The complete-unit test is also called a “String” test. It consists of coupling up all the components and auxiliaries of a compressor train, and running them together in a mechanical spin test. This test is strictly mechanical, and can be performed in place of or in addition to separate mechanical tests of individual components. The purpose of the test is to confirm the mechanical compatibility of the components and auxiliaries. The auxiliaries can include the contract couplings, the lube and seal oil system(s), and the basic instrument and control systems. If the compressor train includes a gearbox, the test agenda may include torsional vibration measurements to verify the vendor’s analysis.
Sometimes it is impossible to test the actual driver with the rest of the components owing to its size or lack of power or fuel in the shop. In this case a shop driver may be used. Although this test is not as informative as a complete string test, it still has merit when the compressor train is complex.