Filter elements are economically used only if their dirt holding capacity is fully exploited. This is achieved by using filter housings with a maintenance indicator. MAHLE manufactures maintenance indicators of the following designs:
Differential pressure indicators Pressure indicators/switches/gauges Vacuum switches/gauges - With any filter element the collection of dirt particles continously reduces the number of open pores or, in other words: The open cross section for allowing the liquid to flow is continously reduced. Thus the pressure on the upstream side of the element (dirt side) increases continously.
With pressure filters, the pressure is measured upstream and downstream of the filter element (differential pressure). With return line filters the pressure is measured only on the upstream side because, depending on the tank design, atmospheric pressure exits on the downstream side of the filter element is measured analog. With suction filters the vacuum is measured downstream.
A piston with attached magnet is moved against the force of a spring, with which the indicating point is determined by the piston surface. A homopolar poled magnet is fitted in the outer part in the indicating button.
The closer the pole-springs move towards each other, the stronger is the force with the magnets mutually repel, until finally the red button on the indicator pops out
This red button remains visible until it is pushed in during the daily check which is to be performed while the plant is at operating temperature. If the button pops out immediately after being pushed in, the filter element must be replaced latest at the end of the shift.
This optical function may also be used for generating contactless electrical signals. For this purpose an electrical upper part is pushed over the hydraulic/optical part. This upper part incorporates all electrical switching elements.
Optical and electrical indicator with standard check function
Normally open/normally closed combination - standard feature
Electrical function, easy to install at a later time