US20060034711A1 - Linear pump with sound attenuator - Google Patents
Linear pump with sound attenuator Download PDFInfo
- Publication number
- US20060034711A1 US20060034711A1 US10/918,278 US91827804A US2006034711A1 US 20060034711 A1 US20060034711 A1 US 20060034711A1 US 91827804 A US91827804 A US 91827804A US 2006034711 A1 US2006034711 A1 US 2006034711A1
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- United States
- Prior art keywords
- pump
- cavity
- intake
- orifice
- air
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B35/00—Piston pumps specially adapted for elastic fluids and characterised by the driving means to their working members, or by combination with, or adaptation to, specific driving engines or motors, not otherwise provided for
- F04B35/04—Piston pumps specially adapted for elastic fluids and characterised by the driving means to their working members, or by combination with, or adaptation to, specific driving engines or motors, not otherwise provided for the means being electric
- F04B35/045—Piston pumps specially adapted for elastic fluids and characterised by the driving means to their working members, or by combination with, or adaptation to, specific driving engines or motors, not otherwise provided for the means being electric using solenoids
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B39/00—Component parts, details, or accessories, of pumps or pumping systems specially adapted for elastic fluids, not otherwise provided for in, or of interest apart from, groups F04B25/00 - F04B37/00
- F04B39/0027—Pulsation and noise damping means
- F04B39/0055—Pulsation and noise damping means with a special shape of fluid passage, e.g. bends, throttles, diameter changes, pipes
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B39/00—Component parts, details, or accessories, of pumps or pumping systems specially adapted for elastic fluids, not otherwise provided for in, or of interest apart from, groups F04B25/00 - F04B37/00
- F04B39/0027—Pulsation and noise damping means
- F04B39/0055—Pulsation and noise damping means with a special shape of fluid passage, e.g. bends, throttles, diameter changes, pipes
- F04B39/0061—Pulsation and noise damping means with a special shape of fluid passage, e.g. bends, throttles, diameter changes, pipes using muffler volumes
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B39/00—Component parts, details, or accessories, of pumps or pumping systems specially adapted for elastic fluids, not otherwise provided for in, or of interest apart from, groups F04B25/00 - F04B37/00
- F04B39/12—Casings; Cylinders; Cylinder heads; Fluid connections
- F04B39/121—Casings
Definitions
- the present invention relates to pumps and in particular to compact linear piston pumps.
- Pumps for certain duties such as oxygen concentration and sewage aeration, generally need to be compact and operate discreetly. It is thus important to properly muffle the working air as well as reduce vibration during operation of the pump without relying on a large, thick-walled housing to attenuate the sound and vibration. Discreet operation of the pump can be obtained by insulating the housing, however, this adds bulk and can cause cooling problems. Mufflers can be added at the output, however, this adds hardware and cost.
- Such compact linear pumps/compressors are often single cylinder devices with a small piston that reciprocates rapidly within a small cylinder to pressurize the air.
- the rapid movement of the single piston generates considerable vibration. These vibrations are often transferred directly to the pump housing, via a direct rigid mounting connection.
- Pulsations in the air downstream from the outlet has been found to alter the resonant frequency of pump when different lengths and/or diameters of output lines are attached to the pump. Changing the operational frequency of the pump causes inefficiencies that can ultimately render the pump unusable for particular applications. It can also exacerbate noise and vibration issues.
- This invention is a linear pump with improved sound attenuation characteristics. Lower overall sound is accomplished by introducing the air through a multi-cavity intake in which the intake air is allowed to re-expand before passing further downstream into the pump.
- the linear pump includes an electro-magnetically driven piston reciprocating within a cylinder in communication with the multi-cavity air intake.
- the intake has at least two cavities.
- the first cavity is in communication with ambient air and is in communication with the second cavity through a first orifice.
- the second cavity has a second orifice allowing the intake air to pass downstream to an intake chamber and ultimately to the cylinder.
- the second cavity is sized to allow the intake air to re-expand before exiting the second orifice.
- the linear pump includes a cover mounted to a pump housing to define the intake air passage, which preferably extends essentially around the entire periphery of the cover.
- the cover encloses (but for the intake air passage) the two cavities, one being located inward of the other outer cavity.
- the pump housing at least in part defines both the inner and outer cavities.
- a partition is mounted beneath the cover to seal off the inner cavity, except for at a pair of orifices in the partition.
- the outer partition orifices are preferably located near to one side of the intake than are the pair of orifices in the inner cavity. This offset arrangement causes the intake air to turn, approximately 90 degrees, in a serpentine path as it passes from the outer to the inner cavity.
- the intake also preferably include a filter.
- the filter can be any suitable foam, paper or mesh screen air filter commonly used to screen particulates from the intake air.
- the filter is disposed in a retainer having a plurality of spaced apart riser elements spacing the filter from a base surface of the retainer, which defines the outer orifice, such that intake air can pass between the inner and outer cavities through the filter and around the riser elements.
- the present invention thus provides a quieter linear air pump.
- the unique intake design attenuates the noise, particularly a low pulsating rumbling noise, that is generated by the air rushing into the intake valve as the valve is opened and closed rapidly.
- the pulsations in the intake air are diminished in the cavities of the intake, particularly the inner cavity where the intake air is allowed to re-expand, and the associated noise is thus reduced.
- the offset arrangement of the orifices, which baffles and directs the intake air in a serpentine path also aids in sound reduction.
- passing the air through an air filter and routing the air around the raised projections of the air filter retainer further reduces noise.
- the pump housing enclosure reduces the noise of the pump as does the remote location of the working components and the intake chamber of the pump from the intake.
- FIG. 1 is a perspective view of a linear pump according to the present invention
- FIG. 2 is a perspective of the pump of FIG. 1 shown with a housing shroud removed;
- FIG. 3 is an exploded assembly view of the pump
- FIG. 4 is an exploded assembly view of a drive components of the pump
- FIG. 5 is a sectional view taken along line 5 - 5 of FIG. 6 ;
- FIG. 6 is a top view showing the pump with an inlet filter and top cover removed;
- FIG. 7 is a partial sectional view taken along line 7 - 7 of FIG. 6 albeit with the inlet filter and top cover in place;
- FIG. 8 is a top view of the pump with the housing shroud removed and the drive components shown in phantom;
- FIG. 9 is a top view of a pump base showing the intake and exhaust chambers thereof;
- FIG. 10 is a sectional view take along line 10 - 10 of FIG. 9 ;
- FIG. 11 is a partial sectional view taken along line 11 - 11 of FIG. 9 ;
- FIG. 12 is a sectional view taken along line 12 - 12 of FIG. 1 ;
- FIG. 13 is an enlarged partial sectional view taken along arc 13 - 13 of FIG. 12 ;
- FIG. 14 is a sectional view taken along line 14 - 14 of FIG. 2 albeit shown with the housing shroud in place;
- FIG. 15 is a partial sectional view taken along line 15 - 15 of FIG. 2 albeit with the outer housing in place;
- FIG. 16 is a view of a retainer ring shown in isolation as viewed from line 16 - 16 of FIG. 12 ;
- FIG. 17 is a view of a leaf spring shown in isolation as viewed from line 17 - 17 of FIG. 12 .
- the present invention provides an axial or linear piston pump.
- the term pump used herein includes a device for providing either positive or negative pressure, and thus either acting as a vacuum pump or a compressor.
- the pump has a compact form factor, with a preferred operating range of 2-30 psi depending upon the application (however, the pump could be designed to operate at other pressures) with low external vibration and noise and less sensitivity to pump attachments (lines, hoses, tubing, etc.) downstream from the outlet.
- the pump generally referred to in the drawings by reference number 20 , has a compact housing 22 including a base 24 , a shroud 26 and a top cover 28 .
- the shroud 26 is bolted to the base 24 (via bolts 23 ), with a gasket 30 therebetween (see FIG. 15 ), and the cover 28 is bolted (via bolt 69 ) to the shroud 26 .
- the base has four feet 32 to support the pump 20 and provides an opening for connecting a fitting 34 (see FIG. 11 ).
- the shroud 26 has an opening 35 for an electrical socket (or power cord).
- the cover 28 is spaced off of the shroud 26 slightly to define an air intake passage 36 along the periphery of the cover 28 , as will be described in greater detail below.
- the top of the shroud 26 and the cover 28 are recessed on opposite sides to provide a hand gripping area 38 .
- the pump 20 breathes through an air intake assembly generally designated 40 .
- the air intake 40 is configured to reduce the low, rumbling noise associated with pulsations in the intake air caused by rapid movement of the intake valve.
- the air intake 40 includes an inner cavity 42 defined in part by a recess in the top of the shroud 26 , a seal partition 44 , a filter tray 46 , a filter 48 and the cover 28 , which provides the upper boundary for an outer cavity 50 .
- the recessed top of the shroud 26 defines the inner cavity 42 , in the floor of which are two spaced apart orifices 52 near one end (the right end in the drawings).
- the inner cavity 42 is bounded at the top by the partition 44 which seals against a peripheral wall 54 of the inner cavity 42 .
- the partition 44 has a pair of spaced apart orifices 56 located at a (left) end of the inner cavity 42 opposite the orifices 52 .
- the partition 44 includes another set of orifices 56 ′ at the opposite end, however, these are not used when the partition 42 is oriented as shown in the drawings.
- intake air flows through only the one set orifices 56 (or 56 ′), which is located opposite the orifices 52 in the floor of the inner cavity 42 .
- the filter tray 46 Resting on the partition 44 is the filter tray 46 which holds the filter 48 in the outer cavity 50 .
- the filter tray 46 has a bottom wall with a pair of openings 58 which align with orifices 56 in the partition 44 .
- a small alignment feature 59 extends down from the underside of the filter tray 46 and fits into an opening 61 in the shroud 26 to ensure that the filter tray 46 is assembled in the proper orientation.
- the filter 48 is held spaced off of the bottom of the filter tray 46 by a number of small spaced apart risers 60 , and is retained by a short peripheral wall 62 ringing the filter tray 46 .
- the wall 62 has a cut-out 64 at one end (opposite the openings 58 ) allowing intake air to flow laterally into the filter 48 .
- the cover 28 fits onto the shroud 26 over the filter 48 to define the outer cavity 50 . Ribs 66 on the inside of the cover 28 contact the wall 62 of the filter tray 46 to keep the bottom edge of the peripheral wall 68 of the cover 28 spaced slightly from the shroud 26 , and also to funnel the intake air into the outer cavity 50 through the cut-out 64 .
- the space between the top cover 28 and the shroud 28 defines the intake air passage 36 , which extends around the periphery of the cover 28 .
- Aligned center openings in the cover 28 , filter 48 , filter tray 46 and partition 44 allow a bolt 69 to screw into a threaded opening 70 in the shroud 26 to secure the assembly.
- the shroud 26 also integrally defines a pair of vent tubes 72 which extend down form the orifices 52 in the floor of the inner cavity 42 .
- the vent tubes 72 inject the intake air passing from the intake 40 to the inside of the shroud 26 past the drive assembly, described in detail below, through three openings 80 in a base plate 82 (and elongated opening 84 in the gasket 30 ), which is bolted to the base 24 , and into an intake chamber 86 in the base 24 of the housing, as shown in FIG. 5 .
- the base plate 82 is bolted to the base 24 by bolts 87 (see FIGS. 2 and 3 ).
- the intake chamber 86 is defined in the base 24 with an exhaust chamber 88 in a yin-yang-like configuration, each with a wide portion and a narrow portion in opposite orientation.
- the intake air is drawn from the intake chamber 86 up through an intake opening 90 in the base plate 82 (and an associate opening the gasket 30 ) and an intake tube 92 connected to the intake side of the drive assembly, as shown in FIG. 10 .
- Exhaust tube 94 runs between an exhaust opening 96 in the base plate 82 (and an associated opening in the gasket 30 ) to the exhaust side of the drive assembly.
- the intake 92 and exhaust 94 tubes are of bellowed construction allowing the tubing to flex in response to vibrations of the drive assembly, without transferring the vibration to the housing base 24 .
- the intake 92 and exhaust 94 tubes simply snap into the base plate 82 and are clamped (via clamps 98 ) to an associated nipple in the drive assembly.
- the drive assembly generally includes a valve head 100 , a cylinder 102 , a piston 104 and an electromagnet motor 106 , all aligned concentrically about a piston axis 108 (see FIG. 12 ).
- the entire drive assembly is bolted (via bolts 109 ) to a motor mount 110 and mounted to the base plate 82 via resilient mounts 112 .
- the four resilient mounts 112 have narrowed necks between enlarged heads and bodies that slideably snap into four open ended slots 114 in the motor mount 110 .
- the resilient mounts 112 are preferably made of a suitable rubber, such as an EPDM with a durometer of about 60, so as to provide enough stiffness to securely mount the drive assembly while allowing enough flexibility to isolate the vibrations of the drive assembly.
- the valve head 100 defines an intake side 120 and an exhaust side 122 each having a respective nipple 124 and 126 to which the intake 92 and exhaust 94 tubes connect via clamps 98 .
- a valve plate 128 mates with the valve head 100 .
- the valve plate 128 has a groove for a double D-shaped (bisected circle) o-ring 130 sealing against the valve head 100 to isolate the intake side 120 from the exhaust side 122 .
- the valve plate 128 is generally disk-shaped and defines a pair of intake ports 131 (shown in phantom in FIG. 4 ) and a pair of exhaust ports 132 .
- Each pair of ports is covered by respective thin metal flapper valves 134 and 135 (the flapper valves 134 and 135 can be supported by valve stops (not shown)).
- the intake 131 and exhaust 132 ports are in communication with the associated sides of the valve head 100 and the inside of the cylinder 102 , which fits into another groove in the back side of the valve plate 128 sealed with another o-ring 136 (see FIG. 13 ).
- the opposite side of the cylinder 102 fits around a hub of a retainer collar 138 .
- the retainer collar 138 has four threaded openings, which receive four bolts 140 fit through four ears of each of the valve head 100 and valve plate 128 to clamp the cylinder 102 tightly together with these components.
- the other side of the retainer collar 138 clamps one or more leaf springs 142 with a recessed groove (having alignment features as discussed below) in a spacer ring 144 .
- the opposite side of the spacer ring 144 receives a stator 146 of the electromagnet motor 106 .
- the stator 146 is a slotted annular member having a circular base and concentric inner 148 and outer 150 cylindrical walls (with axial slots 169 in outer wall 150 ), which define an annular channel 152 therebetween.
- a wire coil 154 is disposed in a bobbin 156 within the channel 152 .
- the bobbin 156 has three posts that extend through openings in the base of the stator 146 and are engaged by retainers 153 to retain the bobbin 156 and coil 154 .
- a diode (not shown) may be electrically coupled to the coil 154 to rectify the alternating current input signal so that it drives an armature (or shuttle) 158 in only one direction, preferably toward the stator 146 .
- Conductive tabs 160 for coupling the coil 154 to the power are also included.
- the armature 158 has a series of axial bores therethrough and slides in and out of a side (right in the drawing) of the stator 146 when the coil 154 is energized.
- the armature 158 has a short hub with an axial bore 162 that receives a bottom end of a connecting rod 164 .
- the connecting rod 164 is suspended along the piston axis 108 by the leaf springs 142 and passes through the center bore in the stator 146 .
- the connecting rod 164 is secured to the armature 158 and the piston 104 by a long bolt 166 threaded into the piston 104 and mounting a mass disk 168 under its head.
- the stator 146 is clamped between the spacer ring 144 and another spacer ring 172 . That spacer ring 172 clamps one or more additional leaf springs 142 against a second retainer collar 174 .
- Four tie rods 173 extending through ears in the first retainer collar 138 are threaded into openings in ears of the second retainer collar 174 to unite the components of the motor 106 .
- the retainer collars 138 and 174 also have threaded openings receiving bolts 109 to connect the motor mount 110 and thereby mount the entire drive assembly to the base plate 82 via the resilient mounts 112 , as described above.
- the retainer collar 174 (as well as spacer ring 144 ) has a circular groove 176 about its inner periphery with three alignment pockets 178 , the sides of which taper asymmetrically away from the groove 176 .
- One or more leaf springs 142 fit into the groove 176 and their asymmetrically tapered alignment tabs 180 fit into the pockets 178 . Due to the asymmetric configuration of the pockets 178 and tabs 180 , the leaf springs 142 can seat properly into the retainer collar 174 (and the spacer ring 144 ) in only one angular and axial orientation (relative to the piston axis 108 ).
- the alignment tabs 180 are spaced apart about 120 degrees so that the springs can be mounted in one of three angular orientations. If a single angular orientation is desired, the alignment tabs 180 could be spaced asymmetrically. This facilitates and ensures the assembly of multiple leaf springs 142 in the same orientation at both ends of the connecting rod 164 .
- the web pattern (and arcuate slots) of the leaf springs 142 are aligned, and any curvature or bowing of the leaf springs 142 out of the plane perpendicular to the piston axis 108 (which can occur from the die cutting process) will be in the same direction for each leaf spring 142 .
- the pump is tuned to operate at a frequency at or near its natural resonant frequency.
- the pump is operated with a load applied and using a calculated spring-mass system (i.e., the combination of spring rate of the springs 142 and mass of the moving components, namely the piston 104 , armature 158 , connecting rod 164 and any mass disk 168 ).
- the frequency of the input signal to the motor 106 is varied as various parameters are measured.
- the spring-mass system can also be adjusted to operate efficiently at different pressures. For example, by increasing mass or spring rate the spring-mass system can be made to operate at or near resonant frequency while the pump is providing increased pressure output. It should be noted that the mass disk 168 is used as a cost effective alternative to increasing or decreasing the mass of the piston, armature and/or connecting rod.
- the piston 104 is driven by movement of the armature 158 , when energy is supplied to the wire coil 154 , to reciprocate within the cylinder 102 .
- the piston 104 has an enlarged head with a peripheral groove holding a split piston ring 170 that seals against the cylinder 102 when pressure is developed.
- the stroke length is approximately 8 mm (4 mm in each direction) and is positioned approximately 1 mm from the top of the cylinder when at top dead center.
- the reciprocating piston 104 , armature 158 and connecting rod 164 can cause the drive assembly inside the housing to vibrate.
- the leaf springs 142 absorb much of the energy from these moving components.
- the number, size and thickness of the leaf springs 142 are selected to achieve a spring rate determined primarily according to the mass of the piston 104 and the input frequency.
- the leaf springs 142 are selected so that in combination (between the two stacks) they result in a resonant frequency of the piston 104 and springs 142 (i.e., the spring-mass system) approximately equal to the input frequency, which is typically 50 or 60 Hertz.
- the springs 142 could be of a thinner gauge, in which case the number of springs may be increased to three in each stack to achieve the same spring rate.
- the pressure of the intake air drops as it passes through the small openings into the inner cavity 42 .
- the inner cavity 42 is effectively larger than the outer cavity 50 , which allows the intake air to expand.
- the expansion of the intake air in the inner cavity 42 helps to dissipate the pulsations in the intake air arising from the operation of the intake valve.
- the intake air After entering the inner cavity 42 , the intake air turns through a bend of about 90-180 degrees and travels to the other end of the inner cavity 42 to the orifices 52 where it travels down the vent tubes 72 and into the interior of the housing shroud 26 . As shown in FIG.
- the vent tubes 72 are located to direct the intake air into the slots 169 in the stator 146 of the motor 106 so as to convectively cool the coil 154 .
- the intake air passes through the openings 80 in the base plate 82 into the wide part of the intake chamber 86 .
- the air is routed through the narrowed part and up through the intake opening 90 in the base plate 82 and the intake tube 92 to the intake side 120 of the valve head 100 , as shown in FIG. 10 .
- Reciprocation of the piston 104 draws air into the cylinder 102 and compresses it.
- the pressurized air is then passed through the exhaust side 122 of the valve head 100 and down through the exhaust tube 94 in the base plate 82 to the wide part of the exhaust chamber 88 through exhaust opening 96 . As shown in FIGS. 9 and 11 , the pressurized air flows through the narrow portion of the exhaust chamber 88 and out through the outlet opening where fitting 34 is attached to suitable hose or tubing (not shown).
- the pressurized air is pulsed at the rate of the input frequency, for example 60 Hz.
- the inventors have determined that pulsations in the output air can adversely effect the operation of the pump.
- the output lines act as resonant chambers, having their own natural frequency. If the pulsations in the output air are at a different frequency, the air will effectively encounter increased resistance going through the output lines. This creates excessive back pressure on the pump so that the spring-mass system can be made to operate at a different (non-resonant) frequency, thereby decreasing the efficiency of the pump. This makes the pump more sensitive to variations in input frequency which can further decrease efficiency. By reducing the amplitude of the pulsations in the air before leaving the pump, this problem can be avoided.
- the pulsations in the pressurized output air leaving the pump are dampened by a diaphragm 190 in the exhaust chamber 88 .
- the diaphragm 190 is preferably a rubber disk mounted to the top of a cup 192 defined by the housing base 24 in the wide part of the exhaust chamber 88 by a support ring 194 bolted (via bolts 198 ) to the base 24 .
- the cup 192 defines a trapped air pocket 196 below the diaphragm 190 .
- the pulsations act against the diaphragm 190 , tending to make it flex into the cup 192 .
- the air pocket 196 will compress slightly, but tend to resist inward movement of the diaphragm 190 . This reactive force on the diaphragm 190 will tend to counter, and thus cancel or reduce the amplitude of, the pulsations in the exhaust chamber air.
- the diaphragm 190 and trapped air pocket 196 act similar to an accumulator, and as a result, allow the pump to output smoother, relatively non-pulsed, air through the output lines. As a result pump inefficiencies are avoided that may otherwise arise from changes in the length or diameter of the output lines or from changes to the input frequency to the motor.
- the inventors have determined that use of the diaphragm in this way allows a single mass-spring system to be used for both 50 and 60 Hz applications.
Abstract
Description
- Not applicable.
- Not applicable.
- The present invention relates to pumps and in particular to compact linear piston pumps.
- Pumps for certain duties, such as oxygen concentration and sewage aeration, generally need to be compact and operate discreetly. It is thus important to properly muffle the working air as well as reduce vibration during operation of the pump without relying on a large, thick-walled housing to attenuate the sound and vibration. Discreet operation of the pump can be obtained by insulating the housing, however, this adds bulk and can cause cooling problems. Mufflers can be added at the output, however, this adds hardware and cost.
- Such compact linear pumps/compressors are often single cylinder devices with a small piston that reciprocates rapidly within a small cylinder to pressurize the air. The rapid movement of the single piston generates considerable vibration. These vibrations are often transferred directly to the pump housing, via a direct rigid mounting connection.
- To facilitate reciprocation of the piston with less vibration, it is known to suspend the drive member, such as the armature of an electromagnetic motor, by springs or like flexible members. Stacks of thin metal leaf springs are well-suited for this. However, when multiple springs are used, it can be difficult to achieve the prescribed spring rate to which the piston drive components of the pump have been tuned. Changes in the angular (about the piston axis) and/or axial (along the piston axis) orientation of the springs relative to one another can effect the spring rate. To ensure that the pump operates efficiently, it is thus important to achieve the intended spring rate and thus ensure the consistent orientation of the suspension springs, which can make pump assembly difficult.
- Another problem is that the intake and exhaust valves of the valve head must open and close rapidly for each stroke of the piston. Typically, thin metal flapper valves are used for this purpose because of their ability to seat and unseat very rapidly. Since the exhaust port opens under the force of the compressed air, a valve stop is used to support the valve and prevent it from being hyper-extended beyond its elastic range. The rapid contact between the intake valve and the valve head or the exhaust valve and the valve stop can generate tapping or clicking sounds. Another problem is that the rapid opening and closing of the intake valve can cause pressure fluctuations or pulsations in the air flow upstream from the valve head. These air pulsations can generate a low-frequency, rumbling noise.
- Another problem confronting the design of compact linear piston pumps is eliminating pulsations in the output air stream. Pulsations in the air downstream from the outlet has been found to alter the resonant frequency of pump when different lengths and/or diameters of output lines are attached to the pump. Changing the operational frequency of the pump causes inefficiencies that can ultimately render the pump unusable for particular applications. It can also exacerbate noise and vibration issues.
- Yet another persistent problem in compact linear pump design is cooling. To decrease noise, or perhaps to make immersible or suitable for outdoor use, the working components of these pumps are often enclosed in a pump housing. With operation of the pump, friction and the current in the electromagnet coil generate heat. As is well understood, heat adversely affects the pump efficiency and life. Many times the need to keep the pump operating efficiently requires the housing to be vented or to have other measures taken which destroy, or at least significantly reduce, the noise retarding features of the housing or other components.
- Accordingly, an improved linear pump is needed that addresses the aforementioned problems.
- This invention is a linear pump with improved sound attenuation characteristics. Lower overall sound is accomplished by introducing the air through a multi-cavity intake in which the intake air is allowed to re-expand before passing further downstream into the pump.
- In particular, the linear pump includes an electro-magnetically driven piston reciprocating within a cylinder in communication with the multi-cavity air intake. The intake has at least two cavities. The first cavity is in communication with ambient air and is in communication with the second cavity through a first orifice. The second cavity has a second orifice allowing the intake air to pass downstream to an intake chamber and ultimately to the cylinder. The second cavity is sized to allow the intake air to re-expand before exiting the second orifice.
- In preferred forms, the linear pump includes a cover mounted to a pump housing to define the intake air passage, which preferably extends essentially around the entire periphery of the cover. The cover encloses (but for the intake air passage) the two cavities, one being located inward of the other outer cavity. The pump housing at least in part defines both the inner and outer cavities. A partition is mounted beneath the cover to seal off the inner cavity, except for at a pair of orifices in the partition. The outer partition orifices are preferably located near to one side of the intake than are the pair of orifices in the inner cavity. This offset arrangement causes the intake air to turn, approximately 90 degrees, in a serpentine path as it passes from the outer to the inner cavity.
- The intake also preferably include a filter. The filter can be any suitable foam, paper or mesh screen air filter commonly used to screen particulates from the intake air. Preferably, the filter is disposed in a retainer having a plurality of spaced apart riser elements spacing the filter from a base surface of the retainer, which defines the outer orifice, such that intake air can pass between the inner and outer cavities through the filter and around the riser elements.
- The present invention thus provides a quieter linear air pump. The unique intake design attenuates the noise, particularly a low pulsating rumbling noise, that is generated by the air rushing into the intake valve as the valve is opened and closed rapidly. The pulsations in the intake air are diminished in the cavities of the intake, particularly the inner cavity where the intake air is allowed to re-expand, and the associated noise is thus reduced. The offset arrangement of the orifices, which baffles and directs the intake air in a serpentine path, also aids in sound reduction. Similarly, passing the air through an air filter and routing the air around the raised projections of the air filter retainer further reduces noise. Still further, the pump housing enclosure reduces the noise of the pump as does the remote location of the working components and the intake chamber of the pump from the intake.
- These and other advantages of the invention will be apparent from the detailed description and drawings.
-
FIG. 1 is a perspective view of a linear pump according to the present invention; -
FIG. 2 is a perspective of the pump ofFIG. 1 shown with a housing shroud removed; -
FIG. 3 is an exploded assembly view of the pump; -
FIG. 4 is an exploded assembly view of a drive components of the pump; -
FIG. 5 is a sectional view taken along line 5-5 ofFIG. 6 ; -
FIG. 6 is a top view showing the pump with an inlet filter and top cover removed; -
FIG. 7 is a partial sectional view taken along line 7-7 ofFIG. 6 albeit with the inlet filter and top cover in place; -
FIG. 8 is a top view of the pump with the housing shroud removed and the drive components shown in phantom; -
FIG. 9 is a top view of a pump base showing the intake and exhaust chambers thereof; -
FIG. 10 is a sectional view take along line 10-10 ofFIG. 9 ; -
FIG. 11 is a partial sectional view taken along line 11-11 ofFIG. 9 ; -
FIG. 12 is a sectional view taken along line 12-12 ofFIG. 1 ; -
FIG. 13 is an enlarged partial sectional view taken along arc 13-13 ofFIG. 12 ; -
FIG. 14 is a sectional view taken along line 14-14 ofFIG. 2 albeit shown with the housing shroud in place; -
FIG. 15 is a partial sectional view taken along line 15-15 ofFIG. 2 albeit with the outer housing in place; -
FIG. 16 is a view of a retainer ring shown in isolation as viewed from line 16-16 ofFIG. 12 ; and -
FIG. 17 is a view of a leaf spring shown in isolation as viewed from line 17-17 ofFIG. 12 . - The present invention provides an axial or linear piston pump. The term pump used herein includes a device for providing either positive or negative pressure, and thus either acting as a vacuum pump or a compressor. The pump has a compact form factor, with a preferred operating range of 2-30 psi depending upon the application (however, the pump could be designed to operate at other pressures) with low external vibration and noise and less sensitivity to pump attachments (lines, hoses, tubing, etc.) downstream from the outlet.
- Referring to
FIGS. 1-3 , the pump, generally referred to in the drawings byreference number 20, has acompact housing 22 including abase 24, ashroud 26 and atop cover 28. Theshroud 26 is bolted to the base 24 (via bolts 23), with agasket 30 therebetween (seeFIG. 15 ), and thecover 28 is bolted (via bolt 69) to theshroud 26. The base has fourfeet 32 to support thepump 20 and provides an opening for connecting a fitting 34 (seeFIG. 11 ). Theshroud 26 has anopening 35 for an electrical socket (or power cord). Thecover 28 is spaced off of theshroud 26 slightly to define anair intake passage 36 along the periphery of thecover 28, as will be described in greater detail below. The top of theshroud 26 and thecover 28 are recessed on opposite sides to provide ahand gripping area 38. - Referring to FIGS. 3, 5-7 and 12, the
pump 20 breathes through an air intake assembly generally designated 40. Theair intake 40 is configured to reduce the low, rumbling noise associated with pulsations in the intake air caused by rapid movement of the intake valve. In particular, theair intake 40 includes aninner cavity 42 defined in part by a recess in the top of theshroud 26, aseal partition 44, afilter tray 46, afilter 48 and thecover 28, which provides the upper boundary for anouter cavity 50. - As mentioned, the recessed top of the
shroud 26 defines theinner cavity 42, in the floor of which are two spaced apartorifices 52 near one end (the right end in the drawings). Theinner cavity 42 is bounded at the top by thepartition 44 which seals against aperipheral wall 54 of theinner cavity 42. Thepartition 44 has a pair of spaced apartorifices 56 located at a (left) end of theinner cavity 42 opposite theorifices 52. To facilitate assembly thepartition 44 includes another set oforifices 56′ at the opposite end, however, these are not used when thepartition 42 is oriented as shown in the drawings. In any event, intake air flows through only the one set orifices 56 (or 56′), which is located opposite theorifices 52 in the floor of theinner cavity 42. Resting on thepartition 44 is thefilter tray 46 which holds thefilter 48 in theouter cavity 50. Thefilter tray 46 has a bottom wall with a pair ofopenings 58 which align withorifices 56 in thepartition 44. Asmall alignment feature 59 extends down from the underside of thefilter tray 46 and fits into an opening 61 in theshroud 26 to ensure that thefilter tray 46 is assembled in the proper orientation. Thefilter 48 is held spaced off of the bottom of thefilter tray 46 by a number of small spaced apartrisers 60, and is retained by a shortperipheral wall 62 ringing thefilter tray 46. Thewall 62 has a cut-out 64 at one end (opposite the openings 58) allowing intake air to flow laterally into thefilter 48. Thecover 28 fits onto theshroud 26 over thefilter 48 to define theouter cavity 50.Ribs 66 on the inside of thecover 28 contact thewall 62 of thefilter tray 46 to keep the bottom edge of theperipheral wall 68 of thecover 28 spaced slightly from theshroud 26, and also to funnel the intake air into theouter cavity 50 through the cut-out 64. The space between thetop cover 28 and theshroud 28 defines theintake air passage 36, which extends around the periphery of thecover 28. Aligned center openings in thecover 28,filter 48,filter tray 46 andpartition 44 allow abolt 69 to screw into a threadedopening 70 in theshroud 26 to secure the assembly. - Referring now to
FIGS. 5, 7 , 8 and 12, theshroud 26 also integrally defines a pair ofvent tubes 72 which extend down form theorifices 52 in the floor of theinner cavity 42. Thevent tubes 72 inject the intake air passing from theintake 40 to the inside of theshroud 26 past the drive assembly, described in detail below, through three openings 80 in a base plate 82 (and elongated opening 84 in the gasket 30), which is bolted to thebase 24, and into anintake chamber 86 in thebase 24 of the housing, as shown inFIG. 5 . Note that thebase plate 82 is bolted to thebase 24 by bolts 87 (seeFIGS. 2 and 3 ). - As shown in
FIG. 9 , theintake chamber 86 is defined in the base 24 with anexhaust chamber 88 in a yin-yang-like configuration, each with a wide portion and a narrow portion in opposite orientation. The intake air is drawn from theintake chamber 86 up through anintake opening 90 in the base plate 82 (and an associate opening the gasket 30) and anintake tube 92 connected to the intake side of the drive assembly, as shown inFIG. 10 .Exhaust tube 94 runs between anexhaust opening 96 in the base plate 82 (and an associated opening in the gasket 30) to the exhaust side of the drive assembly. Importantly, theintake 92 andexhaust 94 tubes are of bellowed construction allowing the tubing to flex in response to vibrations of the drive assembly, without transferring the vibration to thehousing base 24. Theintake 92 andexhaust 94 tubes simply snap into thebase plate 82 and are clamped (via clamps 98) to an associated nipple in the drive assembly. - Referring now to
FIGS. 2, 4 , 5, 12 and 14, the drive assembly generally includes avalve head 100, acylinder 102, apiston 104 and anelectromagnet motor 106, all aligned concentrically about a piston axis 108 (seeFIG. 12 ). The entire drive assembly is bolted (via bolts 109) to amotor mount 110 and mounted to thebase plate 82 via resilient mounts 112. The fourresilient mounts 112 have narrowed necks between enlarged heads and bodies that slideably snap into four open endedslots 114 in themotor mount 110. Slightly enlarged bottom ends of theresilient mounts 112 can be pushed straight down throughopenings 116 in thebase plate 82, thereby, themotor mount 110 is captured by theresilient mounts 112 and flexibly mounted to thebase plate 82. The resilient mounts 112 are preferably made of a suitable rubber, such as an EPDM with a durometer of about 60, so as to provide enough stiffness to securely mount the drive assembly while allowing enough flexibility to isolate the vibrations of the drive assembly. - With primary reference to
FIGS. 2, 4 and 12, the drive assembly will now be described in detail. Thevalve head 100 defines anintake side 120 and anexhaust side 122 each having arespective nipple intake 92 andexhaust 94 tubes connect viaclamps 98. Avalve plate 128 mates with thevalve head 100. Thevalve plate 128 has a groove for a double D-shaped (bisected circle) o-ring 130 sealing against thevalve head 100 to isolate theintake side 120 from theexhaust side 122. Thevalve plate 128 is generally disk-shaped and defines a pair of intake ports 131 (shown in phantom inFIG. 4 ) and a pair ofexhaust ports 132. Each pair of ports is covered by respective thinmetal flapper valves 134 and 135 (theflapper valves 134 and 135 can be supported by valve stops (not shown)). Theintake 131 andexhaust 132 ports are in communication with the associated sides of thevalve head 100 and the inside of thecylinder 102, which fits into another groove in the back side of thevalve plate 128 sealed with another o-ring 136 (seeFIG. 13 ). The opposite side of thecylinder 102 fits around a hub of aretainer collar 138. Theretainer collar 138 has four threaded openings, which receive fourbolts 140 fit through four ears of each of thevalve head 100 andvalve plate 128 to clamp thecylinder 102 tightly together with these components. - The other side of the
retainer collar 138 clamps one ormore leaf springs 142 with a recessed groove (having alignment features as discussed below) in aspacer ring 144. The opposite side of thespacer ring 144 receives astator 146 of theelectromagnet motor 106. Thestator 146 is a slotted annular member having a circular base and concentric inner 148 and outer 150 cylindrical walls (withaxial slots 169 in outer wall 150), which define an annular channel 152 therebetween. Awire coil 154 is disposed in abobbin 156 within the channel 152. Thebobbin 156 has three posts that extend through openings in the base of thestator 146 and are engaged by retainers 153 to retain thebobbin 156 andcoil 154. A diode (not shown) may be electrically coupled to thecoil 154 to rectify the alternating current input signal so that it drives an armature (or shuttle) 158 in only one direction, preferably toward thestator 146.Conductive tabs 160 for coupling thecoil 154 to the power are also included. - The armature 158 has a series of axial bores therethrough and slides in and out of a side (right in the drawing) of the
stator 146 when thecoil 154 is energized. The armature 158 has a short hub with anaxial bore 162 that receives a bottom end of a connectingrod 164. The connectingrod 164 is suspended along the piston axis 108 by theleaf springs 142 and passes through the center bore in thestator 146. The connectingrod 164 is secured to the armature 158 and thepiston 104 by along bolt 166 threaded into thepiston 104 and mounting amass disk 168 under its head. - The
stator 146 is clamped between thespacer ring 144 and anotherspacer ring 172. Thatspacer ring 172 clamps one or moreadditional leaf springs 142 against asecond retainer collar 174. Fourtie rods 173 extending through ears in thefirst retainer collar 138 are threaded into openings in ears of thesecond retainer collar 174 to unite the components of themotor 106. Theretainer collars motor mount 110 and thereby mount the entire drive assembly to thebase plate 82 via theresilient mounts 112, as described above. - As shown in
FIGS. 16 and 17 , at the side opposite thecylinder 102, the retainer collar 174 (as well as spacer ring 144) has acircular groove 176 about its inner periphery with threealignment pockets 178, the sides of which taper asymmetrically away from thegroove 176. One ormore leaf springs 142 fit into thegroove 176 and their asymmetrically taperedalignment tabs 180 fit into thepockets 178. Due to the asymmetric configuration of thepockets 178 andtabs 180, theleaf springs 142 can seat properly into the retainer collar 174 (and the spacer ring 144) in only one angular and axial orientation (relative to the piston axis 108). Thealignment tabs 180 are spaced apart about 120 degrees so that the springs can be mounted in one of three angular orientations. If a single angular orientation is desired, thealignment tabs 180 could be spaced asymmetrically. This facilitates and ensures the assembly ofmultiple leaf springs 142 in the same orientation at both ends of the connectingrod 164. In particular, the web pattern (and arcuate slots) of theleaf springs 142 are aligned, and any curvature or bowing of theleaf springs 142 out of the plane perpendicular to the piston axis 108 (which can occur from the die cutting process) will be in the same direction for eachleaf spring 142. - This is important to ensure that the
motor 106 has the spring rate for which it was designed. Specifically, during development the pump is tuned to operate at a frequency at or near its natural resonant frequency. In particular, the pump is operated with a load applied and using a calculated spring-mass system (i.e., the combination of spring rate of thesprings 142 and mass of the moving components, namely thepiston 104, armature 158, connectingrod 164 and any mass disk 168). The frequency of the input signal to themotor 106 is varied as various parameters are measured. For example, because power consumption goes up as the input frequency strays from the resonant frequency of the spring-mass system, power consumption measurements can be used to adjust the spring-mass system so that its natural frequency will be at or near that of a typical input signal, for example 60 Hz. Operating the pump at the resonant frequency improves efficiency, and reduces vibration, and thereby noise. The spring-mass system can also be adjusted to operate efficiently at different pressures. For example, by increasing mass or spring rate the spring-mass system can be made to operate at or near resonant frequency while the pump is providing increased pressure output. It should be noted that themass disk 168 is used as a cost effective alternative to increasing or decreasing the mass of the piston, armature and/or connecting rod. - As is well understood, the
piston 104 is driven by movement of the armature 158, when energy is supplied to thewire coil 154, to reciprocate within thecylinder 102. Thepiston 104 has an enlarged head with a peripheral groove holding asplit piston ring 170 that seals against thecylinder 102 when pressure is developed. The stroke length is approximately 8 mm (4 mm in each direction) and is positioned approximately 1 mm from the top of the cylinder when at top dead center. - Given the single cylinder arrangement of the
pump 20, thereciprocating piston 104, armature 158 and connectingrod 164 can cause the drive assembly inside the housing to vibrate. The leaf springs 142 absorb much of the energy from these moving components. The number, size and thickness of theleaf springs 142 are selected to achieve a spring rate determined primarily according to the mass of thepiston 104 and the input frequency. The leaf springs 142 are selected so that in combination (between the two stacks) they result in a resonant frequency of thepiston 104 and springs 142 (i.e., the spring-mass system) approximately equal to the input frequency, which is typically 50 or 60 Hertz. For example, in one preferred embodiment there is a stack of two springs in thesecond retainer collar 174 and a stack of two springs in thespacer ring 144 near thepiston 104. If the stroke length were to be increased, for example if the pump to be used in an application requiring more air flow, thesprings 142 could be of a thinner gauge, in which case the number of springs may be increased to three in each stack to achieve the same spring rate. - With reference to
FIGS. 5-7 , 9-11 and 13, air flow through the pump will now be described in detail for a preferred compressor embodiment of the pump. When the drive assembly is operating, ambient air is drawn into the pump intake through theintake air passage 36 around the periphery of thetop cover 28. As shown inFIGS. 5-7 , the intake air is drawn through theintake air passage 36 flowing upwardly along theribs 66 and makes its way into theouter cavity 50 through the cut-out 64 in theperipheral wall 62 of thefilter tray 46. Intake air then moves from that end of theouter cavity 50 through thefilter 48 and around therisers 60 in thefilter tray 46 to theopenings 58 in thefilter tray 46 and thepartition 44 where it enters theinner cavity 42. The pressure of the intake air drops as it passes through the small openings into theinner cavity 42. Theinner cavity 42 is effectively larger than theouter cavity 50, which allows the intake air to expand. The expansion of the intake air in theinner cavity 42 helps to dissipate the pulsations in the intake air arising from the operation of the intake valve. After entering theinner cavity 42, the intake air turns through a bend of about 90-180 degrees and travels to the other end of theinner cavity 42 to theorifices 52 where it travels down thevent tubes 72 and into the interior of thehousing shroud 26. As shown inFIG. 5 , thevent tubes 72 are located to direct the intake air into theslots 169 in thestator 146 of themotor 106 so as to convectively cool thecoil 154. After passing through and around themotor 106, the intake air passes through the openings 80 in thebase plate 82 into the wide part of theintake chamber 86. The air is routed through the narrowed part and up through theintake opening 90 in thebase plate 82 and theintake tube 92 to theintake side 120 of thevalve head 100, as shown inFIG. 10 . Reciprocation of thepiston 104 draws air into thecylinder 102 and compresses it. The pressurized air is then passed through theexhaust side 122 of thevalve head 100 and down through theexhaust tube 94 in thebase plate 82 to the wide part of theexhaust chamber 88 throughexhaust opening 96. As shown inFIGS. 9 and 11 , the pressurized air flows through the narrow portion of theexhaust chamber 88 and out through the outlet opening where fitting 34 is attached to suitable hose or tubing (not shown). - Since the pump has only a single cylinder, the pressurized air is pulsed at the rate of the input frequency, for example 60 Hz. The inventors have determined that pulsations in the output air can adversely effect the operation of the pump. In particular, the output lines act as resonant chambers, having their own natural frequency. If the pulsations in the output air are at a different frequency, the air will effectively encounter increased resistance going through the output lines. This creates excessive back pressure on the pump so that the spring-mass system can be made to operate at a different (non-resonant) frequency, thereby decreasing the efficiency of the pump. This makes the pump more sensitive to variations in input frequency which can further decrease efficiency. By reducing the amplitude of the pulsations in the air before leaving the pump, this problem can be avoided.
- To that end, as shown in
FIGS. 3, 9 and 13, the pulsations in the pressurized output air leaving the pump are dampened by adiaphragm 190 in theexhaust chamber 88. In particular, thediaphragm 190 is preferably a rubber disk mounted to the top of acup 192 defined by thehousing base 24 in the wide part of theexhaust chamber 88 by asupport ring 194 bolted (via bolts 198) to thebase 24. Thecup 192 defines a trapped air pocket 196 below thediaphragm 190. As the pressurized air flows through theexhaust chamber 88, the pulsations act against thediaphragm 190, tending to make it flex into thecup 192. The air pocket 196 will compress slightly, but tend to resist inward movement of thediaphragm 190. This reactive force on thediaphragm 190 will tend to counter, and thus cancel or reduce the amplitude of, the pulsations in the exhaust chamber air. Thediaphragm 190 and trapped air pocket 196 act similar to an accumulator, and as a result, allow the pump to output smoother, relatively non-pulsed, air through the output lines. As a result pump inefficiencies are avoided that may otherwise arise from changes in the length or diameter of the output lines or from changes to the input frequency to the motor. As an example of one advantage, the inventors have determined that use of the diaphragm in this way allows a single mass-spring system to be used for both 50 and 60 Hz applications. - An illustrative embodiment of the present invention has been described above in detail. However, the invention should not be limited to the described embodiment. To ascertain the full scope of the invention, the following claims should be referenced.
Claims (22)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US10/918,278 US20060034711A1 (en) | 2004-08-13 | 2004-08-13 | Linear pump with sound attenuator |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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US10/918,278 US20060034711A1 (en) | 2004-08-13 | 2004-08-13 | Linear pump with sound attenuator |
Publications (1)
Publication Number | Publication Date |
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US20060034711A1 true US20060034711A1 (en) | 2006-02-16 |
Family
ID=35800132
Family Applications (1)
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US10/918,278 Abandoned US20060034711A1 (en) | 2004-08-13 | 2004-08-13 | Linear pump with sound attenuator |
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US (1) | US20060034711A1 (en) |
Cited By (5)
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WO2013016795A1 (en) * | 2011-08-02 | 2013-02-07 | Whirlpool S.A. | Discharge muffling chamber for refrigeration compressors and process for closing a discharge muffling chamber |
CN103925192A (en) * | 2014-05-06 | 2014-07-16 | 苏州铉动三维空间科技有限公司 | Air pump housing |
US20180024264A1 (en) * | 2015-02-27 | 2018-01-25 | Halliburton Energy Services, Inc. | Ultrasound color flow imaging for oil field applications |
US20180135615A1 (en) * | 2015-05-05 | 2018-05-17 | Parker-Hannifin Corporation | Miniature vacuum/pressure diaphragm pumps with noise mitigation boot |
WO2018170632A1 (en) * | 2017-03-18 | 2018-09-27 | 深圳市方鹏科技有限公司 | Breathing device for bionic robot |
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WO2013016795A1 (en) * | 2011-08-02 | 2013-02-07 | Whirlpool S.A. | Discharge muffling chamber for refrigeration compressors and process for closing a discharge muffling chamber |
CN103925192A (en) * | 2014-05-06 | 2014-07-16 | 苏州铉动三维空间科技有限公司 | Air pump housing |
US20180024264A1 (en) * | 2015-02-27 | 2018-01-25 | Halliburton Energy Services, Inc. | Ultrasound color flow imaging for oil field applications |
US10451761B2 (en) * | 2015-02-27 | 2019-10-22 | Halliburton Energy Services, Inc. | Ultrasound color flow imaging for oil field applications |
US20180135615A1 (en) * | 2015-05-05 | 2018-05-17 | Parker-Hannifin Corporation | Miniature vacuum/pressure diaphragm pumps with noise mitigation boot |
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WO2018170632A1 (en) * | 2017-03-18 | 2018-09-27 | 深圳市方鹏科技有限公司 | Breathing device for bionic robot |
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