commercial practice and is merely illustrative insofar as the compressor itself is concerned each cylinder bank 12 14 and 16 defines a compression cylinder 20 within which a piston 22 is slidingly disposed cylinder bank 14 is illustrated with a capacity control system 24 while cylinder bank 16 is illustrated without capacity control system 24 as detailed below one or more of cylinder banks 12 14 and 16 may include capacity control system 24 cylinder bank 16 includes a cylinder head 26 which closes cylinder 20 and which defines a suction chamber 28 and a discharge chamber 30 a suction valve 32 controls the communication between suction chamber 28 and cylinder 20 and a discharge valve 34 controls the communication between discharge chamber 30 and cylinder 20 a suction passage 36 extends between suction chamber 28 and a common suction chamber not shown of compressor 10 which is in turn open to the inlet of the compressor discharge chamber 30 is in communication with the outlet of compressor 10 through a discharge passage not shown referring now to fig1 and 2 cylinder bank 14 is illustrated incorporating capacity control system 24 capacity control system 24 comprises a cylinder head 40 a control piston assembly 42 and a solenoid valve assembly 44 cylinder head 40 closes cylinder 20 and it defines a suction chamber 46 and a discharge chamber 48 a suction valve 32 controls the communication between suction chamber 46 and cylinder 20 and a discharge valve 34 controls the communication between discharge chamber 48 and cylinder 20 a suction passage 50 extends between suction chamber 46 and the common suction chamber of compressor 10 discharge chamber 30 is in communication with the outlet of compressor 10 through a discharge passage not shown cylinder head 40 defines.