Abstract: A method of reducing the effects of fluctuating fluid pressure differential between the inlet and the outlet of a filtering unit operating in a system for filtering metal contaminants from a lubricating coolant and for recycling a constant volume flow of filtered lubricating coolant to a workpiece to be subsequently machined by pumping metal-contaminated lubricating coolant from a holding vessel to a filtering unit-modulator valve combination, monitoring the pressure or flow rate of filtered lubricating coolant downstream of the filtering unit-modulator valve combination, and operating the modulator valve in response to any changes in the downstream monitored flow parameter so as to maintain a predetermined constant fluid pressure differential across the filtering unit-modulator valve combination, thus compensating for fluctuations across the filtering unit during filtering operation, resulting in the maintenance of constant head pressure at the outlet of the pump, as well as for maintenance of a constant vol

Abstract: In a system having a fluid filter that is automatically backwashed each time the differential pressure thereacross reaches a predetermined value, the desired base rate at which the drop across the filter should increase during its initial filtering sequence (i.e., before backwash) is determined and stored in digital format in a process controller along with a preset maximum differential pressure at which backwash is set to occur. During use of the filter the actual rate of change of the pressure drop thereacross is monitored continuously and compared with the rate that is stored in the controller. Whenever the actual rate of change of the pressure drop across the filter differs from the base rate, which is the usual case, the present backwashing pressure is automatically adjusted--usually downwardly. This reduction continues until the actual drop across the filter finally reaches the adjusted value of the preset backwashing pressure, at which time backwashing of the filter is automatically commenced.