Description
The Triplex Mast has three rails; outer, middle,
and inner. The rails are telescopic and use load
rollers (bearings) and brass set screws to keep
them in alignment. Two single-stage outer (main)
lift cylinders and a center (free-lift) cylinder are
used to raise the carriage and extend the mast
rails. It is called a full free-lift mast because the
carriage can travel to the top of the inner rail
without extending the inner rail.
Load rollers are installed at the top inside of the
outer and middle rails. Load rollers are also
installed at the bottom outside of the middle and
inner rails. The load rollers travel along the
flanges of the rails. The angle of the load rollers
permits them to control the forces from the front,
back, and sides of the mast. The load rollers are
adjustable with shims.
The brass set screws are installed at the top rear
of the outer and middle rails and help keep the
correct clearance between the rails. The brass set
screws at the top of the outer rail are adjustable
and are locked in place by stainless steel set
screws. The brass set screws at the top of the
middle rail are adjustable and are locked in place
by jam nuts.
The two outer (main) lift cylinders are installed at
the back of the outer rail. The base of each lift
cylinder sits in a mount at the bottom of the outer
rail and is secured with a roll pin. The top of each
outer lift cylinder (cylinder rod) is bolted to the top
crossbar of the middle rail. The center (free-lift)
cylinder is mounted in the inner rail and is held in
place with a snap ring and strap. All three lift
cylinders are displacement-type cylinders
equipped with internal hydraulic cushioning (see
Figs. 7.2 and 7.3).
One pair of lift chains is connected to adjustable
anchor bolts near the top of the outer rail. These
chains go over sheaves (pulleys) at the top of the
middle rail and fasten at the bottom of the inner
rail. The free-lift chains are connected to
adjustable anchor bolts at the middle crossbar of
the inner rail. These chains go over sheaves on
the head of the center cylinder and fasten to the
carriage.
The three hydraulic cylinders are connected by
hoses and tubes as shown in Fig. 7.4. To extend
the mast, oil from the main control valve flows to
all cylinders at the same time. The center cylinder
extends first because it lifts the least amount of
weight and has the larger area. The center
E
lectric
C
ounterbalance
H
igh
O
utput
Elevating
3/10/00
7.1
2
1
3
5
6
7
4
1. Outer Rail
2. Middle Rail
3. Inner Rail
4. Outer Lift Cylinder
5. Center Lift Cylinder
6. Free-Lift Chain
7. Carriage
FIGURE 7.1 - TRIPLEX MAST
