Shockless Valve Of Boom Cylinder Pilot Line - Function - Kubota KX080-3 Workshop Manual

WSM KX080-3 Mechanism
(2) Function
(Let s discuss the ports A and 1 here. The same is true of the ports B and 2.)
Port A to Port 1: Flow control
The pressure oil out of port A flows this way: through the hole (b) of plunger (1), orifice (8), the lateral
hole (a) of plunger (1) and into the port 1.
The resistance in passing through the orifice (8) makes the pressure of chamber (i) higher than that of
chamber (ii).
This pressure difference moves the plunger (1) downward.
When the plunger (1) has reached down, the hole (a) gets closed and the pressure of chamber (ii) rises.
When the pressure of chamber (i) and that of chamber (ii) become the same level, the plunger (1) is
brought back to the neutral position by the spring force (3).
These steps are repeated. Finally the plunger (1) reaches the position at which the force of spring (3)
and the passing resistance of orifice (8) get balanced each other. This is expressed in the following
equation. (The more flow through orifice (8), the higher the resistance at the orifice. The hole (a) gets
then closed.)
FS = FA x FB (FA = P1 x a
Where, FS: Force of spring (3)
FA: Downward force upon plunger (1)
FB: Upward force upon plunger (1)
P1: Pressure in chamber (i)
P2: Pressure in chamber (ii)
a, b: Pressure receiving area on plunger (1) (a = b)
Accordingly, the flow of pressure oil through the orifice (8) is
kept at a level that is required to produce the passing resis-
tance proportional to the force of spring (3). This takes place
regardless of the pressure at port A. In this way, the flow rate
from port A to port 1 can be controlled at a constant level.
A: Boom C/V section pilot chamber
1: Boom down pilot line to return
See Fig. 2.
P2 x b = FB)
IV-M-110
IV Hydraulic System
(i)
(b)
(a)
(ii)
Fig. 2.