Sealed compressor

A sealed compressor comprising:

• an electric element;
• a compression element driven by the electric element;
• and
• a sealed container accommodating the electric element and the compression element;
• wherein the compression element includes a cylinder block defining a compression chamber;
• a piston which is reciprocatable inside the compression chamber;
• and a valve plate disposed to close an opening end of the compression chamber and having a discharge hole which provides communication between inside and outside of the compression chamber;
• the piston has a first groove on a tip end surface thereof which faces the valve plate, the first groove having a predetermined width and extending from an outer peripheral edge portion of the tip end surface toward a portion of the tip end surface which faces the discharge hole;
• the piston is provided with a projection having a top surface, on the tip end surface of the piston which faces the valve plate;
• the projection is positioned in the portion of the tip end surface which faces the discharge hole;
• the projection is inserted into the discharge hole of the valve plate in a state where the piston is at a top dead center,
• the projection has a flat surface facing a flow of a working fluid,
• an angle θ formed between the tip end surface of the piston and the flat surface of the projection protruding from the tip end surface is equal to or larger than 95 degrees and equal to or smaller than 110 degrees;
• and
• a ratio of an area of the top surface of the projection with respect to an area of a bottom surface of the projection, the bottom surface being connected to the tip end surface of the piston, is in a range of 0.2 to 0.75;
• a ratio of an area of the bottom surface of the projection with respect to an area of an opening of the discharge hole is set to a value in a range of 0.3 to 0.6;
• and
• a ratio of a height of the projection with respect to a thickness of the valve plate is set to a value in a range of 0.65 to 0.75.