A ram pump (hydraulic ram) is a water pump that uses the energy of falling water to lift a portion of that water to a higher elevation. The pump operates without any external power source, using only the momentum of water flowing through a drive pipe. Ram pumps are used for off-grid water lifting in streams, springs, and ponds, delivering water to livestock tanks, garden [[Irrigation]], or storage tanks at higher elevations.
The hydraulic ram was invented by John Whitehurst in 1772 in England. The design was refined by Joseph Montgolfier in 1796 and later improved by Boulton and Watt. By the late 19th century, ram pumps were widely used for rural water supply. The Rural Electrification Administration in the 1930s provided electric pumps to many farms, but ram pumps continued to be used in remote locations. The modern revival of interest in off-grid living has brought renewed attention to ram pumps.
Water from a source flows downhill through a drive pipe to the pump. The pump has two valves: a waste valve and a check valve. The waste valve is open during normal flow, allowing water to rush through and gain momentum. When the velocity reaches a certain point, the waste valve slams shut, creating a pressure surge that forces a small volume of water through the check valve and into the delivery pipe. The waste valve then opens again, and the cycle repeats. The pump operates at a rate of 40 to 100 cycles per minute.
The pump requires a vertical drop (fall) of at least 1 meter from the water source to the pump, and a drive pipe length of 3 to 10 times the fall distance. The delivery lift can be up to 10 times the fall distance for a [[Well Systems]]-designed system. For example, a 2 meter fall can lift water 20 meters. The drive pipe must be straight, rigid, and free of air pockets. The pump is installed on a solid foundation and protected from freezing.
A ram pump delivers 5 to 20 percent of the water flowing through the drive pipe, depending on the ratio of lift to fall. A 2.5 centimeter (1 inch) pump with a 2 meter fall and 10 meter lift delivers approximately 2,000 liters per day. Larger pumps with 5 to 10 centimeter (2 to 4 inch) drive pipes can deliver 20,000 to 50,000 liters per day. The pump requires no maintenance beyond periodic valve inspection and cleaning.