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Impeller with anti-vapor lock mechanism

Impeller with anti-vapor lock mechanism description/claims

1. Field of the Invention

The present invention is directed to an impeller, and more particularly, an impeller provided with an air-release mechanism to prevent air-lock of a pump.

2. Description of the Related Art

Rotary pumps are well known structures employed to pump fluids from one location to another. Rotary pumps have been developed for a number of different uses, ranging from fire engine apparatus to volumetric dosing of commercially important materials. Rotary pumps may be classified according to structural features of their material propelling elements. An example of the most commercially important types of rotary pump is the centrifuge pump.

Most centrifuge pumps comprise a generically cylindrical casing and an impeller, or a plurality of impellers mounted inside the casing to drive a fluid through the pump. The pumps typically operate by taking in a fluid and adding energy from the fluid by kinematics means; thus, the fluid pressure is increased, by the interaction of rotating blades or vanes with the fluid as it passes through. This energy, however, provides several undesired side effects such as air-locking of the pump.

The pressure of the fluid in a pump drops as it flows from the suction flange through the suction nozzle and into the impeller. The amount of pressure drop is a function of many factors, including pump geometry, rotational speed, frictional and hydraulic shock losses, and flow rate.

If the pressure at any point within the pump falls below the vapor pressure of the fluid being pumped, vaporization or cavitation will occur. Bubbles are formed as a result of this pressure drop. Lower pressures in the impeller center axis are caused by variations in velocity of the fluid and friction losses as the fluid enters the impeller.

The bubbles are caught up and swept outward along the impeller vane. Somewhere along the non-visible side of the impeller vane, the pressure may once again exceed the vapor pressure and cause the bubbles to collapse, producing the phenomenon called air-lock.

During air locking, the pump not only fails to serve its basic purpose of pumping the liquid, but also may experience excessive noise and vibrations, internal damage, leakage from the seal and casing, bearing failure, etc. The extent of the air-locking damage can range from a relatively minor amount of pitting after years of service to catastrophic failure in a relatively short period of time. In summary, air-locking is an abnormal condition on the pump that can result in loss of production, equipment damage, and worst of all, personnel injury.

In the prior art, air-lock is cleared from the pump by turning the pump off, thus releasing the back pressure of air and allowing the water in the pump outlet hose to descend back through the pump, thereby forcing any trapped air out of the impeller chamber. The pump is then restarted, and in theory, but not always in practice, the pump resumes the normal pumping of liquid.

Numerous attempts have been made over the years to design a pump, which prevents or relieves air-lock. One is an “anti-airlock” pump manufactured by Rule. This pump incorporates a device, which is designed to periodically detect whether there is air present at the pump impeller. If air is detected at the pump impeller, the device shuts the pump off, allowing air to leave through the impeller output line. However, this device does not proactively clear the air-lock, and the impeller pump may remain air-locked during the interval between testing for air-lock.

U.S. Pat. No. 4,913,620 entitled “Centrifugal Water Pump” to Kusiak et al. teaches a centrifugal water pump in which the pumping chamber is horizontally oriented, and such chamber has two wall portions or sectors of different radius. One wall portion has a radius substantially the same as the outer most radial path of the impeller blades, and the other wall portion has a radius substantially constant, but slightly greater than the radius of the radical path of the impeller blades. Connecting the two chamber wall portions are terminal walls, one of which is located adjacent to the outlet port. A first deflecting wall directs the pumped water upward into the outlet port. A second deflecting wall breaks up any air and air bubbles, and fills any space wherein air or air bubbles could collect. The device of Kusiak et al. is mechanically complex, and in order to function properly, the device requires the divider wall to create a positive and negative pressure (as opposed to a normal flow of water), which actually reverses the flow of water, thereby allowing any trapped air to escape.

U.S. Pat. No. 4,087,994 entitled “Centrifugal Pump with Means for Precluding Airlock” to Goodlaxson discloses a centrifugal pump with means for precluding air lock wherein the impeller of the pump includes finger-like projections on each blade which extend radially outwardly from the impeller body into the outer annulus of the pumping chamber. These projections cut through the liquid, which has been centrifuged to the outer annulus, thus causing a turbulence, which draws a portion of the liquid into the body of the impeller for mixing with trapped air.

This mixing action causes the air to be centrifuged with liquid and alleviates air lock in the pump. However, it should be noted that the vortex formed at the inlet of the pump is not reduced in size or eliminated.

U.S. Pat. No. 5,213,718 entitled “Aerator and Conversion Methods,” and U.S. Pat. No. 5,275,762 entitled “Aerator” to Burgess, teach aerators wherein an impeller draws a water and air mixture down through an upwardly directed impeller inlet into a cavitation zone (i.e., the centrifugal pump is mounted upside down compared to the normal operating position). When the centrifugal pump rotates, the vacuum formed in the cavitation zone by rotation of the impeller will draw air through the air tube into the cavitation center axis where a portion of the air will be entrained in the water flowing through the vane impeller and out the water flow, directing means into the tank. Excess air drawn into the cavitation center axis through the inlet tube can escape upwardly through the water inlet, thereby preventing air-locking of the impeller, as would occur if air were to accumulate in the cavitation zone of a centrifugal pump mounted in the “normal” pump operating position, with the water inlet opening downwardly. The pump preferably floats on the water with the air/water inlet for the centrifugal pump immediately below the surface. Such a system has a number of attendant problems. First, a centrifugal pump is designed to be operated in a certain orientation. The pump may be operated upside down near the surface for periods of time without damage; however, if operated upside down at depth for any length of time, air in the motor housing will exit through the seal between the motor shaft and the impeller, and water will enter the motor housing, thereby causing damage. Further, if the pump is operated on the surface, oxygenation of the water will occur near the surface of the tank, and the lower reaches of the bait well will not be aerated.

Further yet, if the pump is operated at depth, the design must permit escape of excess air out through the water inlet so as to prevent air-locking of the pump, or to permit flooding and restarting of an air-locked pump. The design must thus anticipate the various depths at which the pump may be operated, and the air-escape parameters for each depth. Such a design cannot optimize the air/water mixture for maximum oxygenation of the pump at every given depth. As a result of these design constraints, the oxygenation efficiency is adequate, but much less than optimal.

U.S. Pat. No. 4,917,577 entitled “High Speed Centrifugal Aerator” to Stirling teaches a high speed centrifugal aerator including (1) a frustro-conical shaped impeller chamber within which is mounted a similarly shaped mismatched impeller with blades significantly smaller than the chamber, the impeller chamber having a bottom inlet, and the bottom inlet having a venturi gas inlet for mixing gas with the flowing liquid. To be effective, the impeller must operate at a very high speed in order for the flow of fluid through the bottom inlet to be sufficient to create a suction on, and draw gas through, the venturi gas inlet. This high flow rate would render the aerator impractical for use in small applications such as bait wells, since the high turbulence would be injurious to the baitfish. More importantly, since the impeller blades are significantly smaller than the impeller chamber, most of the fluid does not come into contact with the blades. This may be desirable where the objective is to achieve high flow and low agitation. However, where the object is to achieve a high rate of mixing of air into a relatively small volume of water, as would be required in a bait well application, this high-speed centrifugal aerator is entirely unsuitable. Finally, the venturi gas inlets must be narrow to be effective as the pump is cycled through many ON-OFF periods, during which the venturi gas inlets will be flooded and dried, resulting in sedimentation and encrustation. The venturi jets will require attention and cleaning over time.

It would therefore be an advantage in the art to provide an impeller that eliminates or minimizes the above-mentioned and other problems, limitations and disadvantages typically associated with conventional pumps, and to prevent air lock of the pump impeller.

It is an object of the present invention to provide an impeller designed to prevent air-lock of the pump.

It is yet another object of the present invention to provide an impeller, which prevents air lock of the pump and does not require constant monitoring by the operator.

It is yet another object of the present invention to provide a mechanism by which air-lock may be prevented in currently available pumps.

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