Oil equalization system for parallel connected compressors

A compressed gas distribution system comprising:

• a plurality of compressor units,
• said compressor units including a hermetic outer casing defining a sump for the accumulation of oil, means forming a closed volume for gas compression, and a compressor inlet and outlet,
• said gas distribution system further comprising a suction manifold and discharge manifold,
• means for connecting said suction manifold to the compressor inlets of respective compressor units,
• the compressor outlets opening to the interior of the respective compressor unit casings such that the lower portion of each casing defines a sump for the accumulation of oil within the casing interior, at compressor discharge pressure,
• each outer casing being provided with a unit gas outlet port well above the level of accumulated oil and opening to said discharge manifold such that said compressor units are connected in parallel,
• the improvement comprising an oil equalization port within each outer casing below the normal level of accumulated oil,
• small diameter oil equalization lines connected at one end to an oil equalization port of one compressor unit and at the other end to an oil injection port opening to the closed volume of another compressor unit at a point cut off from suction and discharge sides of the compressor, and vice versa
• a control valve within each oil equalization line, and
• means for sensing a drop in oil level below a minimum in each compressor unit and being connected to at least one of said control valves such that said sensing means for one unit acts to open the control valve in the equalization line leading from said other compressor unit to effect redistribution of the oil to said one unit and increase the amount of oil within that compressor unit, due to the pressure differential between said one unit sump and the other unit injection port and vice versa.