With respect to reaction turbines, Governing reaction turbines is done by altering the position of the guide vanes.

• Governing of reaction turbines is usually done by altering the position of the guide vanes and thus controlling the flow rate by changing the gate openings to the runner.
• The guide blades of a reaction turbine are pivoted and connected by levers and links to the regulating ring.
• Two long regulating rods, being attached to the regulating ring at their one ends, are connected to a regulating lever at their other ends.
• The regulating lever is keyed to a regulating shaft which is turned by a servomotor piston of the oil pressure governor.
• The guide blades are rotated to increase the water flow area to the turbine runner.
• The penstock feeding the turbine inlet has a relief valve better known as a Pressure Regulator.
• When the load suddenly falls on the reaction turbine, a pressure relief valve is operated by a speed governor.
• A portion of water from the spiral casing is allowed to flow directly through the relief valve to the tailrace without striking the turbine runner.
• The pressure relief valve performs the function of a protection system to avoid water hammer effects during sudden load drop.