TM 5-3805-281-24-1
Theory of Operation
ARM ROD END AND BOOM REDUCED
LEAKAGE VALVES OPERATION
The function of a reduced leakage valve to reduce
cylinder drift by reducing leakage from the cylinder back
through the control valve.
Reduced leakage valves (H and J) are used in the arm
rod end and boom head end circuits. The design and
operation of the arm rod end and boom reduced leakage
valve are the same. Arm rod end reduced leakage valve
is shown. The boom reduced reduce leakage valve has a
boom manual lower needle valve mounted between the
leakage valve and pilot cap. (See Boom Manual Lower
Needle Valve Operation in this group.)
In neutral, the pressure generated in the circuit to arm
cylinder rod end (F) or boom cylinder head end by the
load on the cylinder is applied to the check valve spring
chamber (G) through the pilot valve (A). The check valve
poppet (E) is held closed against the seat in housing.
Actuating the pilot controller for arm-in or boom down
function also sends the pilot pressure signal (C) to shift
the pilot valve (A). The pressure applied to the check
valve spring chamber is released to hydraulic oil tank (B)
through the pilot valve. The return oil flow from the pilot
9025
valve is through the warm-up and air bleed circuit in the
05
pilot cap to the hydraulic oil tank. The return pressure
62
from the cylinder pushes the poppet off its seat opening
the passage for oil to flow to return. The poppet is pushed
off its seat because the OD of the upper land at the head
end of poppet is slightly larger than the lower land.
For arm out or boom up function, the pressure oil from the
arm valve (D) or boom valve increases until it overcomes
the pressure in the circuit to arm cylinder rod end (F) or
boom cylinder head end opening the check valve poppet
(E) so pressure oil flows to the cylinder.
Continued on next page
CED,TX08227,3165
1902JUN981/2