Water Blow Off Tower

The Department's description

Exterior description and setting

A free-standing tower situated in a field on the east side of a hill. It is approached along a track running north from Rosevale Road.

The tower is of rubble blackstone brought to courses, with roughly dressed quoins, slightly advanced chamfered base, and moulded concrete crown. It is of square cross-section and stands to its full height of c.6m, tapering inwards from c.1m at its base to c.0.6m at its top.

Immediately south of the tower is an above-ground grass-covered water service reservoir, with concrete cap and concrete steps thereto up its NE side.

Setting

The tower and reservoir are enclosed by a post and wire fence. The site is grass and gorse.

Historical information

This tower is on the line of a water pipe running from Foffany Reservoir, in the Mourne Mountains, to Banbridge and Portadown.

This pipeline was laid by Messrs Collen Brothers of Portadown between 1904 and 1906 at the behest of the Portadown & Banbridge Joint Water Board and at a cost of £36,000. The water was drawn from the Shimna River, in the north-western foothills of the Mournes, and ran underground along a 9-inch diameter cast-iron pipe to the Banbridge service reservoir at Drumnahare (NE of Loughbrickland), whence it continued 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. The water first flowed on 5 July 1906. Initially, it was drawn directly from the river as it was not until 1909 that the reservoir at Foffany was completed. 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 OS six-inch map; it is captioned ‘Blow-off Tower’ and the pipeline as ‘Aqueduct (Portadown & Banbridge Water Works)’. There is a second such tower on the same pipeline at Derrydrummuck, near Loughbrickland (grid J 1411 3978).

The tower contained a vertical running up from the underground pipe. Its purpose was to relieve any excess water pressure if, say, the pipe became blocked further along and 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 of the tower. 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 in normal circumstances. However, had there been a blockage, the pressure in the pipe would have built up (as the water was still flowing in from the Foffany end), thus forcing up the column of water until it eventually over-spilled 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 the air was best released (air will always rise to a high point in a pipe). If the tower had been sited at a low point on the pipeline, a much taller one would have been needed to contain the column of water present during everyday operations.
The 1971 OS map also shows a covered reservoir beside the tower. This 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.

References – Primary sources:
1. PRONI OS/6/3/26/4. Fourth edition OS six-inch map, Co Down sheet 26 (1903-17).
2. PRONI LA/51/29/B/14. Document relating to objections by Lords Roden and Annesley to proposed water abstraction
scheme at Foffany, 1903.
3. PRONI OS/11/220/7/1. First edition OS 1:2500 IG map sheet 220-07 (1971).

References - Secondary sources:
1. Portadown and Banbridge Regional Waterworks Joint Board, ‘A brief history Portadown and Banbridge Regional
Waterworks Joint Board’, in official programme to accompany opening of Spelga Dam and Fofannybane Filtration Works,
30 June 1960.
2. S. C. Lutton, ‘Portadown and Banbridge Regional Waterworks - Foffany Catchment Area’, in Review - Journal of the
Craigavon Historical Society, vol.1 (1), 1969.
3. Information from Mr Francis McGrath, 9 Rosevale Road, Banbridge; his father previously owned the land where the tower
and reservoir are situated.
4. Information on tower’s operation from Mr John Collins, Information Manager Unit, Northern Ireland Water (email of 9 Dec
2011).

Criteria for listing: architectural interest

A. Style
B. Proportion
C. Ornamentation
D. Plan Form
J. Setting

Criteria for listing: historic interest

X. Local Interest
Z. Rarity

Evaluation

A rubble-masonry blow-off tower of c1905 on the Foffany-Banbridge/Portadown water conduit. This tower is scaled-down version of a conventional 19th century boiler chimney in terms of its proportions and fabrication. It was sited at a high point on the pipeline to enable any build-up of water pressure and/or trapped air to be released. It is one of two such towers on this pipeline (the other is HB17/008/038) and is a rare provincial example of this type of waterworks structure.