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"I suffer cold start-up problems in the morning with respect to the filters. How can I overcome this?"
Typically, the problems associated with cold start-ups include the filter differential pressure exceeding the limit owing the higher viscosity to the cooler oil. This results in the pressure differential indicator tripping and the filter going into bypass mode allowing unfiltered oil to pass through.
If the system has a very short warm-up period, and there are no critical components, it may be worth considering allowing the filter to go into bypass mode for a short period, but remember to install an indicator that either has a thermal lockout or has an automatic reset function. As the filter blocks-up in the normal course of events, the period of bypass will increase, and this can be monitored by the length of time the auto-reset takes to activate. Regular particle counting is essential to highlight a problem with the bypass valve sticking in the open position.
However, on critical systems, possibly at an outdoor hydraulic plant with a longer warm-up period, ensure the filter is selected according to the worst-case viscosity conditions as a result of the lowest ambient temperature likely to be encountered. This will result in a larger than required element at operating conditions, and it should result in a longer element life requiring less frequent changes.