Compressed air operated drum pumps are used in environments where electric drum pumps may not hold up well and can be subject to breakdowns such as in very wet environments or very dirty environments. As long as some compressed air is available for operation they offer a reliable means for transferring fluid into a drum. In fact reversible units can transfer fluid both into and out of a drum. Some common uses are for coolant transfer in machine shops and for general cleanup in food and bottling operations.
The compressed air operated drum pumps are mounted on a normally sealed metal drum into the small hole on the drum. This is because you need to avoid leaks for the system to work. A standpipe is connected through the large bung hole on the drum into the drum. Then a hose is attached to the standpipe and may have various attachments to handle liquid. In two way units, a vacuum is created in the drum by the drum pump which draws liquid into the drum. Via a knob on the drum pump the air can be reversed so that the drum is pressurized and pushes liquid out of the drum through the bottom of the standpipe. The typical setup is shown below courtesy of Nex Flow Air Products and their Drum Angel system.
As the above shows, there should be a built in float to avoid over filling when in suction mode. There should also be a built in pressure relief valve when operating under pressure in emptying the drum. The pressure subjected to the drum should always be low enough to avoid drum deformation, hence the pressure relief valve.
Handling flammable liquids should be avoided with these units.
For any questions on the use of compressed air please feel free to ask.