As late as possible, as early as necessary: that is the concise formula for the optimum time to replace filter elements in the high-pressure and medium-pressure filters in hydraulic systems. If the element is replaced too early, it causes unnecessary maintenance costs and wastes resources. If the user waits too long, the performance of the hydraulic circuit can be affected because the differential pressure in the filter rises to a level which has a negative impact on the overall performance of the system. In the worst case, the filter will fail completely, putting the function of individual components at risk and resulting in an expensive downtime of the entire system.
The revised version of the HI-D024 contamination indicator presented by Stauff now makes it significantly easier to monitor the remaining capacity of filter elements. Compared to the previous model, the new version can output four instead of two alarm messages – from green (everything OK) through yellow and orange to flashing red (filter spent).
This allows the user to identify early on that the differential pressure is approaching a critical value and has the opportunity to react accordingly. If no action is taken and 75% of the factory-set differential pressure of 5 bar has been reached, a signal is sent, providing e.g. the machine operator or the responsible maintenance engineer with an advance warning. When 100% of the defined differential pressure has been reached, a second output signal can be used to automatically shut down the system.
Additionally, the temperature of the hydraulic fluid is determined. This prevents false alarms which can be caused by high oil viscosity in the cold start phase. Another new feature is that this Thermostop function is output as an additional visual alarm (blue).
The remaining capacity – i.e. the differential pressure before and after the filter – is determined by a microprocessor-controlled pressure switch. To trigger a switching process, the corresponding pressure has to be exceeded for at least four seconds. This can effectively prevent malfunctions caused by transient pressure spikes.
During the development, the Stauff engineers were also able to minimise the dimensions of the capacity indicator – despite the additional functions. This is another feature that makes it easy to retrofit existing systems where pressure filters were previously used without indicators or with conventional, single-stage capacity indicators.