A "cracking valve" for use in a volumetric pump. A volumetric pump (30) includes a plunger (48) for compressing a pumping portion (34b) of a flexible tubing that extends through the pump. An inlet cracking valve (46) and an outlet cracking valve (52) are disposed so that they compress the flexible tubing...http://www.google.co.uk/patents/US5078362?utm_source=gb-gplus-sharePatent US5078362 - Spring-biased valve for use in a positive displacement volumetic pump
