Saves up to 90% solvent in isocratic HPLC. By monitoring the output signal at the detector, the solvent is returned to the solvent reservoir by means of a solenoid valve when the baseline is reached, which means that up to 90 % can be recycled. If the output signal increases, the valve switches over and directs the mobile phase into the solvent waste. If the output signal drops to the baseline, the unit switches back to recycling mode. A safety circuit prevents contaminated solvent from flowing to the reservoir in the event of a malfunction.