Wednesday, 3 December 2014

Repairing a Kerosene Blow Torch

This kerosene or paraffin blowtorch belonging to my grandfather hadn't been used for years, simply because a  propane/butane torch is much more convenient. A kerosene torch however is a lot more economical to run, and a litre of kerosene would probably provide well over an hour of run time for less than a "dollar". For those of you who have never come across this "ancient technology", a kerosene blow torch or blow lamp has a hand operated pump (like a bicycle pump) to pressurise the fuel in the tank.  This forces fuel up out of the tank through a brass tube and coil surrounding the burner. On its way through the coil, it is heated by the flame and vaporised to gas which emerges from the jet and is burned. On initial startup you have to burn some methylated spirits in a bowl section at the top of the tank. This preheats the oil in the coils and turns it into vapour so that pumping can start. A screw valve is used to release pressure in the tank and extinguish the torch. These torches can be somewhat dangerous if you are not careful! If you pump prematurely before the heat exchanger coil is sufficiently heated up, the torch becomes a flame thrower, so it is better to start them up outside. In the US, gasoline (petrol) torches were available which didn't require pre-heating, but were potentially more dangerous because of the volatile nature of petrol. Several oil appliances used this system including Tilley lamps for lighting and Primus stoves for heating. The kerosene vapour burned more thoroughly with a cleaner hotter flame than that produced by a wick system used in earlier kerosene appliances (which could be smoky if not trimmed properly).

If the nut holding the main pipe leaks oil, the nut may be loose or possibly the ring on the pipe and seat on the threaded section which it tightens against may not be mating properly. It's worth trying to clean the surfaces with a plastic scouring pad or rough cloth to see if that improves the situation. Abrasives should probably be avoided to avoid damaging the surfaces. Possibly Evo-Stik  Plumbers Mait or similar would help to seal the threads.
The leather washer on the pump had dried and worn out so it needed a replacement. Finding parts for a blow torch such as this was out of the question so I decided to make one.  I tend to be a hoarder and lots of stuff gets sorted and stored which should be thrown out! However the parts do become useful when something needs to be repaired, and it saves money. Leather is a very tough, durable material and can be used for making washers and gaskets. It's not totally waterproof (think of how water soaks through your shoes) but does stand up to high temperatures and doesn't melt. I used a piece of leather from a shoe to make a part for the pump. It needed to be reasonably thick so that it bulged out during the downward pump stroke and relaxed during the upward stroke.


  1. The blog is absolutely fantastic. Lots of great information and inspiration about repairing a kerosene blow torch.

  2. Does your blowtorch have any sort of seal up under the bolt holding the main pipe up to the head. I have been refurbishing one the same as this and it seems to leak kerosene up from around the pipe and nut into the method tray.

  3. Hi, sorry for not replying but comment notifications seem to be going to an old unmonitored email address.
    I've never removed the nut so I don't know what the arrangement looks like, but will take a look today. How was the bolts fitted into the tank of the blow torch during manufacture? Was this done before the base was attached? You could probably use a fibre washer or plumbers hemp for sealing.

  4. Just removed the main pipe from the tank (see new photos above). As you can see there is no separate seal. The fuel pipe has a ring which tightens against a seat on the threaded section of the tank and this seals everything. You could try cleaning the seat and ring with a plastic scouring pad or rough cloth or whatever to remove any deposits which could be preventing sealing. The ring is copper and the seat brass, so using abrasive could cause damage. Maybe toothpaste or sink cleaner would work which is mildly abrasive.