Flow meter with hollow blocking rotor

A flow meter is disclosed with a hollow blocking rotor. The flow meter includes a housing that has a cavity with an inlet and an outlet. The flow meter also includes a pair of displacement rotors with a blocking rotor disposed between the displacement rotors. The blocking rotor includes a pair of convex walls and a pair of concave walls. The blocking rotor further includes a shaft coupled to the pair of concave walls. Each concave wall is disposed between and coupled to a pair of opposing convex walls. The concave walls provide clearance for rotation of the displacement rotors when the displacement rotors sweep along the concave walls. The hollow configuration of the blocking rotor reduces the impedance of the flow meter.

TECHNICAL FIELD

This disclosure relates to improvements in positive displacement fluid flow meters, and more particularly to a blocking rotor for such flow meters.

BACKGROUND

Gasoline storage tank facilities, gasoline transport trucks, underground natural gas delivery systems, or other fluid storage or delivery systems generally have a positive displacement flow meter connected in line in the fluid delivery system. Pumping of the fluid, whether gas or liquid, through the delivery line causes movement of the rotors in the flow meter which drives a mechanical or electrical counting device to measure precisely the volume of fluid flow through the meter.

Some flow meters have a housing that defines a cavity within which three rotors are rotatably mounted. The three rotors include a pair of displacement rotors and a blocking rotor disposed between the displacement rotors. One of the displacement rotors is disposed towards the inlet of the flow meter; the other displacement rotor is disposed towards the outlet. As the blocking rotor rotates, it mates with the inlet displacement rotor disposed to close off part of the cavity to define a flow path along which the fluid must pass, thereby causing the displacement rotors and blocking rotor to rotate. The rotation of the displacement and blocking rotors creates a motion that can be correlated to the fluid volume passing through the meter, making it possible to translate the rotation of the displacement rotors into a meter reading showing fluid volume flow.

Typically, the entire fluid flow through a conduit is diverted through the flow meter in order to provide a flow throughput reading. Therefore, it is desirable that the flow meter add as little flow impedance as possible to the flow to minimize energy losses and to maintain the intended flow rate. To that end, it is desirable to provide a flow meter with rotors having low mass but sufficient strength for a long and accurate service life. For obvious reasons, it is also desirable to provide housings for flow meters that are as compact as possible.

A continuing need then exists to provide flow meters of the type utilizing blocking and displacement rotors of lightweight yet strong construction. Specifically, flow meters used for dispensing liquefied petroleum gas (LPG) are subjected to sudden focus in the event the LPG flashes. As a result, prior art blocking rotors are prone to breakage. Specifically, despite the use of reinforcing ribs1400, the blocking rotor115ofFIG. 2Ais prone to breakage along the ribbed wall140near the spindle155while the blocking rotor315ofFIG. 2Cis prone to breakage on the wall340on either side of the shaft355. Finally, the shaftless blocking rotor215ofFIG. 2Bis prone to breakage near the axial center of the wall240.

Another problem with the prior art blocking rotors115,215,315ofFIGS. 2A-2Cis the high moments of inertia associated with each rotor115,215,315that require more energy to initiate rotation of the rotors115,215,315and more time to stop rotation of the rotors115,215,315. The slower stopping ability of the rotors115,215,315in unwanted leakage through the flow meter after the dispensing has stopped thereby compromising the accuracy of the dispense.

SUMMARY OF THE DISCLOSURE

In one aspect of this disclosure, a blocking rotor for a rotary fluid displacement device is disclosed. The rotary fluid displacement device also includes a pair of displacement rotors that flank the blocking rotor. The blocking rotor includes a pair of convex walls and a pair of concave walls. The blocking rotor further includes a shaft coupled to the pair of concave walls. Each concave wall is disposed between and coupled to the pair of convex walls. As a result, the concave walls provide clearance for rotation of the displacement rotors.

In another aspect of this disclosure, a flow meter is disclosed. The disclosed flow meter includes a housing having a cavity with an inlet and an outlet. The flow meter also includes a pair of displacement rotors with a blocking rotor disposed between the displacement rotors. The blocking rotor includes a pair of convex walls and a pair of concave walls. The blocking rotor further includes a shaft coupled to the pair of concave walls. Each concave wall being disposed between and coupled to the pair of opposing convex walls. As a result, the concave walls provide clearance for rotation of the displacement rotors when the displacement rotors sweep along said concave walls.

A method of casting a blocking rotor of a flow meter is also disclosed. The method includes providing a mold for a hollow blocking rotor having a pair of convex walls and a pair of concave walls. Each concave wall is disposed between and coupled to the pair of opposing convex walls. The mold further includes gates and overflows and the gates and overflows are disposed on the concave walls and not the convex walls. The method further includes injecting material into the mold through the gates.

In any one or more of the embodiments described above, the shaft includes opposing ends. Each end of the shaft is coupled to a journal. In any one or more of the embodiments described above, the shaft extends beyond the convex walls to form journals that extend beyond the convex walls. In any one or more of the embodiments described above, the shaft couples the concave walls together. Further, in any one or more of the embodiments described above, the shaft couples the concave walls together at apexes of the concave walls. In any one or more of the embodiments described above, the shaft may be hollow or solid. In any one or more of the embodiments described above, the concave walls may be coupled together at apexes of the concave walls. In any one or more of the embodiments described above, the blocking rotor may be cast with gates and overflows being disposed on the concave walls as opposed to the convex walls.

DETAILED DESCRIPTION

Turning first toFIG. 1, a flow meter10is disclosed that includes a housing11, an inlet port12, an outlet port13and a cavity14that defines a flow path and accommodates the rotors15,16,17. The rotors15,16,17include a blocking rotor15, the design of which is disclosed herein, and a pair of displacement rotors16,17. The displacement rotor16will hereinafter be referred to as the inlet displacement rotor16as it rotates in the direction of the arrow18thereby pumping fluid entering the inlet12in the direction of the arrow19and through the first arcuate chamber22. The displacement rotor17will be referred to as the outlet displacement rotor17as it rotates in the direction of the arrow23and sweeps fluid from the second arcuate chamber24in the direction of the arrow25towards the outlet13.

In the embodiment illustrated inFIG. 1, the housing11forms the cavity14which, with the exception of the inlet and outlets12,13, forms a generally trefoil shape or clover shape due to the triangulated relationship between the blocking rotor15and inlet and outlet displacement rotors16,17. The cavity14includes a pair of arcuate pumping chambers22,24. As the displacement rotors16,17rotate, the vanes26,27of the displacement rotors16,17sweep along the interior surfaces28,29of the arcuate chambers22,24to propel the liquid towards the outlet13. The position of the displacement rotors16,17and the length of the vanes26,27also enables the vanes26,27to sweep along the exterior surfaces31,32of the concave walls33,34of the blocking rotor15as the blocking rotor15rotates in the direction of the arrow36.

The wiping contact between the distal ends37,38of the vanes26,27of the displacement rotors16,17along the exterior surfaces31,32of the blocking rotor15helps to keep from fluid leaking past the vanes26,27when the vanes are rotating along the concave walls33,34so that the fluid passing through the flow meter10follows a flow path indicated by the dashed line41.

Referring to the blocking rotor15and FIGS.1and3-8, the blocking rotor15is substantially hollow and is fabricated from the pair of concave walls33,34that are disposed between and connected to a pair of convex walls43,44. The convex walls43,44include outer surfaces45,46that engage the protuberances48,49formed on the inner surface51of the third arcuate chamber52to limit leakage of fluid into the arcuate chamber52and maintain fluid flowing through the meter along the flow path41. Again, the goal of the flow meter10is to provide as little impedance to the flow of fluid flowing between the inlet12and the outlet13. To provide structural integrity to the blocking rotor15, a shaft-like structure54(FIGS. 1,6and8) is utilized to couple the concave walls33,34together. As seen inFIG. 8, the shaft54includes distal ends that extend beyond the convex and concave walls33,34,43,44to form journals55,56. The journals55,56may be integral to the shaft-like structure54or they may be coupled to the shaft54separately. The journals55,56are received in the openings57,58in the end plates61,62respectively (seeFIG. 9).

Thus, instead of the entire cross section of the blocking rotor15being filled with material, the blocking rotor15only has four walls33,34,43,44of a prescribed thickness. The convex walls43,44define the outer diameter of the rotor15. The concave walls33,34is designed to be wiped by the vanes26,27of the displacement rotors16,17to reduce hydrodynamic losses that occur with traditional rotor designs. As an option, the rotor15may include internal ribbing to add additional rigidity. Such internal ribbing is shown in phantom at63,64ofFIG. 6.

A benefit of the disclosed design for the blocking rotor15is provided when casting is used to fabricate the blocking rotor15. Specifically, when using casting as the casting technology to cast the rotor15, the gating and overflows are preferably disposed on the concave walls33,34as opposed to the convex walls43,44. By placing the gating and overflow on the concave walls33,34, tear-out/break-out of material on the critical outer surfaces45,46of the convex walls43,44is avoided thereby reducing leakage into the third annular chamber52(FIG. 1).

The shaft54may be solid, partially cord or hollow, depending upon the meter size and application. Such an optional through opening66is illustrated inFIGS. 6 and 8. As another option, the concave walls33,34may meet at their apexes to form a rigid structure that would function like the shaft-like structure54.

ComparingFIGS. 2A and 3A, the disclosed rotor15has a substantially reduced mass in comparison to the prior art blocking rotor115shown inFIG. 2A. The addition of the convex walls33,34enables the convex walls43,44of the blocking rotor15to be substantially thinner than the convex walls143,144of the blocking rotor115. Further, the cumulative mass of the concave walls33,34is less than the ribbed wall140that connects the convex walls143,144together in the prior art rotor115. The lighter weight of the blocking rotor15provides improved performance and, despite the use of less material to fabricate the blocking rotor15than the amount of material used to fabricate the blocking rotor115, the blocking rotor15is stronger, particularly with respect to transverse bending or bending about an axis defined by the shaft54. Further, by placing the gates and overflow along the concave walls33,34, the outer surfaces45,46of the convex walls43,44remain smooth for proper engagement with the protuberances48,49disposed along the inner surface51of the arcuate chamber52(FIG. 1). The casting technique where the gates and overflows are disposed along the concave walls33,34as opposed to the convex walls43,44also produces less rejects and improved castability. The improved castability also leads to lower porosity and thereby increased strength. The lighter weight provided by the disclosed blocking rotor15provides a reduced moment of inertia and a reduced static bearing load, which contributes to decreasing any impedance to the flow of fluid through the flow meter10. The reduced moment of inertia also enables the rotor15to stop more quickly which results in a more accurate throughput reading and a more accurate dispense.

Further, as noted above, the blocking rotors215,315ofFIGS. 2B-2Calso have high moments of inertia and, like the blocking rotor115ofFIG. 3A, the rotors215,315are prone to breakage along the center walls240,340that connect the convex walls243,244and343,344together. In contrast, the shaftless hollow blocking rotor415ofFIG. 3Bhas a lower moment of inertia and superior strength compared to the rotors115,215,315ofFIGS. 2A-2C. The convex walls431,432are coupled together at or near the apexes of the concave walls431,432and, like the rotor15ofFIG. 3A, the concave walls431,432are disposed between and connect the convex walls445,446.

Briefly turning toFIG. 9, an exploded view of the flow meter10is provided illustrating the two end plates61,62and the housing11in greater detail. The displacement rotors16,17also include journals67,68and71,72respectively that are received in the openings73,74of the end plate61and the openings75,76of the end plate62. Gears78,79,80are coupled to the journals67,55,71respectively and maintain the timing of the rotation of the three rotors16,15,17.

INDUSTRIAL APPLICABILITY

Thus, an improved flow meter is disclosed that features a hollow, lightweight blocking rotor. Instead of the cross section of the blocking rotor being filled with material, the blocking rotor is formed from a pair of convex walls and a pair of concave walls of a prescribed thickness that results in a rotor of substantially reduced mass. A shaft-like structure may optionally be used to connect the concave walls together or the concave walls may meet at their respective apexes. The convex walls are purposely structured in order to reduce hydrodynamic losses that occur in the third chamber52as with traditional rotor designs. Because of the improved strength provided by the disclosed hollow blocking rotor, additional internal ribbing is unnecessary. The disclosed hollow blocking rotors have lower moments of inertia, resulting in faster stopping abilities and therefore more accurate throughput readings and dispense.

The improved rotor is also easier to cast with improved results as the gating and overflows are disposed on the concave walls that are wiped by the vanes of the displacement rotors as opposed to the outside surfaces of the convex walls which are used to provide a seal and prevent hydrodynamic losses in the upper or third chamber in which the blocking rotor is disposed. Flexability is also provided in the design of the shaft that connects the concave walls together as this shaft-like structure may be solid, hollow, etc. As noted above, the shaft-like structure may be provided in the form shown in the drawings or a suitable structural element may be created by coupling the convex walls together at their respective apexes.