48 



C. M. BREDER, JR. 



this will cause the water flowing through 

 it to move with less speed. The value of 

 this arrangement as a detritus remover is 

 thus lessened, for the slower-flowing water 

 will not lift as heavy particles as will the 

 faster. 



As such a system is usually intended to 

 be operated continuously for long periods 

 without attention, a safety feature may 

 be built in which would shut down the 

 pump if the water in the reservoir should 

 rise too high or fall too low. The one in 

 current use, shown in figure 9, was im- 

 provised from the tube of a mercury 

 switch. This was mounted on a rotatable 

 glass shaft running through a support of 

 plastic. It was actuated by a chemical- 



flask float by means of a thread over a 

 small drum so that the motion of the float 

 was transmitted to the pump switch. Any 

 unusual change in the water level, either 

 positive or negative, would indicate some 

 radical failure at some point in the sys- 

 tem. Since the aquariums which held the 

 fish were drained by an o^'erflow, they 

 would continue to hold their water level 

 so that stopping the pump would insure 

 the retention of water there. Even if one 

 of the aquariums leaked and lost its con- 

 tents the others would not suffer by drain- 

 ing through the system to it because of 

 this protective device. 



To prevent normal evaporation from 

 stopping the pump, a supply was provided 



Figure 9. — Safety control for closed circulation. Its relation to the system is indicated in figure 8. 



At the right are the pump intake and excess return. 



