HYDRAULICS – CX130/CX160
5 - 26
CX EXCAVATORS
ATTACHMENT
Boom Lower
1) When a built-in anti-drift valve in the control valve is opened and boom1 spool is shifted,
the boom can be lowered.
2) A regeneration circuit inside the control spool and valve provides additional speed.
3) Only one pump flow is used.
Oil flow from pump1 (front pump) enters the PR port of the control valve. When the boom
hand control is operated for boom down pilot pressure is directed through the cushion valve
to the boom1 control spool of the main control valve. Pilot pressure is also sent to the boom
down anti-drift valve. When the anti-drift valve and boom1 control spool is shifted boom down
is achieved.
Cylinder return oil must over come a spring applied check valve to get to the return circuit.
This creates backpressure in the cylinder circuit. When the supply pressure drops this return
pressure oil is routed through a check valve to the cylinder supply circuit to prevent cavitation
and maintain boom down speed. When the boom is raised the spring chamber of the anti-
drift valve is ”charged” with boom up pressure. This is done through an orifice in the anti-drift
valve. With equal pressure on both sides of the valve the spring is able to hold the valve
closed. This keeps boom drift through the control spool at a minimum. When the boom
control spool is shifted for lowering pilot pressure is sent through the control spool to the anti-
drift check valve. This opens the check valve an allows the “charged” oil in the spring
chamber to exit to the return circuit, which allow the anti-drift valve to open and boom
lowering is activated.
Whenever the boom is lowered part of the pump supply is allowed to bleed off through the
open center circuit through an orifice. This is to turn the pump “on” more slowly. This is to
prevent the pressure spike that occurs when the boom starts to lower. A part of the cylinder
return oil can enter the center bypass by way of an orifice and check valve inside the control
spool. This makes up for the shortage of pressure without the pumps full operation in order to
maintain neutral de-stroke pressure at a certain level.
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