Abstract: A maintenance alarm actuator for a fluid filter actuates an alarm when contaminant has accumulated in the filter. The actuator is connected to fluid lines upstream and downstream of the filter. Included in the actuator are a valve and a biasing mechanism which biases the valve. The valve responds to the difference in the line pressures, and the actuator is initially triggered when the pressure of the upstream line exceeds that of the downstream line by an amount sufficient to overcome the force of the biasing mechanism. When initially triggered, the actuator vents the downstream line to the alarm, thereby increasing the difference in line pressure and causing itself to trigger completely.

Abstract: An improved interlocking assembly for an air filter, air lubricator, filter-regulator piggyback or the like which includes a pressure vessel normally retained by a head member and an interlocking collar. The pressure vessel nests in the collar to prevent accidental separation of the head member and pressure vessel. Locking tabs on the collar from being removed unless it is sequentially raised, rotated and lowered.