NP92A

NP92A in helicopter hydraulic systems

The NP92A is an aircraft variable-delivery axial plunger hydraulic pump used in helicopter hydraulic systems. It is designed to generate working pressure of hydraulic fluid and supply onboard hydraulic circuits during helicopter operation. The pump is installed on the drive gearboxes of main helicopter reducers, so hydraulic pressure can remain available while the main rotor is rotating. This is important for helicopters because hydraulic power may still be required during autorotation or abnormal engine operating conditions.

Hydraulic pressure generation by the NP92A pump

The main function of the NP92A is to create hydraulic flow and pressure for helicopter control and service systems. The pump supplies aviation hydraulic fluid to the main, backup or auxiliary hydraulic circuits depending on helicopter type and system layout. It is not a simple transfer pump; it is a pressure-generating unit for onboard hydraulic consumers. Stable pump output is important for flight control assistance, actuator response and normal hydraulic system operation.

Automatic delivery regulation of the NP92A

The NP92A has a built-in delivery regulator. Pump delivery is adjusted automatically by changing plunger stroke through a movable sleeve mechanism. This allows the pump to maintain pressure within the required range instead of constantly delivering maximum flow. When system demand increases, the pump provides the necessary flow; when pressure reaches the regulated level, delivery is reduced. This helps reduce hydraulic heating, unnecessary load and pressure instability in the system.

Valve-slot distribution in the NP92A

The NP92A belongs to axial piston / plunger pumps with valve-slot distribution. This design is used in aviation hydraulic systems where a compact unit must provide stable pressure and reliable delivery. The pump works with AMG-10 aviation hydraulic oil and requires clean fluid, correct inlet conditions and proper hydraulic tank pressurization. Contamination, air in the suction line, poor tank pressure or blocked filters can lead to cavitation, noise, heating and accelerated wear of the plunger group.

Installation of NP92A on helicopter main gearboxes

The NP92A is installed on the drive gearbox of the helicopter main reducer, such as VR-24 or VR-252 type installations depending on helicopter model. This installation allows the pump to receive mechanical drive from the rotor transmission system rather than only from a separate engine accessory gearbox. As long as the rotor and main gearbox continue rotating, the pump can continue supplying hydraulic pressure according to system design. During installation, the drive interface, flange, shaft, sealing surfaces and hydraulic connections must be checked carefully.

NP92A-4 and NP92A-5 modifications

The most common NP92A modifications include NP92A-4 and NP92A-5. The NP92A-4 version is associated with Mi-family helicopters, including Mi-24 applications where pumps may be used in main, backup and auxiliary hydraulic systems. The NP92A-5 version is associated with Ka-family helicopters such as Ka-27, Ka-28, Ka-29 and Ka-32, including installations on the VR-252 main gearbox. These versions should not be treated as automatically interchangeable without checking the helicopter documentation, mounting arrangement and hydraulic system requirements.

Helicopter application of NP92A

The NP92A is used on domestic helicopter platforms, including Mi-24, Ka-27, Ka-28, Ka-29, Ka-32 and Mi-26 depending on configuration. On Mi-24 helicopters, three NP92A-4 pumps may be used in separate hydraulic circuits. On Ka-27 / Ka-32 family helicopters, NP92A-5 pumps are used in main and backup hydraulic systems. The actual pump version must be confirmed by the helicopter parts catalog, main gearbox documentation and hydraulic system layout before procurement or replacement.

Supply and inspection of NP92A

For procurement, the full modification should be specified: NP92A-4, NP92A-5 or another version if required. Before installation, the pump should be checked for housing condition, drive shaft and spline wear, flange surfaces, port threads, regulator condition, leakage traces, corrosion, storage condition and internal cleanliness. For aviation use, bench testing is recommended to confirm delivery, pressure regulation, leakage level and stable operation with AMG-10 hydraulic fluid. Passport, storage, repair or test documentation should be requested whenever available.

Product Type: Variable axial plunger / axial piston helicopter hydraulic pump
Designation: NP92A
Common Modifications: NP92A-4, NP92A-5
Function: Generation and automatic regulation of hydraulic pressure and flow
Application / Where Used: Helicopter hydraulic systems
System / Installation Area: Main, backup and auxiliary helicopter hydraulic systems depending on aircraft type
Installation Area: Drive gearbox of the main helicopter reducer
Associated Gearboxes: VR-24, VR-252 and related main gearbox installations depending on helicopter model
Pump Type: Axial piston / plunger pump with valve-slot distribution
Regulation Principle: Built-in delivery regulator with plunger stroke variation by movable sleeve
Working Fluid: AMG-10 aviation hydraulic oil
Nominal Rotational Speed: 2500 rpm
Maximum Flow Rate: 30 L/min at 2500 rpm and 65 kgf/cm²
Nominal Working Pressure: 75 kgf/cm²
Automatic Regulation Range: Approximately 64–80 kgf/cm² depending on helicopter system setting
Working Pressure Range: 64–90 kgf/cm² depending on helicopter type and hydraulic circuit
Maximum Allowable Pressure: 90 kgf/cm²
Hydraulic Tank Conditions: Works with pressurized / air-boosted hydraulic tank conditions to reduce cavitation risk
Compatible Aircraft / Equipment: Mi-24, Ka-27, Ka-28, Ka-29, Ka-32, Mi-26 depending on configuration
NP92A-4 Application: Mi-family helicopters, including Mi-24 hydraulic systems
NP92A-5 Application: Ka-family helicopters, including Ka-27 / Ka-32 family hydraulic systems with VR-252 gearbox
Dry Weight: Approximately 6.5–7.2 kg depending on modification and transition flange
Approximate Dimensions: Length 260–280 mm; flange diameter approx. 140–150 mm
Body Design: Cylindrical body with projecting regulator and flange mounting
Technical Documentation: Product passport, bench-test documents and helicopter hydraulic system documentation as applicable

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