Function

This is a cutaway view of an Express blow lamp manufactured by Léon Guilbert et Fils in France.

The design of the blow lamp varies depending on the fuel used and there are also several different methods of adjusting the fuel pressure and the flame. Furthermore, many blow lamps were made for a specific task and consequently the design would be adapted to this.

We will start by having a look in general how the blow lamp works. Further on we will also take a look at different designs.

Warning!
Never attempt to start a blow lamp unless you are absolute sure of its condition and how to operate it.
Always refer to the operating instructions issued by the manufacturer.

Lets start by having a look at the various parts of the blow lamp. The cutaway view below shows the different parts of a Sievert #251 but other makes and designs are very similar.

1. Nozzle and flame chamber. Over the nozzle and flame chamber there is also a windshield placed (on models for out-door use). 2. Piping for pre-heating of the fuel. Cup for pre-heating fuel is located under the nozzle and piping. 3. Adjusting knob. 4. Filler cap (with built-in safety valve). 5. Filler neck (to prevent overfilling). 6. Pump which also acts as handle. 7. Non-return valve. 8. Fuel tank. 9. Wind shield.

General function description

• Unscrew the filler cap (4) and fill the fuel tank (8) to 3/4 with the fuel that the blow lamp has been designed for. This will allow for a cushion of air above the fuel as well as for the fuel to expand when it gets warm.

• Close the nozzle (1) by turning the adjusting knob (3) clockwise.

• Pump up a slight overpressure with a few strokes of the air pump (6). This will allow the fuel to rise up in the piping (2) for pre-heating, which allows it to vaporise easier. A non-return valve (7) at the bottom of the pump prevents the fuel from leaking out via the pump seal.

• Fill the pre-heating cup under the nozzle and flame chamber up to the rim with alcohol. This will ensure that enough heat is generated to start the blow lamp. Use a special filler container designed for this purpose to avoid spillage. Ignite the pre-heating alcohol it with a match. Some blow lamps for kerosene of later design are equipped with a so-called quick start. This is a device that allows the blow lamp to be pre-heated with its own fuel with the aid of a vaporising nozzle fitted on the tank. The US blow lamps for gasoline are normally pre-heated with gasoline.

• When the pre-heating alcohol has almost burnt out the adjusting valve is opened slowly to allow the fuel to vaporise in the nozzle and be ignited by the flames from the burning pre-heating alcohol. A match can also be used to ignite the vaporised fuel in case the alcohol flames have gone out.

• When the blow lamp is running, the torch flame does the pre-heating of the fuel by itself.

• The flame is now adjusted with the aid of the pump (pressure) and the adjusting knob (volume) to suit the application.

• Closing the adjusting knob turns off the blow lamp. This should remain closed until the blow lamp is used next time. If the blow lamp is not going to be used for some time, it is advisable also to open the filler cap to release the pressure. This will reduce the risk of fuel leakage while stored.

Different design principles

Below you will find some basic designs of blow lamps. Most blow lamps will fall under one of these categories but when you browse through this site don't be surprised to find other designs.

1. With adjusting knob and with pump

Sievert, Sweden (cut-away view).

This is the most common type and it works as described above. Can be designed for gasoline or kerosene. The blow lamp in the picture is designed for gasoline and has an external coil for pre-heating of the fuel. It has also has an external sleeve that slides outside the burner so that the combustion air can be adjusted.

Another interesting feature is the safety pin. It is connected to the bottom of the container and its tapered top goes through to top of the container. In case the pressure should increase beyond the safety limits, the concave bottom of the container will be pushed out. This will pull the safety pin down and let out the pressure to prevent the blow lamp from exploding. On later designs, a spring-loaded safety valve was normally built in to the filler cap.

2. With adjusting knob but without pump

Sievert, Sweden (cut-away view).

This design was used for the small, early gasoline blow lamps. The cup for the pre-heating fuel is placed on top of the fuel tank, under the burner. The burning pre-heating fuel increases the temperature and thereby also the pressure in the fuel container. This forces the fuel out through the nozzle when the adjusting knob is opened.

A wick in the pick-up pipe also helps to draw fuel up to the nozzle. When the blow lamp is burning, the heat is transferred to the container to maintain the pressure. The adjusting knob controls the flame.

On this particular model, the filler cap is placed in the bottom of the fuel tank.

3. Without adjusting knob but with pump

Bladon, England.

This is a common design on smaller blow lamps (normally 1 litre or less) intended for kerosene. At the filler neck there is normally a ventilation screw that should remain open to prevent pressure build-up during the pre-heating. The indentation in the top of the container is for the pre-heating fuel.

Closing the ventilation screw and pumping a few strokes will start the blow lamp. To turn off the blow lamp, the ventilation screw is opened to release the pressure.

The blow lamp in the picture has the pump mounted on the outside of the tank which is quite unusual for this type. Normally the pump is fitted inside the fuel tank or in the handle.

4. Without both adjusting knob and pump

Scoville, England.	Lenk, USA.

This design is only used for small blow lamps intended for alcohol or gasoline as fuel. Very little or no pre-heating is necessary to start the blow lamp. This particular model is designed for pre-heating by holding a burning match just below the burner.

There is a wick inside that helps to draw up fuel to the burner. When the blow lamp is burning, heat is transferred to the tank and creates an over-pressure.

No adjustments of the flame can be done and to extinguish the blow lamp you simply put a cap over the tip of the burner.

Another type of blow lamp (the one to the right) heats up alcohol that evaporates and is ignited over a burning wick.

5. Blow pipes

Lenk, USA.

The blow pipes are the predecessors of the blow lamps and operate by a different principle than those above. However, they are quite often referred to as blow lamps.

A wick in the fuel tank draws up fuel and burns with a normal flame after being ignited by a match. A fine stream of air is then blown across the burning wick, which creates an intensive flame with high temperature.

The flame can to some extent be controlled depending on how hard you blow. To extinguish the blow lamp you simply put a cap over the wick.

On this particular model, air is blown by the mouth of the operator into a hose that is connected to the pipe fitted outside the fuel tank. However, there are also other ways of creating the airflow, for instance by different pump designs.

Blow lamp fuel

Always make sure that you use the fuel that the blow lamp is designed for.

Some blow lamp manufacturers marketed their own brand of fuel.

Gasoline (petrol)
Very common fuel in the small lamps but also used in bigger. Be extremely careful when working with blow lamps for this fuel, as it is highly flammable.

Kerosene (paraffin)
Used in anything from small blow lamps to the biggest. Kerosene is in most countries cheaper than gasoline and less flammable but on the other hand it has the tendency to cause carbon build-ups inside the blow lamp.

Alcohol
Normally only used in small blow lamps and less efficient than gasoline or kerosene. Alcohol is also used for pre-heating of the blow lamp.

Diesel
Less common but similar to kerosene.

Benzene
Less common and similar to gasoline.

Maintenance

This kit of cleaning needles is supplied by Otto Bernz, USA.

The only regular maintenance that is required is to keep the nozzle free from carbon deposits. The manufacturers provided special cleaning needles for this purpose. It is important to use a needle with the correct diameter to avoid damage to the nozzle.

On some blow lamps, a cleaning needle is built into the adjusting valve and this will automatically clean the nozzle every time the valve is closed. If fuel of poor quality is used, this can also cause excessive built up of carbon and other deposits inside the fuel channels and require a clean out. On some blow lamps there are plugs fitted to these channels that can be removed to facilitate cleaning.

On blow lamps equipped with pumps, the leather seal may occasionally also require a few drops of oil to prevent it from drying out. Also make sure that other seals and gaskets are tight to prevent fuel leakage that can cause a fire.

Trouble shooting

A nicely operating blow lamp (Monitor, England).

When the blow lamp is operating correctly, it should give an intensive blue flame.

If the flame is yellow and flickering, this indicates that the pre-heating was insufficient and that the fuel is not vaporised correctly.

Turn off the blow lamp and repeat the pre-heating procedure. Before filling the pre-heating cup, make sure that there is no remaining flame that can ignite the pre-heating fuel. To be on the safe side, it is better to let the blow lamp cool down before the new starting attempt.

Other design features

Fuel tanks

This blow lamp from Otto Bernz, USA has a cast aluminium tank.

The fuel tanks are normally produced out of brass sheets that are pressed to form the tank without any seams. The tank bottom is then soldered on the tank with a double folded joint to withstand high pressures. Furthermore, the bottom is made concave to withstand higher pressure.

After assembly, the tanks were polished and then sometimes coated to prevent oxidising. On some models, the brass tanks were nickel-plated.

Sometimes other material like copper, aluminium or steel was used to produce the fuel tanks. This was more common during war times when the brass was needed for ammunition shell production.

Less common are fuel tanks made of castings. These castings could be brass, aluminium or steel .

Safety valve

This illustration shows a Sievert blow lamp with the safety pin connected to the bottom of the tank. You can click on the picture to enlarge it.

In the beginning of the blow lamp era, it was quite common with accidents caused by exploding fuel tanks due to high pressure build-up.

To prevent this, the early European (Swedish) blow lamps were equipped with a safety device in form of a pin in the tank. This pin is connected to the concave bottom of the tank and if the pressure in the tank increased too much, the bottom of the tank will be pushed out thus pulling out the pin and releasing the pressure before any accident would happen.

Later on, this safety device was replaced by a spring-loaded safety valve normally located in the filler cap.

Usually, it was only gasoline blow lamps that were fitted with safety valves.

Pressure gauge

Some blow lamps were equipped with a pressure gauge to ensure better and safer operation. Some manufacturers offered pressure gauge as an accessory which would then be fitted in a modified filler cap.

Burners

Burner with double nozzle from Turner, USA. This design increased the heat output needed for bigger brazing applications.

To withstand the high operating temperatures of around 2000 °C, the burners were often made of bronze or cast iron. However, also brass burners are quite common.

The pre-heating procedure required that the operator of a kerosene blow lamp carried two kinds of fuel. The introduction of the "Quick Start" device, where kerosene was used for pre-heating was a major step forward. A special separate burner, also burning kerosene, was used to pre-heat the main burner.

Hook for soldering iron

The hook that you often see on the top of the burner is not for hanging the blow lamp in but is intended to support a soldering iron.