MINIATURE CIRCULATING SYSTEMS FOR SMALL LABORATORY AQUARIUMS 41 



siphon to a small board which is affixed to 

 a pivot at its upper end so that it is free 

 to rotate on the stationary part attached 

 to the aquarium frame. A small handle 

 pointing upward from there makes its ad- 

 justment simple and marks on the latter 

 in reference to some stationary part make 

 return to a former rate of flow exactly 

 possible. The action is simply that by 

 rotating the part of the siphon so that 

 the horizontal part of the tee raises or 

 lowers, the level in the aquarium follows 

 accordingly. This in turn affects the float 

 valve, which is described below. The rate 

 of flow will increase if the siphon outlet 

 is lowered and decrease if it is raised. 

 This is useful where the exact level of 

 water is not of any importance but where 

 it is desired to vary the amount of water 

 flowing through the aquarium by specific 

 amounts and where it is necessary to re- 

 peat such changes in flow at will. 



If the water supply has considerable 

 pressure, such as is ordinarily encountered 

 in city water systems, or approaches it, a 

 pressure-reducing valve which may be reg- 

 ulated should be employed. This can 

 bring the pressure down to a value which 

 will not burst or otherwise destroy the 

 light equipment to be employed. This 

 valve placed someplace in the supply line 

 should be set so as to deliver little more 

 than the maximum amount of water 

 w^hich will be required of it. Another way 

 to accomplish the same purpose is to per- 

 mit the supply water to run into a small 

 reservoir of no more than sufficient height 

 to provide enough head of pressure. Into 

 this reservoir the supply water is allowed 

 to run continually, of a little more volume 

 than the aquariums will ever need. This 

 is necessary to maintain a constant head 

 in the reservoir. A small excess will over- 

 flow and go to waste by this method. It is 



Figure 2. — Constant-level siphon in operation. 



