Rotary expansible chamber devices – Multistage
Patent
1990-05-29
1993-03-23
Vrablik, John J.
Rotary expansible chamber devices
Multistage
418 39, 418 48, 418182, 403 3, F04C 2107, F04C 500, F16D 110, F16D 310
Patent
active
051958805
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an eccentric screw pump.
Eccentric screw pumps are known as distribution or conveyor devices for abrasive solid-liquid mixtures, such as for example slurries, mortar and the like. Their essential feature is a rotor which rotates eccentrically within a cylindrical stator, with the rotor being designed as a screw conveyor, and wherein delivery chambers are formed between the threaded internal profile of the stator and the screw profile, said delivery chambers moving in the longitudinal direction of the stator as a result of rotation of the rotor. The volume of these delivery chambers remains constant during the movement along the stator--the volume changes only in respect of position and shape. One can regard the space defined between two thread turns of the screw helix and the internal profile of the stator--in relation to the rotor--as being one such delivery chamber so that one has one or more stages, according to the number of thread turns of the screw conveyor, in which stages the pressure of the medium delivered by the respective stages can increase in the output direction The driving of the eccentric screw pump is effected in the conventional way by means of a universal-joint shaft coupled to the rotor and by means of which the eccentricity of the rotor can be balanced.
In the transportation of for example mortar and other such matter laden with abrasive components, increasing amounts of wear occur in the chambers with increasing pressure, with the wear occurring both on the rotor and also on the stator Therefore, in the course of time, this leads to a tapering erosion of the profile of the conveyor screw, so that finally one no longer has a sufficient seal between the various stages and one has at least partial backflow of the matter being conveyed, so that the efficiency of the conveyor, particularly in terms of the achievable conveyor height and output pressure, becomes insufficient.
Although the manufacturing cost of a rotor is on average five times that of a stator, the majority of the measures adopted until now and directed to increasing the life of the eccentric screw pump, have been expended on the stator whose shape has been changed in accordance with the progressive wear.
Thus, for example, DE-AS 1 553 199 described an adjustable stator for an eccentric screw pump which is designed as a resilient, double-turn or multi-turn hollow screw which is arranged within a longitudinally slotted tubular sleeve which is extensible by means of an adaptor sleeve. By a tightening of the tubular sleeve one can compensate, within certain limits, for a change in the geometry of the rotor.
A further variant, likewise associated with this technology, is known from DE-PS 33 04 751. According to this, a rotor which has a constant thread cross-section throughout the length of the pump is located within a stator whose cross-section reduces continuously from the input suction side through to the output pressure side, so that the mechanical stress imposed on the rotor increases correspondingly at the output side, namely at the position at which the maximum wear is expected.
It is characteristic of these known eccentric screw pumps that an unbalanced rotor which becomes worn that is in the output side region must be discarded, since because of the dimensions of the universal-joint head connected in a driving manner to it, a reversed setting of the rotor in the stator is not possible. Consequently, in spite of the aforementioned cost relationship between the rotor and the stator, in practical use there is insufficient, construction-related utilisation of the rotor.
Screw conveyors are conventionally formed with several stages, in order to be able to achieve a predetermined delivery height. Since the pressure increase which can be achieved per stage is limited, as a consequence the achievable delivery height and the achievable output pressure are determined essentially by the number of stages. Screw conveyors can be manufactured quickly and at favourable cost by means of the known technology of
REFERENCES:
patent: 1287030 (1918-12-01), Jones
patent: 4711006 (1987-12-01), Baldenko et al.
GD-Anker GmbH
Striker Michael J.
Vrablik John J.
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