US2291889A - Pump - Google Patents

Description

Aug.4,1942f waivmsm; 2,291,889 PUMP i Y Y Filed April 18', Y194CA of stroke, displacement efficiency Patented Aug. 4, 1942 romevr william G. Evans and Gordon B. Zimmerman,

Chicago, Ill., assignors to Universal Oil Products Company, Chicago, Ill., a'corporation of Delaware Application April 18, 1940, Serial'No. 330,25?. s claims. (ci. s-38) The invention relates to an improved form of pump, which will be found particularly useful in small scale pilot plant and laboratory work, designed to handle small quantities of 'liquid at any desired pressure and at a substantially constant discharge rate which is adjustable over a relatively wide range.

In pumping small quantities of liquid, such as is often required in laboratory vwork and small scale pilot plant operation, a piston or plunger type pump has-certain well recognized advantages overv pumps of the centrifugal, gear or diaphragm types, particularly when operated against high superatmospheric pressure .or when handling hot or corrosiveliquids. Since the discharge capacity of piston or plunger type pumps is governed by the piston or plunger area, length and number of strokes per unit time, the minimum discharge capacity is limited by these factors inthe f ollowing way: The number of strokes perl'minute should/be fairly hig particularly witha single cylinder pump, to maintain a fairly constant ow from the pump discharge. Fewer than 30 strokes per minute is ordinarilyunsatisfaetory. The displacement eiiiciency should be high to insure positive action, but with a short stroke the. discharge volume will vary considerably due to the n stroke and sufliciently rapid stroke togive good accuracy and fairly constant flow through the discharge valve. v

'I'he accompanying diagrammatic drawing illustrates one specific form ofpump embodying the features of the invention.

Figure 1 is aside elevation of the pump shown partially in longitudinal section.

Figure 2 is an elevational view. of a portion of the stroke adjusting mechanism of p the pump, this view being taken, at right angles to the view shown in Figure 1. f v f l Figure 3 is an enlarged detail, shown partially in section, illustrating the valve mechanism of the surge block type-which may be employed in.k conjunction with the pumping cylinder shown inFigurel. p

Referringl to `the drawing, the specific form of pump here illustrated hasa bed-plate designated by the reference numeral ,I uponjwhich a pedestal 21s mounted, the pedestal'journaling a. rotary drive-shaft-3 in a suitable bearing 4. 'I-'he driveshaft may conveniently be operated by a suitable constant speed motivating mechanism, such as, for example, a synchronous.. motor, not shown, operating through a 'suitable speed reducing mechanism, not illustrated. Preferably, the mo- .tor and speed reducerarealso mounted by any elasticity or play of the parts and, with an adjustable stroke, minor variations in the adjustment and any small amount of play in the adjusting mechanism. 'Ihe sizeof'the'piston-or plunger is particularly important. With a. reciprocating shaft of less than about 1A inch in diameter, the problem of packing tight joint is extremely difficult.

The improved form of plunger. pump provided to maintain a by the invention overcomes the difficulties normally encountered in the design .of pumps of this class for low capacity' and high pressure operation. We through the pumping cylinder and is packed at opposite ends thereof. plunger within the pumping cylinder is'of smaller diameter than the remaining portion. The smallest end` of the plunger which passes through the packing gland at one end of the cylinder is of sufficiently large diameter to perm' packing without leakage and the effective area of the plunger, in computing the discharge capacity, is, of course, the difference between the area ofthe large portion of the plunger and the area of the small portion of the plunger. 'I'his difference may be as small or as large as desired to give any One portion of the` v4l) employ a plunger.which passes desired discharge capacity with a sufficiently long well known means, not illustrated; on bed-platel l. A suitable crank which, in' the particular. case here illustrated, comprises a disc shaped member ,5 'provided withv crank-pin Sis attachedy to the drive-shaft 3, the center to center distance between crank-pin 6 and drive-shaft 3 correspond-- ing -to one-,half the desired maximum stroke of the pump plunger. Y 1

A suitable connectingrod-'or lpitman. ,'I is v mounted ,on crank-pin 6 and operatively connects the crank with ythe reciprocating pump plunger `8. As illustrated in Figure 2, a slotted 4opening 9 is provided` throughthe upper end member I0 of pitman 1 to ing action imparted to the latter by the crank. l v 'I'he upper end ofplunger 8 is threaded, as indicated at Il,` and two knurled thumb nuts I2 are provided on the threaded portion ofthe plunger. Beneath the threaded portion of the plunger the vshaft is emerged for a short distance or alternately provided witha member I3 which, in the particular case here. illustrated, ispxed to the plunger by set screw- Il. l

To vary the strokeof nuts l2, one of which serves as a lock nut, are

turned to vary the distance between the same accommodate the tiltthe plunger .8. thumb upper end of pitman 1 between lock nuts I2 and member 8 and varying the effective throw of the crank since no upward motion of the plunger will occur until member I strikes the low thumb nut I2 and no downward motion of the plunger will occur until member I0 on its return stroke strikes member I3. Thus, by turning thumb nuts I2 the stroke of plunger 8 and the displacement of the pump may be adjusted to suit requirement even while the pump is in operation.

A bracket I5 is provided on pedestal 2 which supports the'pumping cylinder I5, the latter being secured, in the vcase here illustrated, to bracket I5 at the desired position by set screw I1.

The plunger 8 passes through the pumping cylinder I6 and is packed adjacent the opposite -ends of the latter, as indicated at I8, suitable packing-nuts I9 and followers 20 being provided to compress packing I8.

' ,As illustrated in Figure I, the lower portion of plunger 8 is of reduced diameter and the bore of the pumpingcylinder between the packing glands corresponds approximately or may, when desired, be somewhat greater in diameter than the large portion of the plunger. Thus, the effective area of the plunger for computing the displacement of the pump is the diierence between the areas of the large and small diameter portions of the pump.

'An inlet and discharge port 2| is provided in the pumping cylinder adjacent the lower end of the large diameter bore, this port communicating with a surge line 22 through which liquid from the valve blocks is intermittently drawn into and discharged from the pumping cylinder as plunger'8 reciprocates.

It will, of course, be understood that any type of valve mechanism capable of functioning properly at small pumping capacities may be employed within the scope of the invention. In the case here illustrated, a valve arrangement of the surge type is employed, the details of the valve mechanism being illustrated in Figure 3. A surge type valve mechanism is particularly advantageous as applied to pumping hot or corrosive liquids, but no novelty is claimed per se for the specic form of valve mechanism illustrated.

Referring to Figure 3, an inlet valve block 24 and an outlet valve block 25 are provided, the two communicating through member 23 which, in turn, communicates through surge line 22 and port 2I with the pumping cylinder. Ball- checks 26 and 21 are provided in valve block 2l 'and similar ball-checks 28 and` 29 are provided in valve block 25. A suction conduit 30 communicates with the lower end of valve block' 2l and a discharge conduit 3| communicates with the upper end of valve block 25.

Upon the upward strokelof. plunger 8, liquid from the surge line 22 is drawn into. the pumping cylinder and, in turn, draws the liquid to be pumped from conduit 30 past the ball- checks 26 and 21 into member 23, ball- checks 28 and 29 in valve block 25 being closed by suction from the pumping cylinderwhich draws in against their seats. On the downward stroke of plunger 8. liquid is forced into surge line 22 from the pumping cylinder through port 2| and forces the liquid being pumped from member 23 past ballchecks28 and 29 tor discharge conduit 3l, ballchecks 26 and 21 in valve block 24 being closed by pressure from the pumping cylinder which forces them against their seats.

It will be apparent from the above that a pump embodying the features of the dual size pump provided by the invention may be designed for an extremely small minimum capacity since the eiective area of the plunger which, when multiplied by the length of the plunger stroke and the displacement eillciency, determines the displacement, is the difference between the cross-sectional areas of the large and small diameter portions of the plunger. Thus, the minimum displacement obtainable is not limited by the minimum satisfactory plunger diameter and the difilculty of tightly packing plungers of excessively small diameter is obviated. For example, assuming a plunger stroke of 1 inch, a maximum plunger diameter of Qi@ of an inch and la minimum plunger diameter of 1/4 inch, the theoretical displacement is 0.0277 cubic inch, which corresponds to the theoretical displacement which would be obtained with a conventional plunger of only e of an inch diameter. With the same .length of stroke, a maximum plunger diameter of V16 of a ninch and a minimum plunger diameter of %2 of an inch, the theoretical displacement is approximately 0.015 cubic inch which corresponds to the theoretical displacement which would be obtained with a conventional plunger only slightly more than 1/5 of an inch in diameter.

Since at the small capacities for which pumps of the type provided by the invention may be employed to particular advantage, it'is diiiicult, if not possible, to accurately vary the discharge capacity by means of a by-pass or a throttling valve, we have, in the preferred embodiment of the invention, provided means for varying the stroke of the plunger in order that the capacity may be thus regulated to suit requirements. The relatively simple formof stroke adjusting mechanism illustrated in the drawing is only one of many specic forms which may be employed within the scope of the invention in conjunction with its other features, but we preferably employ a stroke adjusting mechanism which'can conveniently be manipulated while the pump is in operation.

We claim as our invention:

l. In a pump, a pump cylinder having an opening therein, a plunger adapted to operate within said cylinder, a surge valve operatively associated with said opening, means for driving the plunger including a pitman, said pitman having an arm provided with a slotted aperture and means for varying the stroke of said plunger comprising upper and lower adjustable members mounted at one end of said plunger, said lower adjustable member being provided with a projection adapted to slidably engage said slotted aperture.

f 2. In a pump, a pump cylinder having an openingA therein, a plunger adapted to operate within saidk pump cylinder, one portion of said plunger beingsmaller in cross'sectional area than another portion thereof, guide means at opposite ends of said cylinder adapted to receive said respective portions of said plunger, means for driving said plunger including a pitman, said pitman having an arm'y provided with a slotted aperture and means for varying the stroke of said plunger comprising upper and lower adjustable members mounted at one end of said plunger, said lower adjustable member being provided with a projection adapted to slidably engage said slotted aperture.

3. In a pump, a pumpcylinder having an opening therein, a plunger adapted to operate within members mounted on said plunger, 'the inner sides of said members being substantially concave, the convex sides of said projection being adapted to engage the concave inner sides of said lad- 5 justable members.

WILLIAM G. EVANS. GORDON B. ZIMMERMAN.

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