US2772931A - Piston for reciprocating pumps - Google Patents

Description

De@ 4 1956 P. R. G. BlEDl-:RMANN 2,772,931

PIsToN FOR REG IPRocATJ-.NG PUMPS Filed Nov. 6, 1953 W r l I I g IIIIIIIIII J/Vyw rmQA/Eys.

` vr2,772,931 y .l

It is still another object of my invention to provide a piston equipped with an interchangeable adapter,which will fit various tapers of different piston rods though the outside piston diameter may be the same, thus aiding the supply stores and iield forces to meet emergency requirements more readily and at lesser costs.

These and other objects of my invention have been achieved by providing a piston construction that comprises a centrally located metal body of minimum weight which is adapted to be attached to the piston rod. This body has a pair of spaced, radially extending flanges which are at opposite sides of an annular recess extending around the body. In this recess is a sealing ring of a rubber-like material which extends radially beyond the flanges to engage the inside walls of the cylinder. In its normal or unrestrained condition, the outside diameter of the sealing ring is greater than the inside diameter of the cylinder. Likewise the inside diameter of this sealing ring is preferably greater over most of its area than the outside diameter of the piston recess so that there is a slight clearance between the sealing ring and the piston body. Alternatively or in combination with such a structure, one or more cavities may be formed in the sealing ring or in the metal piston body, or in both, which serve the same purpose.

When the piston is inserted in the cylinder, the sealing ring is compressed radially by engagement with the cylinder wall. This deformation brings the sealing ring into uid tight engagement with the piston body. Since the material of the ring is resilient, radial compression of the ring produces internal strains that tend to expand the ring to its normal diameter; and this inherent expansive force within the ring brings it into firm contact with the cylinder wall over the entire area of the ring, positioning it concentrically of the cylinder and allowing it to compensate for wear that occurs locally.

The expansive character of the sealing ring causes it to press tightly at all points around the cylinder; and even if some wear occurs on the underside of the piston in a horizontal cylinder, the piston does not drop down a corresponding amount in the cylinder thereby reducing the tightness of the seal at the top of the piston. Rather the natural expansion of the sealing ring keeps the piston concentric withinrthe cylinder and exerts equal opposing forces against the cylinder walls at the top and bottom sides of the piston. The activated force exerted by the zing against the cylinder walls is enough to offset the decreased support given the piston by the piston rod at the end of its outward stroke.

Although I prefer to make the piston body in a singley piece in order to obtain minimum weight and simplest construction, in a variational form of my invention the body is made in two parts. By bringing the two parts together while in contact with the inside face of the sealing ring, the ring may be expanded in size to a diameter which is larger than the diameter of the cylinder before it is inserted in the cylinder. As mentioned above, the sealing ring is then compressed as it is inserted in the cylinder to reduce its maximum diameter to that of the internal diameter of the cylinder. This combination is particularly adapted to cylinders worn oversize or out of round as it permits of an even greater amount of expansion of the sealing ring. l

For simplicity I prefer a'piston having a unitary body and a single ring, butmy invention is not limited thereto. Just as the body may be made in two parts, two or Emre similar rings may be mounted on a single'unitary ody.

How the above objects and advantages of my invention, as well as others not specifically referred to herein, are attained will be more easily understood by reference to the following description land to the annexed drawings, in which: A

Fig. l is a combined side elevation and median sectionl 4 1 through a piston embodying a preferred form of my in vention as seen when removed from'a cylinder;

Fig. 2 is a view similar to Fig. 1 showing the position occupied by the sealing ring of Fig. 1 when inside the cylinder so that the ring is confined or radially restrained;

Fig. 3 is a half-section of a piston showing a modified form of my invention;

Fig. 4 is a half-section showing another variational form of my invention; and

Fig. 5 is a half-sectional view showing another modilied form of my invention in which the piston body is made in two parts. Y

There is shown in Figs. 1 and 2 a presently preferred form of my invention in which the metal body of the piston is gf unitary design. This unitary construction is preferred since it permits a maximum strength for a given weight of metal in the body and also reduces to a minimum the number of engaging faces which offer possible leakage paths for uid within the piston. `It particularly fits oil field needs because of its simplicity.

Body 10 includes a hub portion 11 which is provided with a central bore that may be either cylindrical or tapered, but is here shown as having two cylindrical sections of different diameters joined by a sloping shoulder 11a. The hub lits over an adapter sleeve 12 mounted on the end of piston rod 13 which is preferably tapered, the bore of the adapter sleeve matching the taper of the piston rod. A nut 13a on the end of the piston rod engages one end of the hub in order to secure the piston in place on the piston rod. Use of a sleeve 12 is a simple means for fitting a piston body to any one of a number of piston rods of'different dimensions. Pumps made by dilerent manufacturers have piston rods of different sizes and shapes at the point of connection of the piston, even for pumps of the same size of cylinder. A supply of adapters 12 with different inside bores to t different piston rods can all have the same external dimensions to tit a piston of a given size. This reduces the number of pistons of different styles required to be carried in stock at a supply house to meet all demands.

At each end of body 10 is a radially extending ange 14 which extends outwardly beyond the rest of the body. This pair of spaced flanges define the ends of an annular recess that goes entirely around the body. The third w all of this recess is the outside or peripheral surface 15 of the body lying between the anges. In this form of my invention, the external surface 15 of the body is cylindrical in shape except where it is interrupted midway between the two flanges 14 by a rib 16 which preferably extends around the body.

The sealing ring generally indicated at 20 is made of rubber or a rubber compound or of some similar material having rubber-like characteristics. There are various synthetic compounds which are resistant to the action of hydrocarbons and therefore may be preferable in some instances to natural rubber itself; yet these compounds are all suiciently similar to rubber in their physical properties of being easily deformable-and being resilient that they lmay beincluded in the term rubber-like material. Sealing ring 20 is a continuous annular member mounted upon metal body 10 in the recess between spaced flanges 14. The ring extends radially outwardly beyond flanges 14 so that the outer surface of the ring comes into contact with the cylinder walls and the outer ends,

of the anges are slightly spaced from the cylinder walls but afford endwise support and engagement with the sealing ring up to a short distance from the cylinder wall.

VIn Fig. l the sealing ring is shown as it is when mounted upon the pistonbody but the piston is outside of the cylinderin'which it is to be used. This is referred to as the normal or unrestrained position of the ring since it isfree of any peripheral confinement by the cylinder.

, It will benoted that the normal outside diameter of the sealing Vring is slightly greater than the inside diameter of lthecylinder in which it is to be used, the inner face .of the cylinder walls being indicated by the broken lines 22'. The exact amount by which the normal diameter of the sealing ring exceeds the diameter of the cylinder depends to some extent upon various factors including the physical characteristics of the material from which the ring is made and also the diameter of the cylinder. In a typical case the diameter of the ring for a piston for av 6. cylinder when unrestrained exceeds the diameter of the cylinder by about Mt or about 4%. However, with a larger diameter or a relatively softer material or by' making changes in dimensions of the body, displacementof portions of the sealing ring becomes easier so that the proportional amount of oversize may be increased.

The outside diameter of the sealing ring preferably is alittle greater at each end to improve contact of the ring with the cylinder walls at the ends of the ring and provide a` wiping action over the cylinder wall which cleans off abrasive particles. It may also be greater at they center where the space'between the body and the ring is greatest. The result is a slightly convex profile for the sealing ringi as seen in Fig. 1.

In its unrestrained or normal condition, it will be noticed from Fig. 1, the insider diameter of the sealing ring is at most points in excess of the outside diameter of the piston body at points betweenv flanges 14. This leaves an annular space 21 between the body and the ring which may be of variable size. In the embodiment of Fig. l, the inside surface of the sealing ring lightly engages the surface of the recess in the metal body near each end of the Iring. At either side of this area of engagement, the inner surface of the sealing ring has a slight inclination relative to surface 15 of the piston body so that the space between the sealing ring and the metal body isl greatest at the center of the ring and is' tapered when viewed in cross section. The sealing ring is centrally recessed in order to receive body rib 16 which reduces longitudinal strains due to high pressures and frictional resistance.

The outside surface of sealing ring 20 is preferably provided with a number of circumferential grooves 23 which extend into the body of the ring for a short distance; The width and depth of these grooves should be such that they do not completely close when the ring is inside the cylinder and thereby they form a plurality of annular edges which each have a wiping action over the cylinder wall as the piston reciprocates, similar to the wiping action of the leading. edges 20a.

The piston, consisting -of metall body 10 with sealing ring 20mou`njted upon it, is forced endwise into the cylinder against the resistance offered by the oversized ring; In order to'facilitate insertion of the piston, it is preferable that the ends ofv the cylinder liner 24 be beveled or tapered as indicated at 25r in Fig. 2. Movement of the piston axially over this inclined surface 25 gives a wedgng action which progressively compresses the piston ring -as it is moved axially into the cylinder.

As may be seen from a comparison of Figs. 1 and 2, when the sealing ring is confined by the Walls of the cylinder, the ring is deformed with respect to its unrestrained shape by having most parts of it, though not necessarily every portion, displaced radially inward. Although this may be regarded asf compressing the ring because the outside diameter is reduced, the total volume of the ring may remain substantially unchanged since the rubberlike material-is itself substantially incompressible. Actually, there is a radiallyv inward displacement of most of the sealing ring` which is accompanied by a certain amount of axial displacement of portions of the ring. Thus it will be noticed that in Fig. 2 displacement inwardly of t-he ring from its normal or unrestrained position brings it into liquid-tight contact with outsidesurface 1S of the pi-'ston body and also with the opposing faces ofanges 14. These opposing faces. of the two flanges are given a slight inclination so thatthey converge outwardly. in order to resist any tendency of the r-ingy to move outof the recess around the body.

Axial displacement of portions of the ring is limited by flanges 14- which also prevent relativel axial movement of the ring and body when the piston is in operation. Axial displacement of the outer portions of thesealing ring beyond flange 14 is relatively unlimited as shown by the fact that the overall axial dimension ofthe ring` at its periphery is slightly greater than that of the rn'etal body 10 whereas in the free or normal condition, the ring. and body have substantially the same' maximum axial dimen-v sion, `As-showninFig. 2, grooves 23 are narrowed down at their outside ends,- the material in the ribs between thev grooves being displaced into the grooves to some extent as a result of the confinement of the ring by the cylinder wall. The amount of axial elongation is'variable andcan be controlled by'the design. p

When the assembled piston is forced into' the cylinder', the outside diameter of the sealing ringis reduced and the material of the ring is placed under compression at all positions because of the confinement ofthe ring by the cylinder wall. This produces within the bodyy of the ring internal strains whichl tend to expand the ring to its normal diameter and thus the ring presses tightly against the cylinder wall atY all times.` This tendency of the ring to expand against the wall is a result of the inherenti characteristics of the rubber-like materialY and is created by thecompression of the ring when it is forced into the cylinder. This expansive tendency remains for a considerable time-sincethe ringV as a whole would necessarily be wornV down until its normal outside'diameter when-unrestrained becomes equal to the internal diameter of the cylinder` before relieving these strains tending to expand the ring.` The ring wears evenly around' its entire circum` ferencethus providing aneffective pressure-tight fit foras long as outward tension acts. This tendencyv to expand presses the ring into fluid-tight engagement not only with.. the cylinder Wallslbut also with the outside surfaces of. the piston body, thus assuring a continuous pressuretightV seal withvthe ring` at all locations.l

Itisrpreferred,v although not necessary, to provide rib 16"to assist flanges 14 in applying axially directed forces tothe ring tof-move it Within the cylinder as the piston reciprocates. p

At and just behind the leading edges 20aA the ringfis preferably made with agreater diameter thany at the central portion because the ring is long enough at these ends to overhang the metalbody,.as seen in Fig. 2. Since Vtheringy is thinner hereand 'not backed up by the more orless semi-rigid portion of the ring between an'g'es 14, thisportion can be` more easily displaced inwardly, thereby conforming readily to variations inthe cylinder diameter at all stages of piston movement, and providing an effective wiping action against' the cylinder wall that prevents abrasive particles from beingforced between the sealing ring and cylinder wall. Fluid pressure acts to force the leading edges against the' cylinder wall.

There is shown in Fig. 3 a modified form of the inven-v tion in whichbody10a of the piston is the same as already described except that body rib 16'has been omitted and this case, the inner surface of sealing ring 20a is made cylindrical,` or substantially so.- Asl a consequence, the sealing ring and piston body engage each other at or near flanges 1.4 but are normally slightly spaced apart at 21a over most-of. the length of the ring thus creating a cavity substantially as shown; Space 21a between the ring and the' bodyf is tapered;` viewed in` cross-section, with. itsVV greatest dimension at or near the center of the ring and body.

The inner surface of the ring is provided with a plurality of annular grooves 28, each of which forms a space or cavity into which adjoining portions of the ring may be displaced when the piston i-s confined within the cylinder. These grooves serve much the same function as space 21a, since all these spaces allow the ring to be displaced inwardly, filling up these spaces to a greater or lesser extent. The outer surface of ring 20a is made smooth, the external grooves 23 of the previous form being omitted.

The central portion of the ring is made a little thicker than at either side of the center. This causes a little greater stressing or compressing of the ring at the center to force rib 27-intoV recess 26.

Another modified form of my invention is shown in Fig. 4 in which piston body 10b is essentially the same as shown in Fig. l except for the omission of rib 16. Sealing ring 20b is likewise similar to the ring shown and described in connection with Fig. l except that the recess has been greatly enlarged in order to accommodate a body of sponge rubber V30 which is firmly glued to the inside cavity of the sealing ring.

In the form of piston shown in Figs. l and 2, the oversized sealing ring could be displaced inwardly when confined by the cylinder because of the space normally occurring between the body of the piston and the sealing ring when the latter is free or unrestrained. This condition exists in Fig. 4 because the body of sponge rubber 30 is compressible within its own volume, thus providing an equivalent to the space 21 between the ring and the metal body of the piston. However, this space occupied by the sponge rubber does not entirely disappear when the ring is confined it is simply reduced in size. It is at all times filled by the sponge rubber which continues to exert an outward pressure against the ring to expand it against the cylinder wall. At the same time the pressure of the sealing ring at its end-portions against the body of the piston and in the middle section against the sponge rubber body is adequate to provide a fluid-tight seal with the metal piston body.

In Fig. 5 is shown another modication of my invention in which the unitary body construction is replaced by a two-piece body. The piston body indicated generally at c comprises a section 32 having a tapered bore adapted to receive the tapered section on piston rod 12a. The second body section 33 has a central cylindrical bore adapted to slide upon the cylindrical portionrof piston rod 12a. The two body sections 32 and 33 telescope on each other, have `complementary cylindrical surfaces which` slide on each other at 34. The cylindrical surface on body section 32 is shorter than the corresponding surface on body section 33 so that the two body sections come into tight engagement along radial shoulder 35 but there is a small clearance left between them at 36. A nut 38 is screwed on to the end of the piston rod to bear against sec-- pressure-tight t even in a greatly worn or oversized cylinder.

Sealing ring 20c may be of any of the designs already described, but advantage is preferably taken of the division of theV metal body into two parts to modify somewhat the diameter of the internal surface of the ring as compared with the outside diameter of the surfaces 15e of the body. If the body is made of slightly larger external diameter than the inside of the ring, then as the two halves of the body are moved axially together with the ring in position between flanges 14a, the inclined outer surfaces 15C of the body exert an expanding force on the ring. As a result, the ring and body are brought into uid-tight engagement with each other. Also the ring can be expanded readily to compensate for excessive wear or oversize due to reboring. In practice it increases the volumetric factor of expansion by about 50%.

This is not intended to replace the oversize character of the ring, since it is originally made larger than the internal diameter of the cylinder and is then compressed radially inward, as described before, when the piston is inserted in the cylinder. However, the final amount of oversize may be somewhat increased by expanding the ring to larger than its original size by bringing the body sections together. This construction is particularly useful when liners or cylinders are considerably worn by abrasion and lightly scored or have been rebored to oversize.

From the foregoing description it will be apparent that various changes may be made in the detailed sizes or dimensions and arrangements of parts of my improved piston without departing from the spirit and scope of my invention. Also, it is contemplated that other changes than those specifically pointed out may be made while still within the practice of my invention. Accordingly, it is to be understood that the foregoing description is considered to be illustrative of, rather than limitative upon, the appended claims.

I claim:

l. A piston construction for use in a cylinder of a reciprocating pump or the like that comprises: a centrally located metal body adapted to be attached to a piston rod for reciprocation within a cylinder; and an annular sealing ring of rubber-like material surrounding and mounted upon the metal body, said ring having a normal diameter in excess of the cylinder diameter when free of externally applied compressive forces so that when in place on the body and confined within the cylinder the ring is under radial compression at all positions and has internal strains tending to expand the ring radially to its normal diameter.

2. A piston construction as in claim 1 in which the sealing ring has a plurality of circumferential grooves in the outside surface that reduce in size to permit relocation of peripheral portions of the ring when the ring is confined within the cylinder.

3. A piston construction for use in a cylinder of a reciprocating pump or the like that comprises: a metal body of unitary construction provided with a central bore to receive a piston rod for connection thereto, the body having a pair of fixed radially extending anges spaced apart axially of the body and defining an annular recess around the body; and a sealing ring in the recess of resilient deformable material of substantially the same axial dimension as the spacing between said flanges and extending radially beyond the flanges to engage the inside wall of a cylinder when within and confined by the cylinder, the normal outside diameter of the ring when externally unrestrained being greater than the internal diameter of the cylinder.

4. A piston construction for use in a cylinder of a reciprocating pump or the like that comprises: a metal body of unitary construction with a central bore to receive a piston rod for connection thereto, the body having a pair of fixed radially extending flanges spaced apart axially of the body and defining an annular recess around the body; and a sealing ring in the recess of resilient deformable material Vof substantially the same axial dimension as the spacing between said flanges and extending radially beyond the flange to engage the inside wall of a cylinder when within and confined by the cylinder, the normal inside diameter of the'ring when unrestrained being in general slightly greater than the outside diameter of the body at said recess whereby there is normally a slight clearance between the body and ring within the recess.

5. A piston construction for use in a cylinder of a reciprocating pump or the like that comprises: a r'netal body provided with a central bore for connection -to a piston rod, said body having a pair of spaced radially extending flanges with an intervening, outwardly facing surface; and a sealing ring of rubber-like material surrounding the body between the flanges and extending radially outward beyond the flanges, the normal outside diameter of the sealing ring when unrestrained being greater than the internal diameter of said cylinder, said ring having an inwardly facing surface; said surfaces normally being in contact at positions near said anges and otherwise spaced apart with slight clearance when the ring is unrestrained, and said surfaces being in engagement over substantially their Whole areas when the ring is within and externally restrained by said cylinder.

6. A piston construction for use in a cylinder of a reciprocating pump or the like that comprises: a metal body provided with a central bore for connection to a piston rod, said body having a pair of spaced radially extending flanges with an intervening, outwardly facing surface; and a sealing ring of rubber-like material surrounding the body between the flanges and extending radially outward beyond the flanges, the normal outside diameter of the sealing ring when unrestrained being greater than the internal diameter of said cylinder, said ring having an inwardly facing surface; one of said surfaces being formed in two sections oppositely inclined to the other surface whereby the two surfaces are in contact at positions near the ends of the surfaces and are spaced apart over their central portions when the ring is unrestrained, and said surfaces being in engagement over substantially their whole areas when the ring is within and externally restrained by said cylinder.

7. A piston construction as in claim 6 in which the metal body is formed in two relatively movable and separable parts of which one part is adapted to be mounted directly on the piston rod and the other part is mounted on the one part, and the outwardly facing surface of the body has two oppositely inclined sections formed one on each of the two body parts.

8. A piston construction as in claim 6 in which the inwardly facing surface of the ring is formed with a plurality of annular grooves forming spaces into which portions of the ring can be displaced when the ring is confined within the cylinder.

References Cited in the le of this patent UNITED STATES PATENTS

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