MIL-J-26149E
3.8.5.1 C over.
A weatherproof fabric protective cover shall be provided
to cover the upper portion of the retracted ram and cylinder assembly when the jack is not in use. The cover shall be attached to the jack. with a permanent corrosion-resistant cable or strap(s) to prevent loss. This requirement for a cover shall apply to tripod jacks and wheeled axle jacks.
3.8.6 Principle of Hydraulic Operation. A typical schematic for a hydraulic actuated aircraft jack is shown in Figure 1.
3.8.7 External pumping source connector. The hydraulic circuit shall have provisions for operating the jack from an external hydraulic pumping source when specified. A male connector conforming to Drawing 43A13906 shall be provided on the jack for this purpose. (The female connector P/N43A13905 shall be the mating connector on the hose). The hydraulic circuit shall be designed to provide positive assurance that pressurized fluid from the external pumping source will not enter the jack fluid reservoir during external pumping operations. A positive isolation of the hydraulic fluid
reservoir from the pumping circuit shall be provided when the external pumping
source is connected to the jack.
3.8.8 Ram screw extension. The ram screw extension, if so equipped, shall have a positive stop to prevent its over-extension.
3.8.9 Release valve. The release valve is located between the high pressure side of the ram and the reservoir. The opening of this valve shall release the hydraulic fluid that is under pressure so that it is returned to the reservoir. When this valve is opened the maximum flow of the fluid shall not cause any pressure increase in the reservoir. The existing air in the reservoir shall be vented by means of the dumping or safety valve.
* 3.8.10 Two Way Valve. For those aircraft jacks equipped with an external pumping source connector, a two-way valve (not shown in Figure 1) may be installed in the high pressure line between the connector and the connection
to the hydraulic cylinder. This valve will be used to switch the hydraulic pumping function from either the hand pump or the external pumping source (console) and it will also be used in the exact same manner during the release of the hydraulic pressure.
3.9 C ontrols.
Operating controls shall be grouped and conveniently
located to provide maximum safety to the operator and equipment. The response to control actuation shall be smooth and positive. All operating and service
controls shall be readily accessible to an operator wearing heavy gloves.
3.10 B earings.
The ram and cylinder bearings used in the jack shall be
of sufficient size and contact area to provide maximum stability under the maximum load conditions. The bearings shall be fully protected to the most practical extent from abrasive particles encountered during the use of the
jack under normal service conditions.
3.11 Packing. Jack ram and pump piston packings shall be of the O-ring type conforming to MIL-P-25732 or MIL-P-83461 with V-type teflon backup
rings.
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