Bubble detection and recovery in a liquid pumping system

• US RE37,553 E1
• Filed: 02/09/1999
• Issued: 02/19/2002
• Est. Priority Date: 05/29/1996
• Status: Expired due to Term

• Current Assignee: Waters Investments Limited (Waters Corporation)
• Original Assignee: Waters Investments Limited (Waters Corporation)
• Inventors: Ciavarini, Steven J., Dumas, Robert J.
• Primary Examiner(s): KIM, TAE JUN
• Application Number:
  US09/248,327
• Time in Patent Office: 1,106 Days
• Field of Search: 210/101, 210/198.2, 210/656, 417/2, 417/216, 417/244, 417/254
• US Class Current: 417/216
• CPC Class Codes: F04B 2201/0201 Position of the piston
• CPC Class Codes: F04B 2205/05 Pressure after the pump outlet
• CPC Class Codes: F04B 2205/503 of gas in a liquid flow, e.g. gas bubbles
• CPC Class Codes: F04B 49/06 Control using electricity regulating by means of floats actuating electric switches F04B49/04
• CPC Class Codes: F04B 53/06 Venting

Abstract

A serial, dual piston high pressure fluid pumping system that overcomes the difficulties of gas in the fluid stream without the need for added mechanical valves or fluid paths. A bubble detection and recovery mechanism monitors compression and decompression volumes of the serially configured dual pump head pump, and the overall system delivery pressure. Bubble detection is effected by sensing a ratio of compression to decompression volume and determining if the ratio exceeds an empirical threshold that suggests the ratio of gas-to-liquid content of eluent or fluid in the system is beyond the pump'"'"'s ability to accurately meter a solvent mixture. The magnitude of the ratio of compression to decompression volume indicates that either the intake stroke has a bubble or that the eluent has a higher-than-normal gas content. Once a bubble has been detected, recovery is effected by forcing the pump into a very high stroke volume with the compression and decompression stroke limits constrained to obtain the largest delivery stroke compression ratio that will expel a bubble or solvent that has detrimental quantities of gas.

Claims

1. A method for detecting gas in a fluid transported through a fluid delivery system comprising a first pump head having a first piston actuating in a first direction and a second direction within a first piston chamber and a second pump head having a second piston actuating in a first direction and a second direction within a second piston chamber, said first pump head receiving said fluid and pressuring said fluid to form a pressurized fluid and said second pump head receiving said pressurized fluid from said first pump head, comprising the steps of:

monitoring compression volume of said pressurized fluid compressed by said second first piston within said second first piston chamber to determine a compression volume;

monitoring decompression volume of said pressurized fluid within said second first piston chamber to determine a decompression volume;

determining a compression to decompression volume ratio representing a ratio of said compression volume to said decompression volume;

selecting a threshold level of said ratio of said compression volume to said decompression volume;

determining if said compression to decompression volume ratio exceeds said threshold level;

if said compression to decompression volume ratio exceeds said threshold level increasing a stroke length of at least said second first piston.

2. The method of claim 1 wherein said step of monitoring compression volume includes the steps of:

using a first pressure transducer to sense a pressure of said pressurized fluid output from said first piston chamber during a precompression stroke of said first piston prior to delivering said pressurized fluid to said second pump head;

determining a system pressure with a second pressure transducer that senses pressure of output from said second piston chamber;

determining an amount of travel of said first piston in said first piston chamber required for said pressure of said pressurized fluid output from said first piston chamber to equal said system pressure.

3. The method of claim 2 wherein said amount of travel of said first piston is determined using an encoder.

4. The method of claim 1 wherein said step of monitoring decompression volume includes the steps of,

using a first pressure transducer to sense a pressure of said pressurized fluid output from said first piston chamber during an intake stroke of said first piston;

and

monitoring a position of said first piston during said intake stroke to determine position of said first piston whereat said pressure of said pressurized fluid output from said first piston chamber is substantially equal to atmospheric pressure.

5. The method of claim 1 wherein said compression volume, said decompression volume and said system pressure are input to a state machine.

6. The method of claim 5 wherein said state machine is enabled by a ratio of said compression volume to said decompression volume exceeding a first selected threshold.

7. The method of claim 5 wherein said state machine effects a state wherein a pump control system controls said first pump head and said second pump head to increase stroke length of at least one of said first pump head and said second pump head.

8. The method of claim 7 wherein said stroke length is increased until said ratio of said compression volume to said decompression volume reaches a second selected threshold.

9. A fluid delivery system including an apparatus detecting gas in a fluid transported through said system, comprising:

a first pump head having a first piston actuatable in a first direction and a second direction within a first piston chamber, said first pump head receiving said fluid and pressurizing said fluid to form a pressurized fluid;

a second pump head having a second piston actuatable in a first direction and a second direction within a second piston chamber, said second pump head receiving said pressurized fluid from said first pump head and pumping said pressurized fluid at a system pressure;

a first pressure transducer that senses a first pressure of said pressurized fluid output from said first piston chamber during a precompression stroke of said first piston prior to delivering said pressurized fluid to said second pump head;

a second pressure transducer that senses a second pressure of output from said second piston chamber;

an encoder to provide an indication of an amount of travel of said first piston within said first piston chamber;

a control system monitoring compression volume of said pressurized fluid compressed by said first piston within said first piston chamber to generate a compression volume signal, monitoring decompression volume of said pressurized fluid within said first piston chamber to generate a decompression volume signal, and monitoring said second pressure of output from said second piston chamber; and

a bubble detection and recovery mechanism receiving from said control system an indication of said second pressure of output from said second piston chamber, said compression volume signal, and said decompression volume signal, said bubble detection and recovery mechanism affecting a pump control system that controls said first pump head and said second pump head to increase stroke length of at least one of said first pump head and said second pump head.

10. The fluid delivery system of claim 9 wherein said bubble detection and recovery mechanism includes a state machine receiving from said control system an indication of said second pressure of output from said second piston chamber, said compression volume signal, and said decompression volume signal, and said state machine is enabled by a ratio of said compression volume to said decompression volume exceeding a first selected threshold.

11. The fluid delivery system of claim 9 wherein said state machine effects a state wherein said control system controls said first pump head and said second pump head to increase stroke length of at least one of at least one of said first pump head and said second pump head.

12. The fluid delivery system of claim 1110wherein said stroke length is increased until said ratio of said compression volume to said decompression volume reaches a second selected threshold.

13. The fluid delivery system of claim 9 wherein a ratio of said compression volume of said decompression volume exceeding a first selected threshold indicates presence of a bubble in said fluid and said state machine includes a detect state used to qualify presence of said bubble before performing an automatic recovery sequence in order to minimize sensitivity of said bubble detection and recovery mechanism from momentary upsets of either compression or decompression volumes.

14. The fluid delivery system of claim 9 wherein a ratio of said compression volume to said decompression volume exceeding a first selected threshold indicates presence of a bubble in said fluid, and wherein said state machine includes a recovery state in which said control system alters pump stroke of said first pump head and said second pump head to achieve a desired high compression ratio.

15. The fluid delivery system of claim 9 wherein a ratio of said compression volume to said decompression volume exceeding a first selected threshold indicates presence of a bubble in said fluid, and wherein said state machine includes an armed state in which said bubble detection and recovery mechanism remains idle while it waits to detect a bubble.

16. The fluid delivery system of claim 9 wherein a ratio of said compression volume to said decompression volume exceeding a first selected threshold indicates presence of a bubble in said fluid, and wherein said state machine includes a restoring state in which said bubble detection and recovery mechanism invokes a delay until said control system restores said first pump head and said second pump head back to an original stroke volume.

17. The fluid delivery system of claim 9 wherein a ratio of said compression volume of said decompression volume exceeding a first selected threshold indicates presence of a bubble in said fluid, and wherein said state machine includes a rearming delay state in which said bubble detection and recovery mechanism delays before re-arming for another bubble detect event to allow said fluid delivery system time to stabilize before accepting new compression volume and decompression volume values for a next bubble detect event.