Two separate chains are used, one as a load chain
and the other as the hand chain. The hand chain drives
a pocketed chain wheel sheave that in turn drives the
spur gears. The spur gears drive a single load sheave.
One end of the load chain is attached to the swivel
load hook. The chain then passes over the load sheave.
The other end is attached to the hoist frame. A me-
chanical brake, consisting of a ratchet and pawl or
friction disk unit plate, is used to sustain the load. To
lower, pull the operating chain in the reverse direc-
tion, slipping the friction brake or releasing the
ratchet-pawl device.
The worm-geared hoist and the spur gear chain
hoist operate in the same way except the gearing is
reduced with the use of a worm gear drive. The lead
(pitch) of the worm gear makes the hoist nonoverhaul-
ing.
Lever-Operated Chain Hoist
One of the widely used pieces of lifting equip-
ment is the ratchet hoist. In more common terms it is
usually called a come-along (fig. 2-22).
The ratchet hoist (come-along) has an operating
handle similar to a ratchet wrench, hence its name. It
is normally light in weight and comes in a variety of
sizes, depending on the job to be done. A hoist has a
ratchet and pawl or a friction disk brake incorporated
in its mechanism to hold the load when the handle is
released. Ratchet hoists are reversible so the load may
be raised or lowered. Ratchet chain hoists come
equipped with the load chain either of the roller
sprocket (bicycle) or link chain type.
Load chains should be lubricated and should
show no indication of binding. Do not exceed the load
Figure 2-22.—Lever-operated chain hoist (come-along).
rating of the hoist or use extensions on the ratchet
lever. Inspect load chains for wear, reduction in link
bar diameter, and increase in unit lengths. Use the
manufacturer’s data sheet or manual for reference.
PIPE PATCHES
While not a tool in the normal sense of the word,
pipe patches are an integral part of the ABF’s tool-
room. There are miles of pipes in a fuel system, and
damage to this piping can result from battle, accident,
or merely the wear and tear of daily use. The ABF
should know how to locate and repair piping system
troubles.
Repairs to piping are classified as permanent or
temporary. Permanent repairs are made when the time
and the material are available. Temporary are made
when the correct material is not available and/or the
system cannot be secured for the time needed.
Temporary repairs are usually made by securing
some type of patch over the damaged section of pipe.
The material used for the patch depends upon the type
of piping that is being repaired. A good general rule is
to make the temporary patch from the same type of
material that is used for the flange gaskets in the
system. Back up the patch with a piece of sheet metal,
and secure the sheet metal to the pipe with bolted
metal clamps or similar devices. A sealing compound
may be applied between the patch and the pipe to help
seal the patched area.
Jubilee pipe patches (fig. 2-23) are frequently
used to stop leaks in piping. These patches may be
obtained from standard stock or they may be fabri-
cated on board ship. When making up a patch of this
type, be sure to reinforce the flange so it will be strong
enough to hold against the pressure of the system. The
main disadvantage of the Jubilee patch is that assorted
sizes must be stocked since each patch is manufac-
tured to fit only one size of pipe.
Temporary repairs to some piping systems also
may be made by using plastic patching materials. The
materials required for plastic patching are furnished
in a special kit.
Emergency Damage Control
Metallic Pipe Repair Kit
Most water and fuel lines can be easily repaired
and service restored to the system in as little time as
30 minutes by using the emergency damage control
metallic pipe repair kit, often called a “plastic patch. ”
2-14
