Spearhead TWIGA
120
27
27
27
27
Non Return Valve
The non return valve prevents the feedback of oil from the service ports. It is unlikely to
need attention but if removed for cleaning a new ‘O’ Ring should be used when refitting.
Replacing Spool 'O' Rings
Note: Owing to the sharp edges in the design of the spool failure to carry out the following
procedure could result in damage to the 'O' rings resulting in external leakage.
• Disconnect cable assembly.
• Remove the cover at the opposite end of the spool and unscrew the return spring or
detent assembly whichever is necessary.
• Pull the spool through the block from the handle end until the 'O' ring marked 'A' is
accessible - remove the 'O' ring from its groove using a smooth edged hook.
• Completely remove the spool from the block out of the return spring end.
• Remove the ‘O' ring marked 'B' and refit the new 'O' ring.
• Lightly oil the spool and replace it in the block from the return spring end pushing it
through far enough to clear the 'O' ring groove 'A’.
• Fit new 'O' ring in groove ‘A’.
• Push the spool back through from the handle end far enough to re-assemble the return
spring or detent assembly plus the cover.
• Attach cable assembly.
Main Relief Valve
The main relief valve is pressure set at the factory to 1450 PSI (100Bar) and is non
adjustable. A sticking relief valve will probably cause overheating and/or loss of power. If
this is suspected it should be dismantled and examined for dirt and damage. Undo the
large hexagon housing, the relief valve spring, needle and seat can now be withdrawn. If
difficulty is experienced in extracting the seat remove the non-return valve at the opposite
end of the gallery and drive out with a soft brass drift - take care not to damage the copper
sealing washer positioned between the seat and the locating shoulder in the block.
Blow out the valve with compressed air and examine the components for damage. These
components are especially hardened steel and should only display a seating witness – any
further damage will require the complete valve to be replaced.
CAUTION: Under no circumstances be tempted to add shims into this valve in a
misguided attempt to increase the power of the machine. This could damage the
tractor and may cause personal injury.
