- The refrigeration compressors are delivered in a standard execution with built-in heating coils or rod in the crankcase.
- The purpose of the heating coil or rod is to keep the oil in the crankcase warm even during standstill of the compressor. This ensures a low content of refrigerant in the oil.
- Too much refrigerant in the oil makes it loose its lubricating properties. This may lead to damage of the movable parts in the compressor.
- Further, the danger exists that the oil, during start-up of the compressor, foams so vigorously that the lubricating pressure will disappear.
- Before start-up the heating rod should be switched on for at least 8 hours.
- The heating coil or rod must not be switched on if the oil level in the vessel is below minimum in the sight glass. While the compressor is operating, it is usually switched off.
- Further, remember to switch off the heating rod if the compressor crankcase is opened for inspection.
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.