Patent ID: 8714284

Claim:
An apparatus for signaling when a weight-on-bit value is greater than an upper limit during the drilling of wellbores, the apparatus comprising: (a) a tubular body for connection within a drill string including a first mandrel and a second mandrel, and a central bore defining a longitudinal axis of the tubular body and creating a flow path permitting a flow of fluids between the two mandrels and through the tubular body, the second mandrel secured, at least partially, within an annular bore of the first mandrel so that the second mandrel is telescopically arranged with and axially moveable within the first mandrel between a telescopically extended position defining a first length and a compressed position having a length shorter than the first length; (b) a biasing member that biases the first mandrel and the second mandrel into the telescopically extended position, the biasing member having a biasing strength; and (c) a first sealing part and a second sealing part; one sealing part being secured to the first mandrel and the other sealing part being secured to the second mandrel, both sealing parts being within the flow path of the tubular body, the first sealing part and the second sealing part being positioned to come together when the biasing strength of the biasing member is overcome by the weight-on-bit, together the sealing parts form a fluid seal in the central bore to resist the flow of fluids through the tubular body.