334 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



are placed in separate circular wells, is shown by Figs. 328 to 

 330. When these pumps are started, the sluice T, between the 

 two circular wells, is closed, and each pump acts independently 

 until the water-level in the dock is so reduced that the lift of the 

 pumps is equal to about 15 feet. The sluice T is then opened, 



15 20 FEET 



BOILERS 



FIG. 328. 



and the water discharged from the lower pump passes into the 

 well below the level of the higher pump at D (Fig. 330). When 

 this takes place, the self-acting flap-valve at H (Fig. 330) closes 

 and prevents the return of the water to the dock. The wat-r 

 discharged by the lower pump is thus passed through bth 

 pumps, and the lift is divided between them. 



