Bathing Capacity per Day Assuming 24-Hour Operation on Basis of Refiltration
The period of refiltration of the pool takes into account the amount of water per bather per day, determined empirically.
The pump requirements depend up various factors comprising the head and upon the rate of refiltration and backwash of the filter. In this case, the head is comprised of total friction in the pipes leaving the pool and draining it into the filters, as well as of the back pressure at inlets, strainers, and the resistance to the filter beds. On the average, total head is usually figured between 40 and 60 feet, depending on the size of the pool in question.
In selecting the capacity of the pump, the local requirement of the minimum period of refiltration (if any) is used. In addition to the duty of recirculating, the pump must also be capable of supplying water for backwash. The flow through each filter when backwashing is four times the normal flow.
When the filter installation consists of three or more filters, and only one is backwashed at a time, then the pool circulating pump will have ample capacity for backwashing.
If a single filter is used, a separate backwash pump should be provided with a capacity approximately four times that of the circulating pump.