More than you wanted to know
Army flamethrowers weigh 74 LBS. The backpack portion contains both compressed air and napalm in separate tanks.
The burn time is only a few seconds. They are intended to be used in short bursts. The scenes shown in the movies are clipped together shots of several flamethrowers used in sequence, something like the 23 shot movie revolvers.
Ordinary gasoline is treated with a thickener (M1 Thickener -- I think) and loaded in the tank. The compressed air drives the thickened gasoline (napalm) out of the nozzle. I never saw any with blank cartridge igniters, they are probably obsolete.
Most flamethrowers were converted to CS dispensers during the late sixties and early seventies. They were issued to riot control units.
Problems -- if you use it without the thickening agent it may burn your hand off. It works with plain gasoline but the stuff is nearly explosive and the fire won't go out at the nozzle. There were very few volunteers to carry that d@mn thing in combat. Many are resistant to being burned alive if a booby trap sets off the napalm. It is far too heavy especally in the tropics.
I'd rather shoot the 106RR than carry a flamethrower!