A normally open oil well sampler valve which provides a fully open testing flow path therethrough is presented, wherein the sampler valve is closed under hydraulic control after a predetermined pressure increase in the well annulus pressure. The sampler includes two spaced apart ball valves having a...http://www.google.es/patents/US4063593?utm_source=gb-gplus-sharePatente US4063593 - Full-opening annulus pressure operated sampler valve with reverse circulation valve
Full-opening annulus pressure operated sampler valve with reverse ...
