NR-3VM

Fuel metering role of the NR-3VM unit

In operation, the NR-3VM supplies and meters fuel for the combustion chamber over the full engine operating range. During start-up, it provides the required fuel schedule for ignition and stable acceleration. During throttle movement, it controls fuel increase or reduction so that the engine responds without surge, flameout or overtemperature. At steady modes, the unit maintains the fuel flow needed for stable power output. This is why the NR-3VM is treated as a fuel control unit, not only as a pressure pump.

NR-3VM in the automatic engine control system

The NR-3VM is part of the hydromechanical control system of the TV3-117 engine and works together with electronic and limiting devices. On helicopters with two engines, it also participates in power synchronization, helping the engines operate evenly when they drive the common transmission. The unit limits key parameters, including turbocompressor speed and free turbine speed, and supports protection against overspeed. Its operation is closely tied to engine safety, power response, and correct transition between ground idle, flight modes and take-off power.

Interaction of NR-3VM with ERD-3VM and IM-3A

The NR-3VM can work in coordination with the ERD-3VM or ERD-3VMA electronic engine regulator. Electrical correction commands are sent through the IM-3A actuator, which acts on the control elements inside the fuel control pump. This allows the engine control system to adjust fuel metering more accurately in response to operating conditions. The NR-3VM therefore combines hydromechanical regulation with external correction from the electronic control system. If there are problems with engine response, fuel scheduling or parameter limiting, the pump-regulator and its related control units must be checked as one system.

Fuel supply path through the NR-3VM

Fuel reaches the NR-3VM from the low-pressure side of the helicopter fuel system, typically through booster equipment such as the DTsN-70A centrifugal fuel pump. After receiving fuel at the inlet, the NR-3VM raises pressure, meters the required amount and sends fuel further to the engine fuel manifold and working nozzles. Fuel is supplied to the combustion chamber through the relevant circuits according to the engine mode. Because the unit works with high pressure and precise metering clearances, fuel cleanliness, storage condition and correct preservation are especially important for serviceability.

NR-3VM control of compressor mechanization

The NR-3VM also uses fuel pressure as a hydraulic working medium for engine control functions beyond simple fuel delivery. It is connected with compressor variable geometry control, including the inlet guide vanes and guide vane stages through the related hydraulic actuator system. It also participates in control of compressor bleed valves, which help maintain compressor stability during start-up, idle and transient modes. This makes the NR-3VM part of the engine’s mechanical and hydraulic control architecture, not only the fuel supply line.

Aircraft application of the NR-3VM pump-regulator

The NR-3VM and NR-3VM-T are associated with TV3-117VM and TV3-117VMA engines used on Mi-8MTV, Mi-17, Mi-171, Mi-172, Mi-24, Mi-35 and Mi-14 helicopters, depending on engine version and aircraft configuration. The exact applicability must be checked by engine series, modification, installation standard and aircraft parts catalog. In practical procurement, this is important because similar fuel control units may have different settings, tropical execution, connection points, or adjustment requirements for a specific engine variant.

Inspection, repair and supply of NR-3VM

For supply or replacement, the full designation NR-3VM or NR-3VM-T should be stated clearly. The unit is normally supplied as an aircraft engine aggregate with passport, repair, test or storage documentation, depending on condition. Before installation, the technical state of the drive shaft, mounting flange, fuel ports, control levers, sealing plugs, preservation, adjustment status and documentation should be checked. Because the NR-3VM is a regulated fuel-control aggregate, bench testing and proper documentation are much more important than external appearance alone.