US1821218A - Pump and method of pump construction and operation - Google Patents

Description

Sept. 1, 1931. F. G. HOBART 9 ,218

PUMP AND METHOD OF PUMP CONSTRUCTION AND OPERATION Filed Feb. 21. 1927 4 Sheets-Sheet 1.

p T F. cs. HOBART 7 1,821,218

PUMP AND METHOD OF PUMP CONSTRUCTION AND OPERATION Filed Feb. 21. 1927 4 Sheets-Sheet 2 .47'7'0 ENC 15.

- Sept 1, 1931. F. G. HOBART 1,321,213

PUMP AND METHOD OF PUMP CONSTRUCTION AND OPERATION Filed Feb. 21, 1927 4 Sheets-Sheet 3 firrole/wsm.

Sept. 1, 1931. HOBART 1,821,2218 v PUMP AND METHOD OF PUMP CONSTRUCTION AND OPERATION Fil'ed Feb. 21, 1927 4 Sheets-Sheet 4 I WW A'i ORN FLY Patented Sept. 1, 1931 are Fries FRANKLIN G. HOBART, OF BELOIT, WISCONSIN, ASSIGNOR TO FAIRBANKS, MORSE 86 00., OF CHICAGO, ILLINOIS, A

CORPORATION or ILLINOIS PUMP AND METHOD OF PUMP CONSTRUCTION AND OPERATION Application filed. February 21, 1927. Serial No. 189,923.

This invention relates to improvements in pumps and methods of pump construction and operation, more particularly. applicable to multi-cylinder reciprocating pumps adapted to operate at comparatively high speed.

An object of this invention is the elimination of a critical or resonance speed, or the raising of such speed far beyond the normal speed at which the pump is adapted to operate.

Another object is the elimination of noises in pump operation due to harmonic pulsations in the pump discharge, usually known as the water-hammer efiect.

A further object is a minimization, which may approach elimination, of pressure variations and speed fluctuations in the discharge of the pump.

A further object incidental to that set forth above is the damping of pressure waves in the pump discharge, so that the fluctuations from the mean pump discharge rate are less marked than in pumps of prevailing design.

My invention does not of necessity involve any constructional difierences over existing designs, other than a change in the relative angular setting of the cranks. The novel ideas herein disclosed may thus be easily incorporated in existing pumps of great varieties of design, simply by changing the angular setting of the crank throws or the substitution of a different crank shaft. By way of example only, and for simplicity of representation, I have described my invention as applied to a duplex double acting'pump, and embodied therein by a novel arrangement of the cranks. Other means of attaining the same result may equally well be employed, such as by locating the axes of the several cylinders in dilferent'planes.

Although my invention consists largely in the construction and arrangement of parts hereinafter described and particularly pointed out in the claims, yet I do not limit my invention to the precise method, form or construction of parts shown or the several parts thereof, inasmuch as various alterations may be made without changing the scope of my invention.

,In a duplex double acting power pump the rate of water discharge passes above and below the mean discharge of the pump four times per revolution. In such a pump the prevailing practice is to set the cranks 90 degrees apart. WVith such a setting the maximum variations above the mean are not uniform, and in like manner the variations below the mean differ greatly. In a pump which operates at a fairly high speed these variations cause objectionable noises, due to the production of large pressure waves and speed fluctuations 1n the dischar e of the liquid.

I have found by experiment that by setting the cranks of a pump of the above sort at an angle slightly greater or slightly less than the usual 90 degree setting, that much is done toward reducing objectionable speed variations and speed fluctuations.

In the drawings, Fig. l is a diagrammatic sketch of a duplex double acting pump of a usual sort having the cranks set 90 degrees apart. Fig. 2 is a showing identical with that of Fig. 1 except that the cranks areset 93 degrees apart. Fig. 3 is a diagram showing graphically the rate of discharge of the four separate cylinder ends in a double acting duplex pump having its cranks set 90 degrees apart, showing also the resultant discharge obtained by the summation of the four separate discharges, and showing for purposes of comparison the average discharge of the pump per revolution; Fig. 4 is a diagram analogous to Fig. 3, showing by curves the characteristics of a double acting duplex pump, the cranks of which are located 93 degrees apart. The curves shown in Fig. 3 and Fig. 4: are derived determinations made in connection with pumps of the preferred types indicated in Figs. 1 and 2 respectively.

The reference characters used in the drawings are clearly indicated in Figures Land 2, but may for convenience be set forth as follows: The letter alpha or a denotes the angle in degrees described by the crank from the outer dead center, and the crank radii of the pump represented by 7'. L is used to indicate the finite length of each of the rods. In certain of the diagrams, omega or e) is the value of the angular velocity of the crank, per second, and equal to The angular setting of the cranks is indicated by gamma y.

Figs. 5 and 6 show in graphic form the acceleration of the piston in each cylinder of a duplex double acting power pump, through a period of one revolution, Fig. 5 being drawn for a pump having a crank setting of 90 degrees, and Fig. 6 showing analogous characteristics for a pump having a crank setting of 93 degrees. In the diagrams of Figs. 3, l, 5 and 6 the curves in light lines apply to the individual cylinders or stages and the double line curves indicate result ants derived by the summation of the results for separate cylinders. In Figs. 3 and t the average discharge per revolution is shown by the straight double lines.

In Figs. 3 and 4c the rate of discharge for a double acting duplex pump is represented by the ordinates and the abscissae represent time intervals during one revolution of the pump shaft. Each curve for the rate of discharge is derived from the piston speed multiplied by the piston area for successive crank positions 15 degrees apart during one revolution. The differences between the rates of discharge of each of the four separate cylinder ends will appear from the diagram.

In Figs. 5 and 6, the acceleration of the piston is represented by the ordinates and time periods through one revolution are represented by the abscissae. As in Figs. 3 and 4, the finite length of the connecting rods and the difference in area between the crank end and head end of the piston is taken into consideration. The resultant acceleration shown by the double line curves, is obtained by the summation of the separate accelerations of the two coacting piston sides. Figs. 5 and 6 indicate respectively, diagrams which were made for crank settings of 90 and 93 degrees. The resultant curves show the acceleration ofthe liquid in the pump discharge.

Figs. 7 and 8 show, diagrammatically modified pump structures having operating characteristics similar to those shown in Figs. 1 and 2, and which are hereinafter explained.

An examination of the graphs shown in the various figures indicate that substantial differences exist in the resultant discharge during one revolution. Theses differences produce pressure waves in the chamber of the pump which are transmitted to the dis charge pipe. In like manner the velocity of discharged liquid varies according to the fluctuations of the discharge rate.

It is well established that every pump has a critical speed, or a so-called resonance speed. As the speed of a'given pump is increased, a point is reached at which the pressure and speed fluctuations in the discharge result in a number of pressure waves substantially equal to, or a multiple of, the number of pump impulses per revolution. l/Vhen this'condition is reached, i. e., at resonance speed, the pump becomes very noisy due to water impacts or the Water-hammer effect. In order to operate satisfactorily the pump should deliver its normal output at a speed far away from the resonance speed, or the detrimental fluctuations in the discharge must be eliminated or greatly reduced. In pumps of prevailing construction an en tire elimination of such pressure and speed waves in the pump discharge is possible only in a pump having a great number of stages or cylinders. To obtain the result in this manner necessitates a complicated and expensive pump design. A much better and economical means is the decrease or elimination of these detrimental waves which may be accomplished among other ways in the manner herein indicated.

It will be noted from the curves that in a pump wit-i1 a 90 degree crank setting the pressure and speed waves are practically isochronous, i. e., the time-period of each successive wave is the same. 5] hen the time between pump impulses producing these waves is different, the regularity of the waves in the discharge is necei-sarily disturbed. This effect can be attained by setting the cranks at an angle slightly different than the usual 90 degrees, and by this means the magnitude of the fluctuations in the discharge can be lowered considerably. The eilect is shown by a comparison of Figs. 3 and at. lVith the 93 degree crank setting the resultant discharge volume per unit of time shows excesses above and below the average discharge, but it will be seen that the time periods between the four separate discharges are different, and each discharge period endures a longer or shorter time than the one preceding or the one following it. It is evident for this reason that a harmonic pulsation in the pump discharge is no longer possible because the four pump impulses are no longer in harmony with the pressure waves. Two of the impulses given by the pump are of longer period, and two other impulses are of a shorter period than those of uniform duration in the 90 degree pump. As will be seen in Figs. 5 and 6, the diagrams for a setting of cranks 93 degrees apart show different times of period of the four resultant accelerations, i. e., the same characteristics as for the resultant discharge rates.

The displacement of the two cranks from the usual setting of 90 degrees in a duplex pump cannot be carried to too great an eX- tent because the two rates of discharge would difler too greatly. The most convenient crank setting different from 90 degrees must depend upon the design and peculiarities of each type of pump. Experiments conducted along this line indicate that the deviation of the crank angle from 90 degrees is usually limited to a very small number of degrees. The exact angle between successively operating'cranks may be determined by experiment, as hereinafter set forth, for each type of pump, ac-

cording to the number of cylinders or stages, and according to the operative characteristics and performance tests of the pump in question.

As an aid to the determination of the best crank setting for a pump of a given type, it is suggested that in the first instance, the cranks be connected in the crank shaft or to each other by a coupling, for example, a flange coupling to permit angular variations between the cranks, for initial experimental determination of the angle, which will, of course, vary with pumps of different types and characteristics. Having once determined the optimum angular setting of the cranks, uniform unitary cranks or crank shafts may thereafter be formed by conventional production methods. Any relative angular setting of the cranks which will enable the operating speed to be kept safely away from the resonance speed, will prove satisfactory in use.

I have discribed in some detail my preferred method of obtaining the results brought out by the graphs in Figs. 3, 4, 5, and 6, namely, by varying the usual angular setting of different cranks. It will, of course, be understood from the remarks above that I have contemplated, as within the scope of the present application, other means of constructing and operating pumps to obtain the same characteristics. Among such other means may be mentioned the location of the axes of the pump cylinders in different planes.

In a pump having the cranks set 90 apart and the axes of the cylinders in the same plane, the dead center positions of the cranks are in the same plane. Thus, when one crank is in dead center position, the other is in a mid-position. If, however, with crank settings of 90 in a duplex pump, the axes of the pump cylinders are disposed in different planes as shown in Figs. 7 and 8,. the dead center positions of the cranks are in different planes. Thus, when one crank it at a dead center position, the other crank is at a position other than its halfway point. Such a construction obviously has an effect analogous to that described above, to vary the discharge pulsations and the time period between such pulsations. In Fig. 7, one of the cylinders is disposed above the other, in different horizontal planes; in Fig. 8, the cylinders are shown substantially at the same height, say above the base, but with the cylinder axes in nonparallel relation. In a cross-head pump construction, either of the arrangements last shown will result in the pair of crossheads operating in different planes. The reference characters'and symbols appearing in Figs. 7

and 8 correspond to those used in connection with Figs. 1 and 2.

Any one, or several, of the suggested constructions may I be employed in the same pump. The constructional features incident to the adoption of any of the described methods, are thought to be at once apparent to those skilled in the art, hence not necessary to be illustrated and described in detail.

What I claim is: I

1. In a reciprocating pump having a pair of adjacent cylinders and a pair of pistons, means including successively operating cranks each operatively connected with one of said pistons, said cranks being relatively disposed with respect to each other andto the pistons to produce resultant pump discharge periods of unequal duration. 2. A reciprocating pump having a plurality of cylinders with pistons therefor and.

aplurality of successively operating cranks each operatively connected to one of said pistons, the cranks being arranged to operate the several pistons through uniform discharge periods, the cranks being relatively angularly disposed to produce alternately long and short periods of pump discharge as a'resultant of the combined displacement of said pistons.

3. The herein described method of operating a duplex reciprocating pump having paired cranks, pistons and cylinders, which consists in operating one of said pistons to bring it to an intermediate position representing other than a substantial aliquot part of its path'of travel, and at such piston posi tion, beginningthe stroke of a second piston.

4. The herein described method of operating a duplex reciprocating pump which consists in operating one of the pistons to bring it to an intermediate position other than its central point of travel, and at such piston position, beginning a stroke of the other piston.

5. The herein described method of constructing and operating a pump having as elements, at least a pair of cranks and a pair of cylinders, which consists in shifting the position of one of a pair of said like elements with respect to the companion element, whereby the resultant discharge periods of said pump are of unequal duration.

6. The herein described method of changing the resonance speed of a pump having a plurality of displacement members, which consists in displacing a fluid through said pump by subjecting the several displacement members to uniform movements, and in .com-

bining the fluid displaced by said members to produce alternately longer and shorter periods of resultant fluid discharge during a given cycle of operation of the pump.

7. A duplex reciprocating pump comprising a pair of cranks, cylinders, and pistons adapted to operate to deliver a fluid at periodically varying discharge rates, one of said cranks being adapted to move one of the pis- 5 tons to an intermediate position other than its central point of travel, and the other crank being adapted at the same time to move the other piston to the beginning of a stroke, whereby the time intervals of the resultant rates of discharge of the pump,'are unequal.

8. A reciprocating pump comprising a plurality of cranks, cylinders, and pistons adapted to operate to deliver a fluid at periodically varying discharge rates, said cylinders being so associated with said cranks, that said cranks are adapted to move one of said pistons to the beginning of its stroke, and the other of said pistons to an intermediate position representing other than a substantial Z9 aliquot part of its path of travel, whereby the time intervals of the resultant rates of discharge of said pump are unequal.

9. A reciprocating pump having a pair of adjacent cylinders and operating elements, 1.5 and a crank shaft, one of the cylinders being so disposed that the aXis of rotation of said shaft is beyond the prolonged axis of said cylinder.

10. A duplex reciprocating pump having a plurality of adjacent cylinders and operating elements, and a crank shaft, the crank shaft and one of said cylinders being so disposed that the axis of rotation of said shaft and the aXis of the last mentioned cylinder, are 3 non-intersecting.

FRANKLIN e. HOBART.

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