Gradall 534B (9103-1390) Service Manual - Manual (Page 56)

CROWD (Boom In-Out) CIRCUIT
The crowd circuit allows the operator to extend and
retract the boom sections a total of 18 feet. Nine foot
extension is obtained from the movement of a.
hydraulic cylinder joined to the first section and the
second section. Movement of the 2nd section and a
combination of cables and sheaves moves the 3rd
section.
The control lever is the same as used to raise and
lower the boom, but for the crowd the operator
moves it to the right and left. Moving it to the right
extends the booms and moving it to the left retracts
the booms.
Oil from the 3rd valve section routes the oil to the
base of the crowd cylinder. A counterbalance valve
is used on the cylinder for protection and speed
control.
When the control lever for the crowd action is
activated, the 2nd and 3rd boom sections move in
and out equally.
Power to move the booms in and out come from a
hydraulic cylinder which is located under the main
1st boom section. It moves the 2nd boom section. As
the 2nd boom section moves in or out, a
combination of a push assembly and sheaves and
cables move the 3rd boom section. The push beam
assembly is fastened to the 2nd boom section at the
rear sheave pin and moves with it.
B O O M C R O W D ( I N - O U T ) M O V E M E N T
Two cables are used. The top one is bolted to the
rear of the main boom and runs forward around the
push beam front sheave and back to the anchor
point at the bottom rear of the 3rd boom section.
The lower cable is anchored near the front bottom
of the main boom and passes back around the rear
sheave and is anchored at point (H) of the 3rd boom
section. As the 2nd boom section moves out, forcing
the push beam and sheaves with it the, the top cable has
to move forward at point (H) taking the 3rd boom
section with it.
When retracting the booms, the 2nd section moves
in, forcing the lower cable to pull at point (H) and
the 3rd boom section moves in.
15
THREE SECTION BOOM (RECTRACTED)
THREE SECTION BOOM (PARTIALLY EXTENDED)