Bubble detection and recovery in a liquid pumping system

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.

Description

FIELD OF THE INVENTIONThe present invention relates to liquid pumps, and more particularly to a method and apparatus for detecting and recovering from gas bubbles in a liquid stream being pumped by the liquid pump.BACKGROUND OF THE INVENTIONHigh-pressure pumping systems are known for delivering liquid at high pressure. Such a system is described in U.S. Pat. No. 4,883,409 ("the '409 patent"). The '409 patent describes a pumping apparatus for delivering liquid at a high pressure, such as for high performance liquid chromatography ("HPLC") applications. The pumping apparatus comprises two pistons which reciprocate in respective pump chambers. The pistons and pump chambers are connected "serially" in that the output of the first pump chamber is connected via a valve to the input of the second pump chamber. The pistons are driven by linear drives, e.g., ball-screw spindles, and are synchronized so that a first or primary pump head receives its fluid intake at atmospheric or ambient pres...

AI Technical Summary

Benefits of technology

The present invention provides 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.

Features of the invention include provision of a solvent delivery system for HPLC which can automatically recover from a potential loss of prime during many hours of unattended chromatography runs of hundreds of injections. The detection of a bubble can be logged and recorded during each HPLC injection run, to provide a cross-check mechanism to notify the user that chromatography in a given run may be impaired. If the magnitude of a bubble or the degree of gas absorption by the solvent is not too severe, then automatic recovery can maintain acceptable chromatographic results under most typical and adverse external influences of solvent conditioning. Thus solvent conditioning at the input may be minimized. Initial detection of bubbles or gas is qualified using system delivery pressure to substantially prevent false triggering of the recovery sequence whenever the pump is delivering flow in a non-chromatographic context, e.g. during purging of the system. User defined flow rates and solvent composition settings are not affected by the recovery sequence. The design according to the invention avoids the use of spring-loaded check or other mechanical valves, and as such, does not additionally require a purge valve to pass bubbles. Reliability and maintainability of the system is enhanced accordingly. Bubble detection according to the invention permits operation at short piston stroke lengths which minimizes delay volume and compositional ripple with low gas compression ratios. The bubble detection desensitizes operational sensitivity to low gas compression ratios.

Problems solved by technology

The bubble detection desensitizes operational sensitivity to low gas compression ratios.

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