Patent Publication Number: US-6220837-B1

Title: Progressing cavity pump having a ratio of eccentricity, rotor diameter and stator lead

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to progressing cavity pumps and particularly to such pumps suitable for pumping liquid/solid mixtures having a high proportion of relatively incompressible solids. 
     2. Description of the Prior Art 
     In, for example, mining applications it is necessary to pump explosive mixtures having liquid and solid components from a truck carrying bulk supplies of the components to pre-drilled holes in the rock to be quarried or mined. Normally the solids content of the mixture is about 35-40% of the total, the remainder being liquid. It is desirable from a cost point of view to reduce the liquid content so that the mixture is about 50% solids. However, existing progressing cavity pumps have excessive power requirements when pumping mixtures of such high solids content and are prone to entrapment of solid material and stalling. Examples of such pumps have been described in U.S. Pat. No. 4,773,834, U.S. pat. No. 4,591,322, GB 1,542,786 and GB-A2,228,976. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a progressing cavity pumps capable of pumping mixtures having a relatively high proportion of entrained solids. 
     According to the present invention there is provided a progressing cavity pump comprising a stator having a bore therethrough formed with a female, two start, helical gear formation of a given pitch. A cooperating rotor formed with a male, single start, helical gear formation of the same pitch and a drive arrangement for causing the rotor to rotate and orbit relative to the stator are provided. The ratio of the eccentricity, e, of the gear formation of the rotor to its minor diameter, d, is in the range of between 1 to 4.6 and 1 to 5.2 and the ratio of the eccentricity, e, of the gear formation of the rotor to stator lead, p s , is in the range of between 1 to 11 and 1 to 15. 
     Preferably, the ratio of the eccentricity (e) of the rotor gear to its minor diameter (d) is in the range of from 1:4.8 to 1:5.0 and the ratio of the eccentricity (e) of the rotor gear to the stator lead (p s ) is in the range of from 1:13 to 1:13.6. Ideally the ratio e:d is about 1:4.9 and the ratio e:p s , is about 1:13.3. 
     Pumps according to the present invention are able to pump liquid/solid mixtures with a solids content of about 50% with a reduced power requirement and a reduced risk of entrapment of solid material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which: 
     FIG. 1 is a part-sectional view of a progressing cavity pump according to a first embodiment of the present invention; 
     FIGS. 2A, B and C are sketches illustrating the parameters e, d and p; 
     FIG. 3 is a graph illustrating power requirement vs. solids ratio of the first embodiment of the invention and two known pumps and 
     FIG. 4 is a schematic view of a vehicle on which a progressing cavity pump according to the invention is mounted. 
     In the Figures, like parts are identified by like reference numerals. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a first presently preferred embodiment of a progressing cavity pump  10  embodying the present invention. The pump  10  has, as its major components, inlet chamber  11 , pumping section  12 , drive section  13  and discharge section  14 . It is driven by via input shaft  15 . 
     The inlet chamber  11  has an inlet  111  for the mixture to be pumped and will have suitable fittings for direct connection to a reservoir of the mixture or appropriate supply conduits. 
     Pumping section  12  comprises a stator  121  and rotor  122 . The stator  121  is a cylinder of compliant material, e.g. rubber, with an axial bore having a female, two start, helical gear surface  121   a . The rotor  122  is an elongate rod with its outer surface machined to form a male, one start, helical gear  122   a  corresponding to the female gear surface  121  a of the stator. The rotor may be made from stainless steel or carbon steel coated in hard chromium. The helical gear surfaces  121   a  and  122   a  have the same pitch but the stator gear surface  121   a  has twice the eccentricity as the rotor gear surface  122   a . As the female gear  121   a  on the stator has two starts, its lead, p s , is twice the lead, p r  of the male gear  122   a  on the rotor. 
     Drive from the input shaft  15 , which may be via a hydraulic motor of known type, is transmitted to the rotor  122  of the pumping section  12 . The rotor  122  is driven to rotate and is caused to orbit by the interaction of the male and female gears. The orbiting motion is permitted by the elongate drive shaft  131  which has a certain degree of flexibility. The rotation and orbiting of the rotor relative to the stator causes cavities formed between the gears to progress from the inlet chamber  11  to the output  14 . 
     FIGS. 2A, B and C show the configuration of the stator and rotor. FIG. 2A is a sketched partial cross-section of the rotor and stator. As shown, the rotor is circular in cross-section with a minor diameter, d. The bore in the stator is track shaped, i.e. has two semicircular ends joined by straight sides, in cross-section. Its long axis diameter is equal to the minor diameter of the rotor plus four times tile eccentricity. 
     FIG. 2B is a sketch of part of the rotor. As shown, the major diameter, D, of the rotor is equal to the minor diameter, d, plus twice the eccentricity, e. The pitch of the rotor, as shown, is equal to the lead, p r . 
     FIG. 2C is a sketch of capsulism profiles of progressing cavity pumps for different values of the ratio of eccentricity, e, to the stator lead, p s . Whilst typical progressing cavity pumps have a ratio of e:p s  of between 1:25 and 1:50, in this embodiment of the present invention the ratio of eccentricity, e, to minor diameter of the rotor, d, is 1:4.9 and the ratio of eccentricity, e, to stator lead, p s , is 1:13.3. The pump may therefore be described as having a 1:4.9:13.3 ratio. 
     FIG. 3 is a graph showing power consumption in kilowatts on axis Y vs. solids content of the pumped fluid on axis X. Line A is the pump of FIG.  1  and lines B and C are prior art pumps of ratios 1:5:26 and 1:6:27 respectively. As can be seen the pump of the present invention uses 12% less power than pump B and nearly 20% less than pump C. 
     The described embodiment of the invention has two stages but pumps of more or fewer stages may also be constructed with the same geometry. 
     The embodiment of FIG. 1 is adapted to be mounted on a vehicle, such as a truck bearing reservoirs of explosive components to be mixed prior to pumping. 
     FIG. 4 shows a truck  20  having mounted a progressing cavity pump  10  as well as a mixer  21  for mixing explosive components from reservoirs  22 ,  23 .