The steam shovel, bucket or elevator dredge will do efficient service in raising material, but none are capable of delivering the material except within a very short radius of the dredging operation. The centrifugal dredge not only raises the material, but also delivers it at the place wanted, at one operation. Besides, it is practically impossible to build any other type with the enormous capacity that some hydraulic dredges have.
Fig. 499.
Fig. [499] is a perspective view of a centrifugal vertical pump of the submerged type. This pump is used largely by contractors in excavations and coffer dam work and for keeping pits drained.
A double suction centrifugal pump, driven directly by a steam engine, is shown in Fig. [497]; these are generally and very satisfactorily used for circulating water through surface condensers and the cooling pipes in refrigerating systems. The engine and pump thus combined occupy small floor space and consequently little masonry is required for a foundation.
Fig. 500.
The Buffalo centrifugal pump is shown in Fig. [500]. These are built by the Buffalo Forge Co. in two types, viz., the submerged and the suction; the latter is the one shown in the cut. The suction type is employed for pumping from mines, pits, etc., and all places where the supply will not allow of a horizontal pump to be used, or in others where the supply is either below the pump, or sometimes above and at other times below. This type possesses merit above the submerged design in that it will work equally well, when set either above or below the liquid to be pumped.
Multi-stage centrifugal pumps. Experience has demonstrated that by placing several pumps together and discharging from one into the other, water can be delivered to almost any height. For a long time after the introduction of centrifugal pumps, it was supposed that about sixty feet was the limit for their economical working, owing to the high speed at which they had to be run to accomplish the results desired.