Liquid delivery pump for liquid chromatograph

Abstract

A liquid delivery pump includes a pump room for transferring liquid, a plunger having one end located in the pump room for moving reciprocally therein for delivering the liquid in the pump room, and a base end, and a crosshead for reciprocal movement situated adjacent to the pump room and having a flat end surface. A ball is attached to the crosshead to contact the flat end surface thereof. The base end is attached to the crosshead so that the plunger rotates freely relative to the flat end surface through the ball.

Description

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to a liquid delivery pump for a liquid chromatograph, and more specifically, relates to a structure for holding a plunger moving reciprocally within a pump room.

FIG. 2 is a sectional view of a conventional liquid delivery pump for a liquid chromatograph. In the figure, reference numeral 1 is a pump head; reference numeral 2 is a plunger; reference numeral 3 is a sealing material for allowing the plunger 2 to slide while preventing leak; reference numeral 4 is a pump room formed within the pump head 1; reference numerals 5 and 6 are inlet and outlet for liquid to be delivered, respectively, and having check valves 5a and 5b; reference numeral 7 is a pump body; reference numeral 8 is a bearing; reference numeral 9 is a spring; reference numeral 10 is a crosshead; reference numeral 11 is a cam rotationally driven by a motor not shown in the figure; and reference numeral 12 is a cam follower that rolls along the circumference of the cam 11.

A tip side (left side in FIG. 2) of the plunger 2 is inserted into the pump room 4 through the sealing material 3, and a base side (right side in FIG. 2) thereof is connected to the crosshead 10. The crosshead 10 axially supported by the bearing 8 moves reciprocally within the tubular pump body 7 with force imparted by the rotating cam 11 via the cam follower 12 in a forward direction (toward the left side in FIG. 2) and force imparted by the spring 9 in a retreating direction (toward the right side in FIG. 2). The plunger 2 moves reciprocally within the pump room 4 accompanying with the movement of the crosshead 10. Accordingly, the pump room 4 is alternately pressurized and depressurized, and associated operations of the check valves 5a and 6a cause liquid to flow from the inlet 5 to the outlet 6, thereby delivering liquid.

The plunger 2A is formed of a material with high hardness, and good wear and chemical resistance such as sapphire. A metal having a surface coated with a ceramic film may be used (for example, see Patent Reference 1).

FIG. 3 illustrates a connecting structure between the plunger 2 and the crosshead 10 in more detail. In FIG. 3, the elements same as those shown in FIG. 2 are given the same reference numerals, and their descriptions are omitted. Reference numeral 15 is a plunger holder. One end of the plunger holder 15 is fixed to the base side of the plunger 2, and the other end thereof is machined to form a spherical end 15a. The plunger holder 15 is fixed to the crosshead 10 with a screw cap 16, so that the plunger 2 and the crosshead 10 are connected. The spherical end 15a of the plunger 2 abuts against a flat end face 10a of the crosshead 10 with point contact. Accordingly, the plunger 2 freely rotates while moving reciprocally along the crosshead 10. With such a structure, it is possible to prevent grinding or shifting off center between the plunger 2 and the sealing material 3 shown in FIG. 2 when the plunger 2 moves and slides reciprocally against the sealing material 3, thereby minimizing wear of the plunger 2 and the sealing material 3.

Patent reference 1: Japanese Patent Publication (Kokai) NO.

In the connecting structure between the plunger and the crosshead described above, it is necessary to machine the spherical end of the plunger holder with a high degree of sphericity to ensure smooth rotation of the plunger, thereby increasing production cost. Moreover, when the plunger is worn out, it is necessary to replace the plunger holder fixed to the plunger together with the plunger, thereby increasing maintenance cost as well.

In view of the problems described above, an object of the present invention is to provide a liquid delivery pump for a liquid chromatograph with production and maintenance costs lower than those of the conventional device.

Further objects and advantages of the invention will be apparent from the following description of the invention.

SUMMARY OF THE INVENTION

In order to attain the objects described above, according to the present invention, a plunger holder is formed in a ball, and a plunger is connected to the plunger holder with a screw. In other words, according to the present invention, a liquid delivery pump comprises a crosshead moving reciprocally accompanied with a rotational movement of a cam, and a plunger having a tip portion inserted into a pump room via a sealing material and a base portion connected to the crosshead so as to rotate freely. The ball abuts against a flat end surface of the crosshead at a connection section between the crosshead and the plunger, and the base portion of the plunger is screwed in the ball.

In the field of bearings or the like, manufacturing technology has been established to produce a ball with a high degree of sphericity. Accordingly, it is possible to manufacture or obtain a high-quality ball at low cost. According to the present invention, such a ball can be used as the plunger holder, thereby reducing production cost. In terms of performance, the plunger can move freely and follow deformation of the sealing material, thereby reducing wear of the sealing material. As a result, it is possible to provide a highly durable liquid delivery pump for a liquid chromatograph. When the plunger is worn, it is possible to replace only the plunger, thereby reducing maintenance cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a liquid delivery pump according to an embodiment of the present invention;

FIG. 2 is a schematic view showing a conventional liquid delivery pump; and

FIG. 3 is a detailed view showing the conventional liquid delivery pump.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, embodiments of the present invention will be explained with reference to the accompanying drawings. FIG. 1 is a schematic view showing a liquid delivery pump according to an embodiment of the present invention. FIG. 1 corresponds to FIG. 3, and an overall structure of the liquid delivery pump is substantially the same as that shown in FIG. 2. In FIG. 1, the same reference numerals are used for elements functionally same as those in FIG. 3, and descriptions thereof are omitted.

As shown in FIG. 1, in the embodiment, a difference from the conventional pump is that a plunger holder 15 is formed in a ball. Manufacturing technology for a ball with a high degree of sphericity has been established in the field of bearings, and it is possible to produce balls at relatively low cost and high-quality. Such a ball thus manufactured or obtained is provided with a screw hole 15b for screwing a female screw to form the plunger holder 15.

The plunger 2 is provided with a male screw 2a at a base portion thereof, so that the male screw 2a is screwed into the screw hole 15b. When the male screw 2a is screwed into the screw hole 15b as indicated by the arrow, the plunger 2 and the plunger holder 15 are connected.

In the embodiment, an operation of the pump constructed as described above is basically the same as the conventional pump shown in FIG. 3. A surface (spherical surface) of the plunger holder 15 abuts against a flat end surface 10a of the crosshead 10, so that the plunger 2 rotates freely. Different from the conventional pump, the spherical body with a high degree of sphericity (for example, a ball bearing) is used as the plunger holder 15, so that the plunger 2 moves smoothly and slides without grinding against the sealing material 3 shown in FIG. 2, even when the sealing material 3 is slightly off-centered or deformed. As a result, it is possible to reduce wear of the plunger 2 and the sealing material 3.

Moreover, the plunger 2 is screwed in the plunger holder 15, so that it is easy to replace the plunger 2 when it is worn out. It is necessary to replace only the plunger 2, thereby reducing replacement cost as compared with the conventional pump.

The disclosure of Japanese Patent Application No. 2004-088924, filed on Mar. 25, 2004, is incorporated in the application.

While the present invention has been explained with reference to the specific embodiments, the explanation is illustrative and the invention is limited only by the appended claims.

Claims

1. A liquid delivery pump for a liquid chromatograph, comprising:

a pump room for transferring liquid,

a plunger having one end located in the pump room for moving reciprocally therein for delivering the liquid in the pump room, and a base end,

a crosshead for reciprocal movement situated adjacent to the pump room and having a flat end surface, and

a ball attached to the crosshead to contact the flat end surface thereof, said base end being attached to the crosshead so that the plunger rotates freely relative to the flat end surface through the ball.

2. A liquid delivery pump according to claim 1, further comprising sealing means attached to the pump room, through which the plunger passes, and a cam for reciprocally moving the crosshead.

3. A liquid delivery pump according to claim 2, wherein said base portion of the plunger is screwed into the ball.