72 



L. J. HALE 



The pump I use here is provided with 12 

 bubblino; tubes of i/^-inch bore. The base 

 of the pump (figs. 2 and 3) is fashioned 

 of Perspex. Water from the 'last' tank is 

 led to the central 2-inch-diameter water 

 inlet by a polythene tube from a similar 

 adapter attached to this tank (fig. 4). 

 The water then passes out into the ring of 

 Inibbling tubes. These are of PVC (poly- 

 vinyl chloride) and carry the w^ater, plus 

 air bubbles, through an adapter (fig. -t) 

 to the 'first' tank. Air is injected into 

 the bases of the bubbling tubes through 

 the outer ring of nozzles; the size of the 

 air orifice has no eti'ect on the efficiency 

 of the bubbling tube. 



Each air inlet must have its ow^n control 

 valve. In the present equipment, air from 

 a compressor passes into a Perspex cham- 

 ber provided with 12 air outlets, each hav- 

 ing a simple Perspex valve. It is possible 

 that a simpler design would be to fit these 



valves to the basal part of the pump. The 

 required pressure of air is that which is 

 sufficient to overcome the pressure of the 

 column of water in a bubbling tube (for 

 example, i/-, atmosphere for a 6-foot tube). 

 When working at an economical rate 

 this pump moves about 250 gallons of 

 water per hour (300 U.S. gallons) for the 

 expenditure of about 121/2 cubic feet of 

 air. Increasing the rate of air injection 

 increases the rate of pumping water but 

 is less efficient ; 25 and 50 cubic feet of air 

 will move respectively about 310 and 375 



Figure 2. — Pump base, made of Perspex, with 

 12 PVC bubbling tubes of i/^-inch bore. 



VIEW THROUGH AA 



Figure 3. — Plan and section of pump base. 



