A spring mounted tube pressing member for peristaltic pumps allows loading and unloading of an elastic tube section between the tube pressing member and a continuously revolving rotor assembly by selectively moving between a locked position for fluid transfer and an open position for unhindered mounting and demounting of the tube section or a replaceable tube cassette. Not only is the pressure on the tube pressing member adjustable by the spring used, its dynamic pressure distribution on the tube section also prolongs the tube flex life and reduces fluid back mixing and pulsation in the tube.