Load compensator for a pipe running tool

A method of compensating a load suspended from a structure, comprising:

• connecting the load to a housing having an inner wall and a piston slidably disposed within the housing and connected to the structure, said piston having an outer wall such that the outer wall of the piston and the inner wall of the housing define an air chamber, said piston and housing further having at least two seals spaced from each other and arranged to provide a fluid seal between the air chamber and the atmosphere, an inlet port being disposed at a predetermined location on the housing such that the inlet port is in fluid communication between a source of pressurized fluid and the air chamber, a sensing port disposed in the housing at a predetermined location spaced from the inlet port such that under specified load conditions the piston slides within the housing sufficiently that the sensing port comes into fluid communication with the air chamber;
• and
• sensing the pressurized fluid such that when the pressurized fluid is sensed at the sensing port the flow of pressurized fluid through the inlet port is prevented such that the position of the piston is adjusted to compensate for the load.

A method of compensating a load suspended from a structure, comprising:

• connecting the load to a housing having an inner wall and a piston slidably disposed within the housing and connected to the structure, said piston having an outer wall such that the outer wall of the piston and the inner wall of the housing define an air chamber, said piston and housing further having at least two seals spaced from each other and arranged to provide a fluid seal between the air chamber and the atmosphere, an inlet port being disposed at a predetermined location on the housing such that the inlet port is in fluid communication between a source of pressurized fluid and the air chamber through a directional control valve, a sensing port disposed in the housing at a predetermined location spaced from the inlet port such that under specified load conditions the piston slides within the housing sufficiently that the sensing port comes into fluid communication with the air chamber;
• and
• sensing the pressurized fluid such that when the pressurized fluid is sensed flowing through the sensing port the directional valve is closed to prevent the flow of pressurized fluid to the inlet port such that the position of the piston is adjusted to compensate for the load.