Hydraulic Ram, Largy Bridge, Roe Valley County Park, Limavady, Co Londonderry, BT49 9EY

This reinforced concrete hydraulic ram house, built between 1920 and 1939, is situated near Largy Bridge within Roe Valley County Park, Limavady, County Londonderry. It is of industrial archaeological interest, notable for its association with the generation of hydroelectricity on the River Roe and its dramatic contrast with the natural rocks of the Dogleap.

The structure is visually striking; when viewed from the south bank of the river, the irregular rock formations are abruptly squared off by an ivy-covered concrete projection, which appears to be part of the natural outcrop due to weathering. From the north bank, a straight concrete line rises gradually from the forest floor, ending abruptly. Features include a suspended pipe crossing the river, a millrace, and a drop to the river.

The system comprises a 600mm-wide concrete channel fed by a 60mm-diameter pipe that crosses the River Roe at a high level. The channel runs 6-7 metres inland before turning parallel to the river. The ground falls away on the landward side, rising to a six-metre-high concrete structure before re-emerging at the riverbank, 20 metres downstream. Cast iron railings and recent timber fencing prevent close inspection at this point.

The structure was built by Miss Dorothy Robertson of Dogleap House in 1924, initially utilizing water to power a mill building via a timber aqueduct built by Robert Thomson, the millwright, from mills at Largy Green on the opposite bank. This aqueduct was described in the Ordnance Survey Memoirs of 1833-5. The concrete channel fed a small hydroelectric turbine, generating 20-25 brake horse power with a head of 24 feet and delivering 12 kilowatts at 220 volts direct current. In 1933, the local electricity company removed the original aqueduct and diverted the water to a new generator, supplying Mrs. Robertson with free electricity. The current pipe was installed along the original aqueduct’s route to provide sufficient water pressure to operate the hydraulic ram, a "simple type of pump which uses kinetic energy of a moving column of water to pump a part of that water column to a greater height than that of the water supply."