-
the annular side of the piston, the piston rod retracts and extends the MLG.
The piston rod range of travel is controlled by:
-
the side stay during the MLG extension cycle
-
the uplock during the MLG retraction cycle.
(c) Restrictor Valve
The restrictor valve is closed by hydraulic fluid flow when the L/G is operated. This decreases the flow of fluid and controls the speed of the piston rod. Near the end of the piston rod travel the piston closes a control orifice. This causes:
1 The remaining fluid to return through the closed restrictor
_
valve to the hydraulic system return.
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2_ An increase in pressure (on the return side of the piston)
which damps the end of the piston rod travel.
The shape of the piston causes a smooth increase in the
damping effect.
(2) Operation
(a) Retraction Sequence (start)
When the piston rod is in the extended position, the piston covers the control orifice of the restrictor valve at the piston rod end. The increased internal diameter of the cylinder prevents the orifice of the one-way restrictor being totally covered.
When a selection is made to retract the piston rod, port A is open to the hydraulic system pressure and port B to the hydraulic system return. The hydraulic fluid enters port A and pressure is transmitted directly to the valve housing at the piston rod end. The fluid cannot go through the control orifice, so the valve of the one-way restrictor is moved to permit full fluid flow. The initial piston movement is slow because the control orifice of the restrictor valve is closed by the piston.
Once the piston has moved past the control orifice of the restrictor valve, the flow is increased and the piston accelerates.
(b)
Damping (start)
At the other end of the retraction actuator, the hydraulic system return fluid goes through the piston end valve housing to port B. The fluid is forced through the control orifice of the restrictor valve and the orifice of the one-way restrictor valve, which is moved to decrease the fluid flow. As the piston covers the control orifice, the fluid flow by this path is reduced and finally stopped. Fluid which returns through the one-way restrictor, causes a pressure build-up in the piston end of the actuator. This decelerates the piston movement and dampens the end of travel stroke.
(c)
Extension (start)
Both restrictor valve sub-assemblies on the retraction actuator are similar in operation. This means that the extension of the actuator is opposite to the retraction
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F. NLG Actuating Cylinder (2527GM)
(Ref. Fig. 025)
**ON A/C 301-399,
(Ref. Fig. 026)
**ON A/C ALL
(Ref. Fig. 027)
(1) Description
The NLG actuating-cylinder is a two-acting type. The body has a valve housing at each end, each of which contains a restrictor.
The actuating cylinder assembly contains these components:
-
a piston-rod assembly
-
a cylinder assembly
-
a rod extension body
-
a rod retraction body
-the hydraulic external fittings.
(a) Piston-Rod Assembly
The piston-rod assembly has:
-
a rod which moves in a spherical bearing
-
a piston with a seal.
The piston is connected to the rod by a lockwasher and a nut, which are locked by a bolt and a nut. The piston has a ring which prevents any sideways movement of the of the piston on the rod.
The piston movement is kept within specified limits by a seal,
and preformed packing and back-up rings.
(b) Cylinder Assembly
The cylinder assembly has:
-
a cylinder
-
a spherical bearing
-
a bearing
-
a retaining ring
-
a plate.
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NLG Actuating Cylinder (2527GM) Figure 025
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NLG Actuating Cylinder (2527GM) - Detail
Figure 026
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1 1 May 01/05
1 1
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NLG Actuating Cylinder - Schematic Figure 027
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The cylinder has a spherical bearing at one end that connects the cylinder to the aircraft structure. The bearing, with a seal and scraper, is held in the opposite end of the cylinder by a ring and plate. The exterior of the cylinder contains ports for the hydraulic connections. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：A320飞机维护手册 AMM LANDING GEAR 起落架4(39)
