ThePilgrim nut system used with the shaft and bore surfaces dry and degreased (except for cast steel propellers where wiping of the bore with an oil soaked rag is recommended) achieves the correct push up by a calculation based on the predictable friction of dry surfaces. The calculation gives the hydraulic pressure suitable for the prevailing ambient temperature lo produce the required push up. The operation is of course checked by measuring the push up and the hub movement relative to the increase of jacking pressure is monitored by a dial gauge.
The Pilgrim nut (Figure a ) employed for propeller mounting. has an internal nitrile rubber tube which when inflated hydraulically, forces a steel loading ring against the hub. Outward movement of the ring from the flush position must not exceed one third of the ring width, to avoid rupture of the rubber tube. Temperature of hub and shaft are recorded and also used to find the correct final push up pressure from the table provided in the instruction book.
The propeller, after a check with the blue marker of the mating surfaces, is positioned and initially jacked on to the shaft taper. before the Pilgrim nut is used to apply an initial loading of perhaps 67 bar pressure. A reference mark is made at this point about 25 mm from the forward end of the hub. The nut is then turned until the loading ring is again flush (venting hydraulic flutd) becore full pressure is applied. During this stage, the dial gauge should show the movement. A second mark 25 mm from the forward face of the hub is then made. Push up, registered by the distance between the two reference marks, is measured and noted.
The nut is again vented and turned to bring the loading ring to the flush position and finally nipped up with a tommy bar. The Pilgrim nut can be reversed and used with a withdrawal plate and studs (Figure b) for removal of the propeller. To safeguard against any violent movement at release, wooden blocks are inserted as shown, and a gap of only a little more than the push up distance is left.
The Pilgrim keyless system owes its name to T. W. Bunyan.