Water Blow Off Tower, Rosevale Rd, Ballyvarley, Banbridge, Co Down, BT32

Water Blow Off Tower

A rubble-masonry blow-off tower of around 1905, situated on the Foffany-Banbridge/Portadown water conduit. The tower is a scaled-down version of a conventional 19th-century boiler chimney in terms of its proportions and construction. It was positioned at a high point on the pipeline to enable any build-up of water pressure and trapped air to be released. One of two such towers on this pipeline, it is a rare provincial example of this type of waterworks structure.

The free-standing tower is located in a field on the east side of a hill, accessed along a track running north from Rosevale Road. Constructed of rubble blackstone brought to courses with roughly dressed quoins, it features a slightly advanced chamfered base and moulded concrete crown. The tower is of square cross-section, standing to its full height of approximately 6 metres, tapering inward from approximately 1 metre at its base to approximately 0.6 metres at its top. Immediately south of the tower stands an above-ground grass-covered water service reservoir with concrete cap and concrete steps on its north-east side. The tower and reservoir are enclosed by a post and wire fence, with the site comprising grass and gorse.

The tower lies on the line of a water pipe running from Foffany Reservoir in the Mourne Mountains to Banbridge and Portadown. The pipeline was laid by Messrs Collen Brothers of Portadown between 1904 and 1906 at the behest of the Portadown and Banbridge Joint Water Board at a cost of £36,000. Water was drawn from the Shimna River in the north-western foothills of the Mournes and ran underground through a 9-inch diameter cast-iron pipe to the Banbridge service reservoir at Drumnahare (north-east of Loughbrickland), continuing onwards to a terminal reservoir at Drumclogher Hill on the eastern outskirts of Portadown. The scheme was conceived by Robert H. Dorman, County Surveyor for Armagh, and John H.H. Swiney, an established water engineer. Water first flowed on 5 July 1906. Initially it was drawn directly from the river, as the reservoir at Foffany was not completed until 1909. In the 1950s this supply was augmented by another from Spelga Dam, fed from the headwaters of the Upper Bann at the Deer's Meadow above Hilltown. The new dam was opened by the Portadown and Banbridge Regional Waterworks Joint Board in 1957 and also entailed a second trunk pipe to Portadown.

The tower is first shown on the 1903-17 Ordnance Survey six-inch map, captioned "Blow-off Tower" with the pipeline marked as "Aqueduct (Portadown & Banbridge Water Works)". A second such tower exists on the same pipeline at Derrydrummuck near Loughbrickland.

The tower contained a vertical shaft running up from the underground pipe. Its purpose was to relieve any excess water pressure should the pipe become blocked further along, which might otherwise have caused the pipe to burst. It also prevented any build-up of air which would otherwise have caused an air lock in the pipe and stopped the water flowing. In operation, there would always have been a column of water in the shaft. The pressure at the bottom of this column of water would have been equal to the hydraulic pressure of water in the pipe. The height of the tower was such that the water did not overflow from the top of the shaft under normal circumstances. However, had there been a blockage, the pressure in the pipe would have built up as the water continued flowing in from the Foffany end, thus forcing up the column of water until it eventually overflowed the crown of the tower. The tower was strategically located at a high point on the pipeline as this is where the water pressure was least and also where air was best released (air always rises to a high point in a pipe). Had the tower been sited at a low point, a much taller one would have been needed to contain the column of water present during everyday operations. The 1971 Ordnance Survey map also shows a covered reservoir beside the tower, which probably dates from the 1950s when the land was acquired by the Joint Board from a local farmer. The blow-off tower has been abandoned, along with the adjoining service reservoir.