A wide variety of applications in industrial and medical fields require fluid metering and pumping systems able to deliver precisely measured quantities of fluids at accurate flow rates to various destinations.  In the medical field especially, precise and accurate fluid delivery is critical for many medical treatment protocols.  Medical infusion and fluid-handling systems for use in the pumping or metering fluids to and/or from the body of a patient typically require a high degree of precision and accuracy in measuring and controlling fluid flow rates and volumes.  For example, when pumping medicaments or other agents to the body of a patient, an infusion flow rate which is too low may prove ineffectual, while an infusion flow rate which is too high may prove detrimental or toxic to the patient. 
Pumping and fluid metering systems for use in medical applications, for example in pumping fluids to and/or from the body of a patient, are known in the art.  Many of such prior art systems comprise peristaltic or similar type pumping systems.  Such prior art systems typically deliver fluid by compressing and/or collapsing a flexible tube or other flexible component containing the fluid to be pumped.  While such known systems are sometimes adequate for certain applications, precise and accurate flow rates in such systems can be difficult to measure and control due to factors such as distortion of the walls of collapsible tubing or components of the systems, changes in relative heights of the patient and fluid supply, changes in fluid supply line or delivery line resistance, and other factors. 
Another shortcoming of such prior art systems is that it is often difficult to determine and maintain accurate volumetric flow rates in real time during operation of the infusion system.  Typically, many such prior art systems utilize volume and flow rate measurement techniques that, in some cases, can have lower accuracy than desirable, or are cumbersome and difficult to implement and cannot be performed in real time as the system is operating.  Some approaches which have been used in such prior art systems for measuring volumes and flow rates include optical drop counting, the weighing of chambers containing infusion liquids, and other approaches. 
Many such prior art infusion systems also employ valving systems which comprise clamps, or other pinching devices, which open and close a line by pinching or collapsing the walls of tubing.  Such valving arrangements can have several shortcomings for applications involving medical infusion including difficulties in obtaining a fluid-tight seal and distortion of the walls of the tubing, which can lead to undesirable fluid leakage and/or irregular flow rates. 
In addition, many typical prior art infusion systems, such as those described above, are constrained to fairly simple fluid handling tasks, such as providing a single or, in some cases, several individual flow paths between one or more fluid sources and a patient.  Such prior art systems are not well suited for performing complex, multi-functional fluid handling and pumping tasks and often do not have sufficient operating flexibility to be used for a wide variety of fluid handling applications, without significant rearranging or retooling of the components of the system. 
Also, for medical infusion applications involving the pumping or metering of fluids to the body of a patient, it is important to detect air present in a line pumping fluid to the body of a patient and to prevent such air from entering the body of the patient.  Typically, prior art infusion systems employed for such applications detect the presence of air in the system by relying only on external air detection components, for example ultrasonic detectors, which are typically downstream of a pump and immediately upstream of the patient.  Also, for such systems, once air has been detected in the line, purging the air from the line before it reaches the patient may require manual intervention and, in some cases, disconnection of lines within the system. 
For pumping and infusion systems utilized for pumping fluids to the body of a patient, it is also typically desirable to pass fluids through a filter or screen prior to their entering the body of the patient in order to remove any insoluble clumps, or aggregates of material therefrom that may be detrimental to the patient if infused into the body.  Such filters are especially important when pumping blood or blood components to the body of a patient; in which case, the filters serve primarily as blood clot filters to remove clots or aggregated cells from the blood or blood components.  Prior art infusion systems used for such applications can include blood clot/particulate filters outside the pumping component of the system, installed on the line providing infused fluid to the patient.  Such assembly requires additional setup time and attention from an operator of the system and often results in another potential location of fluid leakage or site of contamination within the system. 
While the above mentioned and other prior art pumping and fluid handling systems represent, in some instances, useful tools in the art of fluid handling and pumping there remains a need in the art to: (a) provide pumping and fluid metering systems which have an improved ability to control and measure volumes and flow rates; (b) provide improved valving systems; (c) provide increased flexibility for multiple uses; and (d) include air detection capability and integrated fluid filtration.  Certain embodiments of the present invention address one or more of the above needs.