This application is related to and claims priority from U.S. Provisional patent application No. 60/532,307 filed Dec. 23, 2003. Application 60/532,307 is hereby incorporated by reference.
1. Field of the Invention
This invention relates generally to the field of precision fluid dispensing and more specifically to a fluid dispensing system the is prevents dripping and foaming.
2. Description of the Prior Art
Many applications in the field of bio-science and medicine require the precise dispensing of a quantity of fluid into a particular container. There is no tolerance for dripping. Also, some liquids tend to foam if dispensed too rapidly through a standard nozzle or through a tube with too small an inside diameter. For example, an application might require the precision dispensing of 125 ml of a particular liquid (like a salt solution) into a vessel holding exactly 125 ml. Usually such a fill needs to take place very rapidly (within a second or two). No liquid can be lost through dripping.
- SUMMARY OF THE INVENTION
What is badly needed is a system and method for making fast fluid dispenses into containers designed to contain a precise amount of fluid without dripping or foaming.
The present invention relates to a non-drip, anti-foaming fluid dispensing system that can contain a fluid pump that supplies a forward fluid pressure, a coupling tube (preferably of hydrophobic material) that is coupled to the pump for delivering fluid into a fluid container, and an elastomeric tip on the coupling tube that can contain at least one exit orifice. The exit orifice can generally respond in response to the forward fluid pressure and contract when the forward fluid pressure is removed. This contraction prevents air from entering the delivery tube and causing dripping.
DESCRIPTION OF THE FIGURES
The fluid pump can be a positive displacement linear pump or a peristaltic pump or any other type of fluid pump causing a forward pressure on a fluid. In particular, the tip can be a duck bill valve with one or more openings or orifices. The pump can optionally supply a back pressure or suck-back after a predetermined amount of fluid has been dispensed.
FIG. 1 shows a schematic of an embodiment of the present invention.
FIG. 2A shows a duck bill valve on the end of a TEFLON tube.
FIG. 2B shows a duck bill valve on the of a steel tube.
FIG. 3 shows various cut patterns that can be used with a nozzle.
FIG. 4. shows an embodiment of a nozzle with vertical exit slits.
- DESCRIPTION OF THE INVENTION
Several drawings and illustrations have been presented to aid in the understanding of the present invention. The scope of the present invention is not limited to the figures.
FIG. 1 shows a schematic of an embodiment of the present invention. A pump 1, which can be a positive linear displacement pump, a peristaltic pump, or other controllable pump drives a delivery tube 2 that ends in an end control device or nozzle 3. The unique characteristics of the entire system allow a precise amount of fluid to be dispensed without dripping or foaming in to a container 4.
FIGS. 2A and 2B show a tube with a duck bill valve 5 as a nozzle or tip. Here a tube of ½ inch ID or larger can be attached to a duck bill valve of the type sold commercially. The tube 2 shown in FIGS. 1 and 2 can be made of TEFLON. This material can be chosen to make the tube hydrophobic. While it is not critical that all tubes be of a hydrophobic material, much better results are generally achieved when hydrophobic materials are used.
The diameter of the tube usually must be chosen to match the required fill time against the volume of fluid being dispensed. For the example where a 125 ml container is to be filled with exactly 125 ml of fluid in 2 seconds or less, the tubing must have an ID of greater than ½ inch. The problem with large tubes such as this is that after the initial fill, residual fluid on the inside of the tube drips causing the fill volume to be exceeded. The surface tension on such large tubes is not sufficient to stop air from flowing up the tube, and the solution continuing to flow down the tube.
A small nozzle must generally be used on the end of the tube to stop this air flow and drip. An ideal nozzle is one made of an elastomeric material such as rubber or silicone with a small orifice 6. Such a material expands to expel the initial flow under forward pressure from the pump, but then contracts to prevent the entry of air and any subsequent drip. In addition, some pumps can be arranged to create a suck-back where the pump reverses direction and causes a negative pressure on the fluid. A positive displacement linear piston pump is particularly suited for this.
An ideal nozzle is a duck bill valve that can be purchased commercially. FIG. 2A shows such a valve 5 on the end of a TEFLON tube, while FIG. 2B shows such a valve on a steel tube. The duck bill opens when the flow is pumped forward and closes when pumping is stopped. The contraction of the rubber slit helps prevent any further flow that could result in a drip. Suck-back can also be used to assist in fluid stoppage and in duck bill closure. The duck bill reduces the apparent open area of the nozzle so that fluid surface tension is enough to block the air/fluid transfer up the larger diameter tube.
The duck bill nozzle 5 shown in FIGS. 2A and 2B opens for each dispense by an amount based on the fluid volume and the dispensing velocity. Using such a nozzle, it is possible to large tubes and deliver large quantities of fluid exactly. Using such a nozzle (or smaller versions of it) with smaller tubes allows systems that precisely deliver very small volumes. In fact, a single tube/nozzle combination can accurately deliver both very large and very small quantities without drip or foaming.
FIG. 2B shows a steel tube 7 with a duck bill nozzle. The tube can be any size including ½ stainless steel. A possible nozzle 5 is the Vernay VL4513-103 duck bill. This silicon duck bill can be configured either as a single cut or with multiple cuts as shown in FIG. 3.
An alternative embodiment of the present invention is shown in FIG. 4. Here a nozzle head 8 can be made from a part of the tubing 2 equipped with cuts or slits 9 backed by a screen. It is preferred to use several axial cuts around the circumference as shown in FIG. 4 to create a side-port nozzle. Each cut can be backed by filter screens or any other device that will cause a slight back pressure. The side ports 9 provide increased fluid exit area that slows the output stream velocity. The side ports can be made vertical to also aid in keeping the exit velocity low and allow for a more gradual pressure drop from the top to the bottom of each slight. This results in a slightly downward flow angle out of the slot. In generally, the screen prevents dripping. A preferred screen material is around 75 to 105 micron polypropylene screen. Each screen provides a slight amount of back pressure so that fluid in the relatively short nozzle does not drip. It is necessary to keep the fluid column behind the screen from becoming too large or the static pressure behind the screen can still cause dripping.
A duck bill can be combined with the nozzle shown in FIG. 4. This arrangement allows the length of the fluid column to be increased above the duck bill. The duck bill provides an additional pressure to the fluid in a tube or reservoir above the side ports. In addition to a duck bill, multiple screens can be used (not necessarily of the same size) to provide additional pressure drop.
Several illustrations and descriptions have been provided to aid in understanding of the present invention. One skilled in the art will realize that many changes and variations are possible. These changes and variations are within the scope of the present invention.