Oldiron refers to filling level.
The genuine Tilley Lamp has a safe maximum, by design – the lip of the filler bush when the lamp is standing vertically on a level surface. I imagine other makes of paraffin-lamp are similarly provided for.
It must NEVER be filled beyond that, possible anyway only by wrongly tilting the lamp backwards!
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If you use a funnel to aid filling, I suggest if you've not already done so, fitting it with a bent or flexible spout extension, and a wire loop that hooks over the cowl. The loop holds the funnel vertically and give you both hands free for the pouring.
I serviced a Vapalux, a paraffin pressure-lamp like the Tilley brand but used in a markedly different way, and that too gives a yellowish light with a new mantle.
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Pulsing or poor running? They should not pulse but it can indicate low pressure. There are a number of seals etc. that can wear, as listed above, and also the pump's plunger and its delivery-valve.
Spares for wick and pressure lamps? I used Base Camp, (Base-camp.co.uk), with excellent service. They even had the proper instructions for my Vapalux.
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How do I know about these lamps, including that safety warning about filling them?
As a Craven Pothole Club member helping operate the annual (pandemics permitting) event called the Gaping Gill Winch Meet – giving non-cavers a chance to see the huge Gaping GIll Main Shaft and Main Chamber.*
We used to use Tilley Lamps underground, to help in guiding tourists and marking their rendezvous points – and would sometimes heat pebbles on the lamp cowls, to use as hand-warmers!
Nowadays the underground lighting is all-electric, both battery hand-lamps and building-site types supplied from a gas-fuelled 110V generator on the surface; but we still like the warm glow of pressure-lamps in the members' communal tent in the evenings.
*(Ours is In August, and there is a similar event in May, run separately, by the Bradford Pothole Club. Both are currently advertised on the respective web-sites as planned. Obviously though no public events, including of course model-engineering exhibitions, traction-engine rallies and even the Great Dorset Steam Fair, can be guaranteed for 2021 in the present situation. We live in hope….)