Removing liquids from a 55 gallon (208.2 liter) drum or barrel is made infinitely easier using a drum pump. Liquids that may be required to be pumped from a drum include water, oil, and fuel. Since water alone weighs some 8 pounds (3.5 kg) per gallon, a 55 gallon (208.2 liter) drum of water would weigh some 440 pounds (approx. 200 kg). Oil, fuel, and other liquids usually weigh at least that amount, if not more. Simply tipping a drum of that weight is difficult, not to mention unsafe.
Essentially, a drum pump is a pumping mechanism between two hoses, or a tube and a hose. The lower, intake hose, or tube is generally the exact depth of the typical 55 gallon (208.2 liter) drum, while the outflow hose may be longer or shorter, as necessary. The pump mechanism sits on the top of the drum. This small pump is simply inserted into the drum, and is used to pump the liquid from the drum to another container, or vat. Since the terms drum and barrel are essentially interchangeable, drum pumps are very often known as barrel pumps.
As a rule, the intake hose or tube is inserted into a bung hole at the top of the drum. Some drum pumps, however, will have a skirt attached that fits over the top of the drum if no bung is available, and the entire lid must be removed. The typical drum pump is a hand pump. The operator simply cranks a handle on the pump housing, thus pumping the liquid from drum to receptacle.
Though there are electric drum pumps, as well as pneumatic, or air driven drum pumps, the type of drum pump used will depend on the nature of the liquid to be pumped, as well as the complexity of the pumping operation. Many liquids are volatile, thus unsuited to an electric drum pump for obvious reasons. Pneumatic pumps, on the other hand, require air lines and compressors which can be expensive and unwieldy. Often, a hand operated drum pump is used in the food processing industry simply because more accoutrements mean more lubrication, therefore more chance of food contamination.
Though there are drum pumps manufactured with built-in flow metering mechanisms, a drum pump is reasonably easy to configure with a flow-meter attachment, thus allowing metering of the flow of liquids pumped. Additionally drum pumps are manufactured to fit smaller containers, such as 30 gallon (115.36 liter) drums and even five-gallon (18.93 liter) buckets.