Patent ID: 7814982

Claim:
A downhole non-return valve, comprising: a first housing defining a valve inlet, a valve outlet, a housing bore and a shield perimetrically surrounding the housing bore at the valve outlet; a plug having a first seal and a second seal, the plug being moveable between an open position, a partially sealed position, and a fully sealed position, the first seal sealingly engaged with the housing bore defining the partially sealed position, the first seal and the second seal sealingly engaged with the housing bore defining the fully sealed position, and neither the first seal nor the second seal sealingly engaged with the housing bore defining the open position; a second housing engagable by a mandrel of the plug being configured to prevent fluids at well pressure from acting on the mandrel when the downhole non-return valve is in the open position while allowing fluids at well pressure to act on the mandrel when in the fully sealed position; and a biasing member urging the plug towards the fully sealed position wherein the urging force of the biasing member is sufficient to move the plug to the partially sealed position but is selected to be insufficient to move the plug to the fully sealed position.