The document discusses control valves used in hydraulic excavators. It describes the components of the control valve including jet sensors that detect oil flow, relief valves, and valves for straight travel, arm throttle, and swing priority. The jet sensors measure pressure differences to detect when levers are operated. The relief valve maintains maximum work pressure. The straight travel, arm throttle, and swing priority valves control oil flow to prevent deviation during different machine operations.

1. E-OLSSSection 3.3
E-OLSS: Control Valve.E-OLSS: Control Valve.
Section 3.3Section 3.3

2. E-OLSSSection 3.3
E-OLSS Control Valve
Control Valve.
The valve is a Open centre Load
Sensing System with the jet sensors
installed into the control valve.
Jet Sensors detect the flow of return
oil passing through the control valve
and returning to tank. The two
pressures Pt and Pd are sent to the
NC valve.
The main relief valve maintains
maximum work pressure.
Built into the control valves are the
straight travel, arm throttle and swing
priority valves.
Two Stage
relief

3. E-OLSSSection 3.3
E-OLSS Control Valve
Jet Sensors: Levers in Neutral
Oil carry over from the control valve flow through the jet sensors.
When levers are in the neutral position there is a small flow from the pump returning to
tank.
The jet stream coming out of the Jet Sensor Orifice is uninterrupted filling Pt sense line
back to NC valve.
Jet Sensor Out-put
Pressure Pt Jet Sensor Out-put
Pressure Pd
Orifice
Jet Stream

4. E-OLSSSection 3.3
E-OLSS Control Valve
Jet Sensors: Levers Operated.
As the machine starts to operate the oil flow in the control valve increases.
When the differential pressure
Pt – Pd reaches 15 Kg/cm2 (at 40 l/min) the relief valve opens.
Now almost all the carry over oil (Qc) is being discharged through the relief valve.
A small amount is passing through Jet Sensor Orifice.
Pump
pressure Qc
Pt
Pd
Pt (Jet Sensor
output pressure)
Pd (Back pressure)

5. E-OLSSSection 3.3
E-OLSS Control Valve
Straight Travel Valve (PC1250-7).
The straight travel valve is installed into
the control valve.
It acts to prevent and deviation in the
direction of travel if the boom, arm, or
bucket are operated when the machine is
traveling.

6. E-OLSSSection 3.3
E-OLSS Control Valve
Travel operating Independently
The straight travel solenoid is de-
energised, so no pilot pressure is
flowing to the spool.
Ports P1 and P2 are not connected each
circuit remains independent.

7. E-OLSSSection 3.3
E-OLSS Control Valve
When travel and work
equipment are operated
together.
The straight travel solenoid is
excited and pilot pressure is flowing
to spool (6), pushing it across to the
left.
Ports P1 and P2 are now
interconnected so the same amount
of oil is delivered to both travel
motors evenly.
This prevents travel deviation.

8. E-OLSSSection 3.3
E-OLSS Control Valve
Control Valve (PC200-5)
Built into the control valve are:
1. Straight Travel valve.
2. Arm Throttle valve.
3. Swing Priority valve.
The control valve is manufactured in
two halves, they are bolted together
sharing common galleries.
Straight
Travel
Swing
Priority

9. E-OLSSSection 3.3
E-OLSS Control Valve
Arm Throttle Valve.
When the arm control lever and boom control lever are operated at the same time,
most of the pressure oil flows t the arm circuit, where the load is less.
When this happens the arm throttle valve is switched and the flow of oil to the arm
control valve is restricted.
Arm Operated Independently Arm and Boom

10. E-OLSSSection 3.3
E-OLSS Control Valve
Swing Priority Valve.
When operating swing and arm at the same time, most of the oil flows to the arm which
has less load. The flow to the swing circuit is reduced so arm speed is fast.
To prevent this the swing priority valve is switched to restrict the flow of pressure oil
to the arm control valve.
When Swing is not operated
with Arm circuit.
When Swing is operated
with Arm Circuit.

11. E-OLSSSection 3.3
E-OLSS Control Valve
Text

12. E-OLSSSection 3.3
E-OLSS
End ofEnd of
E - OLSSE - OLSS