The Hydraulic Valve enters the hole in the closed position. After the packers are set, setting weight on it opens the tool. This causes the Piston to move in the inner sleeve and aligns flow ports that enable flow from the test zone to flow into the drill pipe.
The hydraulic section forces hydraulic fluid to flow through small passages and delays the opening of the valve. This prevents the tool from opening unintentionally if a bridge is hit while running into the hole. Lifting up on the drill string closes the tool. Check valves in the hydraulic section bypass the dampening action when closing the valve.
