Abstract: A filter comprising a filter head, a canister secured to the filter head and a tubular filter within the canister. The filter head has inlet and outlet ports for connecting into a hydraulic conduit. A first passage normally delivers fluid from the inlet port to the outer cylindrical surface of the tubular filter element. A second passage delivers fluid from the interior of the filter element to the outlet port. The filter head has a sliding element between the inlet and outlet ports. The sliding element is spring biased which bias can be overcome by differential pressure across the filter element. An indicator is associated with said sliding element and extends through the filter head to the exterior thereof. The filter head has a butterfly valve in the second passage. A plunger slidably positioned in said filter head is spring biased to a first position in which it extends into the canister in the space normally occupied by the tubular filter element.

Abstract: An unhooking dirty filter alarm for a filter comprising a filter head, canister and tubular filter element. The filter head has a bypass valve therein. Linkages to the outside of the filter element rotate a pointer indicating whether or not the filter element has been bypassed. The linkages are arranged not to restore the pointer after the bypassing condition has abated to thereby latch the information that the filter was bypassed.