Valve Controlled Reversible Pump With Anticavitation Means

The pumps described herein are intended as replacements for original equipment, for example, on oil burners. The pump drive shaft on some oil burners rotates clockwise, and on others it rotates counterclockwise. This replacement pump discharges liquid from one discharge port, regardless of the direction of rotation of the drive shaft. Furthermore, the port on the pump housing for receiving liquid from the pump may be located in different positions with respect to the drive shaft on different pump housings. This replacement pump is adaptable to deliver liquid to any of various discharge ports. In any particular pump, the discharge port selected is aligned with the receiving port of the pump housing when the pump is in place on its mounting pad. All other discharge ports are blocked.

The pump structures shown are simple and easy to mount on an oil burner or other device with which they are intended to be used. The pumps are quiet in operation, as is particularly required for use on domestic oil burners.

Pumps of the present invention comprise a base plate which engages the mounting pad of the pump housing, a pump plate which encloses the pump elements and a cover plate. The pump rotor has two outlets, only one of which is used for a selected direction of rotation. A valve mechanism responds to the pressures at the pump rotor outlets and directs the flow from the active rotor outlet to the discharge port. That valve mechanism is mounted within the base plate. The valves are simple discs or balls trapped in chambers and moved by fluid pressure to perform their control functions.

The gear pump illustrated is a crescent pump. A single inlet port is located diametrically opposite the point where the gear teeth mesh. This inlet port is used for both directions of rotation of the gears. Two outlet ports are located on either side of the mesh point, each outlet port being used for one direction of rotation only. As the gears rotate, a vacuum is developed in the spaces between the gear teeth as they travel from the point of disengagement of the gear teeth to the inlet port. There the evacuated spaces between the gear teeth are filled with liquid.

The inlet port is made narrower than the width of the teeth on the gears so that each gear tooth closes the inlet port completely and it is never possible for two consecutive spaces between teeth on that gear to be open to the inlet port at the same time. In prior art pumps having a single central inlet port, where such a relationship between the gear tooth width and the inlet port width did not exist, each empty space, as it registers with the inlet, may draw back some of the liquid from the preceding space which has been filled, and which is still in partial registry with the inlet. Hence, as the rotation continues, that preceding space is only partly filled with liquid and the remainder with vapor or a vacuum. This vapor or vacuum is suddenly collapsed as the gears continue to rotate and compress the space. Such a sudden collapse of a vacuum or vapor filled space causes cavitation with accompanying noise. This noise is avoided in accordance with the present invention by making the inlet port narrower than the gear teeth, so that each space between two gear teeth is completely filled with liquid at the inlet port and is then sealed from the inlet port before the next space registers with that port.

FIG. 1 is a view partly in elevation and partly in section of a pump assembly embodying the invention.

FIG. 2 is an exploded perspective view of the pump of FIG. 1, with the cover plate reversed.

FIG. 3 is a view taken on the line 3--3 of FIG. 1, showing the base plate, and with portions of the pump gears shown in dotted lines.

FIG. 4 is a view of the base plate of FIG. 3 taken on the line 4--4 of FIG. 1.

FIG. 5 is a sectional view taken on line 5--5 of FIG. 3.

FIG. 6 is a view of the pump rotor, taken on the line 3--3 of FIG. 1, but in the opposite direction from the arrows, and on a larger scale with the ports shown in dotted lines to illustrate the relationship between the width of the gear teeth and the width of the inlet port;

FIG. 7 is a view similar to FIG. 1, illustrating another embodiment of the invention;

FIG. 8 is an exploded perspective view of the pump of FIG. 6, with the cover plate reversed;

FIG. 9 is a view taken on the line 9--9 of FIG. 7, looking in the direction of the arrows;

FIG. 10 is a view taken on the line 10--10 of FIG. 7, looking in the direction of the arrows;

FIG. 11 is a fragmentary sectional view taken on the line 11--11 of FIG. 10;

FIG. 12 is a view similar to FIG. 6, but showing the embodiment of FIGS. 7-11.

FIG. 1 shows a complete pump assembly including a housing 1 having a mounting pad 1a on which a pump generally indicated at 85 is supported. The housing 1 encircles a drive shaft 4 adapted for connection to a motor-driven shaft on an oil burner. A cover 5 encloses the end of the housing 1 opposite the drive shaft 4. The housing 1 and the cover 5 enclose a chamber 6 filled with oil or other liquid to be pumped. A pressure regulating valve, of conventional construction, is located in another chamber of the housing 1 and delivers the liquid being pumped through a discharge conduit at substantially constant pressure.

The pump assembly comprises a base plate 86, a pump plate 87, and a cover plate 88.

The plates 86, 87 and 88 are stacked and are attached to the mounting pad 1a by means of screws 17. A screen 20 of conventional construction encloses the pump assembly. The base plate 86, as shown in FIGS. 2-4 includes five apertures to receive the screws 17, a central aperture to receive the shaft 4 and two discharge passages 100a and 100b, one of which communicates with a discharge line through a receiving port in the housing 1 (not shown).

In the pump 85, all of the fluid passages and two valves 96 and 97 which control the direction of the fluid flow are located in the base plate 86. The pump plate 87 encircles a ring gear 89 and a pinion gear 90 of a crescent pump. The cover plate 88 closes the outer side of the pump plate 87, and carries a crescent 88a which fills the space between the gears 89 and 90. An inlet 86a (FIG. 2) to the pump 85 is a groove in one side of the base plate 86. The inlet 86a connects with a series of tortuous passages and grooves in the base plate 86, including an axial passage 91, a groove 92 (FIG. 4) in the bottom face of the plate 86, an axial passage 93, and a groove 86d, 86e (FIGS. 2 and 3) in the outer face of the base plate. A shoulder separates the wide groove section 86d from the narrow groove section 86e. Most of the narrow groove section 86e is covered by the crescent 88a. The ends of the narrow groove section 86e are alternately covered and uncovered by the teeth of the rotating gears 89 and 90. The fluid enters the spaces between the gear teeth from the groove section 86e at the point of widest separation of the gears. Thus, the groove section 86e always acts as the inlet port for the pump rotors, in either direction of rotation. The rotation of the pump rotors 89 and 90 forces fluid out through one of two axial passages 86b or 86c, which are the outlet ports for the pump rotors, the particular port selected depending upon the direction of rotation of the pump.

Passage 86b communicates with a groove 94a on the inner face of plate 86 which in turn communicates with an axial passage 95. Passage 95 is a stepped passage having a shoulder 95a (FIG. 5) separating a narrow section 95b from a wide section 95c. The wide section 95c communicates with a groove 98. A ball valve 97 is trapped between the shoulder 95a and the pump plate 87. A spring 99 is retained between pump plate 87 and ball valve 97. The unstressed length of spring 99 is somewhat shorter than the spacing between plate 87 and ball valve 97 when the valve is seated against shoulder 95a. Spring 99 biases the ball valve 97 to a position near shoulder 95a so that any liquid movement from groove 98 through passage 95c toward groove 94a causes ball valve 97 to close against shoulder 95a thereby shutting off flow to groove 94a. When the flow is reversed by reversing the rotation of gears 89 and 90, air moving from passage 94a can open valve 97 without compressing the spring. Since the movement is horizontal, only small friction forces have to be overcome. Once air is purged from the pump, the pressure of the liquid being pumped compresses spring 99, and moves ball 97 far enough to cause the liquid to flow to groove 98. Groove 98 communicates with two discharge ports 100a and 100b one of which constitutes a delivery port and communicates with a receiving port (not shown) formed in the casing 1. In any particular installation, the unused port 100a or 100b is blocked. Note that groove 98 extends through one of the apertures, shown at 102, for receiving a mounting screw 17. The aperture is sufficiently larger than the screw 17 so that the screw does not appreciably restrict the flow through groove 98.

Passage 86c communicates with a valve-controlled flow path similar to that just described in connection with passage 86b, but not shown in as great detail in the drawing. The flow path from passage 86c may be traced through a groove 94b, a passage 101 corresponding in structure and function to passage 95, a valve 96 in that passage and groove 98 to the discharge ports 100a and 100b. Valve 96 corresponds in structure and function to valve 97, and is similarly biased by a spring (not shown).

When the pump rotates clockwise as viewed in FIG. 3, liquid is pumped through inlet 86a, passage 91, groove 92, passage 93 and inlet port 86e and into the pump rotors. It is discharged by the pump rotors through the axial passage 86b, groove 94a and passage 95, where the liquid pressure is effective to move valve ball 97 off shoulder 95a so that liquid passes into groove 98. Flow is then from groove 98 into one of the passages 100a and 100b (whichever is aligned with the receiving port in casing 1) and into passage 101 where the liquid pressure is effective to move ball valve 96 against its seat and hold it there.

When the pump rotates in the counterclockwise direction, the fluid passes through the same inlet route as before. Liquid is then discharged by the gears through passage 86c and groove 94b to passage 101 where liquid pressure is effective to move ball valve 96 off its seat and thereby to allow flow to groove 98. Flow is then from groove 98 through passage 100a or 100b to the receiving port in casing 1. Liquid also flows from groove 98 into passage 95c where the liquid pressure is effective to move ball valve 97 against the shoulder 95a blocking flow to groove 94a.

The noise of operation of the pump 85 is reduced in the structure shown by the tortuous inlet passages 86a, 91, 92, 93, 86d, 86e. These tortuous passages reduce the transmission of noise through the liquid. The teeth of the pump gears 89 and 90 are wider than the pump inlet groove 86e, which is effective to minimize noise due to cavitation, as explained below.

FIG. 6 shows the relationship between the width of the inlet port 86e and the width of the teeth 89a on the ring gear 89 and teeth 90a on the pinion gear 90. As is conventional in crescent type gear pumps, the spaces 89b between the teeth on the ring gear 89 are about three times as wide as the teeth 89a. Conversely, on the meshing pinion gear 90, the teeth 90a are about three times as wide as the spaces between the teeth. Consequently, most of the liquid is pumped by the ring gear and a relatively smaller quantity (about one-third as much) is pumped by the pinion gear.

In accordance with the present invention, the inlet port 86e is made narrower than the teeth 89a on the ring gear, so that as the pump rotates, each space 89b between the teeth on the ring gear is sealed by the following gear tooth from the succeeding space.

In a crescent type gear pump, as shown, having a single central inlet port, the spaces between the gear teeth become evacuated as they move from the point of tooth engagement to the inlet port. If that port is wider than the teeth, as in prior art pumps, the port bridges a tooth, so that a space which has been filled at the inlet port is at least momentarily in fluid communication with the following evacuated space. This causes liquid to be drawn from the preceding filled space through the inlet port to the evacuated space. The previously filled space is thereby partially evacuated. As the rotation of the gear proceeds, the partial vacuum is eliminated by mechanical action, accompanied by noise. This is typical cavitation.

By making the inlet port narrower than the gear teeth, as in the pump disclosed herein, the initial opening of each evacuated space between the gear teeth to the inlet port cannot operate to draw liquid out of the preceding filled space. Hence, no cavitation develops in that preceding space.

Considering the pinion gear 90, the teeth 90a are obviously much wider than the spaces 90b between them, and hence there can be no transfer of liquid from a preceding filled space into the following evacuated space.

It might seem possible that, when one of the spaces 89b in the ring gear is first opened to an inlet port 86e, it might draw liquid through the inlet port from the space 90b in the pinion gear, which is at that time at least partially filled and is in registry with the inlet port. However, it has been found that with the arrangement illustrated there is no observable noise or wear due to cavitation. It is considered that the absence of cavitation at the pinion gear 90 is due to the fact that the distance from a space 90b through the inlet port 86e to a space 89b which is just opening into the inlet port is longer than the distance from that space 89b through the inlet port 86e to the wider groove 86d connected to the main supply of the liquid being pumped. There is consequently less resistance to flow encountered in filling the space 89b from the groove 86d than from the space 90b in the gear 90. No liquid is drawn from the space 90b, and hence there is no cavitation.

These figures illustrate another embodiment of the invention, in which a pump generally indicated at 100 is enclosed in the housing 1 and driven by the shaft 4. Those parts in these figures which correspond in structure and function to their counterparts in FIGS. 1-6 have been given the same reference numerals and will not be further described.

The pump 100 includes a base plate 101, a pump plate 87 and a cover plate 88. The pump plate 87 encircles a ring gear 89 and a pinion gear 90 of a crescent pump. The base plate 101 includes two inlets 101a and 101b (FIG. 8) on opposite sides of the pump. These inlets are connected by a groove 102 in one face of the base plate 101. Groove 102 is concentric with the shaft 4 and communicates with a narrower groove 103 extending radially and serving as an inlet port for the pump. See FIGS. 8 and 9. The same face of the base plate 101 also includes recessed outlet ports 104 and 105 communicating with axially extending passages 106 and 107 respectively. The opposite ends of the passages 106 and 107 communicate with valve chambers 110 and 111 respectively (FIG. 10), defined in part by the mounting pad on the housing 1. A disk valve 112 is trapped in the chamber 110 and a disk valve 113 is trapped in the chamber 111. The chambers 110 and 111 are connected by an arcuate groove 114 in which is received a first leg of each of a pair of L-shaped leaf springs 115 and 116. The second leg of the L-shaped spring 116 is received in a recess 117 (FIG. 11) formed on the base plate 101. The second leg of spring 115 is received in a similar recess 118. The first leg of the spring 116 extends between the disk valve 113 and the housing 1 and is effective to separate the valve 113 from the housing 1 or from a gasket 120 which may be located between the base plate 101 and the housing 1. Leaf spring 115 is similarly located and similarly effective with respect to valve 112. The purpose of the leaf springs 115 and 116 is to keep the valves 112 and 113 from coming into contact with the adjacent surface of gasket 120 or the housing 1. In the event that the pump is run dry, one of the valves 112 and 113 might engage and stick against that surface. The leaf springs 115 and 116 are lightly self-biased to move the valves 112 and 113 away from the housing 1.

The outlet passages 104 and 105 are elongated in the direction of motion of the gear teeth so as to provide a ready outlet for all of the liquid between the gear teeth down to the point where they are fully engaged.

Grooves 121 extend downwardly below the valve chambers 110 and 111, as viewed in FIG. 10. The grooves 121 provide communication between either chamber 110 or 111 and a receiving port (not shown) in the housing 1. In any installation only one of the grooves 121 is used, and the other is filled with a suitable block, e.g., of elastomeric material.

The action of the narrow inlet port 103 (FIG. 12) in preventing cavitation is similar to that of the narrow inlet port 86e in FIG. 6. Note that the distance along the port 103 from the radially outer edge of space 89b to the wide groove 102 is shorter than the distance from the inner edge of space 89b radially across the crescent 88a to the space 90b. The inlet port arrangement shown in FIG. 12 is just as effective in preventing noise and wear due to cavitation as the inlet port arrangement of FIG. 6.

The pumps illustrated are shown with two discharge ports, so that any such pump may be used with a pump housing having an oil receiving port at either of two locations. Commonly, a mounting pad in a pump housing has its receiving port located with respect to the drive shaft in either a right-hand or a symmetrical left-hand location. The discharge outlets in the pumps illustrated have been located with such conventional mounting pads in view. However, if more than two possible locations of the delivery passage may be encountered in a particular situation, additional discharge ports may be provided in the pumps. The ones not used are blocked at the mounting pad.

While the invention is illustrated herein as applied to a crescent pump, it is applicable to other pumps which utilize interengaging rotating members as pumping elements.