(b)
The check valve opens.
(c)
The system fluid flows (through the open MLG vent valve) from the retract sides into the extend sides of the MLG actuating cylinders.
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Landing Gear System - In-line Check Valve Figure 043
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(3)
L/G Return Isolation Check-Valves 2537GM (2748GM)
These check valves 2537GM (2748GM) are installed in the return lines of the L/G system that connect to the Green LP manifold system. If pipe lines in the Green LP system are damaged when an engine fails the check valves will close. This is caused by the drop in pressure in the Green LP manifold circuit. Operation of the check valves prevents loss of oil from the return lines of the L/G system.
(4)
MLG Door Close Check-Valves 2525GM (2529GM)
Each check valve is installed in a MLG 'doors close' return line. These lines connect the MLG Vent Valve (2516GM) to the MLG Door Actuating Cylinders (2523GM/2522GM).
If the pressure increases in one of the MLG 'doors close' return lines, the check valve in the other 'doors close' return line closes. This isolates the 'doors close' return line of each MLG door actuating cylinder from the other.
During a free fall extension of the landing gear:
(a)
The fluid removed from the 'doors close' side of the MLG door actuating cylinders causes the check valves to open.
(b)
The open check valves let the removed fluid flow (through the open MLG vent valve) into the Green LP manifold circuit.
R. In-line Restrictor Valves
(Ref. Fig. 044)
(1) General
There are two in-line restrictor valves installed in the L/G extension and retraction system. They are a NLG door-opening restrictor-valve, and an NLG extension restrictor-valve.
The restrictor valve has a cylindrical body made of stainless steel, which contains a poppet and spring. There is a threaded hydraulic connection at one end of the restrictor valve, and a union nut on the other. These connect the restrictor valve to the hydraulic system. The restriction orifice in the poppet restricts the flow of hydraulic fluid when the poppet is in the closed position.
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Landing Gear System - In-line Restrictor Valve Figure 044
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When the hydraulic pressure on the inlet side is more than that on the outlet side, the poppet opens against spring compression. This lets more hydraulic fluid through the valve. When the hydraulic pressure on the outlet side is equal to (or more than) that on the inlet side, spring compression keeps the poppet against the valve seat. Thus the closed poppet restricts the flow of fluid through the valve.
(2) Restrictor Valve - NLG Door Opening (2535GM)
The restrictor-valve (2535GM) is installed in the 'doors-open' line
to the NLG door actuating-cylinder (2527GM).
The function of this valve is described in the description of the NLG Door Actuating Cylinder (2531GM).
(3) Restrictor Valve - NLG Extension (2691GM)
The restrictor valve (2691GM) is installed in the 'extend' line to
the NLG actuating-cylinder.
The function of this valve is described in the description of the NLG actuating cylinder (2527GM).
S. MLG and NLG Door Ground-Opening
(Ref. Fig. 045, 046, 047)
With the aircraft on the ground, the MLG and NLG doors can be opened independently to get access to the wheel bays for maintenance operations.
The MLG and NLG door ground-opening by-pass valves (2517GM,2518GM,2533GM) have a rigging pin hole for:
-initial installation
-adjustment of the ground door-opening system.
A control lever with two lockable positions is installed in each wheel
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