Daewoo D20-2, Specifications Systems Operation Testing & Adjusting Disassembly & Assembly

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Flow Control And Relief Valve
Earlier design valves were equipped with simple relief
valves in the inlet sections.
The partial flow by-pass system in the LT valve
makes use of a compound type flow control and relief
valve arrangement.
Sensing the pressure drop across an orifice at the
entrance to the by-pass, the valve acting as a control
to limit flow through the by-pass to approximately
seven gallons per minute. The balance of the pump
delivery is diverted through the reservoir passage.
This arrangement greatly reduces pressure drop
through the valve in the neutral position.
When a spool is shifted to operate a portion of a
machine, the flow control is inoperative and full pump
volume is available to the system. The control valve
then functions as an overload relief valve. System
pressure is limited to a prescribed maximum by the
action of this valve. Inlet body type F is not equipped
with a relief valve. Full pump volume is available to
the system at all times.
Use of the optional secondary relief valve allows the
use of lower pressure for tilt and accessory function
while higher pressure is provided for the lift function.
NOTE : The secondary relief valve must be set at a
lower relief setting than the system relief.
Flow Control
(1) Control Valve Sensing Orifice.
(2) Flow Control And Relief Valve.
(3) Tank Passage.
(4) By-pass Flow Control Orifice.
(5) Cylinder Ports. (6) Pressure Passage.
(7) By-pass Passage.
Figure IDCS007B shows the valve operation in
neutral with flow in excess of seven USgpm. Flow
across the by-pass orifice result in a pressure drop.
Decreased pressure is sensed at the spring end of
the valve sub-assembly through a sensing orifice.
The slightly higher pressure at the other end of the
valve permits it to shift down, diverting excess flow to
the reservoir passage. With flow at less than seven
USgpm there would be negligible pressure drop
across the by-pass orifice. Then the control valve
would be held closed by the large spring and all flow
would be through the by-pass passage.
Optional flow control valves are available for all
operating sections. These valves can be set from
1 - 15 US gpm.
20 of 29 New Hydraulic Systems Systems Operation
IDCS007B