the SL for side lit or workmans lamp was used alongside the relighters. workman were not allowed to relight underground.they started phasing them out in the late 70's.
the SL was lit by a low voltage electric current in the lamp room.
the principle of the davy gauze is that the flame will burn inside the gauze but the size of the mild steel gauze ie; 28swg wire with 28 holes per inch sufficiently dissipates the heat so as not to ignite methane or firedamp outside the gauze. so when methane is present it burns in a flame on top of the lamp flame and the height gives the percentage of methane present and thus warns of an explosive atmosphere.
re lighting underground if you relight a lamp in an explosive atmosphere it will detonate and cause an explosion.
re the fuel tank or vessel, the felts inside are designed to soak up the fuel. the filling technique is to fill to the top leave 5 minutes then stand the vessel upside down to drain off the excess fuel. whats left will be sufficient to last 8-12 hours ie a normal shift.
most older pit lamps leak ad it is very difficult to reseal. but if you follow the above you should be ok.
Thank you VERY much for the quick and thorough answer David. I really appreciate it!
Mine is the one with the platinum wire lighter - were those in use before or after the flint ones?
Also - I was wondering a bit about what actually made the lamps safe in gas - is it because the gauzes makes for an increae of nitrogen making the mixture of gases inside the lamp less flameable?
I have failed to find a really good explanation for how the lamp actually works among all info on the net.
One last thing about my lamp; There seems to be a small leak in the bottom soldering on the tank - Do you think I could blow-torch it to seal it again? Or should I use some chemical seal ? I wouldn?t want to burn the felt inside...
Thanks again for the answer!