Patent ID: 8776887

Claim:
A flow stop valve positionable in a downhole tubular, the flow stop valve comprising: a housing, the housing comprising a second abutment surface provided at a second end of the housing; a sleeve slidably located within the housing; a hollow tubular section slidably located within the housing, the sleeve being slidably engaged about the hollow tubular section, wherein the hollow tubular section comprises: a flange provided at a second end of the hollow tubular section such that the flange abuts the second abutment surface of the housing so as to limit a travel of the hollow tubular section in a second direction, the second direction being in a direction towards the second end of the housing; and a port which is selectively blocked by the sleeve, the port and sleeve forming a valve which selectively permits flow from a first end of the housing through the port and a center of the hollow tubular section to the second end of the housing; the flow stop valve further comprising; a first biasing means; the first biasing means acting on the valve such that the first biasing means biases the valve towards a closed position, wherein a pressure difference between one of: fluid outside the downhole tubular and inside the downhole tubular; and fluid on first and second side of the valve, acts on the valve and biases the valve towards an open position, such that the flow stop valve is in the closed position when the pressure difference is below a threshold value, thereby preventing flow through the downhole tubular; and the flow stop valve is in an open position when the pressure difference is above a threshold value, thereby permitting flow through the downhole tubular: the flow stop valve being arranged such that the flange of the hollow tubular section abuts the second abutment surface when the pressure difference increases by lowering the flow stop valve into the downhole tubular; and that the valve stays closed when the pressure difference increases further by further lowering the flow stop valve, until the pressure difference reaches the threshold value, wherein a first abutment surface is provided within the housing between the second abutment surface of the housing and the first end of the housing, such that the first abutment surface abuts the flange of the hollow tubular section limiting the travel of the hollow tubular section in a first direction, the first direction being in a direction towards the first end of the housing, and wherein the sleeve, housing, hollow tubular section and first abutment surface define a first chamber, such that when the valve is closed, the first chamber is not in flow communication with the second end of the housing.