A surge relief valve comprising: a piston housing having a longitudinal axis , the piston housing comprising a head portion and a hollow extension coupled thereto, the extension having an open end opposite the head portion; a valve seat disposed at the open end ;a piston disposed within the housing and configured for reciprocal motion along the axis, and having a first end disposed proximal the head portion and a second end proximal the valve seat ; a biasing member disposed between the piston and the piston housing and configured to bias the piston in a direction away from the head portion and toward the valve seat; and a position sensor configured to resolve axial positions of the piston relative to the piston housing , the position sensor comprising: a sensor body coupled to the piston housing; and a movable element biased towards the piston and having a contact end distal the sensor body in engagement with but not attached to the piston such that the movable element is pushed but not pulled by the piston and is configured to move linearly relative to the sensor body and configured to move axially with the piston ; wherein at least a portion of the sensor body is disposed within the piston housing ; and wherein the sensor is configured to generate a response that correlates to the position of the piston relative to the piston housing ; characterized in that , the movable element engages the first end of the piston . a piston housing having a longitudinal axis , the piston housing comprising a head portion and a hollow extension coupled thereto, the extension having an open end opposite the head portion; a valve seat disposed at the open end ;a piston disposed within the housing and configured for reciprocal motion along the axis, and having a first end disposed proximal the head portion and a second end proximal the valve seat ; a biasing member disposed between the piston and the piston housing and configured to bias the piston in a direction away from the head portion and toward the valve seat; and a position sensor configured to resolve axial positions of the piston relative to the piston housing , the position sensor comprising: a sensor body coupled to the piston housing; and a movable element biased towards the piston and having a contact end distal the sensor body in engagement with but not attached to the piston such that the movable element is pushed but not pulled by the piston and is configured to move linearly relative to the sensor body and configured to move axially with the piston ; a sensor body coupled to the piston housing; and a movable element biased towards the piston and having a contact end distal the sensor body in engagement with but not attached to the piston such that the movable element is pushed but not pulled by the piston and is configured to move linearly relative to the sensor body and configured to move axially with the piston ; wherein at least a portion of the sensor body is disposed within the piston housing ; and wherein the sensor is configured to generate a response that correlates to the position of the piston relative to the piston housing ; characterized in that , the movable element engages the first end of the piston . <EOS>