The principal object of _the churn valve_ is to permit the operation of the pumps without discharging any water through the natural channels; it controls a passage by which the discharging side of the pumps is connected with the suction chamber. In draughting water, when the pumps are first started, _this valve must remain closed_ until the pumps are filled with water, thereby excluding the air which would find its way into the suction chamber if the same were open. It should also be closed when the pumps are at rest, to prevent the dropping of the water into the suction pipe.
When the engine is put to suction, acquire the habit of feeling this valve to assure its complete closure.
If there is anything about the engine that is not fully understood, or if it fails to do its work properly from any cause, the maker should be communicated with at once; inquiries are promptly answered, and usually required information or suggestions are cheerfully furnished.
_The number of appliances and special devices_ used on and about a steam fire engine is not large, as it is the aim of both designers and builders to simplify the machine as much as possible without diminishing its efficiency.
Fig. 434 is an appliance known as the _Siamese connection_. It is used for stand pipes attached to the outside of buildings, etc., and also as a detail of the fire pump. Its use is to lead off two lines of hose.
The valve shown in the figure, closes automatically in case of stoppage of one of the engines or the bursting of the hose.
Fig. 435 exhibits an approved form of _strainer_ for the bottom of the suction pipe.
_The American steam fire engine pump_ is shown in Figs. 431 and 432.
Fig. 431 being the front view, one side of it shown in section, exposing the interior parts for explanation, and Fig. 432, representing the side elevation, also in section.
The pumps, which are double acting, are united in a gun-metal casting, which forms a single body for both, and permits them to be placed much closer as to centers than could otherwise be done. This method provides an ample suction-chamber which is common to both.
In cross section the pump somewhat resembles a box girder. This peculiarity of the pump’s combined form furnishes a rigid base for the entire structure, simplifies the driving mechanism and enables it to endure extraordinary strains without vibration.