Application Notes

The Problem – When is it Time to Change the Oil Filter?

Heavy equipment that runs continuously must be protected against wear by a good oil filtration system. Problem is, when do you shut down the system to change the filter? If you schedule the maintenance for the equipment only by the number of hours that it runs, the type of service, load, and other variables are not taken into account. You might replace an expensive filter before it is really necessary, or you might not replace it soon enough if the service is especially severe. Filters and downtime are expensive; how do you minimize the cost?

The Solution – Measure the Pressure Drop Across the Filter

As wear occurs inside an engine or other piece of moving machinery, small particles are created and lodge in the filter as the oil is circulated through the system. Oil flowing through the filter will have a characteristic pressure drop when the equipment is running normally and the filter is clean. As the particles load the filter, the pressure drop across the filter increases. This can be measured with a differential pressure transducer. The pressure transducer must be able to measure small differential pressures, even while the system pressure may be comparatively large. A clean oil filter might drop just one or two psi while the system pressure may be 100 or even 200 psig. As the filter collects contaminants from the oil, this pressure drop increases. An alarm point can be set to shut down the system (thereby possibly saving it from destruction) if the filter overloads. In any case filter replacement can occur when the filter needs changing, not when an arbitrary number of running hours have elapsed. This lowers cost and improves system protection.

Validyne Products

The most popular Validyne transducer for hydraulic and oil filter measurements is the P55. This transducer accepts fluids and can measure a very small differential pressure even when the system pressure is as high as 3000 psig. The small, rugged P55 is ideal for industrial applications because it features high resistance to shock and vibration, accepts DC Power and provides a convenient +/-5 Vdc or 4-20 mA signal.

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