Patent Application
20090053074
This invention relates generally to fluid pumps. More particularly, this invention relates to positive displacement hydraulic diaphragm pumps driven by a linear motor.
Positive displacement hydraulic diaphragm type pumps are known in the art for delivery of pumped media, typically fluids, by a pumping action between inlet and outlet valves. Hydraulic diaphragm type pumps make use of a deformable diaphragm fluidly connected to a pumping chamber between the inlet and outlet valves between which the pumped media is moved by constrictive pressure exerted by the diaphragm. The diaphragm is in turn forced to move by a powered mechanical displacement mechanism whose displacement is transmitted to the diaphragm via a working fluid. One particular type of diaphragm is the hose diaphragm.
The deformable hose diaphragm is typically a generally cylindrical membrane, or bladder, with 2 openings, one at substantially each end of the diaphragm, to separate the pumped media in a pumping chamber located inside of the diaphragm from a working fluid surrounding the diaphragm. The hose diaphragm is typically constructed from substantially impervious materials permissive of deformation to change the internal volume of the diaphragm, such as pliable and/or elastic materials like polymeric, plastic, metallic foil, rubber materials, in solid or laminated form, for example. Preferably the pumped media flows from one end through to the other end of the hose diaphragm. Due to the substantially straight flow of the pumped media through the hose diaphragm, and the separation between the pumped media and the working fluid and mechanical components of the pump, this type of positive displacement pump is typically suited for pumping highly viscous materials, abrasive, reactive or corrosive materials, slurries and sludges, as well as less viscous fluids at a wide range of pressures. Although hose diaphragm pumps are discussed in particular below, the field of the present invention applies to all forms of hydraulic diaphragm pumps. In the case of hydraulic diaphragm pumps using an alternate diaphragm other than a hose diaphragm, the description below may be interpreted such that the two working surfaces of the alternate diaphragm correspond to the inside and outside of a hose diaphragm.
Hose diaphragm pumps according to the art may typically provide a constrictive pressure around the hose diaphragm to provide the necessary pumping action of the pumped media inside the diaphragm by displacing a working fluid surrounding the hose diaphragm with a reciprocating piston to constrict (effectively decreasing the internal volume of the hose diaphragm and the pumped media within) and expand (effectively increasing the internal volume of the hose diaphragm and the pumped media within) the hose diaphragm respectively. In the hose diaphragm pumps according to the art, the movement of the reciprocating piston is typically provided by the use of a connecting rod to convert the rotating motion of a drive crank to a reciprocating linear motion to drive the piston. This drive mechanism results in a varying piston velocity over the stroke of the piston due to the arrangement of the crank and connecting rod, wherein the peak velocity of the piston is typically greater than the mean velocity of the piston by a factor of at least 1.6. Although the use of cams have been disclosed in the art to reduce this peak/mean piston velocity factor to some extent, the crank and connecting rod drive mechanism of the hose diaphragm pumps according to the art typically result in a substantial period of acceleration and deceleration of the piston at the ends of the piston stroke, and lag while changing direction. Further, in order to cause a given linear displacement of the piston, it is required to impart a varying degree of rotation of the drive crank, depending upon the location of the piston relative to its stroke limits, thus limiting the precision and accuracy of piston displacement control in the hydraulic diaphragm pumps according to the prior art.
As a result of the characteristics of the crank and connecting rod drive mechanism typically employed in the hydraulic diaphragm pumps according to the art, the pumping characteristics of such conventional diaphragm pumps have several limitations. One limitation is that there is a substantial flow variation during the constriction or expansion phase of the pumping chamber, such that pumped media flows from a pump with even three or more pumping chambers operating in staggered phase are uneven or peaky, typically requiring surge control reservoirs and the like to desirably reduce the peakiness of the pumped media output flow. Another limitation is that the flow variation results in the acceleration and deceleration of both the suction and discharge fluid volumes resulting in dissipation of work to frictional losses. A further limitation is that the peak pressure of the pumped media output flow and the corresponding minimum suction pressure (or peak suction) of the pumped media inlet flow into the pump are significantly higher and lower than the mean pressure and corresponding mean suction, respectively. The minimum suction pressure of the pumped media inlet flow is typically a limiting factor in a diaphragm type pumps due to the requirement to maintain a net positive suction head pressure in the pumped media inlet flow to avoid boiling or cavitation of the pumping media. Yet a further limitation is that in order to produce a given volume of pumped media output flow, the required crank drive input varies depending upon the position of the working fluid piston relative to its stroke.
It is an object of the present invention to provide a positive displacement hydraulic diaphragm pump that addresses some of the limitations of the hydraulic diaphragm pump designs, and particularly hose diaphragm pump designs according to the art.
According to one embodiment of the present invention, a positive displacement pump is provided, comprising:
first and second pumped media pumping chambers, comprising first and second deformable hose diaphragms, wherein each said pumping chamber is fluidly connected to an inlet end and an outlet end;
inlet and outlet flow control valves in fluid connection with the inlet and outlet ends of each of the pumping chambers;
a working fluid drive cylinder assembly having first and second ends containing a working fluid;
a working fluid drive piston slidably situated within the working fluid drive cylinder between the first and second ends;
at least one linear motor attached to the working fluid drive piston such that a linear reciprocating motion of the linear motor drives a reciprocating motion of the working fluid drive piston within the working fluid drive cylinder assembly; and
first and second working fluid compression jackets enclosing at least a portion of the first and second pumping chambers wherein the first and second working fluid compression jackets contain a working fluid in fluid communication with the first and second ends respectively of the working fluid drive cylinder assembly such that a reciprocating movement of the working fluid drive piston driven by the linear motor alternatingly applies a constrictive and expansive force to each of the first and second deformable hose diaphragms in opposite phase to each other.
According to another embodiment of the present invention, a method of operating a positive displacement pump comprising at least one pumping chamber comprising a deformable hose diaphragm wherein each pumping chamber comprises an inlet end and an outlet end, a working fluid displacement assembly, a linear motor attached to the working fluid displacement assembly such that a linear reciprocating movement of the linear motor drives displacement of the working fluid within at least one working fluid compression jacket enclosing at least a portion of each pumping chamber, such that displacement of the working fluid driven by the reciprocating movement of the linear motor alternatingly applies a constrictive and expansive force to each of the deformable hose diaphragms is provided. The method comprises controlling the linear motor to generate a linear reciprocating motion characterized by a substantially constant velocity over a range of linear motion between first and second positions.
According to a further embodiment of the present invention, a method of operating a positive displacement pump comprising at least one pumping chamber comprising a deformable hose diaphragm wherein each pumping chamber is fluidly connected to an inlet end and an outlet end, a working fluid displacement assembly, a linear motor attached to the working fluid displacement assembly such that a linear reciprocating motion of the linear motor drives displacement of the working fluid within at least one working fluid compression jacket enclosing at least a portion of each pumping chamber, such that displacement of the working fluid driven by the reciprocating movement of the linear motor alternatingly applies a constrictive and expansive force to each of deformable hose diaphragms is provided, the method comprising controlling the linear motor to generate a substantially constant pumping media flow through the positive displacement pump.
Exemplary embodiments of the present invention are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.
Inlet end flow control valves 10 and 12 and outlet end flow control valves 14 and 16 control flow of pumped media into and out of pumping chambers 6 and 8 respectively, and may comprise any suitable type of flow control valve, typically a one-way passively operated valve, such as ball, cone, or poppet check valves, for example. Alternatively, actively operated valves may also be used. Common pumped media flow inlet 38 is fluidly connected to inlet end flow control valves 10 and 12, and common pumped media flow outlet 40 is fluidly connected to outlet end flow control valves 14 and 16.
Working fluid drive cylinder 18 includes first end 24 fluidly connected to working fluid compression jacket 30 surrounding hose diaphragm 2, and second end 22 fluidly connected to working fluid compression jacket 32 surrounding hose diaphragm 4. Working fluid drive cylinder assembly 18 contains working fluid 35 surrounding working fluid piston 26 which is slidably situated within the working fluid drive cylinder 18. Working fluid 35 may typically be a hydraulic oil although other substantially incompressible fluids can be chosen. Linear motor 28 is attached to working fluid piston 26 such that linear motor 28 can drive a reciprocating linear motion of working fluid piston 26 within working fluid cylinder 18. The reciprocating linear motion of the working fluid piston 26 driven by linear motor 28, is effective to alternatingly displace working fluid 35 in and out of working fluid compression jackets 30 and 32, and thereby to apply alternating constrictive and expansive forces on hose diaphragms 2 and 4 in opposite phase to each other, resulting in the alternate pumping of the pumped media through pumping chambers 6 and 8. The pumping chambers 6 and 8 change their internal volume by substantially the same volume change that is made in first end 24 and second end 22, respectively, of the working fluid piston inside working fluid drive cylinder 18.
In an alternative embodiment, more than 2 hose diaphragms may be used collectively to pump a pumped media in response to displacements of a working fluid surrounding the hose diaphragms, such as 3, 4, 6, or 8 hose diaphragms for example. In another alternative embodiment, a single pumping chamber with one or more hose diaphragms may be used to pump a pumped media, such as in applications not requiring continuous flow of the pumped media, for example.
In one embodiment, linear motor 28 may typically be an electromagnetic linear motor which may be electrically controllable. Suitable such linear motors may comprise induction or synchronous type linear motors operable to provide desirably precise electrically controlled linear movement, such as desirably precise control of linear position, velocity and acceleration, to drive a working fluid piston such as piston 26. More particularly, suitable linear motors may comprise high force brushless AC or DC linear motors, which may comprise permanent (such as neodymium) magnets or electromagnets, and iron or air core moving coil assemblies, such as are available from H2W Technologies Inc. of Valencia, Calif., for example. The linear motor 28 may be directly connected to the working fluid piston 26 as shown in
In another embodiment, the linear motor 28 in the inventive positive displacement hose diaphragm pump includes a control module 34 to electrically control the linear driving motion of linear motor 28. The control module 34 typically includes a control program 36, which may be stored on a computer readable medium such as a logic chip, RAM (randomly accessible memory) or ROM (read only memory) chip, magnetic, optical or magneto-optical computer readable medium, for example. Control program 36 may comprise computer readable instructions to effect control of the linear driving motion of linear motor 34.
In an exemplary embodiment directed to providing a substantially constant flow of pumped media through the inventive positive displacement pump, the control program 36 may desirably comprise instructions to control the linear motor 34 to produce a linear driving motion of substantially constant velocity. Such substantially constant velocity linear driving motion may desirably effect a substantially constant velocity of the working fluid piston 26, and thereby of the alternating contraction and expansion of the volumes of the pumping chambers 6 and 8 and pumping of the pumped media within.
In another exemplary embodiment directed to providing a substantially constant pumped media inlet pressure at the inlet 38 of the inventive pump, the control program 36 may desirably comprise instructions to control the linear motor 34 to produce a varying driving motion of working fluid piston 26 and therefore varying rate of volumetric expansion of the pumping chambers 6 and 8 that corresponds to maintaining a desired pumped media inlet pressure. In particular, it may be desired to control the linear motor 34 to provide a pumped media inlet pressure that is greater than or equal to a net positive suction head pressure for a selected pumped media, to avoid cavitation or boiling of the pumped media at the inlet of the pump 38.
In yet another exemplary embodiment directed to providing a varying flow rate of pumped media through the inventive positive displacement pump, the control program 36 may desirably comprise instructions to control the linear motor 34 to produce a linear driving motion that varies according to a desired linear motion velocity profile. In particular, for use with pumped media that may demonstrate varying rheological properties at different rates of strain, it may be desirable to control the linear motor to produce a linear driving motion with a linear motion velocity profile derived from or based on a rheological profile of the pumped media.
In an exemplary embodiment directed to providing a metered or dosed flow of pumped media through the inventive positive displacement pump, the control program 36 may desirably comprise instructions to control the linear motor 34 to produce a linear driving motion of a desired length in response to a control signal. The desired length of the linear driving motion of the linear motor 34 may desirably correspond to a desired metered or dosed volume of pumped media desired to be pumped by the inventive pump. Alternatively, for applications requiring a precisely metered flowrate (volume/time) of a pumped medium, an exemplary embodiment of the present invention is provided wherein control program 36 may desirably comprise instructions to control the linear motor 34 to produce a linear driving motion of a desired velocity in response to a control signal. The desired velocity of the linear driving motion of the linear motor 34 may desirably correspond to a desired metered flowrate of pumped media desired to be pumped. In some embodiments, the desired metered flowrate of pumped media may vary over time, in which case, the linear motor 34 may be controlled to produce a desirably varying linear driving motion profile to correspond to the desired variable metered flowrate profile for the pumped media. Such embodiments may be particularly suited to applications requiring precise controllable dosing or flow metering of a pumped media, such as in chemical process or treatment applications where the pumped media may comprise a chemical reagent for example.
In the inventive pump embodiment shown in
In an alternative embodiment, a positive displacement pump may be provided using non-piston working fluid displacement assemblies. For example, a positive displacement pump according to the present invention may comprise a plunger or diaphragm type working fluid displacement mechanism utilizing stationary seals to displace working fluid in response to a driving force from a linear motor, in place of the reciprocating working fluid displacement piston(s) moving inside a working fluid cylinder shown in
Similar to as described above in reference to
In an alternative embodiment, individual working fluid drive cylinder assemblies and working fluid pistons may be provided for each compression jacket and enclosed hose diaphragm in the inventive pump. Such individual working fluid pistons may be collectively connected to a single linear motor for collective driving of the pistons, or may alternatively be individually connected to individual linear motors for independently controllable driving of the pistons, and therefore the compression jackets and enclosed hose diaphragms and pumping chambers.
In another alternative embodiment, a first working fluid in fluid contact with the hose diaphragms of the inventive pump may be desirably distinct from a second working fluid contained in the drive cylinder assembly, such as to avoid contamination of the pumped media with the second working fluid or contamination by the pumped media of the second working fluid should a hose diaphragm fail, for example. In particular, in such an embodiment a secondary diaphragm may be used to separate the first working fluid from the second working fluid, but maintain fluid communication between the two working fluids, such that displacement of the second working fluid by a piston in the drive cylinder assembly results in a displacement of the first working fluid in the compression jacket, to contract or expand the hose diaphragm.
In another general embodiment according to the present invention, the use, control and/or programming of a linear motor to drive a pumped media pumping chamber in a positive displacement pump as described above may be applied to any type of hydraulic diaphragm pump. Thus, hydraulic diaphragm pumps having diaphragm means other than hose diaphragms may be driven by one or more linear motors through the displacement of a working fluid, as described above, to realize one or more of controllability, precision, and/or continuity of pumped media flow according to embodiments of the present invention.
As will be obvious to one skilled in the art, numerous variations and modifications can be made to the embodiments disclosed above without departing from the spirit of the present invention.
