Pump for liquid chromatography
The invention provides a pump for liquid chromatography excellent in feeding liquid stably at an extremely low flow rate with high accuracy and in discharging bubbles at startup. At startup, a first plunger feeds solvent at a large flow rate to discharge bubbles in a pump and to fill the solvent into the pump in a short time and in a normal operation, the first plunger is stopped and the second plunger is pushed into a second pressure chamber at a low speed to feed the solvent at a low flow rate. When the second plunger reaches full stroke, the second plunger is pulled back at a high speed and at the same time the first plunger is pushed into a first pressure chamber in synchronization with the pullback of the second plunger to control the flow rate passing a discharge passage to a constant value at all times by a controller. Further, while the second plunger feeds the solvent, the first plunger is slightly pushed into the first pressure chamber to keep pressure in the first pressure chamber at pressure equal to or less than pressure in the second pressure chamber.
1. A pump for liquid chromatography comprising a pressure chamber communicating with an suction passage, a pressure chamber communicating with a discharge passage, and a first plunger and a second plunger that respectively reciprocate in the pressure chambers, wherein the first plunger is provided on an upstream side near to the suction passage and wherein the second plunger is provided on a downstream side near to the discharge passage,
wherein the first and the second plungers are driven independently by separate actuators, respectively,
wherein a maximum flow rate by the first plunger is larger than a maximum flow rate by the second plunger, and
wherein a minimum flow rate by the first plunger is smaller than a maximum flow rate by the second plunger.
2. A pump for liquid chromatography comprising a first pressure chamber communicating with an suction passage and a middle passage, a first plunger reciprocating in the first pressure chamber, a suction valve provided in the suction passage, a discharge valve provided in the middle passage, a second pressure chamber formed on a downstream side of the discharge valve and communicating with the middle passage and a discharge passage, and a second plunger reciprocating in the second pressure chamber,
wherein the first and the second plungers are driven independently by separate actuators, respectively,
wherein a maximum flow rate by the first plunger is larger than a maximum flow rate by the second plunger, and
wherein a minimum flow rate by the first plunger is smaller than a maximum flow rate by the second plunger.
3. The pump for liquid chromatography as claimed in claim 1 or claim 2 , further comprising a drain valve provided on a downstream side of the discharge passage,
wherein the drain valve is opened at startup of test and solvent is fed at a large flow rate by the first plunger to discharge bubbles remaining in the pressure chamber and at the same time to fill the solvent into a downstream passage and
wherein the drain valve is then closed and the solvent is fed at a low flow rate by the second plunger.
4. The pump for liquid chromatography as claimed in claim 2 , further comprising a drain valve provided on a downstream side of the discharge passage,
wherein the drain valve is opened at startup of test and solvent is fed at a large flow rate by the first plunger to discharge bubbles remaining in the pressure chamber and at the same time to fill the solvent into a downstream passage,
wherein the drain valve is then closed and the second plunger is pushed into the second pressure chamber at a slow speed to feed the solvent at a low flow rate, and
wherein when the second plunger reaches near full stroke, the second plunger is pulled back at a high speed and the first plunger is pushed into the first pressure chamber in synchronization with the pullback of the second plunger to control a flow rate passing the discharge passage to a constant value at all times.
5. The pump for liquid chromatography as claimed in claim 4 , wherein time required to push the second plunger in one reciprocation stroke is equal to or more than ten times time required to pull back the second plunger.
6. The pump for liquid chromatography as claimed in claim 4 , wherein the amount of push of the first plunger into the first pressure chamber while the second plunger feeds the liquid is controlled to keep pressure in the first pressure chamber at pressure equal to or less than pressure in the second pressure chamber.
7. The pump for liquid chromatography as claimed in claim 6 , wherein a surface of at least one of a valve seat and a valve body constructing the discharge valve is formed of material such as resin or rubber that has hardness lower than metal.
8. The pump for liquid chromatography as claimed in claim 4 , wherein when the amount of flow rate of the pump is low particularly in a gradient operation, the second plunger is not pulled back except when the second plunger reaches a full stroke position.
9. The pump for liquid chromatography as claimed in claim 1 or claim 2 , wherein a flow rate of liquid by the second plunger ranges from 0.1 nL/min to 50 μL/min.
10. The pump for liquid chromatography as claimed in claim 1 or claim 2 ,
wherein product of sectional area and maximum speed of the first plunger is larger than product of sectional area and maximum speed of the second plunger, and
wherein product of sectional area and minimum speed of the first plunger is smaller than product of sectional area and maximum speed of the second plunger.