Corsair I to IV, guess be the same.
Undercarriage emergency operation
(i) If the undercarriage fails to lower, see that handpump check valve is set to FLIGHT. Set undercarriage control lever to DOWN and operate handpump. About 70 strokes will be required to open the doors during which no resistance will be felt. It then requires another 100 strokes to extend the main undercarriage gear during which time pressure will be felt. This operation takes 3 to 5 minutes.
(ii) If it is clear that the undercarriage will not lower due to complete failure of the hydraulic system, it may be lowered by operation of a CO2 system, and the tailwheel by a spring system.
(a) Close throttle and reduce speed to 110 knots.
(b) Move undercarriage control to DOWN.
(c) Pull emergency undercarriage release handle (left hand side of cockpit). This relieves hydraulic pressure on the down side of the jacks and also operates the CO2 valve.
Note,-On aircraft No. JT.270 and subsequent, the emergency undercarriage release handle is deleted and the CO2 bottle valve (aft bottle) must be opened.
(d) Reduce speed to about 90 knots I,A.S, (Take great care not to stall whilst undercarriage is extending.)
(e) Check indicators to see that undercarriage and tailwheel are down.
Note.-The introduction of CO2 into the hydraulic system precludes the subsequent use of hydraulic power. lf hydraulic pressure is shown on the gauge and the undercarriage will not lower by engine pump or handpump it would indicate mechanical damage, ln this case the CO, system should not be used and a belly landing should be made as it will not be possible to raise the undercarriage again if it does not lock down.