US3781942A - Follower for material containers - Google Patents

Abstract

A flexible follower assembly for use in withdrawing viscous material from bulk containers consisting of a flexible diaphragm coextensive with the transverse cross-section of the container and including annular members attached to the diaphragm sheet for wiping up against the inside walls of the container. The flexible diaphragm and wiping rings are maintained in position within the container by a relatively stiff circumferential frame. The entire follower assembly, wiper and diaphragm and frame, are disassemblable so as to be insertable through the normal access opening of such a container, for assembly therewithin.

Description

United States Patent [1 1 Coleman Jan. 1, 1974 [5 FOLLOWER FOR MATERIAL CONTAINERS 3,159,301 12/1964 Anderson 220/93 X [7 in e to ar ce B. Coleman, Oa land 2,343,154 2/1944 Morgan et a1. 220/93 X Primary ExaminerLeon G. Machlin [73] Assignee: Fabricated Metals, lnc., San Att0rneyManfred W. Warren et al.

Leand ro, Calif. 22 Filed: June 14, 1971 [57] ABSTRACT [21] Appl. No.: 152,721

[52] US. Cl l5/246.5, 220/93, 222/3865 [5 I] Int. Cl B67d 5/64 [58] Field of Search l5/246.5; 220/93; 22l/279, 280; 222/386, 386.5, 389; 217/86; l4l/27, 357; 184/39, 46

[5 6] References Cited UNITED STATES PATENTS 2,328,363 8/!943 Sundholm 220/93 X 775,6l0 ll/l904 Seacrist 217/86 X A flexible follower assembly for use in withdrawing viscous material from bulk containers consisting of a flexible diaphragm coextensive with the transverse cross-section of the container and including annular members attached to the diaphragm sheet for wiping up against the inside walls of the container. The flexible diaphragm and wiping rings are maintained in position within the container by a relatively stiff circumferential frame. The entire follower assembly, wiper and diaphragm and frame, are disassemblable so as to be insertable through the normal access opening of such a container, for assembly therewithin.

9 Claims, 6 Drawing Figures PATENTEU 1 7 INVENTOR. CLARENCE B. COLEMAN Z/W MZW' ,47 TOR/v15 Y5 1 FOLLOWER FORJMATERIAL CONTAINERS This invention relates to certain improvements in bulk material containers, particularly those for receiving, storing and/or transporting relatively viscous materials such as grease, ink, pigment, and the like. More especially, this invention is directed to a flexible follower assembly which may be inserted through the access opening of such a container and then assembled in the interior thereof, thereafter tourge the contained viscous material into apparatus, for example a pump, used to draw the material-out of the container, or force the material out through an outlet.

Removal of viscous materials from bulk containers has long plagued the industry. Heavy greases, for example, are almost impossible to remove completely from the containers in which they are received, stored and transported. While some materials in certain viscosity ranges and at certain temperatures may be removed by means of pumping, such technique is almost totally ineffective with highly viscous materials. The material immediately adjacent to the pump inlet or tank outlet may be drawn out; but, because the adjacent material to too thick to flow no additional material can be withdrawn. Often a void is formed immediately adjacent to the pump inlet and the pump pulls air instead of material, where there is communication to the atmosphere. Often the material must be literally shovelled or scooped out, sometimes even necessitating inversion of the entire container. All in all, a costly, inconvenient, time consuming and generally unsatisfactory state of affairs.

Some improvement has been achieved in the past by means of so-called follower devices. For example, it is known to provide a relatively stiff diaphragm coextensive with the transverse cross section of the container being serviced, with such diaphragms sometimes secured to the inside of the container by means ofa flexible sock secured to the periphery of the diaphragm and around the inside surface ofthe container. As the material is removed, the diaphragm is urged to follow the viscous material by the partial vacuum created by the material removal, and the action of the diaphragm which then bears down upon the material in the container tends to urge the substance into the pump enclosures so that it will keep flowing through the pump. The trouble with such systems, however, as I know them is that l the diaphragm and sock assembly are relatively permanently affixed to the container and not easily transferred from one to another; (2) if transferrable at all, the relatively solid diaphragm is difficult to relocate-one must remove practically the entire top dome of the container from which it is being taken as well as the one to which it is being moved in order to get it in and positioned correctly; (3) it is difficult, if not impossible, to clean out a container utilizing one of the prior art devices, unless the entire assembly is removed; and the same problem occurs generally where the diaphragm requires repairing, or if the container is sought for a use where the follower assembly is neither required nor desired.

Thus it is an object of the present invention to provide a flexible follower assembly that will more readily conform to the cross section of the container as the viscous material is withdrawn from the container therefor, and which may be readily assembled within the container utilizing normal access openings, thus eliminating the need for removing the entire dome of a bulk container, or nearly so, in order to assemble the follower in place.

It is a feature and advantage of the present invention that by being able to utilize a flexible and relatively free follower diaphragm, rather than one that is rigid and/or attached to the sides of the container as has often been used in the prior art with which I am familiar, the viscous material being removed or pumped into the container may be more effectively protected against contact with the surrounding atmosphere.

It is a further object of this invention to provide a follower for the use in pumping viscous materials into and out of bulk material containers which is readily removable and replaceable from one such container to another; may readily conform to inevitable variations within a container size; may be produced for almost any cross section of container; and generally economical to fabricate, maintain and use.

Further objects, features, and advantages will be apparent to one of ordinary skill in the art upon a reading of the specification which follows and with reference to the accompanying drawing wherein FIG. 1 is a side elevation, partially in section, of a container equipped with one embodiment of my invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2;

FIG. 4 is a sectional view corresponding to that of FIG. 3 only of an alternate embodiment of my invention;

FIG. 5 is a sectional view of the bottom portion only of a container embracing a further improvement of my invention which may be used in combination with either the embodiment disclosed by FIGS. 13, or the alternative embodiment of FIG. 4; and

FIG. 6 is a fragmentary sectional view of the bottom portion only ofa container embracing a further alternative embodiment of a portion of my invention which may be used in combination with either the embodiment disclosed by FIGS. 1-3, the alternative embodiment of HO. 4, or the alternative of FIG. 5, omitting grate 218.

It is at once appreciated that in addition to all of the advantages generally associated with follower assemblies, mine has the initial and significant advantage of being able to be placed and thereafter assembled in the interior of a bulk material container through an access opening as normally provided in the top dome of most such containers.

More specifically, to understand the foregoing, I refer first to FIG. 1 wherein there is depicted bulk material container 12 holding viscous material 14 in the process of either being withdrawn or placed into the container through conduit 16 by means of a pump assembly (not shown) whose enclosures are in fluid communication with the conduit part. Container 12 is provided with access opening 18 of a more or less conventional type and size (in large bulk material containers of the type illustrated here, large enough for a man to pass through so as to be able to inspect, repair, and clean the interior of the container). The opening is defined by a lid-receiving lip 20, cover 22, and conventional means to secure the cover in place over the opening (not shown).

The flexible follower assembly 24 comprises a wiper means assembly 26 (see also FIG. 3) and stiffener means 28. In the embodiment shown in FIGS. 1-3, the wiper means includes a flexible sheet 30 fabricated of a relatively thin, cloth-like and liquid impervious material such as neoprene coated canvas, having annular members 321, 32u secured thereto as by conventional adhesives and shaped to provide outer circumferential surfaces 341, 34a for relatively close fitting sliding contact with container inside walls 36. Annular members 321, 32a are of a resilient, foldable material; and l have found the use of neoprene rubber stock material satisfactory.

From the foregoing, it may be seen that wiper means assembly 26, being made up of flexible and foldable components, may be rolled up into a so-called collapsed form, or opened out to an expanded form. When in collapsed form, the entire assembly may be bundled up and manually inserted through access opening 18 of the container. Thereafter, once in the interior of the container, the wiper assembly may be opened to the expanded form (as shown in the drawings).

Stiffener means 28 is also fabricated to be easily demounted to a form passable through access opening 18; and thereafter reassembled within the container. In the embodiment of FIGS. 1-3 such means comprises arcuate segments 38a, 38b and 380, each fabricated of flat bar stock and formed to their respective arcuate shapes, each of which may easily fit through access opening 18. Each of the sections may be adjustably secured to the other in end-to-end alignment to form a circumferential frame, by means of bolting plates 40a, 40b and 40c provided with slotted holes and ordinary nut-bolt-washer sets for conventional securement (the slotted holes providing for some degree of circumferential give and take for final fitting and assembly within a particular container).

Thus stiffener means 28 when collapsed, or disassembled, is insertable through access opening 18 for passage into the interior of the container and reassembly therein and attachment to the wiper means assembly so as to perfect the flexible follower of the present invention, as will be further explained below; but from the foregoing it may now be readily appreciated and understood how I achieve one of the foremost advantages of my invention, that is to say the ability to assemble and disassemble the entire device and insert the components therefor through a normal container access opening for ready reassembly therewithin in a manner relatively easily and speedily accomplished without major disruption of the container itself.

It is a further advantage of my invention, that unlike stiff or rigid diaphragm followers, the flexible diaphragm of my invention is able to maintain intimate contact with the material beingwithdrawn from, or placed into, the container. However, in order to obtain the benefits and advantages of a flexible diaphragm, such a diaphragm must be provided with a circumferential edge capable of wiping down the walls of the container during operation; and generally occupying the entire cross section of the container.

This is achieved in accordance with the present invention by the use of flexible sheet 30 which, in expanded form, opens out to form a flexible diaphragm coextensive with the transverse cross section of the container, and having outer circumferential surfaces 341 and 34a in relatively close fitting sliding contact with inside walls 36 of the container. To provide the necessary body at the outer periphery of the diaphragm and achieve the close fitting desired to effectively wipe down the side walls of the container during operation, and maintain close contact with the material being ejected or admitted, flexible diaphragm 30 is reinforced by annular members 321 and 3414 as described hereinabove. Annular members 341 and 3414 are maintained in their respective positions and in close fitting sliding contact with walls 36 by means of circumferential frame comprising segments 38a and 38b and 38c of assembled stiffener assembly 28. In addition, stiffener means 28 in assembled form within the container maintains diaphragm 30 in its appropriate operating position.

To assure complete and snug fitting of the wiper means about the inside circumference of the container,

I provide a turnbuckle 42 having adjustable threaded rods 44 and 46 whose outer ends are received in sockets 48 and 50, mounted, respectively, on the inner surfaces of segments 38b and 38c. Once assemblled within a container, and carrying the wiper assembly as shown in the drawing and described hereinabove, turnbuckle 42 may be turned to expand the entire frame assembly, before final tightening of the nut bolt-washer assembly at plates 40a, 40b and 40c. I

Also, in the embodiment of FIGS. 1-3, additional tension to support upper annular member 3214 is provided in that portion of the diaphragm cloth immediately circumjacent to the upper annulars. This is achieved by means of draw-string 52 cinchably carried within edge welt 54, the draw-string ends (not shown) being tyable upon pulling to the desired tautness.

An alternative embodiment of my invention is shown at FIG. 4. There I substitute for stiffener frames 38a, 38b, 38c; and annular members 34] and 3414, a single element, that of pneumatically inflatable tube 128. One of the obvious advantages of this embodiment is the few component parts required; and, in many ways, the even easierjob of assembling that is involved than is the case with the primary embodiment of my invention described hereinabove with reference to FIGS. 1-3.

More particularly, the embodiment of FIG. 4 comprises flexible sheet which is drawn about tube 128, after the latter is placed within the container and inflated by means of a conventional valve assembly 140. By appropriately inflating and pressurizing tube 128 (which in some instances may be the inner tube of a conventional vehicle tire assembly, or especially fabricated from suction hose stock, for example), the latter urges the diaphragm cloth wrapped about it into close fitting sliding contact with the inside walls of the container. That is diaphragm 130 acts as diaphragm 30 as explained above with reference to FIG. 3, but at the same time the outer periphery of diaphragm 130 wipes the wall in a manner similar to annulars 32! and 321: as explained hereinabove. A draw-string 152 is provided within seam welt 154 to complete the assembly.

As a further alternative to my invention, and again with reference to FIG. 4, inflatable tube 128 may be replaced with a relatively rigid or semi-rigid stock mate rial. Such a tube (not specifically illustrated in the drawing) may be fabricated of a material flexible enough to be collapsed and inserted through the container opening; and then spreadably held in conformity to the cross sectional perimeter of the container by means of such devices as turnbuckle 42 described hereinabove, or two or more such turnbuckle assemblies arranged in a V, Y or othe suitable configuration, to exert the desired radially outward pressure of the tube against the container walls. Also, such a tube could be sectionalized (also not specifically illustrated) and reassembled within the container by various suitable expedients such as sleeves or other devices apparent to those skilled in the art and hence not described herein.

An additional improvement to my invention may be achieved with certain modifications to the container design and the addition of one element to be described hereinbelow with reference to FIG. 5. The advantage of this additional improvement is that while my invention is more effective than other apparatus and methods with which l am familiar for the removal of viscous material, still a small percentage remains trapped at the bottom of the container and is unable to be removed because the descending flexible diaphragm obstructs the pump conduit 16 opening before complete evacuation occurs.

To cure these ills, and with reference now to FIG. 5, I modify the bottom portion of the container to provide sump 215 below the elevation of the bottom surface 220 of the container. Sump 215 is merely a relatively limited enclosure in fluid communication via opening 222 with the bottom and interior of the container. The sump in turn is also in fluid communication with conduit 216 which, as with conduit 16 in the primary embodiment, is in communication with pump enclosures not shown In addition, I provide a grate 218 which may be fabricated of any stock material, for example that of which the tank body is constructed although in a form more adaptable to grating. The area of grating should be at least somewhat greater than sump opening 222 itself and overlay the latter; preferably the grating should extend over as much of the tank bottom as possible, as shown in the drawing, to provide for maximum material withdrawal. As follower diaphragm 30 (or 130) proceeds downwardly during withdrawal of material, and approaches the lower reaches of the container, instead of prematurely shutting off the flow of material to the pump inlet diaphragm 30, or 130, will continue to urge material downwardly into sump 215, the invasion therein by the diaphragm sheet being prevented by means of grate 218. Now, all that perhaps may not be evacuated from the container is that relatively small amount of material contained in the sump, or below grate 218.

Alternatively, grate 218 may be replaced by means secured directly to diaphragm 30 or 130 to achieve the same end result, yet retain the flexible character of the diaphragm sections. For example, the diaphragm itself may be provided with strips of suitable reinforcement to prevent the diaphragm from collapsing into the sump and obstructing removal of material. Such strips may be of the same material as the grate itself, or other suitable stiffener material such as plastic or the like. Further, the diaphragm may be provided with hob nails" 318 (FIG. 6) secured to the lowersurface thereof and extending downwardly, so as to prevent obstruction of the hump or tank outlet when nearing the bottom of the container. Such alternative diaphragm construction could be utilized in the case of the embodiment of my invention first described hereinabove in respect to FIGS. 1-3. More particularly, the so-called hob nails may comprise relatively small diameter rods fabricated of steel or other suitable material secured by means of adhesive or mechanical fasteners to the bottom face of the diaphragm and extending downwardly therefrom for distance of from one half to two inches, more or less. A plurality of such hob nails may be provided in an array over the bottom face of the diaphragm so as to support and space the diaphragm away from the bottom of the container as the follower assembly descends thereto, thus preventing blockage of the sump or other container outlet.

All the examples of containers described in this specification might appear to some as being of circular cross section; it should be evident to one of skill in the art that this invention may be applied to various containers of different cross section and shapes, and obtain equally salutary results.

Also, in some instances it may be desirable to apply more than atmospheric pressure to the diaphragm in order to purge material from the container. This may readily be accomplished by providing the top cover of the container with an inlet for compressed air, a source thereof for connection to the container, and the use of conventional safety devices including a regulator to control air pressure (if air is usedother fluids are possible), a pressure relief valve, vacuum relief valve, bursting disc, and related conventional equipment known to those of ordinary skill in the art.

It should further be noted that negative pressure arrangements in the portion of the container above the diaphragm may be employed to assist in pumping viscous materials into the container through the input conduit.

The foregoing description of positive and negative pressure assembly additions involve various known prior art devices which are not shown in the accompanying drawing nor described in any greater detail herein.

Finally, it should also be noted that while I have described my invention in terms of introducing and withdrawing material through a conduit or inlet located at the bottom of the container, this is not the only such conduit arrangement that may be used. For example, it is possible to introduce material through the access opening at the top of the container, or through a conduit inlet located at the top or side thereof. ln such instance the inlet conduit includes an extension which terminates at or near the bottom of the container. Diaphragm 30, or 130, is provided with an opening through which such conduit extension passes, and such opening is shaped to fit relatively snugly about the extension. Utilizing such an arrangement, material may be introduced into the container with the follower assembly initially located toward the bottom of the container. As the material accumulates therein, the container fills and the follower is urged upwardly therein. Upon withdrawal of the material, the follower proceeds in the reverse direction and operates in much the same way as described hereinabove in connection with the other embodiments of my invention. lt is also possible to fill the tank using the tube extension as just described, and then withdraw the material through a bottom outlet or sump. If the latter technique is used, then the tube extension itself must be closed off, as by a valve or cap. Alternatively the conduit extension may be removed altogether, in which case the diaphragm opening therefore should be closed off by means of a cap or the like.

1 claim:

1. In a container having an access opening in the top dome thereof and of the type for receiving, storing, and/or transporting relatively viscous material remov able from the container by means of a pump assembly in fluid communication with the bottom interior portion thereof, a flexible follower assembly to urge such viscous material into the pump enclosures during the draw-out operation, comprising:

a flexible sheet fabricated of a relatively thin clothlike and liquid impervious material, said sheet assemblable in a collapsed form and an expanded form, and in collapsed form being insertable through said access opening into the interior of said container for assembly to said expanded form, said sheet in last said form fabricated to provide a diaphragm coextensive with the transverse cross section of said container, said diaphragm having an outer circumferential surface for relatively close fitting sliding contact with the inside walls of the container;

an annular member shaped to provide said outer circumferential surface, said member fabricated of a resilient and foldable liquid impervious material;

means securing said annular member to said flexible sheet; and

stiffener means collapsible to a diminished size and assemblable to an expanded shape, last said means when in said diminished condition insertable through said access opening into the interior of said container for assembly to said expanded shape and attachment to said flexible wiper means to form a relatively rigid frame for maintaining the latter means in its expanded form.

2. The flexible follower assembly in accordance with claim 1 and wherein further said stiffener means comprises:

a plurality of arcuate segments, each fabricated of a relatively rigid material;

securing means to adjustably secure each of said arcuate segments in end-to-end alignment with each other to form a relatively stiff frame defining said expanded shape.

3. The container and flexible follower assembly in accordance with claim 1 wherein said container is further characterized as having a sump at the bottom portion thereof comprising a conduit section secured to the container below the bottom surface elevation thereof and in fluid communication with the interior of the container, said sump adapted for connection to a pump for the withdrawal of viscous materials, and wherein further the combination, with said flexible follower assembly, comprising:

fluid-permeable means located at the bottom surface of said container covering the opening thereof which provides the fluid communication between the interior of the container and said sump conduit, said means fabricated to permit passage of a viscous material therethrough and block passage of said wiper and stiffener means.

4. The container and flexible follower assembly in accordance with claim 3 and wherein further said fluidpermeable means comprises a grate having a planar projection at least coextensive with the opening in the bottom of said container, and means to secure said grate in position over said opening.

5. The flexible follower assembly in accordance with claim 1 wherein said stiffener means comprises an inflatable tube fabricated of a gas-tight, flexible material, said tube when in deflated condition corresponding to the diminished size of said means and when in inflated condition to the expanded shape thereof; and

means for pneumatically inflating and deflating said tube.

6. The flexible follower assembly in accordance with claim 1 wherein said stiffener means comprises a relatively rigid and resilient hollow tube shaped to have at least one separation transverse to the longitudinal axis of said member to form confronting ends thereof, so that the member may be folded and collapsed to said diminished size; and

an insert shaped to fit within said tube to secure the ends of said tube end-to-end and hold the tube in expanded shape.

7. The flexible follower assembly in accordance with claim 1 and wherein further spacer means secured to said diaphragm forming protrusions extending downwardly therefrom to prevent the diaphragm from contacting the bottom of the container when said wiper means descends thereto during operation.

8. The flexible follower assembly in accordance with claim 7 and wherein said spacer means comprises strips of bendable material.

9. The flexible follower assembly in accordance with claim 8 and wherein said spacer means comprises hob nails secured to said diaphragm.

mT n STATES P ENT OFFICE i 01 CQRRECTIUN Patent 3,781,942 I' I I Dated January 1, 1974 I nventor(s) CLARENCE B. COLEMAN It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column l, line 24, "to" is changed to -is Column 4, line 7, "3411" vis changed to --32u--.

Column 4 line '8, "annular members 341 and 34u" is changed to -annular members 321 and 32u--..

Column 4, line 2 1, the Spelling of "assemblled" is corrected to -assembled-,'

Column 4,; line 36, "annular members 341 and 3411; is changed I to -:-a nnular members 321 and 32u,' Y

Column 5, line 2, after "V," insert -X--,

Column 7, line 32fchange said flexible wiper means" to, -said flexible sheet and said annular member-.

Signed and sealed this 1st day of October 1974.

Arrest:

McCGY Mo GIBSON JR." I I C MARSHALL DANN Attesting Officer I Commissioner of Patents USCOMM'DC 60376-1 69 9 U5. GOVERNMENT PRINTING OFFICE I969 0-366-335 FosM PO-IOSO (10-697

Claims (9)

1. In a container having an access opening in the top dome thereof and of the type for receiving, storing, and/or transporting relatively viscous material removable from the container by means of a pump assembly in fluid communication with the bottom interior portion thereof, a flexible follower assembly to urge such viscous material into the pump enclosures during the draw-out operation, comprising: a flexible sheet fabricated of a relatively thin cloth-like and liquid impervious material, said sheet assemblable in a collapsed form and an expanded form, and in collapsed form being insertable through said access opening into the interior of said container for assembly to said expanded form, said sheet in last said form fabricated to provide a diaphragm coextensive with the transverse cross section of said container, said diaphragm having an outer circumferential surface for relatively close fitting sliding contact with the inside walls of the container; an annular member shaped to provide said outer circumferential surface, said member fabricated of a resilient and foldable liquid impervious material; means securing said annular member to said flexible sheet; and stiffener means collapsible to a diminished size and assemblable to an expanded shape, last said means when in said diminished condition insertable through said access opening into the interior of said container for assembly to said expanded shape and attachment to said flexible sheet and said annular member to form a relatively rigid frame for maintaining the latter means in its expanded form.

2. The flexible follower assembly in accordance with claim 1 and wherein further said stiffener means comprises: a plurality of arcuate segments, each fabricated of a relatively rigid material; securing means to adjustably secure each of said arcuate segments in end-to-end alignment with each other to form a relatively stiff frame defining said expanded shape.

3. The container and flexible follower assembly in Accordance with claim 1 wherein said container is further characterized as having a sump at the bottom portion thereof comprising a conduit section secured to the container below the bottom surface elevation thereof and in fluid communication with the interior of the container, said sump adapted for connection to a pump for the withdrawal of viscous materials, and wherein further the combination, with said flexible follower assembly, comprising: fluid-permeable means located at the bottom surface of said container covering the opening thereof which provides the fluid communication between the interior of the container and said sump conduit, said means fabricated to permit passage of a viscous material therethrough and block passage of said wiper and stiffener means.

4. The container and flexible follower assembly in accordance with claim 3 and wherein further said fluid-permeable means comprises a grate having a planar projection at least coextensive with the opening in the bottom of said container, and means to secure said grate in position over said opening.

5. The flexible follower assembly in accordance with claim 1 wherein said stiffener means comprises an inflatable tube fabricated of a gas-tight, flexible material, said tube when in deflated condition corresponding to the diminished size of said means and when in inflated condition to the expanded shape thereof; and means for pneumatically inflating and deflating said tube.

6. The flexible follower assembly in accordance with claim 1 wherein said stiffener means comprises a relatively rigid and resilient hollow tube shaped to have at least one separation transverse to the longitudinal axis of said member to form confronting ends thereof, so that the member may be folded and collapsed to said diminished size; and an insert shaped to fit within said tube to secure the ends of said tube end-to-end and hold the tube in expanded shape.

7. The flexible follower assembly in accordance with claim 1 and wherein further spacer means secured to said diaphragm forming protrusions extending downwardly therefrom to prevent the diaphragm from contacting the bottom of the container when said wiper means descends thereto during operation.

8. The flexible follower assembly in accordance with claim 7 and wherein said spacer means comprises strips of bendable material.

9. The flexible follower assembly in accordance with claim 8 and wherein said spacer means comprises ''''hob nails'''' secured to said diaphragm.

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