The relief valve consists of main valve A and proceeding valve B. When the
spool of the control valve is operated, chamber C linked with the operating cylinder is
filled with high pressure oil. The high pressure oil affects proceeding valve B through
throttle hole D and E. If the system pressure is higher than the setting pressure, the
proceeding valve B will be opened to make the pressure in F chamber lower and thus
causes the main valve A to move right, then the oil in chamber C may directly flow to
low-pressure passage G and reduce chamber C pressure. In this way, the system
pressure may keep unvaried. The setting pressure may be adjusted by adjusting the
screw H.
The construction of the flow divider is quite simple. It is of direct overflow type,
and ensures the constant pressure of the power steering system by balancing the oil
pressure with fixed spring force. When turning, chamber M gets through with the high
pressure passage. If the oil pressure is higher than the spring force, the poppet N
moves right, causing the high pressure oil to flow directly to the low-pressure passage
via. Chamber T and keeping the pressure of the power steering system unvaried The
setting pressure is adjusted by adjusting the screw K.
Poppet L is a balance type spool valve and may move right of left according to
the variety of the oil flow and pressure passing through it to change the opening of
chamber R and S and ensures the oil flow to working chamber Q and to power
steering port PS keeps in balance condition and is smoothly divided in certain
proportion.
All of a. b. and c. are fixed throttle holes.
9.3.3 Action of tilt-lock valve
Tilt spool valve housing contains a tilt lock valve. The tilt lock valve is intended
to prevent vibrations of the mast resulting from the negative pressure I the tilt cylinder
and also to avoid danger incurred from mishandling of the spool. On the conventional
model, even if the engine is not running, the mast can be tilted forward by actuating
the tilt lever. But this newly adopted tilt-lock valve does not allow the mast to tilt
-74-
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