MSTV-1.2A

MSTV-1.2A miniature pressure switch

The MSTV-1.2A is a small aircraft excess pressure switch used in engine and auxiliary power unit systems. It reacts to a preset pressure level and closes or opens an electrical circuit. In the cockpit this signal may be used for a warning lamp or for pressure status indication, depending on the aircraft wiring. The unit is not a pressure gauge. It does not show a value to the crew. It only reports that the pressure has reached the set point.

Pressure monitoring with the MSTV-1.2A unit

The switch is normally used where the crew or control system needs a simple pressure threshold signal. In oil systems it can monitor whether pressure is present after engine or APU start. In air or fluid circuits it can confirm that pressure has reached the required level. The MSTV-1.2A works by contact switching, so the connected circuit should be checked against the aircraft diagram before installation.

MSTV-1.2A in engine and APU systems

The MSTV-1.2A is associated with oil and air systems of Soviet and Russian aircraft engines and auxiliary power units. Typical applications include AI-9 and AI-9V APUs, NK-8-2U engines and TV2-117 turboshaft engines. It is found on Mi-8 family helicopters and An-74 aircraft, with some catalog references also showing use on Tu-154B. Exact installation depends on the engine version, aircraft modification and the local pressure control circuit.

System links around pressure switch MSTV-1.2A

In service, the switch works together with oil pumps, pressure lines, filters, engine accessory units, cockpit lamps and relay circuits. It does not regulate pressure itself. It simply changes contact state when the pressure reaches the calibrated threshold. This is useful in maintenance, because a failed lamp, broken wire or poor connector can look like a failed switch. The full circuit should be checked before replacing the unit.

Identification and ordering of MSTV-1.2A

Before ordering, the marking should be compared with the aircraft or engine parts catalog. The suffix matters, because MSTV switches exist in several pressure ranges and versions. For a correct match, it is better to provide the aircraft type, engine or APU type, system location and the number from the logbook or maintenance list. The product is also known under alternative designations MSTV-1.2A, MSTV-1,2A and МСТВ-1,2А.

Product Type: Miniature heat-resistant vibration-resistant excess pressure switch
Function: Electrical signal output when preset pressure is reached
Application / Where Used: Aircraft engine oil and air systems, auxiliary power unit systems
System / Installation Area: Engine / APU pressure monitoring circuit
Compatible Aircraft / Equipment: AI-9, AI-9V, NK-8-2U, TV2-117, Mi-8 family helicopters, An-74, Tu-154B
Operating Pressure / Set Point: 1.2 kgf/cm², on pressure decrease
Working Medium: Neutral liquids and gases, NGZh fluid, MS-8RK oil
Switching Voltage: 27 V DC
Switching Current: Up to 1.5 A with resistive load; up to 0.5 A with inductive load
Operating Temperature Range: −60 to +180 °C
Vibration Resistance: 10–5000 Hz; amplitude up to 1 mm; acceleration up to 20 g
Dimensions: Ø60 × 105 mm
Weight: 180 g
Service Life / Assigned Resource: 30,000 hours / 30 years
Technical Documentation: Aircraft maintenance manual, engine documentation, parts catalog, manufacturer technical documentation

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