- When 2 pumping units are fitted and only one is running , the idle pump might be driven in the reverse direction by fluid under pressure by the running pump , if non reverse locking gear wear not fitted .This gear is integral with flexible coupling connecting motor and pump.
- The pawl fly outward when the motor is running due to centrifugal force .When the motor stops , they come and engage the ratchet thus prevent the pump to rotate in opposite direction.
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.