Pump with reversible port function

Abstract

A pump has a pump assembly for pumping fluid. The pump assembly includes a fluid pressure changing mechanism in fluid communication with a valve plate which is in fluid communication with a port plate. A pair of flappers are interposed between and sealable with the valve plate and port plate. A head has a head port, and is in sealed engagement with the port plate, so that, in cooperation with the port plate and the valve plate, the flappers control fluid flowing through the head port and to and from the fluid pressure changing mechanism. Rotation of the port plate and valve plate relative to the head reverses flow of the fluid through the head port.

Description

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] This application claims the priority benefit of U.S. Provisional Patent Application No. 60/223,812 filed on Aug. 8, 2000.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] Not Applicable

BACKGROUND OF THE INVENTION

[0003] This invention relates to piston pumps and compressors, and more particularly to a pump with a reversible port function.

[0004] Small-scale fluid pumps are used for many consumer applications. A typical type of pump for these purposes use a wobble piston. Examples of such pumps are found in U.S. Pat. No. 3,961,868, issued Jun. 8, 1976 to Arthur J. Droege, Sr. et al, for “Air Compressor” and U.S. Pat. No. 4,842,498, issued Jun. 27, 1989 to Roy J. Rozek, for “Diaphragm Compressor”.

[0005] In a typical pump, a pump assembly includes a piston which reciprocates in a cylinder to compress air. The piston is a plastic connecting rod having a piston end disposed in the cylinder, and a connecting end connected to an eccentric metal pin mounted to a shaft. As the shaft rotates, the connecting rod having a piston head disposed in a cylinder reciprocates to compress air. A head member in fluid communication with the cylinder feeds air into the cylinder through an intake port, and provides an escape for compressed air through an exhaust port, and ultimately to an outlet in the head member.

[0006] Pumps are typically configured to pump fluid in one direction, that is to provide compressed air, or to provide suction and create a vacuum. Providing a pump which compresses air often requires a different arrangement of parts than a pump which provides a vacuum. As a result separate assembly lines, or at least careful coordination of parts in assembly, is required to produce the desired pump configuration. Therefore, a need exists for a pump having a pump assembly which can be easily reconfigured between a compressor configuration and a vacuum configuration without requiring different parts for each configuration.

SUMMARY OF THE INVENTION

[0007] The present invention provides a pump having a pump assembly for pumping fluid. The pump assembly includes a fluid pressure changing mechanism in fluid communication with a valve plate which is in fluid communication with a port plate. A flapper is interposed between the valve plate and port plate and in sealing engagement with the valve plate and the port plate. A head having a head port is in sealed engagement with the port plate. In cooperation with the port plate and the valve plate, the flapper controls fluid flowing through the head port and to and from the fluid pressure changing mechanism. Rotation of the port plate and valve plate relative to the head reverses flow of the fluid through the head port.

[0008] A general objective of the present invention is to provide a pump assembly which is easily reconfigured between a compressor configuration and a vacuum configuration. This objective is accomplished by providing a pump having a pump assembly having a cylinder and port plate which can be rotated relative to a head to reverse the flow of fluid through the pump assembly.

[0009] The foregoing and other objects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a front perspective view of a pump incorporating the present invention with one cover half removed;

[0011] FIG. 2 is rear perspective view of the pump of FIG. 1;

[0012] FIG. 3 is a front perspective view of a pump frame for the pump of FIG. 1;

[0013] FIG. 4 is a perspective view of the pump frame of FIG. 2;

[0014] FIG. 5 is a partial perspective view of an interior surface of the pump housing of FIG. 1;

[0015] FIG. 6 is a sectional view of the mounting arms of the pump frame engaging the pump housing;

[0016] FIG. 7 is a perspective view of the cylinder, valve plate, flapper, port plate, gasket, and head of FIG. 1 assembled together;

[0017] FIG. 8 is an exploded perspective view of the assembly of FIG. 7;

[0018] FIG. 9 is a cross-sectional view along line 9-9 of FIG. 7;

[0019] FIG. 10 is a plan view of the gasket of FIG. 8;

[0020] FIG. 11 is a plan view of the head side of the port plate of FIG. 8;

[0021] FIG. 12 is a plan view of the flapper of FIG. 8; and

[0022] FIG. 13 is a top plan view of the valve plate of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] Referring to FIGS. 1-13, a pump 10 having a pump assembly 12 includes an electric motor 14 having a rotatable shaft 16 which drives an eccentric assembly 18. The eccentric assembly 18 includes an eccentric pin 20 journalled in a bore 22 formed in a connecting block 24 of a connecting rod 26 which forms a lower end of a wobble piston 30. The piston 30 operates in a cylinder 32 to change the pressure of fluid disposed in the cylinder 32. A valve plate 35 (shown in FIGS. 8 and 13) integrally molded on the end of the cylinder 32, and in fluid communication with the interior of the cylinder 32, sealingly engages a head assembly 34. The head assembly 34 includes a port plate 36 which can be rotated with the valve plate 35 relative to the head 146 to reverse the flow of fluid pumped by the piston 30. Two housing halves (one half 38 shown) are mounted to the motor 14 to enclose the pump assembly 12.

[0024] The motor 14 includes a coil winding 40 supported between upper and lower motor end brackets 42, 44. The coil winding 40 surrounds a laminated core (not shown) fixed to the motor shaft 16. The motor shaft 16 mounts a fan 46 at one end and the eccentric assembly 18 at the other end. Rotation of the shaft 16 drives the eccentric assembly 18 which reciprocatively drives the piston 30.

[0025] Referring to FIGS. 1-4, each molded bracket 42, 44 also functions as a pump frame, and includes an annular plate 48 having a center opening 50. The center opening 50 is surrounded by a integral circumferential skirt 52. A bearing 54 is disposed in the center opening 50 to support the shaft 16 extending therethrough. The skirt 52 engages the coil winding 40 to secure it between the brackets 42, 44. The annular plate 48 can include additional openings 56 to allow air blown by the fan 46 to pass over the coil winding 40 and laminated core, and cool the motor 14.

[0026] Multi-purpose mounting arms 58 extending from the skirt 52 at each bracket 42, 44 to provide alternatives for mounting the housing halves 38 to the pump assembly 12. A slot 68 opening into side 60 can receive a nut (not shown) in the widened part of the slot for threadably engaging a screw (not shown) extending through a hole 70 formed in the end of arm 58. Alternatively, as shown in FIGS. 5 and 6, the arm 58 can be received in receptacles 72 formed on an inner surface 74 of the housing half 38 to support the housing half 38 enclosing the pump assembly 12, without fasteners connecting the arms 58 to the housing halves 38.

[0027] As shown in FIGS. 1, 2, 5, and 6, the housing halves 38 are mounted around the pump assembly by slipping each arm 58 formed on the brackets 42, 44 into an inwardly open receptacle 80 formed on each housing half inner surface 82. The arms 58 support the housing halves 38 which are clamped together using screws (not shown). The screws are inserted into apertures (not shown) formed in one housing half 38, and threadably engage screw bosses 34 in the other housing half 38.

[0028] Cup-shaped elastomeric boots 84 fitted over the arms 58 are interposed between the arms 58 and housing receptacles 80 (shown in FIG. 6) to dampen vibrations generated by the pump assembly 12, and prevent the vibrations from propagating to the housing halves 38.

[0029] Referring back to FIGS. 3 and 4, the pump frame 42 includes a support base 86 for mounting the cylinder 32 and head assembly 34 thereto. The square base 86 is formed as an integral part of the frame 42, and is offset from an axis 43 defined by the plate center opening 50. The base 86 includes a support plate 90 perpendicular to a radial 45 extending from the axis 43. Outwardly extending sides 92 extend at a right angle from each edge 94 of the plate 48. An opening 96 is formed in the base plate 90 through which the piston 30 extends from the eccentric assembly 18 into the cylinder 32. Adjacent base sides 92 are joined at corners 98, and legs 100 extend from each corner 98. Threaded bores 102 formed in a distal end 104 of each leg 100 threadably engage screws 106 (shown in FIG. 1) which secure the head assembly 34 thereto.

[0030] Referring to FIG. 3, cylinder guides 108 are formed as an integral part of the plate 90, and extend from one base 92 side to the adjacent base 92 side around each leg 100. The plate 90 supports the cylinder 32, and the guides 108 position the cylinder 32 with respect to the opening 96 for receiving the piston 30 therein.

[0031] The piston 30 may be of the style and form, such as disclosed in U.S. Pat. No. 5,213,025 issued May 25, 1993 to Roy J. Rozek, for “Conical Rod Piston”. Preferably, the piston connecting rod 26 including the connecting block 24 formed as an integral part of the connecting rod 26, and has the bore 22 formed in the block 24 for journaling the eccentrically mounted pin 20. The piston 30 is formed by providing a piston end (not shown) on the rod section end 110 opposite the connecting block 24, and the frustoconical connecting rod piston end reciprocates in the cylinder 32 to draw fluid into the cylinder 32 and force fluid out of the cylinder 32. Although a piston reciprocating in a cylinder is disclosed, other mechanisms for changing the pressure of a fluid can be used, such as a diaphragm pump, without departing from the scope of the present invention.

[0032] Looking at FIGS. 7-13, the cylinder 32 has an open end 114 and a closed end 116 connected by the cylindrical wall 118. Four pairs 120 of guide posts 122 extend outwardly from the cylindrical wall 118, and engage the base cylinder guides 108 to align the cylinder 32 with the base opening 96. Each guide post 122 of a pair 120 of guide posts 122 extends from the cylinder wall 118 proximal the cylinder open end 114, and at a right angle to the other post 122 of the pair 120 to capture one of the guides 108 therebetween.

[0033] The valve plate 35 is formed as an integral part of the cylinder 32 on the cylinder closed end 116, and includes an inlet aperture 124 and an outlet aperture 126 formed therein. Inner curbs 128 surrounding each aperture 124, 126 positions a flapper construction 130 with an integral flapper gasket 132 on the valve plate 35. The flapper gasket 132 is received in a groove 134 formed between the inner curbs 128 and an outer curb 129 surrounding the inner curbs 128 and apertures 124, 126.

[0034] Alignment posts 136 extending upwardly from the valve plate 35 engage alignment holes (not shown) formed in the port plate 36 of the head assembly 34 to properly align the head assembly 34 with the inlet and outlet apertures 124, 126. The alignment posts 136 are offset from the valve plate center, such that the valve plate 35 can be assembled with the port plate 36 in only one orientation. Keying the valve plate 35 to the port plate 36, such that the plates 35, 36 can be assembled in only one orientation, ensures that the ports 142, 148 in the port plate 36 are aligned with the proper apertures 124, 126 in the valve plate 35.

[0035] As shown in FIGS. 8 and 9, the flapper construction 130 is disposed between the valve plate 35 and the head assembly 34 to maintain fluid flow in the desired direction through the pump assembly 12. The molded flapper construction 130 has a pair of flexible flappers 140 surrounded by the gasket 132. When the pump assembly 12 is assembled, each flapper 140 is surrounded by one of the inner curbs 128, and the groove 134 surrounding the apertures 124, 126 and curbs 128 receives the gasket 132. Although a flapper construction 130 formed as a single molded piece is disclosed, other flapper construction, such as a construction having a pair of flappers which are not joined, can be used without departing from the scope of the present invention.

[0036] The flapper construction 130 prevents fluid compressed in the cylinder 32 from exiting the cylinder 32 through the inlet aperture 124, and prevents fluid from being drawn into the cylinder 32 through the cylinder outlet aperture 126. When fluid is being drawn into the cylinder 32, the flapper 140 disposed adjacent the outlet aperture 126 is drawn against the outlet aperture 126 preventing fluid from passing therethrough. When fluid is forced out of the cylinder 32, the flapper 140 disposed adjacent the inlet aperture 124 is forced against an inlet port 142 in the port plate 36, and blocks fluid from passing through the inlet port 142.

[0037] The head assembly 34 includes the port plate 36 and a head 146. The port plate 36 sealingly engages the flapper gasket 132, and cooperates with the flappers 140 to direct fluid flow to and from the cylinder 32. The inlet port 142 and an outlet port 148 are formed in the port plate 36, and extend between a port plate cylinder side 150 and a head side 152. The screws 106 (shown in FIG. 1) threadably engaging the threaded bores 102 formed in each base leg 100 extend through holes 154 formed in each corner of the port plate 36.

[0038] The port plate cylinder side 150 includes the alignment holes and a circular guide wall 158 which extends from the port plate cylinder side 150 to circumferentially engage the cylinder wall 118. The circular guide wall 158 has a diameter slightly larger than the outer diameter of the cylinder wall 118. Preferably, a plurality of fingers (not shown) extend axially in the annular space defined by guide wall 158 guide the valve plate 35 formed on the cylinder closed end 116 within the guide wall 158 to align the apertures 124, 126 with the port plate ports 142, 148.

[0039] The port plate head side 152 includes a curb 162 surrounding each of the ports 142, 148, and an outer groove 164 surrounding the curbs 162. Two center grooves 168, 170 connect the outer groove 164 between the ports 142, 148 and respective curbs 162. A center wall 156 is formed between the center grooves 168, 170 and curbs 162, and defines a lengthwise edge of each center groove 168, 170. A registration opening 172 formed in each curb 162 receives a finger 174 extending from a port plate gasket 176 received in the grooves 164, 166.

[0040] The port plate gasket 176 is received in the outer groove 164 surrounding the ports 142, 148, and has a center member 180 which is received in one of the center groove halves 168, 170. An inwardly extending finger 182 extending from one side of the gasket 176 is received in the registration opening 172 of one of the curbs 162 to seal around a chamber of the head 146 receiving fluid through the outlet port 148 of the port plate 36.

[0041] Preferably, as shown in FIG. 11, indicators 184 are provided to inform an operator which registration opening 172 should be filled for the desired configuration. In the embodiment shown in FIG. 11, a “V” is formed in the port plate head side 152 adjacent the registration opening 172 which receives the finger 182 when a vacuum configuration is desired, and a “P” is formed in the port plate head side 152 adjacent the registration opening 172 which receives the finger 182 when a pump configuration is desired.

[0042] As best shown in FIG. 9, the head 146 sealingly engages the port plate 36 and is in fluid communication with the ports 142, 148. The head 146 includes a first chamber 186 and a second chamber 188 divided by a wall 190. The wall 190 divides the chambers 186, 188, and when engaging the port plate 36, slips into one of the center groove halves 168, 170 to sealingly engage the port plate gasket center element 180. Preferably, the head 146 is formed from plastic, such as glass reinforced polyethylene teraphthalate.

[0043] The first chamber 186 is in fluid communication with one of the port plate ports 142, 148, a head port 192, a pressure relief valve 194, and a pressure switch port 196. The head port 192 connects, such as through a hose (not shown), to a device (not shown) requiring pressurized fluid, such as an air brush, or a device requiring suction, such as an aspirator, to provide fluid communication between the first chamber 186 and the device. The pressure relief valve 194 releases pressurized fluid above a predetermined level to avoid damage to the assembly 12. The pressure switch port 196 is for connecting to a pressure switch 200 (shown in FIGS. 1 and 2). Although a pressure switch port 196, pressure switch 200, and pressure relief valve 194 are shown, they are not required to practice the invention.

[0044] The second chamber 188 is in fluid communication with outside air through an open port 202 which acts as an inlet port or an exhaust port depending upon the direction of fluid flow through the pump assembly 12. For example, in the pump configuration when the pump assembly 12 provides pressurized air through the head port 192, air is drawn into the second chamber 188 through the open port 202, and pumped into the first chamber 186 by the piston 30. In the vacuum configuration, when the head port 192 draws a suction, air is pumped from the first chamber 186 into the second chamber 188 by the piston 30, and is exhausted to the atmosphere through the open port 202. Of course the open port 202 can be in fluid communication with a container (not shown) containing a fluid which is pumped by the pumping assembly 12, or for receiving a fluid which is suctioned by the pump assembly 12.

[0045] Holes 204 formed in each corner 206 of the head 146 are aligned with the holes 194 formed in the port plate 36. The screws 106 are inserted through the holes 154, 204, and threadably engage the threaded bores 102 in the base legs 100 to sandwich the port plate 36 and the gasket 176 between the head 146 and base legs 100. In addition, threadably engaging the screws 106 urges the port plate 36 against the valve plate 35 to sandwich the flapper construction 130 therebetween.

[0046] In use, the pump assembly 12 can be configured to pump (compress) fluid or to draw fluid (create a vacuum) through the head port 142. In the compressor configuration, the first chamber 186 is positioned over the port plate outlet port 148, and the second chamber 188 is positioned over the inlet port 142. Preferably, the registration opening 172 adjacent the “T” receives the finger 182 extending from the port plate gasket 176. As a result, when the electric motor 14 drives the eccentric assembly 18 and causes the piston 30 to reciprocate, fluid is drawn into the cylinder 32 from the second chamber 188 through the inlet port 142, and exhausted into the first chamber 186 from the cylinder 32 through the outlet port 148. The pressurized fluid in the first chamber 186 passes through the head port 192 to the device requiring pressurized fluid.

[0047] In a vacuum configuration, the first chamber 186 is positioned over the port plate inlet port 142, and the second chamber 188 is positioned over the outlet port 148. Preferably, the registration opening 172 adjacent the “V” receives the finger 182 extending from the port plate gasket 176. As a result, when the electric motor 14 drives the eccentric assembly 18 and causes the piston 30 to reciprocate, fluid is drawn into the cylinder 32 from the first chamber 186 through the inlet port 142, and exhausted into the second chamber 188 from the cylinder 32 through the outlet port 148. The fluid is drawn into the first chamber 186 through the head port 192 from the device requiring suction.

[0048] In order to change between pump assembly configurations, and reverse the direction of fluid flow, the port plate 36 and cylinder 32 are rotated 180° relative to the head 146. More particularly, the screws 106 securing the head 146 to the base 86 are disengaged from the base leg threaded bores 102, and the head 146 is pulled away from the port plate 36 and cylinder 36. The cylinder 36 is pulled away from the cylinder guides 108 formed in the base 86, such that the cylinder guide posts 122 disengage from the guides 108, and the cylinder 32 can be rotated about the cylinder cylindrical axis.

[0049] The cylinder 32, and thus the valve plate 35, and port plate 36 are rotated 180° relative to the head 146, and then the cylinder 32 is slipped back between the cylinder guides 108, such the posts 122 reengage the guides 108. Rotating the port plate 36 180° relative to the head 146 aligns the port plate ports 142, 148 with a chamber 186, 188 in the head 146 which is different from the chamber 186, 188 aligned with the port 142, 148 prior to rotation. Realigning the ports 142, 148 with a different chamber 186, 188 changes the flow of fluid through the head 146.

[0050] Once the port plate 36 and cylinder 32 are repositioned, the gasket 176 received in the grooves 164, 166 formed on the head side 152 of the port plate 36, and having the gasket finger 182 inserted into one of the registration openings 172, is pulled out of the grooves 164, 166. The gasket 176 is then reinserted into the grooves 164, 166, such that the finger 182 is inserted into the other registration opening 172.

[0051] The head 146 is then repositioned adjacent the port plate 36, and the screws 106 are inserted through the holes 154, 204 to threadably engage the threaded bores 102 in the base legs 100. The screws 106 are tightened to sandwich the port plate 36 between the base 86 and the head 146, and sealingly engage the head 146 with the gasket 176. Advantageously, by rotating the valve plate 35 and port plate 36 relative to the head 146, ports extending from the head do not move relative to other pump assembly components and the housing.

[0052] While there has been shown and described what are at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention defined by the appended claims. For example, a gasket can be provided which is received in the entire grooved area of the port plate, such that repositioning the gasket is not required when changing the pump assembly configuration. In addition, the valve plate 35 can be provided as a separate piece from the cylinder 32, such that rotating the valve plate 35 and port plate 36 relative to the head 146 changes the direction of fluid flow through head 146 without rotating the cylinder 32.

Claims

1. A pump comprising:

a fluid pressure changing mechanism;

a valve plate having ports in fluid communication with said fluid pressure changing mechanism;

a port plate sealingly engaging said valve plate, and having ports therein;

a pair of flappers interposed between said valve plate and port plate, and one of said flappers being sealable over a port in said valve plate, and of said flappers being sealable over a port in said port plate;

a head having a head port, and in fluid communication engagement with said port plate, wherein said flappers, in cooperation with said port plate and said valve plate, control fluid flowing through said head port and to and from said fluid pressure changing mechanism, and wherein rotation of said port plate and said valve plate relative to said head reverses flow of the fluid through said head port.

2. The pump as in claim 1, in which said head includes a first chamber in fluid communication with said head port and a second chamber, wherein said fluid pressure changing mechanism pumps fluid into said first chamber when fluid is pumped out of said head port, and fluid is pumped into said second chamber when fluid is drawn into said first chamber through said head port.

3. The pump as in claim 2, in which a gasket is interposed between said port plate and said head, wherein said gasket seals around said chamber in which fluid is pumped.

4. The pump as in claim 3, in which said gasket is repositioned when said port plate is rotated relative to said head.

5. The pump as in claim 4, in which indicators are provided on said port plate which indicate to a user the proper position of said gasket for a desired flow direction of fluid.

6. The pump as in claim 1, in which said fluid pressure changing mechanism is a piston having one end disposed in a cylinder, wherein said piston reciprocates in said cylinder, and said cylinder is in fluid communication with said valve plate ports.

7. The pump as in claim 6, in which said valve plate is formed as an integral part of one end of said cylinder.

8. The pump as in claim 1, said valve plate is keyed to said port plate, such that said valve plate can be assembled with said port plate in only one orientation.

9. The pump as in claim 1, in which said pair of flappers are molded as a single piece.

10. A method of reversing flow of fluid through a pump including a fluid pressure changing mechanism; a valve plate in fluid communication with said fluid pressure changing mechanism; a port plate sealingly engaging said valve plate; a flapper interposed between said valve plate and port plate, and sealingly engaging said valve plate and said port plate; and a head having a head port, and disposed above and in sealed engagement with said port plate, wherein in cooperation with said port plate and said valve plate, said flapper controls fluid flowing through said head port and to and from said fluid pressure changing mechanism, said method comprising:

rotating said port plate and valve plate relative to said head to reverse flow of the fluid through said head port.

11. The method of claim 10, in which said head includes a first chamber in fluid communication with said head port and a second chamber, wherein said fluid pressure changing mechanism pumps fluid into said first chamber when fluid is pumped out of said head port, and fluid is pumped into said second chamber when fluid is drawn into said first chamber through said head port.

12. The method of claim 11, in which a gasket is interposed between said port plate and said head, wherein said gasket seals around said chamber in which fluid is pumped, and said method includes:

repositioning said gasket after said port plate is rotated relative to said head to seal around said chamber in which fluid is pumped.

13. A pump comprising:

a fluid pressure changing mechanism;

an intake port in fluid communication with said fluid pressure changing mechanism, said intake port providing a path for fluid into said fluid changing mechanism;

an exhaust port in fluid communication with said fluid pressure changing mechanism, said exhaust port providing a path for fluid out of said fluid changing mechanism;

a head including a head port, said head having a first position relative to said intake and exhaust ports and a second position relative to said intake and exhaust ports, wherein operation of said fluid changing mechanism when said head is in said first position causes fluid to pass through said head port in a first direction, and operation of said fluid changing mechanism when said head is in said second position causes fluid to pass through said head port in a second direction.

14. The pump as in claim 1, in which said fluid pressure changing mechanism is a piston having one end disposed in a cylinder, wherein said piston reciprocates in said cylinder, and said cylinder is in fluid communication with said intake and exhaust ports.

15. The pump as in claim 13, in which said intake and exhaust ports are formed by a valve plate having openings in fluid communication with said fluid pressure changing mechanism, a port plate sealingly engaging said valve plate, and having openings therein, and a pair of flappers interposed between said valve plate and port plate, wherein one of said flappers being sealable over one of said openings in said valve plate to form said exhaust port, and the other of said flappers being sealable over one of said opening in said port plate to form said intake port.

16. The pump as in claim 15, in which said valve plate is formed as an integral part of one end of said cylinder.

17. The pump as in claim 15, said valve plate is keyed to said port plate, such that said valve plate can be assembled with said port plate in only one orientation.

18. The pump as in claim 15, in which said pair of flappers are molded as a single piece.

19. The pump as in claim 15, in which said head includes a first chamber in fluid communication with said head port and a second chamber, wherein said fluid pressure changing mechanism pumps fluid into said first chamber when fluid is pumped out of said head port, and fluid is pumped into said second chamber when fluid is drawn into said first chamber through said head port.

20. The pump as in claim 19, in which a gasket is interposed between said port plate and said head, wherein said gasket seals around said chamber in which fluid is pumped.

21. The pump as in claim 20, in which said gasket is repositioned when said head is moved between said first position and said second position.

22. The pump as in claim 21, in which indicators are provided on said port plate which indicate to a user the proper position of said gasket for a desired flow direction of fluid.