GUIDE vanes are not stationary, they change their angle as per the requirement to control the angle of STRIKING of water to turbine blades to increase the efficiency.They also regulate the flow rate of water into the runner blades and control the power output of a turbine according to the LOAD on the turbine.DRAFT Tube:The pressure at the exit of the runner of Reaction Turbine is generally less than atmospheric pressure. The water at exit cannot be directly discharged to the tail race.A tube or pipe of gradually increasing area is used for discharging water from the exit of turbine to the tail race.This tube of increasing area is called Draft Tube. One end of the tube is connected to the outlet of runner while the other end is sub-merged below the level of water in the tail-race.Spiral casing:Spiral casing is the inlet medium of water to the turbine. The water flowing from the reservoir or dam is made to pass through this pipe with high pressure.The blades of the TURBINES are circularly placed, which mean the water striking the turbines blades should flow in the circular axis for efficient striking. So the spiral casing is used, but due to circular movement of the water, it looses its pressure.