From The Practical Handbook of Machinery Lubrication

The maximum pressure drop across a full flow filter element is determined by the by-pass valve spring setting. As a result, a filter with a higher by-pass valve cracking pressure will be more effective and provide longer life than a filter which has a low by-pass cracking pressure.

More about The Practical Handbook of Machinery Lubrication

Join Jim Fitch of Noria Corporation in Myrtle Beach, SC on July 25-28 for three days of contamination control training at Effective Contamination Control for Maintenance and Lubrication Professionals.

Here's a checklist for troubleshooting foaming and aeration of lubricating oils:

Ensure there are no leaks introducing air into the oil on the suction side of the circulating pump.

Improper oil viscosity (especially higher viscosity) can increase the risk of foaming.

Outside contaminants such as grease, dust or moisture can retard air release from oil.

Provide maximum separation of the suction and return lines to give air a chance to separate from the oil. Tank baffles provide additional help.

Be sure that the oil return line is below the oil surface in the reservoir. If it is above the oil level, oil could splash into the tank, putting air into the system.

Ensure that there is adequate residence time of the oil in the reservoir to allow the air to release.

Consider employing a diffuser on the return line to allow oil to "ooze" into the tank, reducing agitation.

Here are some steps to consider when flushing a new hydraulic system:

Flush with light rust and oxidation inhibited oil, operate system at maximum flow-rate to generate turbulent flow, check filters, refill with operating charge, reach operating temperature, exercise actuators, drain and flush non-circulating zones.