Hold back pump is a self-regulating evaporation system for fully automatic and environmentally friendly vacuum distillations. The pump operates without a controller by bringing physical condensation laws into practice. The evaporation pressure is adjusted automatically for any solvent or solvent mixture. The distillation process runs automatically without any interruption no matter how many different solvent fractions are to be distilled. This pump guarantees a fully-automatic process without any manual adjustment or regulation and without time consuming and costly electronic controller.