Power Jacks M-Series - Machine - Manual (Page 4)

4
Imperial Series – Machine Screw Jacks
2.4 Important precautions
In order to ensure that Power Jacks machine screw jacks provide good service over a period of years the
following precautions should be taken:
1. Select a screw jack that has a rated capacity greater than the maximum load that may be imposed on it.
2. The structure on which the jacks are mounted should have ample strength to carry the maximum load,
and should be rigid enough to prevent undue deflection or distortion of the jacks supporting members.
3. It is essential that the screw jacks be carefully aligned during installation so that the lifting screws are
perfectly plumb and the connecting shafts are exactly in line with the worm shafts. After the jacks,
shafting, gear boxes etc., are coupled together, it should be possible to turn the main drive shaft by
hand. If there are no signs of binding or misalignment, the jacking system is then ready for normal
operation.
4. The machine screw jacks should have a greater raise than is needed in the actual installation. Should it
be necessary to operate the jacks at the extreme limits of travel, it should be done cautiously.
Caution:
Do not allow screw jack to go beyond specified (catalog) closed height of
actuator or serious damage to internal jack mechanism may result. Refer to
table of specifications (par 1-3) for closed height of respective units.
5.
The worm shaft speed for these jacks should not exceed 500 RPM for light loads of one-fourth (or
less) of the jack load rating.
6. The lifting screw should not be permitted to accumulate dust and grit on the threads. If possible, lifting
screws should be returned to closed position when not in use.
Caution:
Where lifting screws are not protected from airborne dirt, dust, etc., bellows
boots should be used. Inspect frequently at regular intervals to be certain that
a lubricating film is present. Lifting screws should never be run dry.
7.
When using an 1800 or 9000 Series screw jacks periodic check of backlash of the lifting screw thread
is recommended to check wear of the worm gear internal threads. The normal backlash on a new unit
of this type is approximately .010 inch. Backlash of 50% or more of the thread thickness indicates
the need to replace the worm gear.
The 4800 and 9400 Series anti-backlash jacks are designed to
be adjusted for minimum backlash, approximately .002 inch. The worm gear and anti-backlash nut
faces of ½ the thread thickness. When adjustments have been made to the point where all this
clearance is gone, 50% of the thread thickness is gone and replacement is necessary.
(Refer
Section 3.8 for a detailed explanation of how the anti-backlash nut functions).
Note:
For loads from 25% to 100% of screw jack capacity, torque requirements are
approximately proportioned to the load, except for very light loads.
8.
The lubrication procedures for normal and severe service conditions, (refer Section 3.1) should be
closely followed.