Liquid feed pump and liquid chromatograph

A recess into which a protrusion of a plunger seal is to be fitted is provided at a part of a pump head where a plunger is to be inserted into a pump chamber. The plunger seal seals the pump chamber by an outer circumferential surface of the protrusion coming into close contact with an inner circumferential surface of the recess and a surface of a flange on the side of the protrusion coming into close contact with a circumferential edge surface of the recess of the pump head due to the protrusion being fitted into the recess and being pressed by a backup ring toward the pump chamber. The inner circumferential surface of the recess of the pump head and the circumferential edge surface of the recess are covered by a film of an acid-resistant material.

TECHNICAL FIELD

The present invention relates to a liquid feed pump for feeding liquid by repeating suction of liquid from a suction port and discharge of liquid from a discharge port by sliding a plunger inside a pump head, and a liquid chromatograph that uses the liquid feed pump.

BACKGROUND ART

A schematic cross-sectional diagram of a pump chamber and its periphery of a general liquid feed pump is shown inFIG. 4.

A pump body18and a pump head8are provided. Although not shown, a crosshead that reciprocates in one direction (the left/right direction in the drawing) by a cam mechanism is accommodated inside the pump body18, and a plunger3is held at a tip end of the crosshead. The plunger3reciprocates in the axial direction according to the movement of the crosshead.

The pump head8is provided with a pump chamber8afor storing suctioned liquid, and a suction port8band a discharge port8cthat are paths that communicate with the pump chamber8afrom the outside. A tip end of the plunger3penetrates a tip end of the pump body18, and is inserted into the pump chamber8ainside the pump head8. Suction of liquid from the suction port8band discharge of liquid from the discharge port8care performed by a tip end portion of the plunger3sliding inside the pump chamber8a.

With such a liquid feed pump, a plunger seal13for preventing leakage of liquid from a gap between an inner wall of the pump chamber8aand an outer circumference of the plunger3is attached to a portion of the pump chamber8ainto which the plunger3is to be inserted (for example, see Patent Document 1). The plunger seal13is a ring-shaped resin material having a penetration hole through which the plunger3is to penetrate.

The plunger seal13is sandwiched between the pump head8and the pump body18for holding the pump head8. Also, a backup ring for improving the sealing performance of the plunger seal13is sometimes inserted at the back side of the plunger seal13. In this case, the plunger seal13is sandwiched between the backup ring and the pump head. The backup ring is biased toward the plunger seal13by the pump body, and the plunger seal13is biased toward the pump head8by the backup ring.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

Generally, the plunger seal13is configured of a cylindrical protrusion protruding toward the side of the pump head along the axial direction of the penetration hole provided at the center, and a flange provided at the base end of the protrusion. A seal attachment portion of the pump head8for attaching the plunger seal13is provided with a recess for fitting the protrusion of the plunger seal13. The plunger seal13attached to the seal attachment portion prevents leakage of liquid from the pump chamber8aby the outer circumferential surface of the protrusion coming into close contact with the inner circumferential surface of the recess of the seal attachment portion, and the flange coming into close contact with the surface around the recess of the seal attachment portion.

When the plunger3is driven, since the inner circumferential surface of the plunger seal13which slides against the outer circumferential surface of the plunger3is softer than a material of the plunger3, it tends to be worn. On the other hand, since the outer circumferential surface and the flange of the plunger seal13do not slide against the wall surface of the pump head8, the outer circumferential surface of the plunger seal13is not worn. Thus, it was assumed that liquid does not leak from the outer side of the plunger seal13.

However, when the wear of the inner circumferential surface of the plunger seal13progresses, the plunger seal13becomes more likely to move according to the reciprocation of the plunger3, and a slight gap is created between the plunger seal13and the wall surface of the pump head8. As a mobile phase, mixed liquid of highly volatile acid (for example, trifluoroacetic acid, acetic acid, formic acid or the like) and organic solvent is sometimes used. It was found that when this mixed liquid permeates into the gap between the plunger seal13and the pump head8, only the solvent component vaporizes and the metal wall surface of the pump head8may be corroded or etched by the acid left in the gap. When the metal wall surface of the pump head8is corroded or etched, liquid will leak from between the plunger seal13and the wall surface of the pump head8.

Accordingly, the present invention has its object to prevent corrosion or etching of the wall surface of the pump head, and to prevent decrease in the sealing performance of the plunger seal.

Solutions to the Problems

A liquid feed pump of the present invention includes a pump head including a liquid inlet for drawing liquid in, a pump chamber for storing the liquid drawn in from the liquid inlet, and a liquid outlet for discharging the liquid inside the pump chamber, a plunger for sliding inside the pump head with a tip end side inserted in the pump head, a plunger seal, formed into a ring shape, for sealing a gap between the pump head and the plunger while holding the plunger by a hole at a center, and a seal attachment portion, provided at a portion of the pump head where the plunger is inserted into the pump chamber, including a wall surface for receiving the plunger seal, the wall surface being covered by a film of an acid-resistant material.

The “ring shape” does not refer to the precise shape, but refers to the shape of a rotating body having a hole at the center through which the plunger is to pass, the rotating body having a predetermined thickness. The “ring shape” is used in the sense of including one that has a flange, as shown in an embodiment, extending out the body of the ring.

An acid-resistant material is used so that usage in a case where liquid to be delivered includes acid is also possible.

A liquid chromatograph of the present invention includes an analytical path, a liquid feed pump for feeding a mobile phase to the analytical path, a sample injection section for injecting a sample into the analytical path, an analytical column provided on the analytical path, on a downstream side of the sample injection section, the analytical column being for separating the sample into each component, and a detector provided on the analytical path, on a downstream side of the analytical column, the detector being for detecting the component separated by the analytical column, where a liquid feed pump of the present invention is used as the liquid feed pump.

Effects of the Invention

With the liquid feed pump of the present invention, the wall surface, for receiving the plunger seal, of the seal attachment portion for attaching the plunger seal is covered by a film of an acid-resistant material, and thus, even if liquid including acid permeates into the gap between the plunger seal and the wall surface of the pump head, corrosion or etching of the wall surface of the pump head by the acid is prevented. Accordingly, liquid may be fed with high accuracy over a long period of time.

The liquid chromatograph of the present invention uses the liquid feed pump of the present invention that achieves the effect described above, and thus, high feeding accuracy may be maintained over a long period of time, and the reliability of the analysis result may be improved.

EMBODIMENTS OF THE INVENTION

According to a preferred embodiment of the present invention, as an acid-resistant material, a material selected from a group consisting of noble metals, diamond-like carbon (hereinafter DLC), and engineering plastics having resistance to acid may be used.

A noble metal suitable as the acid-resistant material is gold, platinum, rhodium, or iridium. Noble metals include eight types of metals, i.e. gold, silver, ruthenium, rhodium, palladium, osmium, iridium, and platinum, and among these metals, gold, platinum, rhodium, and iridium are particularly superior in acid resistance, and are suitable as the material for a film for preventing corrosion or etching of a wall surface of a pump head.

Since the pump head is formed of metal such as stainless steel, the wall surface on the inner side of the pump chamber is a metal surface. On the other hand, a plunger is formed of ceramics or sapphire. Accordingly, the plunger whose outer circumferential surface slides against the wall surface on the inner side of the pump chamber is a consumable which needs to be replaced due to wear after being used for a predetermined period of time.

A film of an acid-resistant material, therefore, may also be formed on the wall surface inside the pump chamber as well as on a seal attachment portion. By covering the wall surface on the inner side of the pump chamber, which is a metal surface, by a film of an acid-resistant material, wear of the plunger which slides against the wall surface on the inner side of the pump chamber may be suppressed, and the life of the plunger may be made longer. Particularly, the frictional coefficient of diamond-like carbon is low, and thus, the frictional force at the time of the plunger coming into contact with the wall surface of the pump chamber is small, and the life of the plunger may be made longer, and the load on a motor driving the plunger may be made small.

In the following, an embodiment of a liquid feed pump will be described with reference toFIGS. 1A, 1B, and 1C.

First, as shown inFIG. 1A, a liquid feed pump of the embodiment is configured by having a pump head8attached to a tip end of a pump body2across a cleaning chamber12. A pump chamber8ais provided inside the pump head8. A crosshead4is accommodated inside the pump body2in a movable manner.

The crosshead4is biased in a direction away from the pump head8(in the right direction in the drawing) by an elastic body6such as a spring. Although not shown, a cam mechanism is provided at a base-end portion side of the crosshead4. The cam mechanism is a mechanism for rotating a cam by a drive mechanism such as a motor. Since the crosshead4is biased toward the cam mechanism by the elastic body6, the base end portion of the crosshead4follows the circumferential surface of the rotating cam. Then, the crosshead4reciprocates, in the pump body2, in directions toward and away from the pump head8(the left/right direction in the drawing) according to the rotation of the cam.

A base end portion of the plunger3is held at the tip end of the crosshead4. A tip end portion of the plunger3penetrates the tip end of the pump body2and the cleaning chamber12, and is inserted into the pump chamber8ainside the pump head8. The tip end portion of the plunger3slides along the wall surface of the pump chamber8aaccording to the movement of the crosshead4.

The pump head8is also provided with a liquid inlet path8bfor drawing liquid into the pump chamber8a, and a liquid outlet path8cfor pushing liquid out of the pump chamber8a. The liquid inlet path8bis provided with a check valve9aformed of a ball-shaped disc and a seat on which the disc is to be seated. Also, the liquid outlet path8cis provided with a check valve9bhaving the same structure as the check valve9a. Additionally, in the drawing, the check valves9aand9bare provided as a part of the pump head8, but they may alternatively be attached to the pump head8from the outside.

When the plunger3is driven in the direction away from the pump chamber8a(in the right direction in the drawing), and the pressure inside the pump chamber8ais reduced, the check valve9bis closed and the check valve9ais opened, and liquid is drawn into the pump chamber8afrom the liquid inlet path8b. On the other hand, when the plunger3is driven in the direction of insertion into the pump chamber8a(in the left direction in the drawing), and the pressure inside the pump chamber8ais increased, the check valve9ais closed and the check valve9bis opened, and liquid is pushed out of the pump chamber8ainto the liquid outlet path8c. Feeding of liquid is performed by the repetition of such a movement.

A plunger seal10is attached to the pump chamber8a, at the insertion portion for the plunger3. A backup ring11is inserted at the back side of the plunger seal10(on the side of the pump body2). The plunger seal10is for preventing leakage of liquid from the gap between the inner wall of the pump chamber8aand the circumferential surface of the plunger3. The back side of the backup ring11is supported by the wall surface of the cleaning chamber12. The plunger seal10is biased by the backup ring11toward the pump chamber8a.

The cleaning chamber12includes, on the inside, a path for letting cleaning liquid pass, and a space for cleaning the outer circumferential surface of the penetrating plunger3by the cleaning liquid. At the insertion portion for the plunger3in the inner space of the cleaning chamber12, a cleaning seal16for slidably holding the outer circumferential surface of the plunger3is provided to prevent leakage of the cleaning liquid. The back side of the cleaning seal16is supported by the wall surface of the pump body2.

An attachment portion for the plunger seal10will be described with reference toFIGS. 1B and 1C. The plunger seal10is configured from an elastic material such as polyethylene resin, for example, and is a ring-shaped member having a hole for letting the plunger3pass through. At the center of the plunger seal10, a cylindrical protrusion10athat protrudes in the axial direction of the plunger3, and a flange10bthat is provided at the base end of the protrusion10aare provided. A space10chaving a rectangular cross section and opened along the circumference of the protrusion10ais provided to the protrusion10a, on the side of the pump chamber8a. The space10cis provided with the aim of storing liquid which has leaked from between the inner wall of the pump chamber8aand the outer circumference of the plunger3, and of improving the contact between the plunger seal10and the inner wall surface of the pump head8or the plunger3by using a rise in the pressure inside the pump chamber8a.

As shown inFIG. 10, a seal attachment portion8dincluding a recess15ainto which the protrusion10aof the plunger seal10is to be fitted is provided at a part of the pump head8where the plunger3is to be inserted into the pump chamber8a. The protrusion10aof the plunger seal10attached to the seal attachment portion8dis fitted into the recess15a, and the outer circumferential surface of the protrusion10acomes into close contact with an inner circumferential surface15bof the recess15a. Moreover, the surface of the flange10bon the side of the protrusion10acomes into close contact with a wall surface15caround the seal attachment portion8dby the back side of the flange10bof the plunger seal10being pressed by the backup ring11toward the pump chamber8a. The plunger seal10thereby seals the pump chamber8a.

The inner circumferential surface15bof the recess15aof the seal attachment portion8dthat is to come into close contact with the plunger seal10, and the surface15caround the recess15aare covered by a film14(shown by a thick line inFIG. 1B) of an acid-resistant material. In this embodiment, the diameter of the plunger3is 2 mm, and the diameter of the recess8dis 4 mm. In this case, the thickness of the film14of an acid-resistant material is, for example, about 3 μm. As the material of the film14of an acid-resistant material, a noble metal such as gold, platinum, rhodium or iridium, or DLC, for example may be used.

The film14of an acid-resistant material which is of the noble metal or the DLC as mentioned above may be formed by, for example, a PVD (physical vapor deposition) process, a CVD (chemical vapor deposition) process, or an ionized deposition method.

It is also possible to use an engineering plastic superior in chemical resistance such as PEEK or PTFE as the material for the film14of an acid-resistant material. The film14of an acid-resistant material formed of an engineering plastic such as PEEK or PTFE may be formed by powder coating.

As shown by a thick line inFIG. 2, the film14of an acid-resistant material may also be formed on the inner surface of the pump chamber8a. In this embodiment, the film14of an acid-resistant material is formed on the inner circumferential surface and the bottom surface of the pump chamber8a. The DLC is especially superior in wear resistance with a low frictional coefficient of 0.1, and thus, by forming a DLC film on the inner surface of the pump chamber8a, the frictional force at the time of the plunger3coming into contact with the wall surface of the pump chamber8ais made small, and the load on a motor for driving the plunger3is made small. Additionally, also in this case, the film14of an acid-resistant material may be formed of a noble metal such as gold, platinum, rhodium or iridium, or an engineering plastic such as PEEK or PTFE.

An embodiment of a liquid chromatograph that uses the liquid feed pump of the embodiment described above will be described with reference toFIG. 3. A liquid feed pump20is provided on an analytical path24. The liquid feed pump20feeds a mobile phase22in the analytical path24. A sample injection section26is provided on the analytical path24, on the downstream side of the liquid feed pump20. An analytical column28is provided on the analytical path24, on the downstream side of the sample injection section26. A detector30is provided on the analytical path24, on the downstream side of the analytical column28.

The sample injection section26is realized by, for example, one port (an injection port) among a plurality of ports provided to a switching valve forming an auto-sampler. In this case, injection of a sample into the sample injection section26is performed by a needle of the auto-sampler. The injected sample is temporarily retained in a sample loop. Then, when the analytical path24is formed by the switching valve being switched, and the mobile phase22is fed by the liquid feed pump20, the sample retained in the sample loop is lead to the analytical column28. In the analytical column28, the sample is separated into each component, and each component is detected by the detector30.

With the liquid chromatograph, the flow rate of the mobile phase flowing through the analytical path affects a detection signal that is obtained by the detector30, and thus, the feeding flow rate of the mobile phase has to be accurately maintained. In this example, the liquid feed pump of the embodiment inFIG. 1A to 1C or 2is used as the liquid feed pump20, and thus, even if liquid including acid is used as the mobile phase, the metal wall surface of the plunger seal attachment portion of the pump head of the liquid feed pump is not corroded or etched by acid, and leakage of liquid from the outer circumference of the plunger seal is prevented, and the feeding accuracy of the liquid feed pump is maintained over a long period of time. Accordingly, the reliability of the analysis result of the liquid chromatograph is improved.

DESCRIPTION OF REFERENCE SIGNS

2: Pump body

6: Elastic body

8: Pump head

8b: Liquid inlet path

8c: Liquid outlet path

8d: Seal attachment portion

9a,9b: Check valve

11: Backup ring

12: Cleaning chamber

14: Film of acid-resistant material

15a: Recess of seal attachment portion

15b: Inner circumferential surface of recess

15c: Surface around recess

16: Cleaning seal