HELI CPD15, Operation & Service Manual

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(2) Motion of safety relief valve
The relief valve is mounted between “HP” nozzle of oil pump and “LP” passage. Oil
passing through lifting valve C acts on different areas of diameters “A” and “B”, thus, “K”
of check valve and “D” of overflow lift valve are on the valve seat as shown in Fig. 5-7.
When the pressure regulated in “HP” passage of oil pump acts on the spring of pilot valve,
the check valve “E” will open. The oil flows into “LP” side through holes around the
valve as shown in Fig. 5-8.
Fig. 5-7 Fig. 5-8
Once the pilot valve “E” opens, the pressure inside valve “C ” will drop, valve “E”
and valve “C” are on the valve seat. The liquid flowing to the rear of the valve “D” will
be closed, so the pressure inside will be decreased. (See Fig. 5-9)
The “HP” passage pressure and inside pressure of oil pump are not even, the valve
“D” opens with the action of pressure difference and oil directly flows into the low
pressure circuit
“
LP
”
. (Refer to Fig. 5-10).
Fig. 5-9 Fig. 5-10