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Liquid pumpLiquid pump description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070189911, Liquid pump. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001]This application relates to liquid pumps. BACKGROUND [0002]A liquid pump includes a piston that reciprocates in a cylindrical cavity. The piston draws liquid through an inlet valve into the cavity during an intake stroke and forces the liquid out of the cavity through an outlet valve during a delivery stroke. SUMMARY [0003]A housing of a pump apparatus includes an undivided cavity, an inlet valve through which liquid can enter the cavity, and an outlet valve through which the liquid can exit the cavity. A primary piston is configured to reciprocate in the cavity to draw the liquid into the cavity through the inlet valve during an intake stroke of the piston and discharge the liquid out of the cavity through the outlet valve during a delivery stroke. A reservoir structure is configured to add, to the total volume of the cavity, an extra volume that is a smooth positive function of liquid pressure in the cavity. [0004]Preferably, the reservoir structure includes a secondary piston configured to retract by a displacement distance that is a smooth positive function of the liquid pressure. The extra volume equals the displacement distance times a cross-sectional area of the piston. The retraction of the secondary piston is along an axis that is perpendicular to the direction of the reciprocation of the primary piston. BRIEF DESCRIPTION OF THE DRAWINGS [0005]FIG. 1 is a schematic view of a pressure washer that includes a pump; [0006]FIGS. 2-4 are partially-schematic sectional views of the pump at different times during its operation; [0007]FIG. 5 is an expanded sectional view of a portion of the pump, showing additional parts; and [0008]FIG. 6 is a partially-schematic sectional view of another pump with parts similar to those in FIG. 2. DESCRIPTION [0009]The apparatus 1 shown in FIG. 1 has parts that are examples of the elements recited in the claims. The apparatus thus includes examples of how a person of ordinary skill in the art can make and use the claimed invention. It is described here to meet the requirements of enablement and best mode without imposing limitations that are not recited in the claims. [0010]The apparatus 1 is a pressure washer. It includes a pump 10 for pumping a liquid from a supply line 12 to an outlet line 14. The supply line 12 has an inlet hose 20 connectable to a water spigot. The outlet line 14 has an outlet hose 22 connected to a spray nozzle 24. The pump 10 draws water from the inlet line 12 and forces it out the nozzle 24 in the form of a pressurized spray. [0011]As shown in FIG. 2, the pump 10 includes a housing 30 defining a cylindrical primary chamber 32 centered on a primary axis Al. Liquid from the inlet line 12 enters the chamber 32 through an inlet check valve 34. The liquid exits the chamber 32 through an outlet check valve 36 to enter the outlet line 14. [0012]The housing 30 has a cylindrical piston-bearing surface 40 defining an opening 42. A cylindrical primary piston 50 extends through the opening 42 into the chamber 32. The bearing surface 40 slidingly supports the piston 50 and forms with the piston 50 a liquid-tight seal that surrounds the piston 50. A coil spring 52 is wrapped about the piston 50. It is compressed between a spring-support flange 54 of the piston 50 and the housing 30 to bias the piston 50 axially outward. [0013]An outlet shaft 60 of a motor 62 extends parallel to the primary axis Al. The shaft 60 is attached to a wobble plate 64 that has a slide surface 66 that pushes the piston 50 axially inward against the spring bias. The slide surface 66 is inclined relative to shaft 60, for the piston 50 to axially reciprocate as the wobble plate 64 rotates with the shaft 60. [0014]The housing 30 further has a cylindrical secondary surface 70 defining a secondary chamber 72 adjoining the primary chamber 32. The secondary chamber 72 is centered on a secondary axis A2 perpendicular to the primary axis A1. [0015]A secondary piston 80 is slidingly supported by the cylindrical secondary surface 70 and forms, with the secondary surface 70, a seal that surrounds the piston 80 continually as the piston 80 moves axially through the secondary chamber 72. A secondary spring 84 is compressed by and between the secondary piston 80 and the housing 30. The spring 84 biases the secondary piston 80 toward the primary axis A1, to a fully extended position into abutment with a shoulder 86 of the housing 30. [0016]Liquid-filled portions of the first and second chambers 32 and 72 are parts of an undivided cavity 90 that is bounded by the housing 30 and the primary and secondary pistons 50 and 80. The cavity 90 has a total volume that varies gradually with movement of the pistons 50 and 80, being a smooth function of the pistons' displacements D.sub.1 and D.sub.2. The function is "smooth" in that there is no sudden increase or decrease in volume with change in D.sub.1 and D.sub.2. [0017]Reciprocation of the primary piston 50 is defined by an intake stroke and a delivery stroke, while the cavity 90 is continuously filled with the liquid. Due to the density and incompressibility of the liquid in the cavity 90, movement of the secondary piston 80 is dependent on liquid pressure P.sub.cav in the cavity 90 and substantially independent of the secondary piston's own inertia. [0018]The delivery stroke starts with the primary piston 50 fully retracted as shown in FIG. 2, and cavity pressure P.sub.cav equaling supply line pressure P.sub.in plus inlet valve crack pressure P.sub.crack. The secondary piston 80 is fully extended, because the cavity pressure P.sub.cav urging it to retract is too weak to overcome the spring bias pressing the secondary piston 80 against the shoulder 86. [0019]Thereafter during the delivery stroke, the primary piston 50 moves axially inward (arrow 95) as shown in FIG. 3. When the cavity pressure P.sub.cav exceeds outlet line pressure P.sub.out plus crack pressure P.sub.crack, the outlet valve 36 opens to let the liquid into the outlet line 14. Continue reading about Liquid pump... Full patent description for Liquid pump Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Liquid pump patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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