Liquid feeding device

A liquid feeding device includes a primary plunger pump; a secondary plunger pump connected downstream; a check valve provided between the primary plunger pump and the secondary plunger pump; a primary pressure sensor that detects a pressure in the pump chamber of the primary plunger pump; a liquid feeding control part configured to control operations of the primary plunger pump and the secondary plunger pump; and a liquid leakage detector configured to detect liquid leakage in the check valve based on a change in an output value of the primary pressure sensor during the waiting time. The liquid feeding control part is configured to control the operation of the primary plunger pump so that a waiting time, where the primary plunger pump stops without operating, is present while a discharge operation by the secondary plunger pump is performed after a suction by the primary plunger pump is completed.

TECHNICAL FIELD

The present invention relates to a double plunger type liquid feeding device used for liquid feeding a mobile phase in a liquid chromatograph, and in particular, an in-line double plunger type liquid feeding device in which a primary plunger pump and a secondary plunger pump are connected in series.

BACKGROUND ART

As one of liquid chromatograph liquid feeding devices, an in-line double plunger type liquid feeding device is known. The in-line double plunger type liquid feeding device includes a primary plunger pump and a secondary plunger pump connected in series with the primary plunger pump. The primary plunger pump and the secondary plunger pump operate complementarily to each other so that liquid feeding is stably performed at a preset flow rate (see, for example, Patent Document 1).

While the primary plunger pump is performing the discharge operation, the secondary plunger pump performs the suction operation, and the secondary plunger pump sucks part of the liquid discharged by the primary plunger pump. When the discharge operation of the primary plunger pump is completed, the secondary plunger pump performs the discharge operation, and during this time, the primary plunger pump sucks the liquid.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

In the in-line double plunger type liquid feeding device as described above, a check valve is provided between the outlet of the primary plunger pump and the inlet of the secondary plunger pump, and the check valve prevents the liquid from flowing back to the primary plunger pump when the secondary plunger pump performs the discharge operation.

However, the liquid tightness between the valve body and the valve seat of the check valve may deteriorate, and liquid leakage may occur. When liquid leakage occurs at the check valve between the outlet of the primary plunger pump and the inlet of the secondary plunger pump, part of the liquid discharged by the secondary plunger pump flows to the primary plunger pump side, and the liquid feeding flow rate during the discharging process by the secondary plunger pump does not reach the set flow rate, so that the liquid feeding at a constant flow rate cannot be realized, and pulsation occurs, leading to deterioration in reproducibility of holding time of analysis.

Conventionally, there has been no means that detects a backflow from the secondary plunger pump to the primary plunger pump. Therefore, it is difficult to take an appropriate measure when the control accuracy of the liquid feeding flow rate is lowered.

Therefore, an object of the present invention is to make it possible to detect liquid leakage at a check valve between a primary plunger pump and a secondary plunger pump.

Solutions to the Problems

A liquid feeding device according to the present invention includes a primary plunger pump, a secondary plunger pump connected to downstream of the primary plunger pump in series, a check valve provided between an outlet of the primary plunger pump and an inlet of the secondary plunger pump, a primary pressure sensor that communicates with a pump chamber of the primary plunger pump and that detects a pressure in the pump chamber of the primary plunger pump, a liquid feeding control part configured to control operations of the primary plunger pump and the secondary plunger pump, the liquid feeding control part being configured to control the operation of the primary plunger pump so that a waiting time, where the primary plunger pump stops without operating, is present while a discharge operation by the secondary plunger pump is performed after a suction by the primary plunger pump is completed, and a liquid leakage detector configured to detect liquid leakage in the check valve based on a change in an output value of the primary pressure sensor during the waiting time.

In the liquid feeding device of the present invention, a primary pressure sensor that detects the pressure in the pump chamber of the primary plunger pump is provided. The primary plunger pump is configured to suck the liquid after the discharge operation of the primary plunger pump is completed and the discharge by the secondary plunger pump is started, and then stops without operating for a certain period of time. The time for which the primary plunger pump stops after completing suction is referred to as a “waiting time”.

The pressure in the pump chamber of the primary plunger pump after the primary plunger pump has suctioned the liquid is normally atmospheric pressure. Accordingly, the atmospheric pressure is maintained during the “waiting time” during which the operation of the primary plunger pump is stopped. However, when liquid leakage occurs at the check valve between the primary plunger pump and the secondary plunger pump, the liquid flowing backward from the secondary plunger pump flows into the pump chamber of the primary plunger pump, and the pressure in the pump chamber of the primary plunger pump increases. Thereby, the output value of the primary pressure sensor rises.

That is, by monitoring the output value of the primary pressure sensor during the waiting time, it is possible to detect liquid leakage at the check valve between the primary plunger pump and the secondary plunger pump. Therefore, the liquid leakage detector monitors the output value of the primary pressure sensor during the waiting time, and detects the liquid leak based on the change in the output value.

Furthermore, the pressure in the pump chamber of the primary plunger pump during the “waiting time” when the operation of the primary plunger pump is stopped rises in proportion to the amount of liquid flowing backward from the secondary plunger pump and flowing into the pump chamber of the primary plunger pump. From this, it is possible to calculate the backflow amount of liquid to the primary plunger pump, that is, the amount of liquid leakage in the check valve, based on the increasing rate in the output value of the primary pressure sensor.

Therefore, in a further preferred embodiment of the liquid feeding device according to the present invention, the liquid feeding device further includes a relational expression holding part that holds a relational expression indicating a relationship between an increasing rate in the output value of the primary pressure sensor and an amount of liquid leakage per part time in the check valve, wherein the liquid leakage detector is configured to calculate the amount of liquid leakage per part time in the check valve based on the increasing rate in the output value of the primary pressure sensor during the waiting time when the primary plunger pump is stopped and the relational expression held in the relational expression holding part.

The relationship between the increasing rate in the output value of the primary pressure sensor and the amount of liquid leakage in the check valve may be obtained in advance by experiments. However, the relationship between the increasing rate in the output value of the pressure sensor of the primary pressure sensor and the amount of liquid leakage in the check valve varies depending on the compressibility of the liquid, and the compressibility of the liquid varies with temperature and the like.

Therefore, in order to obtain a more accurate relational expression, the liquid feeding device may have a function of deriving such a relational expression. In order to derive the relational expression, the pre-pressure operation of the primary plunger pump can be used. The “pre-pressure operation” here is to cause the primary plunger pump to perform a discharge operation until the pressure in the pump chamber of the primary plunger pump becomes substantially the same as the pressure in the pump chamber of the secondary plunger pump during the discharge operation by the secondary plunger pump after the waiting time has elapsed. The fact that the pressure in the pump chamber of the primary plunger pump is “substantially the same” as the pressure in the pump chamber of the secondary plunger pump includes the fact that in addition to the pressure in the pump chamber of the primary plunger pump being exactly the same as the pressure in the pump chamber of the secondary plunger pump, the pressure in the pump chamber of the primary plunger pump is slightly lower than the pressure in the pump chamber of the secondary plunger pump.

It should be noted that the above relational expression can be derived during this pre-pressure operation only when no liquid leakage occurs at the check valve between the primary plunger pump and the secondary plunger pump. This is because when there is a leak at the check valve between the primary plunger pump and the secondary plunger pump, since the pressure in the pump chamber of the primary plunger pump reaches the same level as the pressure in the pump chamber of the secondary plunger pump during the “waiting time” before the pre-pressure operation, the pre-pressure operation ends without performing the discharge operation by the primary plunger pump.

Therefore, in a further preferred embodiment of the liquid feeding device according to the present invention, the liquid feeding device further includes a secondary pressure sensor that communicates with a pump chamber of the secondary plunger pump and detects a pressure in the pump chamber of the secondary plunger pump, a pre-pressure operation part configured to perform a pre-pressure operation in which a discharge operation of the primary plunger pump is performed until an output value of the primary pressure sensor reaches a value substantially the same as an output value of the secondary pressure sensor while a discharge operation by the secondary plunger pump is performed and after the waiting time has elapsed, and a relational expression deriving part configured to obtain the relational expression based on a driving amount of a plunger of the primary plunger pump and the increasing rate in the output of the primary pressure sensor while the pre-pressure operation is performed. The relational expression holding part holds the relational expression derived by the relational expression deriving part.

In a further preferred embodiment, when liquid leakage is detected in the check valve by the liquid leakage detector, the liquid feeding control part is configured to compensate for a loss of a liquid feeding flow rate due to the liquid leakage by increasing a discharge speed of the secondary plunger pump based on an amount of the liquid leakage calculated by the liquid leakage detector. “Compensate for loss of liquid feeding flow rate due to liquid leakage” means to make the liquid feeding flow rate the set flow rate by increasing the discharge speed of the secondary plunger pump in consideration of the amount of liquid leakage. For example, when the set flow rate is α μL/min and the calculated amount of liquid leakage is β μL/min, the discharge speed of the secondary plunger pump is controlled so that the discharge flow rate from the secondary plunger pump is (α+β) μL/min. In this way, by compensating for the loss of the liquid feeding flow rate due to liquid leakage by the discharge speed of the secondary plunger pump, a decrease in the liquid feeding flow rate in the discharge process of the secondary plunger pump can be suppressed even when a liquid leak occurs at the check valve between the outlet of the primary plunger pump and the inlet of the secondary plunger pump, so that it is possible to suppress the occurrence of pulsation and stabilize the liquid feeding flow rate.

Effects of the Invention

In the liquid feeding device according to the present invention, a liquid leakage in the check valve is detected based on the change in the output value of the primary pressure sensor when the primary plunger pump stops, and the secondary plunger pump is performing a discharge operation, so that a liquid leakage in the check valve provided between the outlet of the primary plunger pump and the inlet of the secondary plunger pump can be detected quickly. When the liquid leakage at the check valve can be detected, accordingly, the discharge speed of the secondary plunger pump can be increased to suppress the decrease in the liquid supply flow rate, so that it is possible to stabilize liquid feeding flow rate.

EMBODIMENT OF THE INVENTION

Hereinafter, an embodiment of a liquid feeding device according to the present invention will be described with reference to the drawings.

First, the configuration of the liquid feeding device will be described with reference toFIG.1.

A liquid feeding device1of the embodiment includes a primary plunger pump2and a secondary plunger pump22. The primary plunger pump2and the secondary plunger pump22are connected in series with each other.

The primary plunger pump2includes a pump head3having a pump chamber4therein, and a pump body6. The pump head3is provided at the distal end of the pump body6. The pump head3is provided with an inlet portion for flowing the liquid into the pump chamber4and an outlet portion for flowing the liquid out of the pump chamber4. A check valve16is provided at the inlet portion of the pump head3to prevent a backflow of liquid.

The distal end of a plunger10is slidably inserted into the pump chamber4. The proximal end of the plunger10is held by a crosshead8accommodated in the pump body6. The crosshead8moves in one direction (left-right direction in the figure) in the pump body6by the rotation of a lead screw14, and the plunger10moves in the one direction accordingly. A primary plunger pump drive motor12for rotating the lead screw14is provided at the proximal end portion of the pump body6. The primary plunger pump drive motor12is a stepping motor.

The secondary plunger pump22includes a pump head23having a pump chamber24therein and a pump body28. The pump head23is provided at the distal end of the pump body28. The pump head23is provided with an inlet portion for flowing the liquid into the pump chamber24and an outlet portion for flowing the liquid out of the pump chamber24. A check valve26is provided at the inlet portion of the pump head23to prevent a backflow of liquid.

The distal end of a plunger32is slidably inserted into the pump chamber24. The proximal end of the plunger32is held by a crosshead30accommodated in the pump body28. The crosshead30moves in one direction (left-right direction in the figure) in the pump body28by the rotation of a lead screw36, and the plunger32moves in the one direction accordingly. A secondary plunger pump drive motor34for rotating the lead screw36is provided at the proximal end portion of the pump body28. The secondary plunger pump drive motor34is a stepping motor.

The inlet portion of the pump head3is connected to a container (not shown) for storing a liquid to be fed via a flow path. The inlet portion of the pump head23is connected to the outlet portion of the pump head3via a connection flow path18. A primary pressure sensor20that detects the pressure (P1) in the pump chamber4is provided on the connection flow path18.

An outlet flow path38is connected to the outlet portion of the pump head23. The outlet flow path38communicates with, for example, an analysis flow path of a liquid chromatograph. A secondary pressure sensor40that detects the pressure (P2) in the pump chamber24is provided on the outlet flow path38.

Operations of the primary plunger pump drive motor12and the secondary plunger pump drive motor34are controlled by a control part42. The control part42includes a liquid feeding control part44, a liquid leakage detector46, a pre-pressure operation part48, a relational expression holding part50, and a relational expression deriving part52. The control device42is realized by a dedicated computer or a general-purpose personal computer. The liquid feeding control part44, the liquid leakage detector46, the pre-pressure operation part48, and the relational expression deriving part52are functions obtained by an arithmetic element such as a CPU provided in the control device42executing a predetermined program. The relational expression holding part50is a function realized by a partial storage area of a storage device provided in the control device42.

The liquid feeding control part44is configured to control the operation of the primary plunger pump2and the secondary plunger pump22so that the primary plunger pump2and the secondary plunger pump22operate in a complementary manner to perform the liquid feeding at a preset flow rate.

The liquid leakage detector46is configured to detect a liquid leakage in the check valve26and calculates the amount of the liquid leakage based on the output value of the primary pressure sensor20during the time in which the secondary plunger pump22performs a discharge operation and the “waiting time” during which the primary plunger pump2is stopped. The calculation of the “waiting time” and the amount of liquid leakage will be described later.

The pre-pressure operation part48is configured to cause the primary plunger pump2to perform a pre-pressure operation described later while the secondary plunger pump22performs the discharge operation and after the “waiting time” has elapsed.

The relational expression holding part50holds a relational expression for the liquid leakage detector46to calculate the amount of liquid leakage in the check valve26based on the output value of the primary pressure sensor20. The relational expression held in the relational expression holding part50is an expression indicating the relationship between the increase value (increase rate) of the output value of the primary pressure sensor20per part time and the amount of liquid leakage per part time in the check valve26. This relational expression may be obtained in advance by experiments, or may be derived by the relational expression deriving part52described later.

The relational expression deriving part52is configured to derive the above relational expression during the pre-pressure operation of the primary plunger pump2. A specific derivation method will be described later.

An example of the operations of the primary plunger pump2, the secondary plunger pump22, and the control device42realized by the above-described parts44,46,48,50and52are shown inFIGS.2and3.FIG.2shows the operation when no liquid leakage occurs in the check valve26, andFIG.3shows the operation when liquid leakage occurs in the check valve26.

First, with reference toFIG.2andFIG.1, the operation when the liquid leakage occurs in the check valve26will be described.

When the primary plunger pump2starts the liquid discharge operation (step S11), the liquid feeding control part44causes the secondary plunger pump22to start the suction operation (step S21). When the primary plunger pump2performs the discharge operation, the check valve16is closed and the check valve26is opened, and the liquid from the outlet portion of the pump head3passes through the connection flow path18, the check valve26and the pump chamber24, and is discharged to the outlet flow path38. The secondary plunger pump22performs a suction operation at a flow rate smaller than the discharge flow rate of the primary plunger pump2, and part of the liquid discharged from the pump head3is stored in the pump chamber24.

The liquid feeding control part44ends the discharge operation of the primary plunger pump2at a predetermined timing, and at this time, causes the secondary plunger pump22to start the discharge operation (steps S12and S22). When the discharge operation of the secondary plunger pump22is started, the check valve26is closed by the pressure in the pump chamber24becoming higher than the pressure in the pump chamber4.

After starting the discharge operation of the secondary plunger pump22, the liquid feeding control part44causes the primary plunger pump2to perform a suction operation at a high speed (step S13), and then waits for a certain period of time. After the primary plunger pump2finishes the suction operation, the time for which the primary plunger pump2waits without operating is referred to as the “waiting time”. During this waiting time, the liquid leakage detector46monitors an output value P1of the primary pressure sensor20and calculates the increasing rate (step S31). When the check valve26does not leak, the pressure in the pump chamber4of the primary plunger pump2does not vary and is maintained at atmospheric pressure, so that the increasing rate in the output value P1of the primary pressure sensor20is substantially equal to zero. In this case, the liquid leakage detector46determines that there is no liquid leakage at the check valve26(step S32).

Note that the fact that the increasing rate in the output value P1is “substantially equal to zero”, includes a value that is considered to be equivalent to zero in consideration of noise and the like in the output signal of the primary pressure sensor20even though it is not completely zero. Whether the increase rate of the output value P1is “substantially equal to zero” can be determined, for example, by whether the increasing rate in the output value P1obtained by calculation exceeds a preset threshold value.

The pre-pressure operation part48causes the primary plunger pump2to perform a pre-pressure operation after the predetermined waiting time has elapsed and before the discharge operation of the secondary plunger pump22is completed (steps S14and S15). The pre-pressure operation means an operation in which the pressure in the pump chamber4of the primary plunger pump2is set to the same pressure as the pressure in the pump chamber24of the secondary plunger pump22before the discharge operation of the secondary plunger pump22is completed. In this pre-pressure operation, the primary plunger pump2is driven to discharge the liquid while the feedback control is performed so that the pre-pressure operation part48takes in the output value P1of the primary pressure sensor20and the output value P2of the secondary pressure sensor40to make the pressure in the pump chamber4substantially the same as the pressure in the pump chamber24.

During the pre-pressure operation, the relational expression deriving part52derives a relational expression between the increasing rate in the output value of the primary pressure sensor20and the amount of liquid leakage per part time at the check valve26(step S33). By monitoring the output value P1of the primary pressure sensor20during the pre-pressure operation, the amount of increase in the output value P1of the primary pressure sensor20when the plunger10of the primary plunger pump2is driven in the discharge direction by a certain distance can be determined. Thereby, the characteristic (compression rate) of the liquid currently fed can be investigated.

As an example, it is assumed that the primary plunger pump2discharges 1.0 μL of liquid when a stepping motor12is rotated by one pulse. In a case where the stepping motor12is rotated by one pulse during the pre-pressure operation, when the pressure value detected by the primary pressure sensor20increases by 5 MPa, the calculation is performed as follows: 1.0 μL/pulse÷5.0 MPa/pulse=0.2 μL/MPa. That is, when the pressure value P1detected by the primary pressure sensor20increases by 1 MPa, it means that 0.2 μL of liquid has flowed into the primary pressure sensor20. Therefore, assuming that the amount of liquid leakage at the check valve26is X (μL/sec)) and the increasing rate in the output value P1of the primary pressure sensor20is ΔP1(MPa/sec), the relational expression for obtaining X is as follows: X=0.2×ΔP1. The relational expression thus obtained is stored in the relational expression holding part50(step S34).

Thereafter, the liquid feeding control part44causes the secondary plunger pump22to end the discharge operation of (step S23), and again causes the primary plunger pump2to start the discharge operation (step S11).

Next, with reference toFIG.3together withFIG.1, the operation when a liquid leakage occurs at the check valve26will be described.

The discharge operation (step S11) of the primary plunger pump2and the suction operation (step S22) of the secondary plunger pump22are the same as the case where no liquid leakage occurs at the check valve26.

After starting the discharge operation of the secondary plunger pump22, the liquid feeding control part44causes the primary plunger pump2to perform a suction operation at a high speed (step S13), and then waits for a certain period of time. During this waiting time, the liquid leakage detector46monitors an output value P1of the primary pressure sensor20and calculates the increasing rate (step S31). When liquid leakage occurs at the check valve26, the pressure in the pump chamber4of the primary plunger pump2increases, and the increasing rate increases depending on the amount of leakage per part time in the check valve26. The liquid leakage detector46calculates the amount of leakage per part time at the check valve26using the calculated increasing rate and the relational expression held in the relational expression holding part50(step S35).

Based on the amount of liquid leakage per part time calculated by the liquid leakage detector46, the liquid feeding control part44calculates the discharge speed (correction discharge speed) of the secondary plunger pump for compensating for the loss of the liquid feeding flow rate caused by the liquid leakage (step S36). For example, when the set value of the liquid feeding flow rate is 100 μL/min, when the amount of liquid leakage at the check valve26calculated by the liquid leakage detector46is 1 μL/sec (60 μL/min), the discharge flow rate of the secondary plunger pump22to compensate for the loss of the liquid feeding flow rate due to the liquid leakage can be calculated as follows: 100 μL/min+60 μL/min=160 μL/min. The liquid feeding control part44calculates the discharge speed of the secondary plunger pump22so that the liquid having the flow rate calculated as described above is discharged from the secondary plunger pump22.

The secondary plunger pump22operates at the discharge speed calculated by the liquid feeding control part44(step S24). As a result, the loss of the liquid feeding flow rate caused by liquid leakage at the check valve26is compensated by the increase in the discharge speed of the secondary plunger pump22, the liquid feeding flow rate is stabilized and the occurrence of pulsation is suppressed.

FIG.4is verification data on the difference in liquid feeding pressure between when the discharge speed of the secondary plunger pump22is not corrected and when it is corrected in a case where a liquid leak occurs in the check valve26. In this figure, the lower graph represents the time change of the measured value (MPa) of the primary pressure sensor20, and the upper graph represents the time change of the measured value (MPa) of the secondary pressure sensor40. In this verification, the discharge speed of the secondary plunger pump22is not corrected in the first half of the liquid feeding cycle, and the discharge speed of the secondary plunger pump22in the second half of the liquid feeding cycle is corrected to compensate for the loss of the liquid feeding flow rate due to liquid leakage at the check valve26.

When there is no liquid leakage in the check valve26provided between the primary plunger pump2and the secondary plunger pump22, the pressure in the pump chamber4of the primary plunger pump2should have been maintained at atmospheric pressure during the waiting time after the suction operation of the primary plunger pump2(denoted as primary suction) is completed. However, in this verification, it can be seen that liquid leakage occurs in the check valve26because the pressure increases immediately after the suction operation of the primary plunger pump2is completed.

In the first half of the liquid feeding cycle in which the discharge speed of the secondary plunger pump22is not corrected, the liquid feeding pressure (measured value of the secondary pressure sensor40) is lost due to liquid leakage at the check valve26, and a pulsation of about 0.22 MPa occurs. In contrast, in the latter half of the liquid feeding cycle in which the discharge speed of the secondary plunger pump22is corrected, it can be seen that the pulsation is suppressed to about 0.05 MPa. As a result, it was found that the liquid feeding flow rate was stabilized by correcting the discharge speed of the secondary plunger pump22and the effect of suppressing pulsation was obtained.

DESCRIPTION OF REFERENCE SIGNS