NS-51A

Boost pressure function of the NS-51A station

The main task of the NS-51A is to maintain positive pressure at the inlet of the main hydraulic pumps. In aircraft hydraulic systems, main pumps such as NP-89D require stable suction conditions to operate correctly. If the inlet line pressure drops too low, cavitation, flow interruption or unstable pump operation may occur. The NS-51A prevents this by taking hydraulic fluid from the tank and supplying it to the suction line with controlled boost pressure. This improves reliability of the main hydraulic system.

NS-51A operation principle

Inside the NS-51A station there is a gear pump combined with a flow regulator. The pump is driven by an internal hydraulic motor. This hydraulic motor receives high-pressure hydraulic fluid from the aircraft hydraulic system and uses that energy to rotate the gear pump. The gear pump then draws AMG-10 hydraulic fluid from the hydraulic tank and supplies it to the suction side of the main pumps. The regulator helps maintain the required boost pressure automatically, so the station adapts to operating conditions without constant manual adjustment.

NS-51A with main hydraulic pumps

The NS-51A works together with main aircraft hydraulic pumps, including NP-89D-type plunger pumps where applicable. Its role is not to replace the main high-pressure hydraulic pumps, but to support their inlet conditions. The station supplies fluid to the pump suction line, while the main pumps create the high working pressure for aircraft hydraulic consumers. In this chain, the NS-51A is a supporting but important unit: if boost pressure is unstable, the main hydraulic pump may lose efficiency or work under damaging conditions.

Hydraulic motor drive of the NS-51A

The NS-51A does not use an electric motor as its primary drive. Its gear pump is driven by a hydraulic motor powered by high-pressure fluid from the aircraft hydraulic system. The nominal pressure supplied to the hydraulic motor is 210 kgf/cm². This design allows the station to operate using hydraulic energy already available on board. During inspection, technicians should check the hydraulic motor feed line, return line, gear pump condition, regulator operation, leakage and pressure stability in the boost circuit.

Working fluid and operating temperature of NS-51A

The NS-51A operates with AMG-10 aviation hydraulic fluid. This fluid must remain clean and within the approved temperature range, because contamination or viscosity changes can affect the gear pump, regulator and hydraulic motor operation. The unit is designed to work with hydraulic fluid temperatures from −60 to +100 °C and ambient temperatures from −60 to +60 °C. Such a wide range is required for aircraft operation in different climates, altitudes and ground conditions.

NS-51A application on Il-76 family aircraft

The NS-51A is associated with the hydraulic systems of Il-76 family aircraft and their modifications, including Il-76MD, Il-76MD-90 and Il-78. These aircraft have high-demand hydraulic systems where stable pressure supply to pumps and consumers is critical. The station’s function is especially important during flight phases and operating conditions where hydraulic demand changes and suction conditions must remain stable. Applicability should always be confirmed by aircraft modification, hydraulic system diagram and maintenance documentation.

Supply and documentation for NS-51A

For supply or replacement, the unit should be requested by its full designation: NS-51A / НС-51А. Since it is a hydraulic system component, condition and documentation are important. Before installation, the station should be checked for hydraulic motor operation, gear pump delivery, regulator function, boost pressure range, leakage, cleanliness of ports and housing condition. If supplied from storage or after repair, passport, acceptance records and available test documentation should be checked before the unit is accepted for aircraft use.