jueves, 28 de junio de 2007

Lothlorien: "Tresaf" system for wheelchairs

1 comentario:

jolabent27 dijo...

Drawing Numbers 30J,30K,30L. The "TRESAF" hoist for wheelchairs.

The "Tresaf" hoist consists of an elevator cabin, a winch, and two blocks.
The head-block, from which the cabin is directly suspended, hangs from a 3/8th tested steel chain which is anchored on a "Freebranch" hanger installed on a good stout branch.
From a similar chain anchored on the tubular steel cabin-frame, leads a flexible steel wire rope of 1/2" diameter, which passes around the sheaf of the head-block and descends to the tail-block at ground level, which is secured to a concrete foundation.
From the sheave of the tail-block the wire rope leads to the drum of the winch, which is also secured to a concrete foundation.
This winch is operated by two men, the winchman and the brakeman.
The Drawing Number 30L shews the system in operation as follows:

Here is the Hoist in operation, about to bring a wheelchair passenger down.
1/ The Cabin is moored to the talan, the doors are open.
2/ At the winch, the pawl is engaged, the screw-brake is on, and so is the over-run check brake, on the handle of which the brakeman is lightly resting his hand.
3/ When the wheelchair is inside the Cabin, the attendant will apply the safety-chains, close the doors, release the mooring-ropes and call "Ready!" to the winchman, who will release the pawl, and slowly release the screwbrake.
4/ When the winchman has done this, the brakeman will bring the Cabin down to earth slowly and steadily by the use of the over-run check-brake.
5/ The brakeman will hold the over-run check-brake slightly "off", in order to allow the cabin to descend.
6/ If for any reason the brakeman releases the handle, the over-run check-brake will immediately come "on", thereby arresting the descent of the Cabin.
7/ The winchman will at all times attend the screw-brake during the operation and in readiness to apply it.

When hoisting a wheelchair, the winchman operates the handle for turning the drum to hoist the Cabin, while the brakeman holds the brake in the "off" position.
The winchman will engage the pawl with the ratchet before beginning the operation of hoisting, in order avoid any possibility of a run-back.
As already expained above, the over-run check-brake is naturally and normally "on", and must be manually held "off" for the winch to be able to turn at all. If released, it immediately stops the system.