The ZHCR® Zero Hysteresis / Constant Run stepper motor driven vacuum pump is specifically designed and developed for membrane degassing of HPLC mobile phase. Employing a micro-stepping RPM control strategy permits the pump to run continuously, cycling between low and high speeds. The high speed provides quick pull-down, while the low speed sustains a consistent vacuum level. Fluctuations in baseline due to vacuum hysteresis are eliminated by not having to repeatedly stop and start a single speed pump. This also greatly reduces wear and noise.

The low wattage DC stepper motor runs quietly and coolly, and is very adaptable in its power supply requirements. The brushless motor is especially appropriate for an environment where solvents vapors may be present.

Flowpath materials were chosen for their ruggedness and compatibility with exposure to organic mobile phase vapors. The need for a vent valve has been eliminated by the continuously purged head design and built-in anti-backflow duckbill check valves. The pump will start into a full vacuum, and vacuum will not be released in the event of a power loss. The entire pump assembly is compact in design