- The interference angle is the angle between the valve seat and the mushroom head of the valve which sits on the valve seat i.e. the difference between the angle of contact of the valve and the valve seat. This angle is required to have the proper contact of the valve and the valve seat when the valve has attained the running temperature. This angle is about ½ degree.
- It gives the inner contact to the valve so that when the valve attains the working temperature it expands and have a proper full contact with the valve seat thus preventing any valve leakage.
- At the same time, it also helps in sitting the valve quickly. The main reason for the interference angle is to sit the valve and valve seat accurately when they have attained the working temperature
- The interference angle is provided for the better sitting of the valve and the valve seat. It has nothing to do with the rotation of the valve or the breakup of the seat deposits because the breakup of the seat deposits is carried out with the help of rotation of the valve. Hence it does not have any connection with the interference angle.
- Due of the interference angle, the sitting will be proper and because of the proper sitting of the valve and the valve seat, whatever deposits are formed will get crushed and get removed when the valve rotates over the valve seat due to the valve rotor.
Any opening in a pressure vessel is kept to a minimum and for a man entry an elliptical hole is lesser in size than the corresponding circular hole. More over it is prime concern to have a smoothed generous radius at the corners to eliminate stress concentration. Hence other geometrical shapes like rectangle and square are ruled out. To compensate for the loss of material in the shell due to opening, a doubler ring has to be provided around the opening. The thickness of the ring depends on the axis length along the dirrection in which the stresses are maximum and the thickness of the shell. It is important to align the minor axis along the length of the vessel, as the stress in this direction is maximum. Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t= thickness of the shell plating Circumferential stress: Pd/4t More over a considerable material and weight saving is achieved as minor is along the direction of maximum stress.