Often the only tests and actions performed on a hydraulic system involve changing the filters, sampling the oil and checking the oil level. As long as the system is operating, the mentality of “if it ain’t broke don’t fix it” frequently prevails. However, on any given system in your plant, you should perform 15 to 20 regular reliability tests while the system is operating. There are also several checks and procedures that should be completed during shutdowns or down days. The following preventive maintenance and reliability tests can help improve the efficiency and operation of your hydraulic systems and machines.