Non-metallic pressure caps and diaphragm pump housings incorporating same

Description

FIELD OF THE INVENTION

[0001] This invention relates to an improved fluid operated, double diaphragm pump, and, more particularly, to the housing construction for such a pump.

BACKGROUND OF THE INVENTION

[0002] Air operated double diaphragm pumps are known for pumping a wide variety of substances. Typically such a pump comprises a pair of pumping chambers with a pressure chamber arranged in parallel with each pumping chamber in a housing. Each pressure chamber is separated from its associated pumping chamber by a flexible diaphragm. As one pressure chamber is pressurized, it forces the diaphragm to compress fluid in the associate pumping chamber. The fluid is thus forced from the pumping chamber. Simultaneously, the diaphragm associated with the second pumping chamber is flexed so as to draw fluid material into the second pumping chamber. The diaphragms are reciprocated in unison in order to alternately fill and evacuate the pumping chambers. In practice, the chambers are all aligned so that the diaphragms can reciprocate axially in unison. In this manner the diaphragms may also be mechanically interconnected to ensure uniform operation and performance by the double acting diaphragm pump.

[0003] In some applications, double diaphragm pumps are utilized to pump caustic chemicals such as acids, in other applications, comestible substances such as flowable foods and beverages can be pumped. In such applications, the component pump parts that are to contact the material to be pumped are often constructed using materials that resist corrosion and are chemically compatible with the material being pumped. In this regard, polymeric materials are often used for various pump components such as the fluid caps of the pumping chambers and the diaphragms and/or their liners. However, polymer materials have not been readily incorporated into the pressure caps of such diaphragm pumps due to the high stresses generated in the pressure chambers of these pumps.

[0004] The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.

SUMMARY OF THE INVENTION

[0005] The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0006]
FIG. 1 is an elevational view of a diaphragm pump housing according to the present invention and showing a housing chamber in partial section;

[0007]
FIG. 2 is a partial sectional schematic view illustrating a pressure cap according to the present invention; and

[0008]
FIG. 3 is a sectional schematic view illustrating the pressure cap shown in FIG. 2 according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention provides improvements to the diaphragm pumps and components shown and described in U.S. Pat. Nos. 4,854,832 and 5,584,666, the specifications of which are incorporated herein by reference.

[0010] As used herein, the term “modulus of elasticity,” commonly referred to in the art as “Young's modulus,” is defined as the ratio of an applied unit tensile stress to the unit strain that results when the stress is applied to a material within the elastic limit and without fracture of the material.

[0011] The drawings illustrate a typical double diaphragm pump incorporating a housing construction of the present invention. Like numbers refer to like parts in each of the figures. Shown in FIG. 1 is a partial sectional view of a double diaphragm pump incorporating a main housing 100 that defines first and second opposed and axially spaced housing chambers. Each housing chamber includes a pressure chamber 26 defined by a pressure cap 27 and a fluid chamber 31 defined by a fluid cap 32 that are separated by a flexible diaphragm 29 as depicted by the partial sectional view of the left housing chamber in FIG. 1. The pressure cap 27 includes a flat, plate portion 25 having a flange portion 23 with a wall portion 24 located between and connecting the plate and flange portions as shown. The pressure chamber, fluid chamber, and diaphragm in the right housing chamber are similarly arranged and form a mirror image of those components in the left housing chamber. Located between the left and right housing chambers and attached to each of their plate portions is a center body housing 6. A valve block or body 2 having an air inlet 121 is attached to center body housing 6 as shown.

[0012] Each of the diaphragms 29 is fashioned from an elastomeric material as is known to those skilled in the art. The diaphragms 29 are connected mechanically by means of a shaft 30 that extends axially through the midpoint of each of the diaphragms. The shaft 30 is attached to the diaphragm 29 by means of opposed plates 33 on opposite sides thereof. Thus, the diaphragms 29 will move axially in unison as the pump operates by the alternate supply and exhaust of air to the pressure chambers of the pump as discussed in greater detail in the '832 and '666 patents. In brief, upon reciprocating the diaphragms of the pump, fluid that passes into each fluid chamber from associated inlet check valves is alternately compressed within and forced outwardly through associated outlet check valves. Operation of the fluid check valves controls movement of fluid in and out of the pump chambers causing them to function as a single acting pump. By connecting the two chambers through external manifolds, output flow from the pump becomes relatively constant.

[0013] Although unfilled (i.e., unreinforced) polymers such as polypropylene have been used in fluid caps of diaphragm pumps, typically, such polymers are not well-suited for use in the pressure caps of these pumps. Without reinforcement, these low rigidity materials can be subject to creep failure at room temperature that can result in deformation, leakage, and eventually cracking in highly stressed areas of the pressure cap. Moreover, although these polymers may be reinforced with glass fibers, such glass-filled polymers are not well-suited for use in pressure caps due to their propensity for cracking and, thus, leaking. Furthermore, in certain applications, glass-filled polymers may also be prone to attack by caustic fumes that may be emitted from a material to be pumped.

[0014] The specific structure of the present invention relates to the construction of the pressure chamber 26 and, more specifically, to the geometry of the pressure cap 27 that defines the pressure chamber. Through the use of finite element analysis, a technique known in the art, and empirical testing it has been determined that a pressure cap may be provided with a geometry that reduces stress in highly loaded areas such that conventional metal pressure caps, including those made of aluminum, aluminum alloys, cast iron, or steel, may be replaced by pressure caps made of a non-metallic material such as a polymeric material. Exemplary polymer materials in this regard are thermoplastic polymers such as polypropylene polymers and thermoset polymers such as vinyl ester polymers. Although these polymers may be glass-filled for reinforcement, the stress reduction in the pressure caps according to the present invention may also be unfilled, i.e., unreinforced, thereby permitting their use in caustic environments. According to the present invention, the flange portion of the non-metallic pressure cap is provided in a thickness that is greater than the thickness of a flange portion of a conventional metallic pressure cap which is to be replaced. More specifically, the features that describe the geometric aspects for minimizing stress and deformation, according to the present invention, relate to the relationship between the modulii of elasticity of the pressure cap metallic material to be replaced with that of the non-metallic replacement material, according to Eqn. 1 below, the parameters for which are described below and shown in FIG. 3:

[0015] Equivalent Non-Metallic Flange Thickness

\begin{matrix} t_{f (nonmetallic)} ≃ {(\frac{E_{m}}{E_{n m}})}^{1 / 3} \times t_{f (metallic)} & [Eqn . 1] \end{matrix}

[0016] where:

[0017] tf(metallic)=metallic flange thickness

[0018] tf(nonmetallic)=equivalent non-metallic flange thickness

[0019] E m=modulus of elasticity of metal

[0020] E nm=modulus of elasticity of non-metal

[0021] Although tf(nonmetallic) is shown above as being approximately equal to tf(metallic) by the cube root of the ratio of their modulii of elasticity according to Eqn. 1, it is to be understood that it is preferred that this relationship be equal. Other design details in the pressure cap, however, may require tf(nonmetallic) to be slightly smaller or greater, hence the approximate expression of the relationship with tf(metallic). Such design details include any thickness variations of the periphery of the flange or the use of an outer rim or other stiffening feature that may be employed in a particular design.

[0022] Additionally, the dimensional relationship between the flange portion 23 and wall portion 24 of pressure cap 27 according to Eqn. 2 below, also minimizes stress and deformation of the pressure cap, the parameters for which are described below and shown in FIG. 3:

[0023] Wall Thickness to Radius Ratio

r
>⅓(tw) [Eqn. 2]

[0024] where:

[0025] r=radius of the outer surface transition between pressure cap flange and wall portion

[0026] tw=wall thickness of the pressure chamber

[0027] Although the observance of one or the other of the criteria above in manufacturing a non-metallic pressure cap will improve the resistance to stress and deformation in a non-metallic pressure cap, it is preferred that the non-metallic pressure cap according to the present invention meet both of the criteria expressed by Eqns. 1 and 2 above.

[0028] There has been set forth a preferred embodiment of the invention. However, the invention may be altered or changed without departing from the spirit or scope thereof. The invention, therefore, is to be limited only by the following claims and their equivalents.

Claims

1. A non-metallic pressure cap equivalent for a metallic pressure cap of a diaphragm pump, the non-metallic pressure cap comprising: a plate portion, a flange portion, and a wall portion located between and connecting said plate and said flange portions, said flange portion having a thickness, tf, wherein said thickness of said flange portion of said non-metallic pressure cap is greater than the thickness of a flange portion of said metallic pressure cap.
2. The non-metallic pressure cap according to claim 1 wherein said non-metallic pressure cap is made of a polymer material.
3. The non-metallic pressure cap according to claim 2 wherein said polymer is selected from the group consisting of vinyl ester and polypropylene.
4. The non-metallic pressure cap according to claim 1 wherein the relationship between the non-metallic flange thickness and the metallic flange thickness is defined according to the following equation:
5. The non-metallic pressure cap according to claim 4 wherein said non-metallic pressure cap is made of a polymer material.
6. The non-metallic pressure cap according to claim 5 wherein said polymer is selected from the group consisting of vinyl ester and polypropylene.
7. The non-metallic pressure cap according to claim 1, wherein said wall portion further comprises a thickness, tw, and a radius, r, defined on an outer surface transition between said wall and flange portions, the ratio between the radius and the thickness of the wall portion being defined according to the following equation:
8. The non-metallic pressure cap according to claim 7 wherein said non-metallic pressure cap is made of a polymer material.
9. The non-metallic pressure cap according to claim 8 wherein said polymer is selected from the group consisting of vinyl ester and polypropylene.
10. A non-metallic pressure cap for a diaphragm pump, the non-metallic pressure cap comprising: a plate portion, a flange portion, and a wall portion located between and connecting said plate and said flange portions, said wall portion having a thickness, tw, and defining a radius, r, on an outer surface transition between said wall and flange portions, the ratio between the radius and the thickness of the wall portion being defined according to the following equation:r>⅓(tw)
11. The non-metallic pressure cap according to claim 10 wherein said non-metallic pressure cap is made of a polymer material.
12. The non-metallic pressure cap according to claim 11 wherein said polymer is selected from the group consisting of vinyl ester and polypropylene.
13. A diaphragm pump having a non-metallic pressure cap equivalent for a metallic pressure cap, comprising: a non-metallic pressure cap having a plate portion, a flange portion, and a wall portion located between and connecting said plate and said flange portions, said flange portion having a thickness, tf, and said wall portion having a thickness, tw, and defining a radius, r, on an outer surface transition between said wall and flange portions, wherein said thickness of said flange portion of said non-metallic pressure cap is greater than the thickness of a flange portion of said metallic pressure cap and the ratio between the radius and the thickness of the wall portion being defined according to the following equation:r>⅓(tw)
14. The diaphragm pump according to claim 13 wherein said non-metallic pressure cap is made of a polymer material.
15. The diaphragm pump according to claim 14 wherein said polymer is selected from the group consisting of vinyl ester and polypropylene.
16. The diaphragm pump according to claim 13 wherein the relationship between the non-metallic flange thickness and the metallic flange thickness being defined according to the following equation:
17. The diaphragm pump according to claim 16 wherein said non-metallic pressure cap is made of a polymer material.
18. The diaphragm pump according to claim 17 wherein said polymer is selected from the group consisting of vinyl ester and polypropylene.

Non-metallic pressure caps and diaphragm pump housings incorporating same

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