These pumps can be thoroughly drained and, with their interior surface well coated with oil and No. 2 pure Graphite, they can be “laid up” indefinitely and with certainty as to their starting promptly when wanted in an emergency. Water accumulated in the steam pipe will pass through this cylinder without causing damage, and the free action of the pump will not be defeated by the “sticking” of valves or the corrosion of exposed parts.
In the operation of rotary pumps trouble is often experienced through an improper adjustment of the ends of the case. If the case is too long there will be leaks of water pass the ends of the impellers and on the other hand if the case is too short the ends of the impellers will bind and cut, through excessive friction. Hence great care is necessary in adjusting the ends of the case so that the pump may run freely yet without leaks. The packing boxes around the shafts must not be screwed up too tight otherwise the shaft will be injured.
It has been found by costly experience that for emergency fire pumps leather belts are unreliable, hence these two pumps, Figs. [482] and [483], are driven by direct connection with the shaft in the first instance and through cast iron friction gearing in the second.
Fig. 484.
Fig. 485.—See page [205].