Measuring and testing – Volume or rate of flow – Expansible chamber
Patent
1994-08-22
1996-11-26
Raevis, Robert
Measuring and testing
Volume or rate of flow
Expansible chamber
F04B 3502
Patent
active
055787525
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process and to an arrangement for determining the conveyance amount or of the conveyance flow of conveyance material transported by means of at least one conveyance cylinder through a conveyance line, in which the number of pressure strokes or the stroke frequency as well as the conveyance volume of the individual pressure strokes are determined and used for the computational determination of the conveyance amount or of the conveyance flow.
By thick substances there are meant in the following solid-liquid mixtures with a more or less high solid substance constituent, as they occur, for example, in partially drained settling sludges, in mixtures of coal dust and fluid or in concrete.
It is a known practice to determine the volume flow of a piston pump by multiplying the time frequency of the strokes (stroke frequency) n by the content of the delivery cylinder V.sub.z :
Here it is not yet taken into account that the conveyance material, by reason of air adsorption and air inclusions, does not fill the entire cylinder volume and must first be compressed to the conveyance pressure before the conveyance material column in the delivery line is set in motion. This effect can be taken into account (1) by adoption of a further factor r<1 defining the degree of filling:
Ordinarily the filling degree r is assumed as a constant factor. There it is not taken into account that the filling degree can be affected by the fact that the absolute pressure in the delivery line is dependent on interfering magnitudes, such as length, nature, shape and cross section, as well as the viscosity of the conveyance material and that the adsorbed air amount can vary in wide limits according to consistency and pre-pressing of the conveyance material adsorbed in the suction stroke from a filling funnel. The assumption of a constant degree of filling leads, therefore frequently to non-tolerable errors in the determination of the volume flow of thick substances.
Underlying the invention is the problem of developing a process and arrangement for the conveyance-amount measurement of thick substances, by which there can be taken into account a variable degree of filling of the delivery cylinder, regardless of its cause.
The invention proceeds from the insight that from the flow or pressure course in the delivery line conclusions can be drawn as to how long the compression time and how long the effective conveyance time continue. From the relation between the effective delivery time and the total stroke time, possibly under additional consideration of the down times, it is possible to determine the filling degree of the conveying cylinder for each stroke, and, namely, independently of the causes that can lead to a variable degree of filling.
Correspondingly, for the solution of the invention it is proposed that there be determined in each pressure stroke the time point of the flow beginning t.sub.a and of the flow ending t.sub.e of the conveyance material in the delivery line and from this the filling degree r of the delivery (conveyance) cylinder for the determination of the delivery volume per pressure stroke, Advantageously there is measured furthermore the piston path h.sub.1 of the conveyance cylinder measured between the time points t.sub.a and t.sub.e and the filling degree of the conveying cylinder from the relation
For the case in which the piston velocity during the conveying stroke is approximately equal, the filling degree of the conveying cylinder in each pressure stroke can be determined from the relation stroke time of the pressure stroke.
For the achievement of as accurate as possible measurement values, according to an advantageous execution of the invention, the flow beginning t.sub.a and/or the flow ending t.sub.e should be measured in the conveyance material in the vicinity of the end of the delivery line away from the conveyance cylinder.
The flow beginning t.sub.a and/or the flow ending t.sub.e can be determined, for example, by means of a measuring body arranged in the delivery line, flowed-a
REFERENCES:
patent: 5106272 (1992-04-01), Oakley et al.
Rockstroh Axel
Schlecht Karl
Putzmeister-Werk Maschinenfabrik GmbH
Raevis Robert
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