The Libra Plus series was introduced in early 2005 to include new patent pending technology. These pumps display flow rate, elasped time and accumulated volume of the sample. Each have built-in turn off timers and utilize high powered Nickel Metal Hydride battery packs. Advanced circuity allows for longer sampling times on a single charge of the batteries. In the case of the LP-5 pump, it runs 20+ hours at 2 LPM with a 37 mm 0.8 micron MCE filter cassette. Improved version of the Libra Plus LP-5 has higher back pressure capability, up to 50"of w.c at 2 LPM. They are the quietest pumps on the market by far.