Patent Publication Number: US-3875806-A

Title: Bellows seal for pump piston rod

Description:
United States Patent H9] Brewster 1 1 BELLOWS SEAL FOR PUMP PISTON ROD Oswald C. Brewster, Litchfield. Conn.  
 [75] Inventor:  
 [73] Assignee: The United States of America as represented by the United States Atomic Energy Commission. Washington. DC  
 [22] Filed: Dec. 12, I944 [2]] Appl. No.: 567,875  
 [52] US. Cl. 74/182; 285/226; 285/299; 138/121 [51] Int. Cl FI6j 15/50 [58] Field of Search .t 286/29; 137/1565;  
 [56] References Cited UNITED STATES PATENTS 1940.924 12/1929 Kellogg 286/29 l 89l.77l 12/1932 Mendenhall et a1... 286/29 X 1305.583 4/1933 Giesler 1 1 t 1 v 286/29 2.333.411] 11/1943 Woods 1 1 i 286/29 X 2 3&#39;I2 3(l2 3/1945 Swindin H 103/148 X FOREIGN PATENTS OR APPLICATIONS 109.131) 1900 Germany 103/148 1 1 Apr. 8, 1975 Primary Eruminer-Samuel Feinberg Attorney, Agent, or Firm.lohn A. Horan EXEMPLARY CLAIM l. A gas-proof seal for reciprocating pumps having a cylinder and a piston reciprocable therein by a piston rod. comprising a tubular axially expansibleeontractable metallic bellows seal having a plurality of bellows convolutions therein, said bellows seal freely surrounding the piston rod and extending continuously between the adjacent cylinder end wall and a relatively remote point on the piston rod, expansiblecontraetible supporting means extending lengthwise of said bellows and connected thereto at predetermined spaced intervals therealong, said supporting means being secured at opposite ends to said cylinder end wall and to said piston rod. whereby said supporting means expands and contracts eoextensivcly with the bellows seal and operates to support the latter and to constrain and guide the same in a predetermined path of linear movement other support members extending lengthwise of the bellows seal. and elements carried by said other support members respectively engaging each bellows convolutions to individually support the same.  
 6 Claims, 3 Drawing Figures PATENTED BIBYS 3.875.806  
 SIZZET 2 or 2 j -SWA/d CBnen s fer BELLOWS SEAL FOR PUMP PISTON ROD This invention relates to new and useful improvements in fluid pumps, and more particularly to fluid pumps of the reciprocating piston type for use with highly corrosive, toxic or poisonous gases.  
  Pumps of this type, when used with such gases. must embody certain characteristics to make them practicable. Thus, such pumps must be proof against the leakage of gas therefrom from the standpoint of safety. Also. they must be proof against the leakage of gas from the economic standpoint for while, for example, in a gas diffusion separation system utilizing a number of stages of such pumps, the volume of process gas handled by a single pump as a whole is quite large, the amounts of gas entering and leaving the system is relatively very small, and hence a very small leakage of the process gas from a later stage pump constitutes a large amount in terms of the feed or product of the system. Conversely, such pumps must be proof against the inleakage of air and other contaminants, such as lubricants, that will react with the process gas.  
  To prevent leakage of the process gas and the inleakage of air and contaminating substances as set forth, it has been proposed to seal the piston rods of such pumps by the use of a suitable metal bellows construction. and while this type of seal has proved quite effective, certain problems and difficulties are presented thereby. In the first place, in reciprocating pumps, the hold-up time. which affects equilibrium time ofthe separation system, is an inverse function of the frequency and, in order to hold this to a minimum, a high operating frequency is essential. Also, because of the limitations upon the amount of compression that can be applied to the bellows seal, and in order to maintain the length of the bellows within reasonable limits, such pumps must of necessity have a substantially short stroke and a relatively large piston diameter to give the pump the desired volumetric capacity. Secondly, to obtain a compression ofthe bellows seal corresponding to the selected pump stroke. it is necessary that the bellows seal have a length considerably greater than the length of the pump stroke, and it has therefor been the practice to construct the bellows seal ofa series of similar bellows sections secured together.  
  It will be apparent that in a bellows column of such length that has one end fixed to the cylinder and the other end reciprocating at the high speed or frequency of operation required, violent inertia waves are generated that set up highly destructive forces in the bellows seal. In addition to the violent inertia waves generated within the bellows column as a whole, it is also apparent that each unit or section of the bellows is subject to the generation within itself of the same type of inertia waves. The bellows section or unit at the active or piston end of the column, of course, is subject to the severest treatment and strong inertia forces operate on each individual convolution of that bellows section. Thus. the maximum acceleration forces in sinusoidal motion are substantial. and the force required to accelerate and decelerate all of the inner convolutions must be transmitted to them through the convolutions at the ends of the sections.  
  The desirability of counteracting these inertia forces in the bellows column and in its component sections will therefore be apparent. and it has been discovered that these destructive forces can be substantially eliminated or effectively counteracted by independently supporting the individual sections of the bellows column with respect to one another while constraining each thereof to move through a proper path of travel, as well as by providing adequate support for each of the several convolutions in each bellows section or unit. Furthermore, such an arrangement enables the over-all compression and expansion of the seal to be distributed equally among its several component sections so that each section is compressed and expanded through but a fraction of the over-all stroke, well within the compression-expansion limit of each section, to thereby insure a long operating life for the bellows seal structure.  
  With the foregoing premises in mind, the principal object of the present invention is to provide a novel support structure for the bellows seal of a reciprocating pump whereby destructive inertia forces generated in the bellows are effectively counteracted.  
  Another object of the invention is to provide a novel supporting structure of the character set forth for a sec tional bellows column wherein the individual bellows sections of said column are effectively supported with respect to one another and constrained and guided through a proper path of travel, thereby counteracting the violent forces generated in the bellows column as a whole.  
  Another object of the invention is to provide a novel supporting structure for a sectional bellows seal column wherein the over-all compression and expansion of said seal is distributed equally among the several sec tions thereof so that each section is compressed and expanded through but a fraction of the over-all stroke and well within the compression-expansion limit of each section, to thereby insure a long operating life for said seal column.  
  A further object of the invention is to provide a novel support structure for the individual convolutions of each bellows section of the column to counteract destructive inertia forces generated within each belows section.  
  These and other objects ofthe invention and the various features and details of the construction and operation thereof, are hereinafter fully set forth and described with reference to the accompanying drawings. in which:  
  FIG. 1 is an elevation view partly broken away of a reciprocating piston type pump having a bellows seal embodying the present invention;  
  FIG. 2 is a view in side elevation of one section of the bellows seal showing one construction contemplated by the present invention for individually supporting the several convolutions of the bellows section; and  
  FIG. 3 is a side elevational view to reduced scale of a seal assembly having associated therewith a sectional bellows seal incorporating the present invention.  
  Referring now more particularly to FIG. 1 of the drawings, the present invention is illustrated in association with a pump of the double acting reciprocating type, comprising the usual working cylinder I provided with an intake connection 2 and discharge connection 3, upper cylinder head and valve chest 4 and lower cylinder head and valve chest 6. A vertically operating piston (not shown) is driven by a continuation of piston rod 5 that passes axially through a bellows seal I0 and is actuated by a driving mechanism located within the crankcase 8 which may be of any suitable type such as. for example, a conventional Scotch yoke. The working cylinder 1 is also provided with suitable intake and discharge valves and the necessary parts and passages in the cylinder heads. The cylinder 1 and crankcase 8 are interconnected and rigidly supported relative to one another by suitable frame supports 9.  
  In the illustrated embodiment of-the invention, the bellows seal 10 has its lower end secured to the piston rod 5 and its upper end is secured to the lower cylinder head 6. The bellows seal may be surrounded by a suitable jacket 7 so that the space surrounding the bellows seal 10 and enclosed by the jacket 7 may be maintained at a pressure equal to the average internal pres sure ofthe seal, thereby decreasing pressure stresses on the bellows and prolonging their life.  
  As will be apparent from the drawings, and particularly FlG. 1 thereof, provision of the bellows seal 10 about the piston rod 5 and intermediate the piston and stationary cylinder head 6, serves effectively both to prevent the gases in the cylinder from coming into contact with oils and greases employed to lubricate the piston rod 5, and to prevent leakage of such gases to the exterior of the pump outwardly along the said piston rod 5.  
  The bellows seal 10 is in the form of a column and is composed ofa plurality or series of similar bellows sections 12 embodying, for example, the construction of the bellows section shown in FIG. 2 of the drawings. As there shown, each bellows section 12 may comprise a pair of annular end rings 13 and 14, respectively, intermediate which is secured a predetermined length of a metallic Sylphon bellows 15 of suitable diameter and having a given number of bellows convolutions of suitable size and configuration. The seal column 10 is formed by securing together in axial alignment, and with their respective end plates or rings 13 and 14 maintained in abutting, fluid-tight relation, the prescribed number of bellows sections 12, for example, as shown in FIG. 3 of the drawings.  
  As previously stated, in pumps of the character here involved it is necessary that the bellows seal 10 be considerably longer than the length ofthe stroke of the piston in order to obtain a corresponding compression of the bellows seal 10. The result of this construction is that, at the high speed or frequency of pump operation required, violent inertia waves are generated which set up highly destructive forces in the individual convolutions of each bellows section 12, as well as in the bellows seal column as a whole. These destructive forces, of course, are proportionately greater at the active or lower end of the bellows seal 10 than at the inactive or fixed end thereof secured to the stationary cylinder head 6.  
  In accordance with the present invention, and for the purpose of individually and yieldingly supporting the Sylphon convolutions of the bellows section, there is secured to each such section 12 a plurality of posts 16 of rubber disposed exteriorly of each section 12 longitudinally thereof at intervals spaced circumferentially thereof, for example, 90 apart. These rubber posts 16 have their opposite ends secured to the end rings 13 and 14, respectively, of each section 12, as indicated at 17 and 18, and the individual convolutions of the Sylphon section 15 are supported from said posts 16 by means of suitable clips or the like 19. These clips 19 may be of generally U-shape as illustrated and arranged to receive therein the peripheral edge of a bellows convolution in the manner shown. The clips 19 may be provided with projecting pin portions 20 adapted to extend radially of the section 12 and through suitable openings or slots 21 in the posts 16 in which they may be secured against displacement by any suitable means such as cotter pins, nuts, or the like 22.  
  The several section supporting posts 16 are coexten sive in length only with the particular section 12 with which associated and are independent of the posts of adjacent sections 12. Hence, while the individual convolutions of each of the several sections 12 are adequately supported by the posts 16 against destructive forces generated within the individual sections, it will be apparent that said posts 16 provide no effective support against such forces operating upon the seal column 10 as a whole.  
  To counteract destructive forces set up by inertia waves in the seal column 10 as a whole, the present invention contemplates the provision of a novel support&#39; ing structure for the column wherein the individual bellows sections 12 are effectively supported with respect to one another and constrained and guided through a predetermined path of linear travel during compression and expansion thereof.  
  To this end, therefore, there may be provided along diametrically opposite sides of the seal column 10, expansible-contractible support structures 23 each comprising a series of articulated pairs of links 24 and 25, respectively, arranged crosswise of each other and pivotally connected together at their midpoints as indicated at 26, the opposite ends of said links being pivotally connected to the ends of the links of adjacent pairs, respectively, as indicated by reference numeral 27, and forming, in effect, substantially a pantograph, or lazy tongs construction. The crossed links 24 and 25 ofeach pair thereof in the structures 23 are pivotally secured at their central pivot points 26 to the seal column 10 at the junction of the adjacent bellows sections 12, as shown in FIG. 3 of the drawings. By virtue of this construction, it will be observed that the structures 23 will expand and contract in accordance with expansion and compression of the several bellows sections 12 of the seal column 10 and operate to support the individual sections 12 with respect to one another and at the same time constrain and guide them through a predetermined linear path of travel, thereby effectively counteracting the destructive forces set up in the column by the inertia waves generated as aforesaid.  
  In the embodiment of the invention illustrated, the seal 10 comprises six bellows sections 12, and, in operation of the pump, each section 12 of the seal undergoes an over-all expansion-contraction equal to onesixth of the length of the stroke of the piston. Thus, for example, in the case of a pump having a stroke of two inches, each bellows section 12 will have a compression-expansion stroke of 0.333 inch. It will be obvious, of course, that the invention is not limited to a bellows seal 10 comprising any particular number of sections 12, and that the foregoing example, as well as the arrangement shown in the drawings, are illustrative only.  
  From the foregoing, it will be observed that the present invention provides a novel supporting structure for a gasproof bellows type seal for reciprocating piston pumps, wherein the component sections of the seal column 10 are individually supported with relation to one another and constrained and guided through a fixed path of linear travel. Likewise, the several bellows convolutions of each seal section 12 are individually supported. The invention also provides a novel supporting structure wherein the over-all compression and expansion of the column is distributed equally among its component sections 12 so that each section 12 is compressed and expanded through but a fraction of the over-all stroke of the column and well within the compression-expansion limit of each section, to thereby insure a long operating life for the bellows seal column. By these constructions, the severe destructive forces set up by the violent inertia waves generated in the be]- lows by the high frequency or speed of reciprocation of the pump are effectively counteracted, thereby substantially prolonging the operating life of the bellows seal.  
  It will be obvious, of course, that in lieu of positioning the seal column between the piston and adjacent wall of the cylinder as in the illustrated application of the invention, the seal column may be variously arranged so long as it extends between a movable part of the piston-piston rod assembly and a relatively fixed part of the pump casing to provide a fluid-tight seal between the interior and exterior of the pumping chamber.  
  While a particular embodiment of the present invention has been shown and described herein, the invention is not to be limited to such disclosures, and it is contemplated that changes and modifications may be made or incorporated within the scope of the claims.  
 l claim:  
  1. A gas-proof seal for reciprocating pumps having a cylinder, and a piston reciprocable therein by a piston rod. comprising a tubular axially expansiblecontractable metallic bellows seal having a plurality of bellows convolutions therein, said bellows seal freely surrounding the piston rod and extending continuously between the adjacent cylinder end wall and a relatively remote point on the piston rod, expansible-contractible supporting means extending lengthwise of said bellows and connected thereto at predetermined spaced intervals therealong, said supporting means being secured at opposite ends to said cylinder end wall and to said piston rod, whereby said supporting means expands and contracts coextensively with the bellows seal and operates to support the latter and to constrain and guide the same in a predetermined path of linear movement, other support members extending lengthwise of the bellows seal, and elements carried by said other support members respectively engaging each bellows convolutions to individually support the same.  
  2. A gas-proof seal for reciprocating pumps having a cylinder, and a piston reciprocable therein by a piston rod, comprising a tubular axially expansiblecontractible metallic bellows seal having a plurality of bellows convolutions therein, said bellows seal freely surrounding the piston rod and extending continuously between the adjacent cylinder end wall and a relatively remote point on the piston rod, expansible-contractible supporting means extending lengthwise of said bellows and comprising articulated pairs of pivotally connected links connected at their respective pivots to the bellows seal at predetermined spaced intervals therealong, said supporting means being secured at opposite ends to said cylinder and wall and to said piston rod, whereby said supporting rneans expands and contracts coextensively with the bellows seal and operates to support the latter and to constrain and guide the same in a predetermined path of linear movement, other support members extending lengthwise of the bellows seal, and ele ments carried by said other support members respectively engaging each bellows convolution to individually and yieldingly support the same.  
  3. A gas-proof seal for reciprocating pumps having a cylinder, and a piston reciprocable therein by a piston rod, comprising a plurality of expansible-contractible tubular axially expansible-contractible metallic bellows sections secured end to end and forming a seal column freely surrounding the piston rod and extending continuously between the adjacent cylinder end wall and a relatively remote point on the piston rod, said tubular bellows sections each having a like number of bellows convolutions therein, resilient support members extending lengthwise of each section at intervals circumferentially thereof, the support members of each section being independent of the support members of adjacent sections, and means carried by each of said support members respectively engaging each bellows convolution of the associated section to individually support each convolution thereof.  
  4. A gas-proof seal for reciprocating pumps having a cylinder, and a piston reciprocable therein by a piston rod, comprising a plurality of expansible-contractible tubular axially expansible-contractible metallic bellows sections secured end to end and forming a seal column freely surrounding the piston rod and extending continuously between a fixed part of the pump and a relatively remote point on the piston rod, said tubular bellows sections each having a like number of bellows con volutions therein, support members extending lengthwise of each section at intervals circumferentially thereof, the support members of each section being independent of the support members of adjacent sections, means carried by each of said support members respectively engaging each bellows convolution of the associated section to individually support each convolution thereof, and expansible-contractible supporting means extending lengthwise of the seal column and connected thereto at the junction of adjacent bellows sections, said supporting means being secured at opposite ends to said cylinder and to said piston rod, whereby said supporting means expands and contracts coextensively with the seal column and operates to support the individual sections relative to one another and to constrain and guide the same in a predetermined path of linear movement.  
  5. A gas-proof seal for reciprocating pumps having a cylinder and a piston reciprocable therein by a piston rod, comprising a plurality of expansible-contractible tubular axially expansible-contractible metallic bellows section secured end to end and forming a seal column freely surrounding the piston rod and extending continuously between a fixed part of the pump and a rela tively remote point on the piston rod, said tubular bellows sections each having alike number of bellows convolutions therein, support members extending lengthwise of each section at intervals circumferentially thereof, the support members of each secion being independent of the support members respectively engaging each bellows convolution of the associated section to individually support each convolution thereof, and expansible-contractible supporting means extending lengthwise of the seal column and comprising articulated pairs of pivotally connected links connected at their respective pivots to the seal column at the junction of the sections thereof, said supporting means being secured at opposite ends to said cylinder end wall and to said piston rod, whereby said supporting means expands and contracts coextensively with said seal column and operates to individually support the sections thereof with respect to one another and to constrain and guide the same in a predetermined path of linear movement during expansion and contraction of the seal by reciprocation of the piston rod.  
 6. As an article of manufacture. the subcombination