Mechanical Drive Mechanism

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Piston-type pump (constant dis-placement)

Aviation Structural Mechanic

Pressure Control

Mechanical Drive Mechanism. The mechani-cal drive mechanism is shown in figure 7-17. Piston motion is caused by the drive cam displacing each piston the full height of the drive cam each revolution of the drive shaft. By coupling the ring of pistons with a nutating (wobble) plate supported by a fixed center pivot, the pistons are held in constant contact with the cam face. As the drive cam depresses one side of the nutating plate (as pistons are advanced), the other side of the nutating plate is withdrawn an equal amount, moving the pistons with it. The two creep plates are provided to decrease wear on the revolving cam.

Fluid Displacement. A schematic diagram of the displacement of fluid is shown in figure 7-18. Fluid is displaced by axial motion of the pistons. As each piston advances in its respective cylinder block

Figure 7-16.Internal features of the Stratopower pump.

Figure 7-17.Mechanical drive.

Figure 7-18.Fluid displacement.

bore, pressure opens the check spring and a quantity of fluid is forced past. Combined back pressure and check spring pressure closes the check spring when piston bypass ports align with the cylinder block bypass passage. The partial vacuum occurring in the cylinder during the piston return causes reservoir fluid to flow from the intake loading groove into the cylinder.