NP-92A-4

Function of NP-92A-4 in the hydraulic system

The main function of NP-92A-4 is to pump hydraulic fluid into the aircraft high-pressure hydraulic system. The pump supplies working pressure for hydraulic circuits that may include main, backup or auxiliary hydraulic systems, depending on aircraft type and configuration. The unit automatically adjusts its output according to system pressure, reducing flow when the hydraulic system reaches maximum operating pressure. This regulation helps limit unnecessary power consumption from the gearbox drive.

Application on helicopter gearbox drives

According to the supplied context, NP-92A-4 and related NP-92-series pumps are installed on accessory drive gearboxes of main helicopter gearboxes, including VR-24 on Mi-24 and VR-14 on Mi-8MT-type helicopters, depending on configuration and documentation. The pump is mechanically driven by a splined shaft connected to the gearbox drive. Exact applicability must be confirmed through the aircraft parts catalogue, gearbox documentation and hydraulic system maintenance manual.

Variable-displacement axial-piston design

NP-92A-4 is described as an axial-piston pump with adjustable output. In this type of pump, working fluid is displaced by pistons arranged along the pump axis. Flow regulation is achieved by changing the working displacement through a swash plate / cradle-type mechanism or by changing piston stroke through a pressure-responsive control mechanism. When system pressure rises to the upper operating limit, the pump transitions toward a low-flow or near-zero-flow mode.

Working fluid and pressure context

The pump is intended for aviation hydraulic fluid service. The supplied data specifies AMG-10 hydraulic oil according to GOST 6794-75 as the working medium. In the context of helicopter hydraulic systems of this class, the nominal operating pressure is stated as 21 MPa, with maximum pressure or valve adjustment level around 24–25 MPa. These values should be checked against the exact aircraft documentation and the individual pump passport before maintenance, installation or bench testing.

Identification and supply of NP-92A-4

When ordering NP-92A-4, the buyer should specify the complete designation, aircraft type, gearbox application and required condition. It is also important to confirm whether the requested item is a serviceable pump, overhauled pump, as-stored unit or pump for repair / exchange. Exact dimensions, mounting flange geometry, splined shaft data and flow characteristics at rated speed should be confirmed through the product passport, technical conditions and certified repair documentation.