Patent Application
20100178179
The invention relates to reciprocating pumps, and more particularly to motor powered reciprocating pumps for developing high pressure.
Reciprocating injection pumps are useful for developing precisely metered quantities of flow at high pressures, particularly in the oil and gas, and the chemical industries. It is desirable to improve the efficiency of such pumps so that they may be operable by means of low power electrical sources, such as by means of a dedicated solar panel.
However, to date the electro-mechanical efficiency of electrically-driven reciprocal injection pumps has made their operation from low power electrical sources such as dedicated solar panels impractical. The motor is generally an alternating current (AC) single phase induction motor that has a typical efficiency of about 30 percent. The normal rotational speed of the motor generally requires some degree of speed reduction to be compatible with the speed of the pump plunger, such as by means of worm gearing. The rotary motion of the motor also requires conversion to reciprocal motion, such as by means of an eccentric and connecting rod, a cam and spring-loaded cam follower that follows the annular outer face of the cam, or a similar arrangement to drive the pump plunger. Such mechanical coupling arrangements add to the conversion inefficiency of the pumping system.
The invention generally comprises a reciprocating pump assembly that comprises: a motor with a rotary motor drive shaft; and a cam coupled to the motor drive shaft with an axis of rotation and a cam channel cut generally axially into a radial face of the cam; multiple reciprocating pump units arranged radially about the cam axis of rotation, each with an inlet valve, an outlet valve, a plunger and a plunger sleeve, with a free end of its plunger coupled to the cam by way of a cam follower riding in the cam channel; wherein rotation of the motor output drive shaft causes the plunger in each pump unit to independently reciprocate in its respective sleeve.
A pinion 24 mounts on the input shaft 16 so that the pinion 24 may have an axis of rotation coincident with the input shaft axis 18. A spur gear 26 that engages the pinion 24 mounts on a main shaft 28 by means of main shaft bearings 30 that mount to the housing 12 and retain the main shaft 28 with a rotational freedom of movement about a main shaft axis of rotation 32. A pulseless cam 34 also mounts on the main shaft 28. The cam 34 may have an axis of rotation that is coincident with the main shaft axis 32. The cam 34 has a cam channel 36 cut generally axially into a radial cam face 38 of the cam 34. The path of the cam channel 36 about the radial cam face 38 is generally eccentric relative to the main shaft axis 32.
The pump assembly 2 has multiple pump units 40 that have a generally radial arrangement about the cam axis of rotation that is coincident with the main shaft axis 32.
Each pump unit 40 has a cam follower 42 that rides in the cam channel 36 of the cam 34. Each cam follower 42 couples to a cross head 44 for its respective pump unit 40. The cross head 44 for each pump unit 40 slides in a respective cross head channel 46 to allow the cross head 44 to move in a reciprocating lineal motion within its cross head channel 46 as its respective cam follower 42 rides in the cam channel 36 of the rotating cam 34. The lineal reciprocation motion is generally radial to the axis of rotation of the cam 34 represented by the main shaft axis 32. Each cross head channel 46 may have a cross head seal 48 to reduce seepage through its interface with its respective cross head 44.
Each pump unit 40 has a piston or plunger 50 that slides in a respective plunger cylinder or sleeve 52 to allow linear reciprocating movement of the plunger 50 within the sleeve 52. Preferably each plunger 50 comprises a ceramic material. Preferably each sleeve comprises stainless steel. Also preferably each sleeve 52 proximate each end has a low-friction composite TFE bearing 54 to reduce stress and mating low-friction composite TFE seal 56 to reduce seepage through its interface with its respective plunger 50.
The plunger 50 and cross head 44 in each pump unit 40 couple together to allow the plunger 50 to move in a reciprocating lineal motion within its sleeve 52 as the cam follower 42 for the cross head 44 rides in the cam channel 36 of the rotating cam 34. This lineal reciprocating motion is generally radial to the axis of rotation of the cam 34 represented by main shaft axis 32.
Each pump unit 40 has a pump head 58 that mates with the sleeve 52. The pump head has a plunger cavity 60 that receives the free end of the plunger 50. The plunger cavity 60 couples in fluidic communication with an inlet cavity 62 and an outlet cavity 64 in the pump head 58. The inlet cavity 62 has a one-way inlet valve 66 for passing fluid into the inlet cavity 62. The outlet cavity 64 has a one-way outlet valve 68 for discharging fluid from the outlet cavity 64. The inlet valve 66 preferably is a ball-type check valve that has composite TFE seats. The outlet valve 68 preferably is a spring-loaded ball-type check valve that has composite TFE seats.
Each pump unit 40 may also have a breather 70 that couples in fluidic communication with a cross head passage 72 between the cross head 44 and the plunger sleeve 52 for providing pressure relief. Each pump unit 40 may also have a grease fitting 74 that couples in fluidic communication with the plunger 50, such as by means of a lubrication cavity 76 that passes through the plunger sleeve 52, for lubricating the plunger 50. Each pump 40 may further have a bleeder 78 that couples in fluidic communication with the outlet cavity 64 for releasing fluid within the pump head 58.
As the motor 10 rotates the input shaft 14, the plunger 50 in each pump unit 40 reciprocates, sequentially causing its respective inlet valve 66 to draw fluid into its respective pump head plunger cavity 60 and its respective outlet valve 68 to discharge fluid. The eccentric path of the cam channel 34 preferably establishes a constant absolute speed for each plunger 50 to maintain a relatively constant discharge flow from its respective outlet valve 68.
The inlet valve 66 of each pump unit 40 may couple in fluidic communication by way of any ordinary inlet header (not shown). Likewise, the outlet valve 68 of each pump unit 40 may couple in fluidic communication by way of any ordinary outlet header (not shown). Coupling to the inlet valves 66 and the outlet valves 68 in such a manner smoothes the output of the pump assembly 2 so that there is no need for use of a pressure damper or fluid accumulator to smooth the fluid output of the pump assembly 2. Alternatively, if the pump assembly 2 has two or more pairs of pump units 40, each pair of pump units 40 may have its own set of inlet and outlet headers so that the pump assembly 2 may produce multiple sets of pump outputs, and each may at different pressures and flow rates.
Referring to
In most low power applications, particularly those that employ a dedicated or self-contained source of power for the motor 10, such as a solar panel or battery, the motor 10 is preferably of the direct current (DC) type, either with or without brushes. In such service, a motor controller with a pulse width modulation (PWM) output is most desirable for regulating the speed of the motor 10. For best efficiency, it is desirable to match the torque requirement of the pump assembly 2 to the motor 10, such as by adjusting the diameter of each plunger 50 and the gear ratio of the reduction gear set between the motor drive shaft 12 and the main shaft 28.
The described embodiments of the invention are only some illustrative implementations of the invention wherein changes and substitutions of the various parts and arrangement thereof are within the scope of the invention as set forth in the attached claims.
