Measuring and testing – Volume or rate of flow
Reexamination Certificate
1999-03-31
2001-05-29
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
C073S239000, C417S063000
Reexamination Certificate
active
06237423
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a device for determining the delivery rate or the mass flow rate of a material conveyed through a delivery conduit by a high-density liquid piston pump comprising at least a conveyance cylinder and a conveyance piston. During a filling stroke (suction stroke) the conveyance cylinder is filled with a material from a material providing container, and during a pressure stroke, with displacement, the material is emptied into the delivery conduit.
2. Description of the Related Art
Principally with high-density pumps, which are incorporated into a process engineering or engineering chemistry process, there is a requirement to measure and document the mass flow rate and to use this measured value in certain cases as the control value or set value for plant units or equipment situated upstream or downstream or and to incorporate this in a feed back system. This is the case for example in the conveyance of sewage sludge for the incineration of sewage sludge.
Volumetric flow meters in the form of cams-counters for Newtonian fluids are known, which are built into the delivery conduit as “motor” and in which a volume wheel is caused to rotate as a consequence of the pumping process. The revolutions of the volume wheel are added via an impulse disk and converted into volumetric flow in an evaluation unit on the basis of the known displacement volume.
Further, it is known in the case of two-cylinder high-density fluid pumps, to derive the delivery flow rate of the high-density liquid pump having a defined displacement volume from the stroke count. In this measurement method, the amount of filling of the high-density liquid pump must be estimated. For this reason the result can strongly fluctuate on the basis of a changing consistency of the high-density fluid. In order to avoid this problem, it was proposed (DE-A-40 35 515) to determine the amount of filling of the cylinder during each stroke with the help of the most diverse indicators. This method has also been found to be too imprecise for many applications, since for the determination of the mass flow rate in interest it is necessary additionally to determine the density of the material, which causes great fluctuations depending upon the consistency of the high-density or thick stock.
SUMMARY OF THE INVENTION
Beginning therewith it is the task of the invention to develop a device and a process for determining the delivery rate or the mass flow rate of the type described above, with which a precise measurement is possible even during fluctuations in the amount of filling of the conveyance cylinder and over a wide ranging variable consistency of the conveyed material.
The inventive solution, in regard to the process aspect, is based on the idea or concept, that the conveyance cylinder is weighed prior to the carrying out of each fill stroke and prior to the carrying out of each pressure stroke and from the difference of the weighed value the respective fill amount is determined, and that the cycle time of each of the stroke cycles is measured, and that the mathematical computation of the delivery rate or the mass flow rate is calculated taking into consideration the measured fill amounts.
In order to make this possible it is proposed, with regard to the construction aspect, that the conveyance cylinder is provided in a housing with radial and axial slack and is suspended from at least one weighing cell provided secured to the housing. The weighing cell makes possible principally in the turn-around phase of the conveyance piston prior to the carrying out of the filling stroke, and prior to the carrying out of the pressure stroke, an exact mass determination of the empty and the full conveyance cylinder inclusive of conveyance piston, so that respectively by determination of the difference the fill amount can be arrived at.
For avoiding the forces which disturb the measurement precision it is proposed, according to a preferred embodiment of the invention, that at least the part of the conveyance piston guided within the conveyance cylinder is suspended relative to the housing, with radial slack. This can be achieved by suspending the conveyance piston preferably Cardanically from its piston rod with radial slack and/or by elastically suspending the conveyance piston or its piston rod with respect to the housing.
It is envisioned in accordance with a further preferred embodiment of the invention that the housing is formed or designed as a round tube or polygonal tube which surrounds the conveyance cylinder and that on the upper side of the housing two weighing cells are provided in axial separation from each other. The weighing cells are therein advantageously provided on a housing-fixed bearing platform and comprise a spring body armed with a stress or strain measuring strip, while the conveyance cylinder is suspended from the spring body via a carrier rod which extends radially through an opening or aperture in the wall of the housing. The spring body can be formed, for example as a transverse beam, a double transverse beam or shear beam. The aperture through the wall should, for avoidance of an accumulation of dirt which would influence the measurements, be sealed by a gland seal inserted under tension between the rod and the housing wall.
In order to keep the frictional forces occurring during the weighing process as small as possible, it is preferred, when the conveyance cylinder on its charge or in-feed end side is radially slideably supported by a metallic slide ring which is axially elastically supported on the housing. For the same reason the conveyance cylinder should be mounted in the housing with radial slack via an elastic yieldable or deformable quad-ring seal. A further improvement in this respect is thereby achieved, when the conveyance cylinder with its drive side end lies with axial slack radially slideably against an abutment ring, and in the area of its drive side end extends through a housing fixed guide jacket with radial slack.
In a two cylinder high density material pump two conveyance cylinders are preferably provided suspended from weighing cells at the housing with the cylinders provided in a housing with radial and axial slack, of which the conveyance pistons are driven in phase opposition or push pull manner by hydraulic means.
REFERENCES:
patent: 4898217 (1990-02-01), Corbo et al.
patent: 5086816 (1992-02-01), Mieth
patent: 5388965 (1995-02-01), Fehn
patent: 5507624 (1996-04-01), Fehn
patent: 5635637 (1997-06-01), Boult et al.
Patel Harshad
Pendorf & Cutliff
Putzmeister Aktiengesellschaft
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