Spool Valve (Pushed In); Spool Valve (Pulled Out); Primary Relief Valve And Priority Spool - Yale A7S1 Service Manual

8000 YRM 2199
Figure 38. Spool Valve Neutral

Spool Valve (Pushed In):

When the valve is pushed in, the middle channel is
closed while the fluid from the inlet port opens the one-
way valve. The fluid flows to the interface B of the
cylinder (item 1, Figure 39), while the fluid from
cylinder interface A (item 2, Figure 39) flows to the
tank through low-pressure channel (item 3, Figure 39).
A return spring returns the valve to NEUTRAL position.
1. FLUID FROM TILT CYLINDER INTERFACE B
2. FLUID TO TILT CYLINDER INTERFACE A
3. RETURNING TO FLUID TANK
Figure 39. Push-in Spool Valve

Spool Valve (Pulled out):

When neutral position is closed, the hydraulic oil from
the inlet port opens the one-way valve and flows to the
cylinder interface A, (item 2, Figure 40) while the oil
from cylinder interface B (item 1, Figure 40) flows to
the tank through low-pressure channel. A return spring
returns the valve to NEUTRAL position.
1. FLUID TO CYLINDER INTERFACE B
2. FLUID FROM TILT CYLINDER INTERFACE A
3. RETURNING TO FLUID TANK
Figure 40. Pull-out Spool Valve

Primary Relief Valve and Priority Spool

Reference Figure 41
The primary relief valve is composed of the two parts,
a main valve and pilot valve. When multi-way valve is
reversed, the high-pressure oils in cavity (P) and
working mechanisms (such as lift cylinder and tilt
cylinder) are connected, the pressurized oil acts on the
pilot valve, through the fixed throttle holes. When
system pressure is larger than the system regulated
pressure, the pilot valve opens, The valve core of the
entire main valve (A) moves rightwards, for the
pressurized oil to be directly connected with low-
pressure channel (G), for cavity for the pressure in
cavity P to lower, in order to ensure the stability of
system pressure. Adjusting screw H on the primary
relief valve will increase or decrease the system
pressure.
The priority spool is in a spool and spring set up. It is
used to divert oil to the Steering Control Unit (SCU)
first and then actuates, to divert oil to provide hydraulic
oil to the hydraulic valve for Mast functions. When the
steering wheel is rotated, the oil cavity (M) is
connected with high-pressure oil circuit. When system
pressure is greater than spring pressure, the valve
Hydraulic System
43