Devices and methods for noise suppression in pumps

Details Devices and methods for noise suppression in pumps Devices and methods for noise suppression in pumps

2001-08-22

2003-04-22

Walberg, Teresa (Department: 3742)

Pumps

Processes

C417S410400

Reexamination Certificate

active

06551070

ABSTRACT:

FIELD OF THE DISCLOSURE
The present devices and methods relate to pumps, particularly gear pumps.
BACKGROUND
Gear pumps as known in the art are particularly advantageous for pumping fluids while keeping the fluids isolated from the external environment. This benefit has been further enhanced by the advent of magnetically coupled drive mechanisms that have eliminated leak-prone hydraulic seals around drive shafts. Gear pumps have been adapted for use in many applications including applications requiring extremely accurate delivery of a liquid to a point of use. Such applications include, for example, delivery of liquids in medical instrumentation and delivery of liquid ink to continuous ink-jet printer heads.
Gear pumps usually include a gear-assembly section and a drive-assembly section. The fluid flowing through the pump passes through the gear-assembly section.
Often there is also a need to provide fluid in the drive-assembly section. For example, the drive assembly may include moving parts that are in contact thereby generating heat and wear. Passing fluid between these moving parts acts as a lubricant that reduces such heat and wear.
In magnetic gear pumps in particular, typically a partition hydraulically isolates a gear-assembly section from a magnet-coupling section. However, the partition includes a flow passage for permitting fluid to flow from the gear-assembly section to the magnet-coupling section. In current commercial designs this flow passage defines a linear fluid-flow path. A magnetic gear pump also includes an outer annular magnet turned or rotated by a motor (i.e., the “driving” magnet). An annular inner magnet is disposed within the outer magnet and is carried on a drive shaft (i.e., the “driven” magnet). The inner magnet is isolated from the outer magnet by a thin metallic or plastic cup (referred to herein as a “magnet cup”).
Cavitation noise in pumps is a general problem, especially when operating in conditions with an inlet pressure at or near the vapor pressure of the fluid. Cavitation is the sudden formation and subsequent collapse or implosion of low-pressure bubbles in a fluid as the fluid flows from an area of higher pressure to an area of lower pressure (area of bubble formation) and then returns to an area of higher pressure (area of bubble collapse). As the bubbles collapse, energy is released that causes structural vibrations within the pump. Such structural vibrations generally result in the production of noise. In certain applications gear pumps operate at very low fluid inlet pressures. In such instances, the low-pressure portion of the pump is upstream from the gears and the high-pressure portion of the pump is downstream from the gears. Cavitation bubbles are formed in such gear pumps, for example, as the fluid moves from low-pressure areas to high-pressure areas, such as at the fluid inlet, and as the fluid travels through the chamber occupied by the gears. In addition, bubbles are present in the fluid as it enters into the pump. The collapse of such pre-existing bubbles also contributes to noise production. There is a continuing need for successful solutions for reducing noise emanating from pumps.
SUMMARY OF THE DISCLOSURE
In order to address the noise-generation problem, the present inventors constructed a magnetic gear pump with clear acrylic plastic parts to visualize the fluid-flow when operated under cavitation conditions. Surprisingly, it was discovered that a significant number of bubbles flow into the magnet-coupling section via the flow passage in the partition between the magnet-coupling section and the gear-assembly section. In particular, some of the bubbles flow into the magnet-cup cavity where they can subsequently implode. The expectation had been that a substantial majority of the cavitation bubbles would implode when the fluid exits the gears and into the high-pressure area; thus, never reaching the magnet-cup cavity. Bubble implosion within the interior of a magnet cup is especially problematic due to the relatively thin width (e.g., about 0.1 to about 0.7 mm) of the magnet-cup wall. It will be appreciated that the width of the magnet-cup wall is limited by the width of the air gap between the driving and driven magnets and associated tolerances.
The device and method embodiments disclosed herein substantially reduce the amount of bubbles flowing into a drive section of a pump, particularly the magnet-coupling section of a magnetic gear pump. In addition, these embodiments substantially interfere with the noise-energy conduction path in the fluid medium passing into the drive section of a pump. Both of these features contribute to an overall dampening of the noise generated and transmitted by a gear pump.
According to a first disclosed embodiment, there is provided a gear pump having a first section that includes a gear assembly, a second section that includes a drive assembly, and at least one passage fluidly connecting the first section and the second section, wherein the passage includes substantially non-movable walls defining a non-linear fluid-flow path. According to one variant there is provided a unitary member that includes the connecting passage defining the non-linear fluid-flow path. The gear assembly may include at least one driving gear and at least one driven gear. The drive assembly may include pump-drive mechanisms such as a magnetic coupling or other mechanical rotary arrangements. A method for reducing noise generated by such a pump is also disclosed. This method includes providing at least one passage fluidly connecting the first section and the second section, wherein the passage defines a non-linear fluid-flow path that substantially reduces the amount of the bubbles flowing from the first section into the second section.
As mentioned above, the devices and methods disclosed herein are particularly useful for suppressing noise in magnetic gear pumps. For example, one embodiment of a magnetic gear pump encompasses a first section that includes a gear assembly, a second section that includes a magnet assembly, and at least one passage fluidly connecting the first section and the second section, wherein the passage defines a non-linear fluid-flow path. Another embodiment includes a first section having a gear assembly, a second section having a magnet assembly received in a cup cavity, and a third section located between the first section and the second section. The third section includes at least one fluid-input port, at least one fluid-output port, at least one conduit for fluidly interconnecting the first section and the second section, and a member having at least one passage in fluid connection with the third section conduit and the cup cavity.
According to a further disclosed embodiment, noise generated in a magnetic gear pump having (i) a first section that includes a gear assembly for conducting a fluid flow, wherein bubbles are formed in the fluid when the fluid flows in the first section, and (ii) a second section that includes a magnet assembly received in a cup cavity, can be suppressed by substantially reducing the number of bubbles flowing from the first section to the second section. One variant of such a noise-suppression method involves providing at least one passage fluidly connecting the first section and the second section, wherein the passage defines a non-linear fluid-flow path.
The devices and methods disclosed herein are also useful for magnetic pumps in general. In particular, there is disclosed a magnetic pump having a first section that includes at least one fluid-input port and at least one fluid-output port for directing a fluid flow such that bubbles are formed in the fluid when the fluid flows through the first section. The pump also includes a second section comprising a magnet assembly received in a cup cavity, a conduit fluidly connecting the first section and the second section, and means for reducing the amount of the bubbles flowing from the first section to the second section.
There is also provided an apparatus including a magnetic gear pump, wherein the magnet

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