Patent Application
20140064996
1. Field of the Invention
The present invention relates to a plunger pump which is a type of delivery pump used for delivering a mobile phase of a liquid chromatograph, for example, and which performs delivery by sliding a plunger inside a pump chamber provided in a pump head.
2. Description of the Related Art
A general plunger pump (see Japanese Patent Laid-open Publication No. 2001-254686) will be described using
A pump head 38 is attached at a tip end of a pump body 30 across a cleaning chamber 44 for cleaning a plunger 33. A crosshead 34 that reciprocates in one direction by a cam mechanism (not shown) and a spring 36 is accommodated within the pump body 30, and a plunger 33 is attached at the tip end of the crosshead 34. A tip end portion of the plunger 33 is inserted into a pump chamber 38a provided inside the pump head 38, and slides inside the pump chamber 38a along the inner wall of the pump chamber 38a.
An inlet path 38b and an outlet path 38c communicating with the pump chamber 38a are provided to the pump head 38. Check valves 39a and 39b that open or close according to the pressure inside the pump chamber 38a are provided to the inlet path 38b and the outlet path 38c. When the plunger 33 is moved to the suction side (the right side in the drawing), the check valve 39a opens and fluid is drawn into the pump chamber 38a from the inlet path 38b, and when the plunger 33 moves to the discharge side (the left side in the drawing), the check valve 39b opens and the fluid inside the pump chamber 39a is discharged from the outlet path 38c.
A concave portion 40 communicating with the pump chamber 38a is provided on a surface of the pump head 38, on the side of the pump body 30. A plunger seal 42 which the plunger 33 penetrates and which holds the plunger 33 in a slidable manner is embedded in the concave portion 40, and a backup ring 43 is inserted on the back surface side of the plunger seal 42 (on the side of the surface on the pump body 30 side). The plunger seal 42 is for preventing the fluid from the pump chamber 38a from leaking to the side of the pump body 30. A cleaning seal 46 for preventing leakage of cleaning fluid is attached to the cleaning chamber 44.
The plunger seal 42 has a ring-shaped concave portion 42a provided on the front surface facing the pump chamber 38a, and is structured to expand the concave portion 42a when the delivery pressure is high by storing the fluid which has leaked from the pump chamber 38a and to improve the sealing performance of the plunger seal 42. Moreover, a ring-shaped metal spring 50 is inserted into the concave portion 42a, and the sealing performance of the plunger seal 42 is further improved by the elastic force of the metal spring 50.
As described above, the fluid which has leaked from the pump chamber 38a is stored in the concave portion 42a on the front surface of the plunger seal 42, and thus, in the cases which the fluid to be delivered is highly corrosive to metal, the metal spring 50 inserted into the concave portion 42a is corroded. Accordingly, under a condition where the delivery pressure is high, delivery of fluid highly corrosive to metal could not be performed. Also, in the case of using the plunger pump to deliver a mobile phase in a liquid chromatograph, even if the mobile phase is not fluid which is highly corrosive to metal, metal ions may dissolve in the mobile phase by the metal spring 50 coming into contact with the mobile phase, and a chemical reaction with a functional group or an analytical sample in a separation column may occur, possibly negatively affecting the analysis result.
The present invention aims to provide a plunger pump capable of delivering even fluid that is corrosive to metal at a high pressure.
A plunger pump, which is the target of the present invention, includes a pump body, a pump head attached to a tip end portion of the pump body, the pump head including a pump chamber, and an inlet path and an outlet path communicating with the pump chamber, a plunger whose base end is held inside the pump body and whose tip end is inserted into the pump chamber, the plunger being adapted to slide in an axial direction along an inner wall of the pump chamber, and a ring-shaped plunger seal arranged between the pump chamber and the pump body with a front surface facing the pump chamber and a back surface facing the pump body, the plunger seal including a penetration hole from the front surface to the back surface, and holding the plunger in a slidable manner with an inner wall of the penetration hole and preventing fluid leakage from the pump chamber to the pump body.
In the present invention, according to such a plunger pump, the plunger seal includes a ring-shaped hollow portion surrounding the penetration hole, an elastic member for expanding the hollow portion in a radial direction of the plunger by an elastic force is provided inside the hollow portion, the hollow portion communicates with a back surface side of the plunger seal and does not communicate with a front surface side, and a metal elastic member is not provided at a position that comes into contact, at the front surface side of the plunger seal, with fluid that is delivered.
According to the plunger pump of the present invention, since a metal elastic member is not attached to the front surface side of the plunger seal, the metal elastic member is not corroded by the fluid from the pump chamber, or metal ions are not dissolved due to the fluid from the pump chamber coming into contact with the metal elastic member. Moreover, the plunger seal includes the ring-shaped hollow portion surrounding the penetration hole, an elastic member for expanding the hollow portion in a radial direction of the plunger by an elastic force is provided inside the hollow portion, and the hollow portion communicates with the back surface side of the plunger seal and does not communicate with the front surface side, and thus, the sealing performance of the plunger seal may be improved by the elastic force of the elastic member, and the pressure resistance may be increased. Since the hollow portion provided with the elastic member is not communicated with the front surface side, even if the elastic member is made of metal, it does not come into contact with the fluid from the pump chamber, and fluid which is corrosive to metal may be delivered at a high pressure.
In another embodiment of the plunger pump, the elastic member is ring-shaped surrounding the penetration hole along the ring shape of the hollow portion. An example of the elastic member is a coil spring that is curved into a ring shape.
In another embodiment of the plunger pump, a ring-shaped pressure space is preferably provided, the pressure space communicating with the front surface side of the plunger seal and being adapted to press, in the radial direction of the plunger, the plunger seal by the pressure caused by the entering of fluid which has been delivered. Then, the sealing performance of the plunger seal may be improved at the front surface side of the plunger seal, using fluid from the pump chamber, and the pressure resistance of the plunger seal may be further increased.
The pressure space is provided inside the plunger seal, and preferably expands in the radial direction of the plunger with the increase in the internal pressure and presses the plunger seal against the plunger and the inner wall surface of the pump head. Then, the sealing between the plunger seal and the plunger, and the sealing between the plunger seal and the inner wall surface of the pump head may be improved using the fluid from the pump chamber.
Moreover, the pressure space may also be a gap provided between the outer surface of the plunger seal and the inner wall surface of the pump head. Also in this case, the sealing between the plunger seal and the plunger may be improved using the fluid from the pump chamber.
An example embodiment of a plunger pump will be described using
A plunger pump includes a pump body 2, and a pump head 8 attached at a tip end of the pump body 2. A cleaning chamber 14 is provided between the pump body 2 and the pump head 8. A crosshead 4 is accommodated inside the pump body 2 in a movable manner. The crosshead 4 is biased in a direction away from the pump head 8 (in the right direction in the drawing) by an elastic body 6 such as a spring, and the crosshead 4 reciprocates along one direction (the left and right direction in the drawing) inside the pump body 2 by a cam mechanism (not shown) provided on a base end portion side of the crosshead 4 and the elastic force of the elastic body 6.
A base end portion of the plunger 3 is attached at a tip end of the crosshead 4. A tip end portion of the plunger 3 penetrates the cleaning chamber 14, and is inserted into a pump chamber 8a provided inside the pump head 8. With the crosshead 4 being driven, the plunger 3 reciprocates along the axial direction thereof, and the tip end portion of the plunger 3 slides along the wall surface of the pump chamber 8a. The pump head 8 includes an inlet path 8b for drawing fluid into the pump chamber 8a, and an outlet path 8c for discharging the fluid from the pump chamber 8a. Check valves 9a and 9b are provided on the inlet path 8b and the outlet path 8c, respectively, so as to prevent reverse flow.
A plunger seal attaching portion 10 is provided on a surface of the pump head 8, on the side of the pump body 2. The plunger seal attaching portion 10 is a concave portion that is coaxial with the pump chamber 8a and has an inner diameter greater than the inner diameter of the pump chamber 8a, and its bottom surface communicates with the pump chamber 8a. A plunger seal 12 is inserted into the plunger seal attaching portion 10, and a backup ring 13 is inserted on the back surface side of the plunger seal 12. The plunger seal 12 has a penetration hole where the plunger 3 is to penetrate, and holds the plunger 3 in a slidable manner and prevents the fluid from the pump chamber 8a from leaking to the side of the pump body 2. The backup ring 13 is supported by a surface, on the side of the pump head 3, of the cleaning chamber 14, and serves the role of pressing the plunger seal 12 to the side of the pump chamber 8a.
The cleaning chamber 14 includes a path through which cleaning fluid flows, and a space where the outer circumferential surface of the penetrating plunger 3 is cleaned by the cleaning fluid. A cleaning seal 16 is provided at a portion in the internal space of the cleaning chamber 14 where the plunger 3 is to be inserted, the cleaning seal 16 holding the outer circumferential surface of the plunger 3 in a slidable manner so as to prevent leakage of the cleaning fluid. The back surface of the cleaning seal 16 is supported by a wall surface of the pump body 2.
With this delivery pump, when the plunger 3 is driven in the direction away from the pump chamber 8a (in the right direction in the drawing), the pressure inside the pump chamber 8a is reduced, the check valve 9b is closed, the check valve 9a is opened, and the fluid is drawn into the pump chamber 8a from the inlet path 8b. On the other hand, when the plunger 3 is driven in the direction of insertion into the pump chamber 8a (in the left direction in the drawing), the inside of the pump chamber 8a is pressurized, the check valve 9a is closed, the check valve 9b is opened, and the fluid is discharged from the pump chamber 8a into the outlet path 8c. Fluid is delivered with this operation being performed repeatedly.
The plunger seal 12 is made of an elastic material such as polyethylene resin. A hollow portion 12a is provided on the back surface side of the plunger seal 12. The hollow portion 12a is a ring-shaped hollow space which is open on the back side and is coaxial with the plunger 3. A ring-shaped metal spring (an elastic member) 18 is inserted from the back side into the hollow portion 12a. The metal spring 18 is for applying an elastic force in the direction of pressing a part 12c of the plunger seal 12 existing between the metal spring 18 and the plunger 3 toward the plunger 3. An example of the metal spring 18 is ring-shaped surrounding the penetration hole of the plunger seal 12, along the ring shape of the hollow portion 12a. A concrete example of such a metal spring 18 is a coil spring that is curved into a ring shape.
According to this structure, the sealing between the inner circumferential surface of the plunger seal 12 and the outer circumferential surface of the plunger 3 is increased by the elastic force of the metal spring 18, and the fluid which has leaked from the pump chamber 8a may be prevented from reaching the back surface side of the plunger seal 12. Since the opening of the hollow portion 12a is on the back side, the fluid which has leaked from the pump chamber 8a does not enter the hollow portion 12a, and the metal spring 18 which is inserted into the hollow portion 12a does not come into contact with the fluid which has leaked from the pump chamber 8a. Thus, the metal spring 18 which improves the sealing performance of the plunger seal 12 is not corroded, and metal ions do not dissolve from the metal spring 18 into the fluid which is to be delivered. Accordingly, even if the fluid to be delivered is fluid which is corrosive to metal, it may be delivered under a condition of high pressure where the fluid may leak from the pump chamber 8a to the front surface of the plunger seal 12.
Furthermore, a pressure space 12b is provided on the front surface of the plunger seal 12, the pressure space 12b being a concave portion which is coaxial with the plunger 3. The pressure space 12b is formed into a ring shape surrounding the plunger 3. The pressure space 12b expands using the increase in the pressure due to the entering of the fluid from the pump chamber 8a, and improves the sealing between the inner circumferential surface of the plunger seal 12 and the plunger 3, and the sealing between the plunger seal 12 and the inner circumferential surface of the plunger seal attaching portion 10. Accordingly, the fluid which has leaked from the pump chamber 8a may be even more prevented from reaching the back surface side of the plunger seal 12.
Additionally, the pressure space 12b does not necessarily have to be provided to the plunger seal 12. For example, in the example embodiment in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-189829 | Aug 2012 | JP | national |
