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ASSEMBLY
SX15 01/09 Assembly Section 3-8
© 2009 Alamo Group Inc.
ASSEMBLY
HYDRAULIC THREE-SPOOL VALVE ACCESSORY (EXTRA EQUIPMENT)
An open or closed center 3-spool valve is available as extra equipment . (FIGURE Asm-R-0180)
1. If a hydraulic three-spool valve is used the valve must be matched to the tractors hydraulic system (open
center or closed center) and must have two spools which have detent position which allows the wing
cylinders to float. When installing the control valve into the tractor’s hydraulic system, consult the
operators manual of the tractor to determine the type of hydraulic system used. Definitions of closed and
open center system follows:
Open Center Hydraulic System - This system pumps oil through the circuit continually. When a resistance to
flow is created in the line or valve, the pressure builds up until, at a certain point, the relief valve opens to pass
the oil back to the tank. This is a constant flow, variable pressure system with a relief valve required.
Closed Center System - This system holds a constant pressure in the line, and when an obstruction to flow
occurs, the pump stops pumping. No relief valve is required or provided. This is a variable volume, fixed
pressure system.
IMPORTANT: If a closed center valve is installed in an open center system, there is no relief valve provided.
When the oil flow is blocked and there is no relief valve, the pump either stops, breaks, a hose is blown or the
engine stalls. Hose failure or a pump shaft failure is most common.
If an open center valve containing a relief valve is installed in a closed center system, the pump cut off
pressure, over 2200 psi, will exceed that of the relief valve and pump oil continually over the relief valve. This
will create a continuous load against the motor with all of this energy going to heat. This in turn, will heat up the
hydraulic system, which is usually the transmission and could result in damage to entire transmission of the
tractor.
NOTE: If there is any doubt as to which type system your tractor has, check with your local tractor dealer. If
there is any doubt as to what type valve bank you have, remove large hex plug from outlet side of valve. If plug
is long as pictured in valve it is a closed center. A closed centered valve will utilize a plug with an extension
past the threads. Which provides a blockage to the return flow, thus allows for closed center function. The
valve can be converted to an open center valve by removing the extension with a saw.
IMPORTANT: Do not connect return line from valve bank into remote outlet unless recommended by your
tractor manufacturer. Damage to valve can result if remote outlet control lever is actuated to pressurize return
line. Always connect return line directly into tractor system reservoir.