Eccentric screw pump with reversible rotor

An eccentric screw pump comprises at least one stator, a rotor having a core and received for eccentric rotation in the stator, a first coupling device adapted to connect one end of the rotor to a drive system, a second coupling device provided at another end of the rotor, the coupling devices having external dimensions which are smaller than a diameter of the core of the rotor.

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 the threaded screw. More difficult however is the 
manufacture of long, comparatively thin screw profiles with a large number 
of stages, in which this technology requires more complex shapes, because 
of the insufficient mechanical stability of the screw profile among other 
things. 
Consequently, these known eccentric screw pumps, with regard to the cost 
situation of the rotor, especially with large delivery heights and high 
output pressures, cannot be regarded as sufficiently cost-effective in 
terms of resistance to wear. 
SUMMARY OF THE INVENTION 
It is the object of the invention to provide an eccentric screw pump of the 
type first referred to above, with an improved life for the rotor, so that 
its suitability for the transportation of abrasive matter in particular, 
over large delivery heights, is improved. 
In keeping with these objects and with others which will become apparent 
hereinafter, one feature of the present invention resides, briefly stated, 
in an eccentric screw pump comprising at least one stator and a rotor 
which is received for eccentric rotation in the stator and which is 
connected at one end to a drive system by means of a coupling device, 
wherein the rotor is provided at both ends with such coupling devices 
whose external dimensions are smaller than the core diameter of the rotor. 
It is essential to the invention that, because of the special design of the 
free ends of the rotor, the rotor can be inserted into a stator in either 
direction, so that with wear occurring at one end, namely on the output 
side, the worn region of the rotor can be replaced in the input-side 
region of the stator, which in many cases is operated substantially 
without pressure, so that even though in this region a worn rotor portion 
is introduced, substantially no adverse effect on the efficiency of the 
conveyor is to be expected. On the other hand, at the output side, 
practically the necessary pressure can be created since here an unworn 
section of the rotor now comes into use. 
In this way, the original tapering by worn rotor is inserted again in the 
reverse direction to this taper, until in the final state the original 
taper is reduced and the rotor then is uniformly worn over its entire 
length. It is assumed for this mode of using the rotor that the rotor can 
be inserted axially in spite of the coupling devices fitted at the ends. 
The latter is achieved by the external dimensions of the coupling devices 
being smaller than the core diameter of the rotor. The rotor now uniformly 
worn over its full length, after having been inserted in the reversed 
sense, can basically be inserted into a stator which is smaller in 
dimensions, in dependence upon the degree of the wear. This is always 
possible in the circumstance in which the layer of the rotor hardened on 
the surface region has not been completely worn away. Consequently, the 
rotor, in a smaller dimensioned stator, can be worn again at both ends in 
the sense described above. 
In accordance with another feature of the present invention, the coupling 
devices can have square profiles or profiles of some other polygonal 
cross-sections, with their central axes extending coaxially in relation to 
the longitudinal center axis of the rotor. 
The shaping of the coupling devices, for example with square profiles, 
whose central axes extend coaxially in relation to the longitudinal 
central axis of the rotor, is very easily produced from the technical 
manufacturing point of view and they can be manufactured particularly 
favourably in terms of cost. The coupling of a drive system to the square 
profiles can be effected basically in any suitable manner. 
Still another feature of the present invention is that at least two stators 
are connected end to end sealingly to one another, and the coupling 
devices which mutually opposed each other in the connecting regions of the 
stators are in engagement with each other. 
The compound system, consisting of stator and rotor, is conventionally 
manufactured with a limited number of stages, so that, by means of this, a 
very simple possibility is opened up of being able to produce a high 
pressure pump arrangement in which in each stator there is inserted a 
rotor which is equipped at both ends with coupling devices, for example 
having square profiles. These coupling devices are shaped in such a manner 
that they can easily be brought into engagement with each other. In the 
case of square profiles this can be achieved in a particularly simple 
manner by a sleeve which is appropriately shaped on the inside. Because 
multi-stage rotors suitable for high pressure pumps are regarded as 
expensive, one can in this way, by means of the eccentric screw pump of 
the present invention, by using simple technical measures, produce a wide 
variety of high pressure pump arrangements of various numbers of stages 
using only a few standard sizes. This can be achieved by mere combination 
of three-stage or four-stage screw pumps which can each be manufactured 
inexpensively and which are designed in the manner described above. From 
the practical point of view, in this way one achieves not only a high 
pressure pump which is particularly resistant to wear but also a pump 
whose number of stages can be adapted in the simplest manner to the 
particular needs, for example different delivery heights. 
Still a further feature of the present invention is that the coupling of 
the coupling device to the drive system is effected by means of a square 
cross-section socket mounted rotatably about a shaft extending at a small 
angle of inclination relative to the longitudinal central axis of the 
rotor, and the eccentricity of the rotor is compensated by the socket 
being oversized in relation to the coupling device. 
These features open up a simple possibility of coupling a centrally 
rotating drive system to the eccentrically rotating rotor. It is this 
coupling of a drive system to the square profile connected to the rotor 
which is in practice possible, since--seen in the direction of flow of the 
matter being conveyed--the eccentric screw pump often is preceded by a 
comparatively long intermediate shaft by means of which the coupling to a 
motor is effected. With an eccentricity of 1 cm to 2 cm of the rotor, the 
length of this intermediate shaft serving to couple the shaft to a mixing 
device or feed device of known form can amount for example to 50 cm so 
that a correspondingly smaller pivot angle of the intermediate shaft 
relative to the longitudinal central axis of the rotor results. 
Various embodiments of eccentric screw pump in accordance with the 
invention will now be described by way of example and with reference to 
the accompanying drawings, in which components having the same function 
are indicated by the respective same reference numbers.

DESCRIPTION OF PREFERRED EMBODIMENTS 
At 1 in FIG. 1 is indicated the cylindrical housing of an eccentric screw 
pump, about whose longitudinal central axis 2 a rotor 3, whose 
longitudinal central axis is indicated at 4, is mounted in a manner known 
per se for rotation eccentrically with the offset 5. During the rotation 
of the rotor 3 its longitudinal central axis 4 consequently describes a 
cylindrical surface centered on the longitudinal central axis 2 of the 
housing 1. 
The housing 1 consists for example of a metallic sleeve 6 whose internal 
surface carries an insert (not shown in the drawings) defining delivery 
chambers for the matter to be transported, here for example mortar, and 
cooperating with the screw profile 7 of the rotor 3 which is shown in FIG. 
2. This insert consists for example of a wear-resistant rubber and is 
vulcanised to the internal surface of the sleeve 6. 
The rotor 3 is made of a hardened steel which is particularly 
wear-resistant to abrasive attack, and comprises a screw profile, for 
example in the form of a continuous thread. 
The internal contour of the insert which together with the sleeve 6 forms 
the stator is in a manner known per se formed as a coarse thread which, 
according to the eccentricity of the rotor 3 with its screw profile 
7--seen in the axial direction--forms delivery chambers of substantially 
the same volume but of different form and orientation. Theoretically, by 
this means, each section formed by two thread turns of the screw profile 7 
can be considered as a closed chamber, wherein, viewed in the direction of 
transportation 8, the pressure to be expected and consequently also the 
abrasive attack exerted on the rotor and stator increases. The rotor 3 is 
equipped at both end faces 9, 10 with square spigots 11 which extend in 
the direction of the longitudinal central axis 4. These square spigots are 
smaller, in terms of their external dimensions, than the core diameter of 
the rotor. 
The square spigots 11 project from both ends of the sleeve 6 and serve for 
the connection of a driving unit which is connected by way of a jointed 
intermediate shaft. For example, with the indicated direction of 
conveyance 8, the input end is at the position 12, from which the square 
spigot 11 located here projects for the drive. The polygonal spigot 
located at the output or delivery end 13 in this case runs freely. In 
practice, with the transportation of mortar, a suitable tube can be 
arranged at the output end, or alternatively an intermediate container. In 
the latter case a stirrer or a comparable device can be fixed for example 
to the output-end square spigot 11. Alternatively the stirrer could be 
made detachable, as a result of which the mixing process which takes place 
in the intermediate container is improved. 
One particularly simple coupling possibility for the eccentrically rotating 
rotor 3 is shown in FIGS. 4 and 5, according to which the drive is 
effected by means of a square socket 15 formed on an intermediate shaft 
14. The longitudinal central axis 16 which is common to the intermediate 
shaft 14 as well as to the square socket 15 is arranged at a small angle 
of inclination .alpha. to the longitudinal central axis 4, with the 
intermediate shaft 14 at its end remote from the said rotor likewise being 
connected to a rotor by means of a square spigot and a square socket. By 
means of the square spigots in combination with the square sockets 
associated with them one consequently has two couplings by means of which 
the intermediate shaft 14 is coupled on the one hand to the rotor 3 and on 
the other hand to a motor. The square socket is oversized in relation to 
the square spigot, in order that the eccentricity of the rotor can be 
balanced. 
The main field of utilisation of the eccentric screw pump according to the 
invention is in the conveyance of prepared mortar of all types, namely 
gypsum, gypsum-chalk, basic plaster, chalk-cement or sealing plaster, 
although also including concreting mortar and flow coatings, with grain 
sizes up to 16 mm. They can additionally be used as pumps for foundation 
mortar and in injection grouting. In this connection, as already 
mentioned, one has increasing wear with increasing pressure, as a result 
of which the contour of the originally cylindrical rotor is increasingly 
worn away, particularly in the output-side end zone, thus resulting in a 
generally overall tapering shape for the rotor. If this wear has reached a 
level which can no longer be tolerated and which is adversely affecting 
the efficiency of the pump, then the rotor is removed axially from the 
likewise worn stator and is turned round and inserted into a new stator, 
so that what was previously the input-side rotor end is now inserted into 
the output-side end zone. This is suitable at the output-side end on the 
basis that only trifling demands are made on the rotor there, in order to 
ensure an adequate seal at the output-side end zone and consequently to 
ensure an adequate efficiency of the pump. The insertion of the worn end 
zone in the input-side part of the pump is in practice justified, since, 
on the basis of the low pressure created here, a nominal impairment of the 
efficiency need not be feared. 
As can be seen from FIG. 6 the rotor which has an axis 4 is provided at 
both ends with identical spigots 21 having a hexagonal cross section. They 
are received in corresponding hexagonal sockets 22 provided on the ends of 
a not shown intermediate shaft which is similar to the intermediate shaft 
of FIG. 5. 
Two eccentric screw pumps which are assembled to form a high pressure pump 
arrangement, are shown in FIG. 7. The housings 1, 1' of the pumps are 
coaxial with one another, and the opposite square spigots 11,11' are 
connected with one another by an intermediate shaft 14. A coupling device 
23 sealingly covers the connecting region of the housings 1,1' from 
outside. Therefore the whole arrangement is assembled starting from its 
inlet side 12 of the first pump to its pressure side 13, the inlet side 
12' of the second pump to its pressure side 13', and a medium to be 
transported flows during the operation in direction of the arrow 8. The 
coupling device 23 can have any construction. Compensation movements 
between the rotors 3,3' are possible due to the play between the square 
spigots 11,11' and the cooperating square sockets 15,15' of the 
intermediate shaft 14. 
FIG. 8 shows the sleeve 6 of a cylindrical housing of the pump with a 
longitudinal central axis 2. An insert of wear resistant rubber 24 is 
provided at the inner side of the sleeve and has for example a steep 
double-thread inner contour. The inner contour of the insert 24 is an oval 
with two semi-circles 25,26 and a rectangle 27. The diameter of the 
semi-circles 25,26 corresponds to the diameter of the rotor cross section 
28. One side of the rectangle 27 corresponds to the diameter of the rotor 
cross section 28, while the other side corresponds to four times the 
eccentricity 5. The broken line 29 corresponds to the projection of all 
inner countors of the insert 24 onto the plane of the drawings. The rotor 
3 or the rotor cross section 28 performs during the operation of the pump 
a rectilinear, oscillating movement along the lien 30 over the stroke 31 
between two extreme points which are spaced form one another by four times 
the eccentricity 5. The diameter of the rotor cross section is identified 
as 28. 
The geometrical parameters produced due to the eccentric movement of the 
rotor of such pumps, especially the cooperation between the inner profile, 
the rotor cross section 28 and the eccentricity 5 are known and do not 
constitute the new features of the invention. FIG. 8 is provided only to 
illustrate the operation and the inner profile of the rubber insert. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
constructions differing from the types described above. 
While the invention has been illustrated and described as embodied in an 
eccentric screw pump, it is not intended to be limited to the details 
shown, since various modifications and structural changes may be made 
without departing in any way from the spirit of the present invention. 
Without further analysis, the foregoing will be fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
form the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.