Pumps – Motor driven – Fluid motor
Patent
1998-07-06
2000-10-10
Freay, Charles G.
Pumps
Motor driven
Fluid motor
417521, 4175551, F04B 1700
Patent
active
061295264
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to improvements to metering pumps of the type comprising: translational motion in a drive chamber having an inlet and an outlet for main liquid, and means for controlling the movements of the piston under the action of the main liquid, connected to the drive chamber and having an inlet for auxiliary liquid, the metering piston being driven in reciprocating translational motion by the drive piston and being equipped with suction/delivery means, metering compartment is proportional or substantially proportional to the flow of main liquid.
BACKGROUND OF THE INVENTION
Metering pumps of this type are known, particularly from EP-A-0,255,791 or from FR-B-2,707,350. These pumps are especially useful for injecting an additive, consisting of the auxiliary liquid, into the main liquid which serves at the same time as drive fluid. Such metering pumps have many uses. They make it possible, for example, to carry out a metering of chlorine (auxiliary liquid) into water (main liquid) or a metering of a drug for cattle into the water of a drinking trough or else to prepare beverages based on water (main liquid) and concentrate (fruit juice concentrate or tea concentrate) forming the auxiliary liquid.
For some uses, such as the metering of chlorine into water or of drugs for cattle into water, the proportion of auxiliary product to be added to the main liquid is low; it is relatively difficult to maintain this proportion exactly, particularly on account of leaks, albeit very slights, when a conventional seal is used, through which a rod slides, for example a connecting rod between the drive piston and the metering piston; such a seal does not make it possible to prevent tiny quantities of liquid on either side of the seal from being carried along due to capillary action.
Metering accuracy is therefore impaired by these, albeit very small, leaks.
In addition to the metering inaccuracy, these leaks eventually lead to various other problems, for example to scale being deposited on the rod, when chlorine is metered into hard water, or to the growth of bacteria, when a sweetened concentrated beverage (auxiliary liquid) is metered into water (main liquid).
These problems only become more serious during operation, since friction causes irreparable wear of the seal, which is accompanied by an increase in the passage of liquid on either side of the seal.
SUMMARY OF THE INVENTION
The object of the invention is, to provide a metering pump of the type defined above, which no longer has the abovementioned disadvantages.
According to the invention, a metering pump of the type defined above, in which the metering chamber comprises its own outlet orifice separated from that of the drive chamber, is characterized in that the metering chamber is isolated from the drive chamber by an extendable tubular element, one end of which is sealingly fastened to a part fixed to the drive chamber and the other end of which is sealingly fastened to the metering piston.
Preferably, the extendable tubular element is produced from a material suitable for withstanding the variations in pressure of the auxiliary liquid and main liquid in the metering and drive chambers, so as to prevent any variation in the volume of the metering chamber other than that attributable to the displacement of the metering piston. Metering accuracy is thus ensured.
Such material for the tubular element consists especially of a suitable plastic, in particular polypropylene.
The extendable tubular element is advantageously formed by a kind of sheath, of which the end fastened to the drive chamber comprises an outer peripheral bead sealingly clamped between a bearing surface of a tubular part fixed to the drive chamber and a clamping element fastened to this part, especially by screwing. The other end of the sheath comprises an inner radial collar, through which passes a central hole, this collar being blocked against the metering piston by clamping between one end of this metering piston and a bearing element fixed to a driving rod
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Evora Robert Z.
Freay Charles G.
Societe DSA
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