GA-77V

GA-77V pump unloading valve in Mi-8 hydraulic systems

The GA-77V is a hydraulic pump unloading valve used in aircraft hydraulic systems, including Mi-8 family helicopters. Its main task is to keep the working pressure within the required range and unload the hydraulic pump when the system no longer needs flow under pressure. It is not a shut-off valve for a single actuator and not a hydraulic filter. The unit works as part of the pressure regulation circuit and helps the pump avoid continuous loaded operation when the hydraulic system has already reached its operating pressure.

Automatic pressure regulation through GA-77V

In operation, GA-77V reacts to pressure in the hydraulic system. When pressure rises to the unloading level, the valve switches the pump to idle flow, sending hydraulic fluid back to the tank instead of keeping the pump loaded against the system. When pressure drops to the engagement level, the valve returns the pump to working mode and fluid is again supplied into the hydraulic circuit. This cycle helps maintain pressure for the connected consumers and reduces unnecessary heating of AMG-10 fluid during periods when flow demand is low.

Hydraulic system work with GA-77V installed

The GA-77V works together with the hydraulic pump, tank, pressure lines, return lines, filters, hydraulic accumulators, boosters, and relief circuits. On Mi-8 type systems, technical materials describe its operation together with the NSH-39M pump and hydraulic accumulators. If pressure does not stay within the required limits, the valve is only one part of the check. Maintenance work usually includes pump condition, fluid level, contamination, leaks, accumulator charge, relief valve operation, and the condition of lines and fittings.

GA-77V in main and standby hydraulic circuits

The GA-77V is used in main and standby hydraulic systems that supply flight control hydraulic boosters. In these circuits, the valve supports normal system pressure and unloads the pump when the hydraulic demand is absent or reduced. This protects the pump from unnecessary load and helps limit fluid overheating. If the automatic part does not work correctly, pressure may rise toward the relief valve setting, where excess fluid is dumped through the protection path. That is why correct adjustment and clean working fluid are important for reliable operation.

Identification and ordering checks for GA-77V

Before ordering, the marking on the installed unit should be compared with the aircraft parts catalog, maintenance manual, or technical description. In English-language requests, the unit is written as GA-77V. In Russian documentation, the same product is written as ГА-77В. For a clear request, it is useful to provide the helicopter type, hydraulic system position, full part number, and a photo of the marking if available. The product is also known under alternative designation ГА-77В.

Product Type: Hydraulic pump unloading valve
Function: Automatic pressure regulation and pump unloading
Application / Where Used: Aircraft hydraulic systems
System / Installation Area: Main and standby hydraulic circuits
Compatible Aircraft / Equipment: Mi-8 family helicopters and modifications
Working Medium: AMG-10 hydraulic fluid
Pump Engagement Pressure: 4.5 ± 0.3 MPa
Pump Unloading Pressure: 6.5 +0.8/−0.2 MPa
Relief Valve Opening Pressure: 7.8 ± 1 MPa
Design Features: Command, intermediate, and main spool valves with electromagnetic control
Technical Documentation: GA-77V Technical Description and Aircraft Maintenance Manual

All shipments are carried out from our international warehouse in Dubai (UAE), as well as from our partners’ remote warehouses.

In Stock — items available in stock at the Dubai warehouse are dispatched within 5–10 business days after receiving 100% prepayment.

Remote Stock — items available at our partners’ remote warehouses are supplied within an average of 30–45 business days after receiving 100% prepayment.

Pre-Order — made-to-order products are manufactured and delivered within an average of 45–60 business days. Payment terms: 50% advance payment to start production, with the remaining 50% paid before dispatch from the Dubai warehouse after full readiness for shipment.

Returns & Changes (Restocking Fee)
For selected items, a RESTOCKING FEE of 10% may apply in case of return, order cancellation, or changes to the order specifications. This condition applies only to certain products and is confirmed at the order approval stage.

Warranty
All products are covered by a standard 6-month warranty.
Extended warranty is available upon request and is agreed individually; it may affect the final product price.