The present invention relates to dispensers for dispensing low volumes of fluids and, more particularly for dispensing small volumes of suspensions.
A conventional syringe pump for dispensing small volumes of fluid is mounted vertically with a three port rotary valve at the top of a syringe chamber and a plunger at the bottom being drawn downwards to draw liquid into the syringe chamber from a reservoir. The aim of mounting a syringe vertically is that it should help to remove air from the syringe as air bubbles rise naturally towards the valve. The valve can be switched to connect the syringe chamber to either an input port or an output port. An inherent problem with the configuration of a three port valve is that there is a dead volume between the syringe chamber and the valve itself. This dead volume results in trapped air being unable to exit the syringe. When the plunger is at the top of its stroke, the air is pushed into the dead volume. However, when the syringe is refilled, because the refilling occurs through the same inlet, the trapped air is pushed back into the syringe ahead of the inflowing fluid. Thus, the configuration of such syringe pump dispensers results in air bubbles becoming trapped and only being persuaded to leave the syringe chamber by manually tapping the syringe. Air bubbles in the syringe can cause the dispensing performance to be reduced to a level at which dispensing reliability is not acceptable, as a result of the fact that the air is much more easily compressed than the liquid to be dispensed, in turn resulting in unacceptable volume variation.
A typical syringe dispenser having a three port valve configuration is shown in
Furthermore, it has been observed that, as a result of the vertical configuration of the syringe, if a suspension is to be dispensed there can be a considerable difference in concentration between the first volume dispensed and the last within a single syringe stoke as a result of the settling of the suspension towards the position of the syringe plunger.
According to the present invention there is therefore provided a dispensing assembly including a dispenser comprising:
a dispensing tip;
a syringe having a tube and a movable plunger,
two two-port rotary valves providing an inlet valve and an outlet valve, at the end of the tube opposite the plunger,
the inlet two-port rotary valve being connected in use to a reservoir of fluid to allow fluid to be drawn into the syringe from the reservoir, and the outlet two-port rotary valve being connected to the dispensing tip to allow fluid to be dispensed therefrom.
The syringe may be arranged to be disposed substantially horizontally resulting in the two two-port rotary valves being positioned one above the other and therefore the inlet valve is positioned below the outlet valve in use.
The syringe plunger may be removable and the end portion of the syringe with a larger cross sectional area. The syringe tube may be a glass tube.
A dispensing array may be formed comprising a plurality of dispensers wherein the dispensing tips and syringe plungers are configured to form substantially parallel arrays.
Such a dispensing array may further comprise an actuator configured to actuate the syringe plungers simultaneously.
The dispensing array may be cleaned and purged of air by the following steps:
lowering the array of dispensing tips into the gutter,
depressing the plunger to force the liquid out through the upper two-port rotary valve, forcing any trapped air bubbles into the upper two-port rotary valve and forcing the fluid through the tips such that it flows up around the tip end.
Preferably, the drawing in and dispensing of fluid is repeated, the first fluid being PBS and the second being a water and alcohol mix.
Furthermore according to the present invention there is provided a method of cleaning syringes in a dispensing array comprising the steps of:
drawing fluid through the lower two port valve until the syringe is full,
continuing to draw fluid forcing the plunger to be disconnected from the syringe tube and allowing fluid to flow out of the end of the tube and into the overflow zone.
An example of a dispenser according to the present invention will now be further described with reference to the accompanying drawings in which:
a-e shows the configuration and operation of a conventional three port valve syringe pump.
a-e shows the sequence of operation and configuration of valves in a dispenser according to the present invention.
a-e show the configuration and operation of an example of a dispenser 10 according to the present invention. The dispenser 10 comprises a syringe 11 with two two-port rotary valves 15 and 16. In use, the syringe 11 is disposed horizontally resulting in the inlet port 17 sloping upwards towards the syringe 11 and the outlet port 18 sloping upwards away from the syringe 11. The syringe 11 consists of a glass barrel 19 and a syringe plunger 12.
It is apparent from
A dispensing array can be formed from a plurality of dispensers 10 as shown in
Number | Date | Country | Kind |
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03232685.7 | Apr 2003 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP04/03964 | 4/15/2004 | WO | 10/3/2005 |