Kubota KX080-4 Workshop Manual page 124

KX080-4, WSM
(Continued)
[When AI signal pressure rises (idling signal)]
• It switches the main spool of each section to either the A or the B port side and cuts off the passage that connects
the PP1 port micro-orifice downstream and the tank circuit.
• This raises the PAI port pressure to the PP1 port pressure (that is, the pilot pump pressure).
• If the switched section above is the arm, bucket S/P1, boom or swing, the passage connecting the downstream
side of the PP3 port micro-orifice and the tank circuit is cut off at the same time.
• This raises the PF1 port pressure, along with the PF2 port, which is connected by external lines, to the PP3 port
pressure (in other words, the pilot pump pressure).
• Raising the PF2 port pressure pressurizes the pressure receiving chamber on the left side of the communication
valve spool, and the pressure acts on the pressure receiving area A1, generating switching force toward the right;
the communication valve spool does not move as it is configured with spring force so it switches when pressure
receiving areas A1 and A are pressurized at the same time.
(communication valve spring pressure setting=pressure receiving area A1 switch force + pressure receiving area
A2 switching force)
[During independent travel operation]
• It switches the main spool of the travel section to either the A or the B port side and cuts off the passage that
connects the PP2 port micro-orifice downstream and the tank circuit.
• This results in the pressure on the spring chamber, which is on the right side of the independent travel valve spool
connected to the downstream of the PP2 micro-orifice, being equal to the PT port pressure, which rises to the
PP2 port pressure (in other words, the pilot pump pressure).
• When the PT port pressure rises, it shifts the independent travel valve spool and P1 and P2 pump pressure is
supplied to the travel sections.
• Further, raising the PT port pressure pressurizes the pressure receiving chamber on the left side of the
communication valve spool, and the pressure acts on the pressure receiving area A2, generating switching force
toward the right; however, the communication valve spool does not move as it is configured with spring force that
makes it switch when pressure receiving areas A1 and A2 are pressurized at the same time.
(communication valve spring pressure setting=pressure receiving area A1 switch force + pressure receiving area
A switching force)
[During travel + front operation]
• When the travel section is switched, as mentioned above, the actuation of the independent travel valve supplies
P1, P2 pump pressure independently to the section. (P1, P2 pump supply is cut off from the closed center section)
• In this situation, if one of the closed center sections (arm, bucket, S/P1, boom, swing) is switched, it pressurizes
the PT port and PF2 port simultaneously.
• When pressure at the PT port and PF2 ports rises at the same time, the pressure receiving chamber on the left
side of the communication valve spool is pressurized, exerting pressure on the receiving areas A1 and A2.
• As the communication valve spool is configured with spring pressure so it switches when receiving areas A1 and
A2 are pressurized at the same time, the communication valve spool shifts to the right.
(communication valve spring pressure setting=pressure receiving area A1 switch force + pressure receiving area
A2 switching force)
• Once the communication valve spool shifts, the passage that connects to the tank circuit via the communication
valve spool is cut off, and the P3 pump pressure presses up on the check valve, communicating with the pump
pressure passage of the closed center section. (operates the communication valve)
• Thus the travel section operates independently via P1 and P2 pumps and the closed center section operates
using pump P3 pressure.
3-M28
HYDRAULIC SYSTEM
RY9212158HYM0024US0
KiSC issued 08, 2015 A