SS-78

Magnetic operating principle inside SS-78

The SS-78 works on a magnetic contact principle. A permanent magnet inside the detector attracts ferromagnetic particles carried by the oil flow. When enough metallic particles collect on the sensing end, they can form a conductive bridge between insulated contacts. This closes the electrical circuit and sends a warning signal to the cockpit indication system. In practical terms, the detector acts as a simple but important condition-monitoring element. Its response depends on the presence of magnetic wear particles, so non-ferromagnetic contamination, dirt or oil sludge does not produce the same signal as steel particles from wearing mechanical components.

SS-78 installation in helicopter oil systems

The SS-78 is used in aircraft engine and gearbox oil systems, including installations on Mi-8 / Mi-17 family helicopters and related configurations. In engine applications, it can be installed in the oil scavenge line, where oil returning from the engine carries wear particles from internal friction pairs. One typical installation area is the line before the oil enters the air-oil radiator. This position allows the detector to monitor contamination before the oil is cooled and returned to the system. Depending on the aircraft and engine configuration, the detector may be associated with left-engine or right-engine warning circuits.

Warning output from the SS-78 chip detector

When the SS-78 contacts close through a bridge of ferromagnetic particles, the aircraft warning circuit activates the relevant cockpit signal. On helicopter installations, this may correspond to a “CHIPS” warning for the left or right engine, depending on the connected circuit. The detector itself does not analyze the quantity or origin of the particles. It only completes the signal circuit when magnetic material accumulates at the sensing element. After such an indication, maintenance personnel normally inspect the detector, clean the sensing end, identify the collected material and assess the condition of the related engine or gearbox system.

Construction features of the SS-78 unit

The SS-78 is generally built as a plug-type detector with a non-magnetic body, permanent magnet, insulated contacts and a connection point for the aircraft wiring. Many installations use a design with an integrated valve, allowing the detector element to be removed for inspection without draining oil from the complete system. This is useful during scheduled maintenance and troubleshooting, because the detector can be checked, cleaned and reinstalled with limited disturbance to the oil circuit. Depending on the installation, the retaining arrangement may use a threaded or bayonet-type locking design.

Identification and service use of SS-78

The SS-78 may also be referenced by drawing or catalog number 0780679740. Before ordering or replacing the detector, the marking, installation type, connection design and aircraft documentation should be checked. The same designation may appear in different catalog contexts, so the target engine, gearbox or oil system should be specified. During maintenance, the detector is normally inspected and cleaned from sludge or collected particles according to the aircraft maintenance schedule. If metallic particles are found repeatedly, the issue should not be treated as a sensor problem only; the related engine or gearbox requires further inspection.