Protective jacket and base for pressure vessel

[57] abstract

A pressure vessel, particularly of the type used in water softening service is encased in a light weight protective jacket preferably molded in one piece from a resilient plastic material. In cross section the jacket is of undulant configuration comprising longitudinally extending grooves and ridges with the inner surfaces of the groove portions in surface engagement with the outer surface of the tank and the inner surfaces of the ridge portions spaced from the surface of the tank, the jacket being capable of expansion and contraction in a radial direction in bellows or accordian fashion. The jacket fits over the tank from the top and at the bottom is provided with a tank supporting base that interlocks with the jacket to retain the tank within the jacket. At its opposite ends the jacket is provided with hand grip recesses to facilitate handling of the jacketed tank. Externally the jacket resembles a fluted column.

Claims, 8 Drawing Figures

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PATENTEDJAN29I974

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SHEET 1 OF 3

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PATENTED JAN 2 91974

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SHEET 2 OF 3

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/ MAKTEA/S

ATTORNEY'S.

PATENTED JAN 2 91974

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SHEET 3 OF 3

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ΜΛΧ)ββ£ / A/M/ZTEA/S #ΤΤύ/?Λ/ΕΥΈ

3,788,511

PROTECTIVE JACKET AND BASE FOR PRESSURE VESSEL

BACKGROUND OF THE INVENTION

Water softening equipment primarily intended for use on the premises of residences is generally of one or the other of two types. One type is self regenerating and is comprised of two principal compartments or tanks, one containing a quantity of resin through contact with which hard water is treated to effect a softening, and the other containing salt from which a brine is derived and at intervals the brine is brought into association with the resin to regenerate it and .renew its capability of softening water. Such an installation may be considered as permanent and requires two maintenance steps by or for the occupant of the residence, one being the replenishment of the supply of salt as it is consumed and the other being the control of valving equipment, either manually or automatically, at predetermined intervals to effect the regeneration of the resin.

The other type of installation is comprised of only one compartment or tank, namely the one which contains the resin. There is no provision for regeneration of the resin on the residential premises but the tank is readily removable and replaceable by another like it, and it is the custom of suppliers of this type of tank to render a resin regenerating service commonly known as Exchange Tank Service, in accordance with which, at predetermined intervals a tank containing regenerated resin is delivered to and installed on the customer’s premises, and the tank approaching exhaustion of its water softening capability is returned to the supplier’s premises for regeneration. It is with tanks for the exchange type of service that the present invention is primarily concerned.

Tanks for water softeners of this type have for the most part been fabricated of metal, usually steel, so that they will resist corrosion and damage during the many handlings to which the tank is subjected during its life. A typical steel tank for a residential water softener usually has a weight 40 to 45 pounds. When there is added to this a normal charge of resin weighing approximately 50 pounds, water weighing 15 to 20 pounds and hardware weighing 5 to 10 pounds, the result is a heavy object that is difficult, if not actually impossible, for one man to handle. If it is necessary for the delivery vehicle to be manned by a driver and a helper an expense is involved which could be avoided if the weight could be limited to an amount that could be easily handled by one man.

One approach that has been considered is the fabrication of the tank of plastic instead of metal. Generally speaking, plastic is frangible and tends to be easily damaged under rough handling. In addition hairline cracks may occur which may go unnoticed. Some of these disadvantages of the plastic tank may be avoided by providing a thick walled plastic tank. Such a tank is likely to approach or equal in weight that of a metal tank and is also likely to be more expensive than a metal tank of adequate strength and of the same capacity· . .

Still another approach to lightening the weight of the tank is a filament wound tank which consists of a liner molded from a plastic and overwound with a fiberglass filament to provide the necessary strength- Such a tank may be lighter than metal but is likely to be considera bly more costly than a metal tank and is also likely to deteriorate and fail from abrasive effects of rough handling if the quantity of material used in its construction can be limited to an amount that is economically feasible by comparison with the cost of a metal tank and that is sufficiently lower in weight than a metal tank to achieve the desired handling ease.

SUMMARY OF THE INVENTION

In order to reduce the weight of a tank sufficiently to enable the handling of a tank by one man without undue strain, it is contemplated in accordance with the present invention, to provide a plastic tank to contain the resin, the water and the accessories and to enclose the tank in a plastic jacket to absorb the impacts and abrasions of rough handling and to protect the tank from damage. A tank having a diameter of 8 inches and a height of 36 inches, fully as durable and as satisfactory in all respects as a cold rolled steel tank of that size that would weigh from 40 to 45 pounds, is comprised, in accordance with the invention, of a plastic tank weighing about 8 pounds and a plastic jacket weighing about 4 pounds. Thus a saving in weight of 28 to 33 pounds is effected. Further weight reduction may be accomplished by substituting for steel accessories, comprised of a closure cap adapted to be connected to inlet and outlet water piping and a collector tube extending generally from one end of the tank to the other inside the tank, which in steel, would weigh from 5 to 10 pounds, corresponding accessory components made from plastic, the total weight of which would be on the order of 2 pounds. The result would be a water softener unit weighing about 80 pounds, which is 30 to 40 pounds less than its steel equivalent.

In accordance with the preferred embodiment of the invention, the molded jacket for the tank is comprised of alternate grooves and ridges so that in cross section the wall of the jacket is undulant. The portions of the wall of the jacket that form the grooves are in contact with the exterior of the enclosed tank and the portions of the wall of the jacket that form the ridges are spaced from the surface of the enclosed tank. The internal diameter of the jacket, measured at the inner surface of the grooves, may be slightly less than the external diameter of the enclosed tank, so that a slight force may be required to fit the jacket over the tank, the diameter of the jacket expanding slightly at the grooves and the expansion being accommodated by the ridges in a manner comparable with the expansion afforded by a bellows or accordian folded structure. In this manner the jacket is caused to cling to the surface of the tank. The jacket provides the protection that makes feasible the use of the plastic tank. The ridge portions of the jacket, being out of contact with the enclosed tank, will absorb jolts without transmitting them to the surface of the tank. The ridges protect the intervening grooves, the inner surfaces of which are in surface contact with the tank, and lessen to a very substantial extent the likelihood of the application of damaging shocks to the grooves. The alternate ridges and grooves minimize the likelihood of abrasive rubbing together of the jacketed tanks when they are being transported on a vehicle, because of the meshing or interlocking of adjacent standing tanks in a manner similar to that of intermeshed gears.

DESCRIPTION OF THE DRAWINGS

For a complete understanding of the invention refer

3,788,511 ence may be had to the following detailed description to be interpreted in the light of the accompanying drawings wherein:

FIG. 1 is a perspective view of a jacketed tank in accordance with the preferred embodiment of the invention;

FIG. 2 is a vertical sectional view of a jacket enclosing a tank, with the tank partly broken away and partly in section to show accessories including a closure cap and a collector tube;

FIG. 3 is an elevational view of the jacketed tank shown in FIG. 1;

FIG. 4 is a plan view looking downwardly on the top of the jacketed tank shown in FIG. 1;

FIG. 5 is a horizontal sectional view taken approximately on the line 5—5 of FIG. 3;

FIG. 6 is a view of the bottom of the jacketed tank;

FIG. 7 is an enlarged fragmentary showing of a portion of the bottom of FIG. 2; and

FIG. 8 is a horizontal sectional view taken generally on the line 8—8 of FIG. 7.

DETAILED DESCRIPTION

Referring now to the drawings and particularly to FIG. 2 the reference numeral 12 designates a pressure tank of the configuration and dimensions generally employed as a water softening tank. Typical dimensions are a diameter of 8 inches and a length or height of 36 inches to provide a volume of approximately of one cubic foot and a liquid capacity of approximately of 7 gallons. The tank 12 is cylindrical throughout most of its length but may be rounded at both ends into a configuration approximating hemispheres. The tank 12 is closed at the bottom and is of greater thickness at the top than at the cylindrical portions or at the bottom, and is provided at the top with a threaded aperture 14 to receive threadedly a closure cap 16. It will be apparent that the reason for the thickening at the top is to provide several turns of threads in the aperture 14 to be entered by the threaded shank 18 of the cap 16. The cap 16 has inner and outer annular shoulders 20 and 22 and the lower surface of the annular shoulder 20 may be provided with an annular groove to receive a gasket, which may be an O-ring. By means of the threaded shank 18 of the cap 16, the annular shoulder 20 of the cap and the gasket 24 a liquid tight seal between the cap 16 and the tank 12 may be established.

The cap 16 is provided with compartments 26 and 28 separated by a barrier 30. The compartment 26 is in communication with the interior of the tank 12 and with a threaded receptacle 32 to which connection may be made to a pipe carrying water to be treated. The compartment 28 is in communication with a collector tube 34 and also with a threaded receptacle 36 to which connection may be made to a pipe to carry treated water to points of utilization. The collector tube 34 terminates near the bottom of the tank 12 and is in communication with the interior of the tank at or in the vicinity of the lower end of the collector tube, in accordance with usual practices.

When the tank is to be used for softening water it is provided, as is well known, with a bed of resin extending upwardly from the bottom of the tank a substantial distance. Water to be treated enters through threaded receptacle 32 and compartment 26 and filters downwardly through the bed of resin, where an exchange of ions takes place, thereby softening the water. The soft ened water rises through the collector tube 34 and flows through the compartment 28 and threaded receptacle 36 to a connected pipe when a tap associated with that pipe is opened.

A material that is suitable for forming a molded tank of the type shown in FIG. 2 is a thermo-setting polyester resin reinforced with fiberglass. Equal parts of these materials will provide a tank capable of adequately withstanding pressures normally encountered in water softening service. One known source of pressure vessels of this type, is STRUCTURAL FIBERS, INC., of Chardon, Ohio.

The jacket in accordance with the preferred embodiment of the invention, which renders feasible the use of tanks of the type hereinbefore described for interchangable tank water softening service is identified, in the several figures of the drawings, by the reference numeral 40. The jacket is open-ended at the bottom, and dome-shaped at the top so that when it is fitted over the tank 12 the inner surface of its upper end will rest upon the top of the tank 12. At its upper end the jacket 40 is provided with an aperture 42 to receive the tank cap 16, and the diameter of the aperture is greater than that of the annular shoulder 20 but less than the outside diameter of the cap 16 so that the annular shoulder 22 of the cap 16 will confine the jacket in position on the tank 12.

From a point near the top of the jacket 40 to a point near the open end at the bottom the jacket is undulant in the configuration of its wall cross-section, producing an exterior appearance of alternating ridges or ribs 44 and grooves 46 extending longitudinally of the jacket, producing an external appearance resembling a fluted column. It may be noted by examining FIG. 5 that a cross sectional showing of the jacket 40 resembles in contour a graphical representation of a clipped waveform, such as a sine wave wrapped around and encircling the tank 12, the clipping being generally symmetrical about the zero axis of the wave-form to produce the inner and outer dwells, which become the grooves 46 and ribs 44, respectively, these dwells being curved into conformity with inner and outer circles having as their centers the axis of the tank 12 by virtue of the wrapping of the wave-form about the wall of the tank. The resultant rib and groove surfaces are in panel configuration conformed to cylinders coaxial with the tank 12. In the embodiment of the invention shown in the drawings there are eight ridges 44, on 45° centers, and eight intervening grooves 46, on 45° centers and the angles subtended by individual ridges and grooves are generally of the same magnitude.

The inner surfaces of the grooves are conformed to a circle the diameter of which is preferably slightly less than the outside diameter of the tank 12. Thus when the jacket is placed above the tank 12 and is moved downwardly to fit it to the tank it must be forced downwardly, accompanied by expansion of the circle of the inner surfaces of the grooves 46. The portions of the wall of the jacket 40 that form the ridges or ribs 44 are spaced outwardly from the circle of the inner surfaces of the grooves, so that when the jacket 40 is fitted to the tank 12 the portions of the wall of the jacket forming the ridges 44 stand away from the surface of the tank 12. The ridges 44 are shown as being conformed to a circle that is concentric with the circle of the grooves. Because of the undulant cross-section configuration of the wall of the jacket 40 the ridges 44 ac3,788,511 commodate expansion of the circle of the inner surfaces of the grooves 46 the action being comparable with that of a bellows. The result of the expansion of the jacket is a deformation from its free state and because the plastic material of which it is made has a memory, as will be described hereinafter, it seeks to return to its free state configuration and in so doing applies pressure between the inner surfaces of the grooves 46 and the outer surface of the wall of the tank 12, causing the jacket to cling to the tank 12.

A material that is relatively inexpensive and is well suited to the type of service to which the jacket 40 will be subjected in use is high-density linear polyethylene. It is a material with a memory so that when force-fitted over the tank it hugs the tank, as previously mentioned. Also because of the memory it resists denting, or if dented beyond its resistive capability dents may be popped out without difficulty. When the material is cold, a sharp impact blow will not produce a fracture. At elevated temperatures it retains its strength and does not flow. Other plastics are known having similar properties and accordingly being suitable for use in the making of jackets in accordance with the present invention but some of them are relatively expensive by comparison with high-density linear polyethylene.

In order that the round-ended tank 12 may stand upright in a stable manner a base 50 is provided. The base 50 is made of plastic and may be injection molded or vacuum formed. A material that has properties well suited to use as a base for the tank 12 is polyvinyl chloride. As shown in FIGS. 2 and 7 the central portion of the base 50 is dished on a radius corresponding to the outer surface of the bottom of the tank 12 so that the tank will rest stably on the base 50. From its center the base 50 has radially extending re-enforcing ribs 52, shown in FIG. 6. Peripherally the base 50 has a vertically extending flange 54 and at intervals, preferably on 90 degree centers, there is an offset in the flange 54 in a direction radially outwardly from the flange, indicated in FIGS. 2 and 7 by the reference numeral 56. The offset 56 preferably subtends an angle somewhat smaller than the angle subtended by the ridges 44 in the jacket 40.

At its lower end the jacket 40 is provided with relief offsets 58, also preferably on 90 degree centers, in alignment with alternate ones of the ridges 44 and subtending an angle slightly exceeding that of the offsets 56 in the base 50.

In order to complete the assembly of the reinforced tank tht jacket 40 is brought down from the top on the tank 12 and the base 50 is brought into position at the bottom of the tank with the relief offsets 58 in alignment with the offsets 56 in the base 50. As shown in FIG. 2 the outer surface of the offset 56 in the base has a taper 60 and as the taper 60 encounters the relief offset 58 in the jacket 40 and pressure is applied between the base 50 and the jacket 40 the taper operates as a wedge to facilitate entry of the offsets 56 of the base into the relief offsets 58 of the jacket. The bottom of the jacket 40 may expand, the plastic of which the jacket is made accommodating this expansion. As the application of pressure between the jacket and the base is continued, the offset 56 moves inwardly of the relief offset 58, and the flange 54 may perhaps yield instead of or in addition to the yielding of the bottom of the jacket 40 accommodate the continued movement. As soon as the offset in the base moves above the lower end of the ridge 40 with which it is aligned a snap action takes place by virtue of which the offset 56 in the base enters the inside of the ridge its the two plastic components return to their normal conditions and the offset 56 becomes a lug to lock the base 50 to the jacket 40.

In the specific arrangement shown in the drawings and as indicated most completely in FIG. 1 the relief offsets 58 that facilitate the fitting of the offset lugs 56 in the base 50 into the jacket 40 are positioned below and in alignment with alternate ones of in ridges 46 of the jacket. Thus the relief offsets 58 are on 90° centers, leaving a substantial space between adjacent ones. In the space intervening two of the relief offsets 58, and accordingly below the bottom of one of the ridges 44 the wall of the jacket 40 is provided with a hand-grip aperture 64, shown in FIGS. 2 and 3. Correspondingly, the flange 54 of the base 50 is provided, between two of the offset lugs 56, with a hand-grip aperture 66. When the base 50 is being fitted to the jacket 40 the base is oriented relative to the jacket to bring the handgrip apertures 64 and 66 into registry. Thus there is provided at the bottom of the jacketed tank a hand-grip aperture into which the fingers of one hand of a handler may be inserted.

At the upper end of the jacket 40 the ridge 43 that is i alignment with the hand-grip aperture 64 extends upwardly above the dome-shaped end. Where this one ridge extends above the others it is widened and curved inwardly toward the axis of the jacket into an inverted U-shape, leaving an aperture 70, preferably of substantially the same width as the aperture 64, facing toward the cap 16 to provide a second hand-grip at the top of the tank assembly. The hand-grip aperture 70 in the extended and widened portion 68 may be reinforced and strengthened by an offset 72. By means of the handgrip apertures 70 and 64, the fingers of one hand entering the aperture 64 inwardly radially of the tank assembly and the fingers of the other hand entering the aperture 70 outwardly radially of the tank assembly, the tank may be lifted and carried with reasonable ease.

The jacket hereinbefore described may be molded in one piece, without seams, including the ribs and grooves, the relief offsets 58 for facilitating insertion of the base 50 and the hand-grip portion 68 by a process known as blow-molding. The blow-molding process avoids the occurrence of strains in the plastic so that the resulting product is stress-free.

As previously stated, it is of the essence of the invention that the jacket be made of plastic. One reason for this is that plastic has a memory and is generally self correcting in case of denting whereas a metallic jacket, once dented, remains dented. A plastic jacket provides thermal insulation and also prevents or reduces the condensation of moisture in the atmosphere on the surface of the unit. In this connection it will be understood that the tank 12 might be of metal instead of plastic, of lighter gauge metal than the usual unjacketed metal tank because of the strengthening and reinforcing afforded by the plastic jacket. The thermal insulation and the prevention of sweating due to condensation could then be of great significance. The plastic tank and jacket, or the combination of a metal tank and a plastic jacket and base, eliminate the possibility of sparks, which is an ever-present hazard of exposed metal tanks if used or handled where inflammable vapors are likely to be present.

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The configuration of the jacket, involving alternating longitudinal grooves, the inner surfaces of which are in engagement with the surface of the tank, and hollow ridges, the inner surfaces of which are spaced from the surface of the tank is also of the essence of the inven- 5 tion. The bellows or accordian-like undulation of the jacket wall completely eliminates requirements for close tolerances in the diameter of jacketed tanks, and accommodates itself to thermal expansion and contraction of the tank while always exerting a gripping action 1θ on the surface of the tank. The hollow spaces provided by the ridges protect the jacketed tank by absorbing mechanical shock so that the shock is not transferred directly to the tank at a localized point. The interlocking or meshing of a plurality of jacketed tanks, whether ¹⁵they are stood on end or are stacked lying on their sides, affords a stability and an absence of likelihood of movement of the tanks with respect to one another, so that relatively little support or restraint is needed. Because of the meshing of jacketed tanks with one an- ²⁰other the possibility of relative rotation among them and consequent surface abrasion is minimized. Moreover the tank having a jacket of the type disclosed herein, if lying on its side free of other tanks, is much ₂₅less subject to rolling than a cylindrical tank.