Emergency Lub systems I think generally had a certain design ethos. The the Super Puma L1 had two pumps the normal pump with a shorter intake and higher pressure than the emergency pump; each pump had its own pressure gauge. Failure of the main pump or oil loss below the pump inlet produced a MGB COOL warning and pressure drop. The emergency pump set at a lower pressure then took over. The MGB P red warning was held off as long as the emergency pump pressure at the pressure switch remained above 1 bar. The only down side was that the ELP pressure was below the filter bypass valve setting. Good pressure on the ELP indicator, COOL light ON normal pressure gauge zero but RED MGB P out, system working as advertised.
The 61 ELS, oil supply to the Emergency pump at the bottom of the gearbox, main pump inlet a distance from the bottom of the sump. Oil leak exposed the pump inlet, RED MGB P warning light ON nil or extremely low pressure on the gauge, this switched the ELP on and delivered oil to the high speed inlet bearings (white metal) through a separate delivery system. Confirmation of operation GREEN run light ON, gauge pressure and RED MGBP. Or the pilot could select the ELS ON from a control switch. Duff Torque indications when on ELS. Least that’s how I remember it worked.
Outhouse.