1.5 COMPRESSED AIR SYSTEMS AIR RECEIVER It is a requirement that there shall be at least two reservoirs whose combined capacity allows the main engines to be started twelve times if they are reversible and six times if they are not, while the e compressors are idle1.5 COMPRESSED AIR SYSTEMS • It is a requirement that there shall be at least two reservoirs whose combined capacity allows the main engines to be started twelve times if they are reversible and six times if they are not, while the compressors are idle