HOT-WATER CIRCUIT IN AN OPEN-CIRCUIT AQUARIUM 



79 



been able to pass through the fiUering 

 beds. The lower part of this component 

 of the filter may be cleaned by opening a 

 gate valve (3), releasing for drainage a 

 few liters of water from the bottom. 

 Finally, the water will be caught by a pipe 

 system above the last compartment of the 

 filter, and will traverse a heat exchanger 

 (Z>) of 18 kw. where it will be reheated 

 to 18° C, the temperature desired, and 

 finally a centrifugal pump (E) which has 

 an output of 2 m.^/h. and is driven by a 

 small 1-kw. electric motor. Even though 

 the pump has a small output, it has enough 

 power for the requirement (about 15 m.^/ 

 day) ; moreover, it does not operate con- 

 tinuously, because the closing and opening 

 of the electric circuit are controlled by an 

 hourly break switch. 



The filtering gravel beds are very easy 

 to clean. The gate valve (2) is opened, 

 and the pressure is sufficient to direct a jet 

 of water to the upper part of the tank. 

 Some 10 minutes suffice for cleaning the 

 gravel almost completely. It is left to 

 drip off for a few minutes, then the sys- 

 tem may be put into operation. 



It is unnecessary to add that the instal- 

 lation operates only during the winter. 

 The open-circuit feeding will be reestab- 

 lished as soon as the pump water reaches a 

 temperature of 16° to 17° C. 



It should be understood that the method 

 explained here is only a makeshift device ; 

 still, its results are acceptable, and it pro- 

 vides a considerable saving of thermal 

 energy. 



