Swimming pool filtering system

DETAILED DESCRIPTION In attempting to provide an energy saving swimming pool filter, the Applicant recognized that the swimming pool filter industry designers had overlooked or did not understand the importance of system head curves.
The industry was so preoccupied by the pressure drop .
DELTA.
H shown in FIG.
6 and the need for sufficient capacity to overcome this drop that they failed to realize that under most normal conditions a much lower capacity pump could be satisfactorily used with substantial energy savings.
It was a common misconception that flow rate is controlled solely by pressure and therefore low capacity pumps could not be used since a slight rise in the filter pressure drop would quickly exceed the shut-off head of the pump, resulting in zero flow.
The Applicant discovered that a lower capacity pump could operate satisfactorily during normal conditions other than vacuuming, system priming or cleaning up after a storm.
Lower flow rates provided excellent filtering and did not require more frequent filter backwashing.
However, the increased capacity was required for the previously mentioned periods of use.
The increased capacity could be provided by the use of an auxiliary pump but this was too expensive for home installations.
Another method of providing the increased capacity would be through the use of a two-speed pump wherein the lower speed would be used for normal operation, and the high speed for vacuuming and establishing a prime.
The two-speed pump would provide a lower speed characteristic as indicated by curve H.
Q.
L.
sub.
o in FIG.
6.
As can be seen from FIG.
6, the flow rates will be approximately one-half of that for the high speed but the shut-off head will not be reached any faster than at the high speed since the increased pressure drop across the filter .
DELTA.
H.
sub.
Lo is substantially less than the drop .
DELTA.
H.
sub.
Hi at high speed operation.
Dual speed operation could be achieved by the use of a single speed motor long coupled to a pump through a speed changing gear train or belt drive arrangement