We take clean swimming pool water for granted nowadays. But the current sand filtration system was only introduced to the Club in the summer of 1934.
For the previous 60 years the only way to get clean water into the swimming pool – or pond as it is typically called – or was to drain all the water out and refill it. We believe that this happened twice a week.
The sand filtration system had major new benefits: cleaner, more sanitary water, lower water bills and more time for swimming:
“Reference was made to the coming installation of the filtration scheme, enabling the Ladies to get two hours longer on Tuesdays. This will be sure to prove a boon, especially to members who are at business.”
2nd May 1935
“Filtration of the pond on the most up to date basis, has proved beneficial in all respects.”
Both from the Ladies Committee Minute Book (TD965/9 – Glasgow City Archives, Mitchell Library, Glasgow).
Recorded in Water attendance, number of bathers, water change, etc 1933-1949 (TD965/119, Glasgow City Archives, Mitchell Library, Glasgow)
How does it work?
The water is pumped from the deep end of the pool and enters the top of the filter. The tank contains approximately seven tons of sand, filled up to the halfway level.
Sand acts as a filtration medium, trapping particulate matter (flakes of skin, hair etc) in the upper layers, together with solidified body fats, mucus and other human detritus.
The clean water leaving the bottom of the filter is then heated, chlorinated and returned to the shallow end of the pond.
As the filter collects debris, pressure rises in the inlet. To clean the filter, pool staff reverse the flow, and dirty water is pumped out into the drains. Once the backwash water runs clear, forward flow is restored and the filtration system resumes its normal operation.
Repairing our 1930s sand filter
Our sand filter has seen continuous use over the last 84 years and is beginning to show its age. By 2017 it had developed holes in the shell, the most serious being in the base of the filter leading to a steady trickle of water leaking into the basement sump. This needed to be repaired, along with replacement of some of the cast pipework and valves.
We brought in a repair team from SP Filtration and Direct Engineering. Welders fixed the leaks by tack-welding steel plates onto the old shell. This was also an opportunity to refresh the sand by purging the filter and chemically cleaning the ‘flock’ (a thin grey tissue of body fats and protein) which forms on the surface of the sand.
A removable hatch on the side of the tank allows access to the interior. There’s enough space for someone to climb inside!
This short film shows some of the remedial work undertaken last year.
The History Group is currently researching the sand filter and related plant installation. We’ll update this blog when we have more to report.
But for more gems on swimming pool design and engineering in the 1930s, see the Baths and Washhouse Historic Archive Engineering page.