing 
accommodates the stroke adjustment screw 9 mounted for displacement 
therein. The stroke adjustment screw 9 is sealingly guided with respect to 
the upper part 3 of the housing by the O-ring 10. In addition, the stroke 
adjustment screw 9 comprises a front end 9' of stepped diameter which acts 
both as a pump piston stop in conjunction with the O-ring 11 embedded 
therein and as a safety valve in conjunction with the facing end of the 
piston pump, as will be described in more detail hereinafter. 
The pump tube 13 surrounding the pump pressure chamber 12 is provided in 
the lower pump zone 1", being fixedly connected at its upper end to the 
middle part 14 of the housing. The middle part 14 of the housing is 
tapered in the manner of a funnel towards the pump tube 13. Together with 
the pump diaphragm 2, the middle part 14 surrounds an additional pump 
pressure chamber 12' which is permanently connected to the above-mentioned 
pressure chamber 12 surrounded by the tube 13. 
The pump piston 15 consisting of soft iron is guided for displacement in 
the pump tube 13 without any sealing. At its upper end 15', the pump 
piston 15 is fixedly connected to the diaphragm 2 through which it 
centrally passes. The fixed connection is established by the bushing 16 
which is designed to be screwed onto the end 15' of the pump piston 15, 
projecting beyond it, and which, in the illustrated inoperative position 
of the pump piston 15, surrounds the front end 9' and the O-ring seal 11 
of the stroke adjustment screw 9 present thereon and, thereby acting as a 
safety valve. 
The pump piston 15 is under the effect of the return spring 17 which seeks 
to keep it in the inoperative position illustrated. The piston 15 is 
additionally provided with a longitudinal bore 18 which extends over its 
entire length and at the upper end of which the piston valve consisting of 
the valve ball 19 and the return spring 20 is installed in the immediate 
vicinity of the diaphragm 2. The abutment 21 built into the longitudinal 
bore 18 of the piston 15 acts as a support for the two springs 17 and 20. 
The transverse channels 22 through which the diaphragm pressure chamber 
12' is permanently connected to the longitudinal bore 18, and hence to the 
pressure chamber 12 are machined into the piston immediately below the 
piston 15 valve ball 19. Accordingly, the chambers 12 and 12' form a 
common pump pressure chamber of comparatively large volume. 
The pump pressure chamber 12 is closed underneath by the closure element 23 
which is fixedly connected to the pump tube 13, and which accommodates the 
pump pressure valve consisting of the spring 24 and the pressure valve 
ball 25, the pump pressure valve enabling the pressure line 26 leading to 
the consumer in the closure element 23 to be shut off and opened. 
Arranged directly around the pump tube 13 is the magnetic coil 27 which, 
after corresponding excitation with current, enables the pump piston 15 to 
be driven against the force of the return spring 17 acting thereon for 
delivery of the particular medium. The magnetic coil 27 is surrounded by 
the plastic jacket 28 which in turn is surrounded by the part 29 of the 
housing on the outside of which the two current or voltage terminals 30 
are provided. A rectifier 31 as schematically shown, is accommodated in 
the housing 29 and electrically connected between a current terminal 30 
and a current lead 32 to the magnetic coil 27, for converting the current 
supplied to the magnetic coil 27 into pulsating direct current. 
If the magnetic coil 27 is excited with current by a pulse generator (not 
shown) which is present in the vicinity of the consumer and which monitors 
the demand for the liquid to be dosed, the pump piston 15 and the 
diaphragm 2 fixedly connected thereto are moved downwards in the drawing 
so that, on the one hand, liquid is delivered from the common pressure 
chamber 12,12' into the consumer line through the pressure valve ball 25, 
while the suction chamber 4 is refilled with the corresponding quantity of 
liquid to be dosed through the diaphragm 2 via the suction valve 6 which 
then opens. The piston valve ball 19 is in the closed position during the 
above-described movement of the diaphragm 2 and piston 15. When the 
electromagnetic drive is switched off after sufficient liquid has been 
dosed, the pump piston 15 and the diaphragm 2 fixedly connected thereto 
return to their inoperative positions shown in the drawing. During this 
return movement, the suction valve ball 6 and the pressure valve ball 25 
are in closed positions, whereas the piston valve ball 19 is moved to an 
opened position so that liquid is able to pass from the suction chamber 4 
into the common pressure chamber 12,12'. Towards the end of this return 
movement under the effect of the spring 17, the fixing bushing 16 screwed 
onto the end 15' of the piston pump 15 travels beyond the O-ring 11 of the 
stop end 9' present on the stroke adjustment screw 9. This establishes an 
additional, effective seal between the suction chamber 4 and the pressure 
chambers 12 and 12', which is particularly important should the piston 
valve balls 19 and also the other two valve balls 6 and 25 no longer 
effectively more to closed positions, for example through the presence of 
crystallized liquid residues.