A circulation valve is disclosed for use in a tubing-conveyed tool string. The valve is adapted to be open as the tool string is run into the well, Balance Valvesenabling circulation flow from the tubing into the well bore. To close the valve, the circulation flow rate is increased. The valve has a housing with an inner bore and defining both a passage in hydraulic communication with the tubing and a side port for hydraulic communication between the passage and the well.Water Power Control Valves A piston disposed within the inner bore of the housing is adapted to be moved along the inner bore of the housing by elevated tubing pressure to block the side port of the housing.REDUCING VALVES A set of shear pins retain the piston in its initial position until broken by the elevated tubing pressure. The piston defines a side port for hydraulic communication between the passage and the side port of the housing with the piston in its initial position, the size of the side port being selected to cause a sufficient pressure buildup within the tubing at a predetermined flow rate to shear the pins and move the piston. Some embodiments have an air chamber between the piston and housing. Methods of use are also disclosed.

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