Capacity control of refrigeration systems

A refrigeration system comprising:

• (a) a compressor unit including a housing, a suction side and a discharge side, an economizer port located at a point after the compression chambers have been closed for compression;
• a variable flow valve associated with said economizer port, which in an opened position provides communication between said compression chamber and an external outlet of said economizer port over said economizer port;
• a body of said valve being a part of a body of said housing and a seat of said valve in a closed position is shaped to be contiguous with internal portion of said housing;
• (b) a closed main circuit including said compressor, a condenser unit, an expansion device, an evaporator unit, connecting piping and appropriate refrigeration control;
• (c) an economizer circuit between said discharge side after said condenser unit and said external outlet including an additional expansion device and an economizing heat exchanger therebetween;
• said economizing heat exchanger providing thermal contact between refrigerant flow in said main circuit after said condenser unit and between evaporating refrigerant in said economizer circuit after said additional expansion device;
• (d) an electrical circuit including said variable flow valve, a control system, and a transducer reading parameters associated with a system capacity demand.