It is advisable occasionally—say once a month—in towns where fires are not frequent, to fire up and take the engine out for practice and drill, and to make sure that it is in proper working order, after which the boiler should be blown off and refilled with fresh water, as hereinafter directed.
Every engine required to pump salt water, or other water unfit for the boiler supply, should be provided with a fresh-water feed tank.
The purpose of the automatic air cock (if there is one) is to prevent the rattling of the check valves when the pumps are being only partially filled; if the supply is to be drawn from a barrel or tank, the entrance of air through this cock must be prevented.
When draughting the water, bear in mind that the greater the perpendicular lift the less the quantity of water which can be pumped, remembering that it is the pressure of the atmosphere which forces the water into the pump, and not any power exerted by the pump itself, which simply produces the vacuum. Thus, the nearer the surface of the water the greater the velocity with which it enters the pump, while the higher the pump the weaker the pressure and the less the quantity of water which enters it, and at a height of about 30 feet no water at all will go into the pump.
If it is suspected that one of the joints in the suction is loose, the speed of the engine may be slackened without stopping entirely, until water is thrown eight or ten feet from the nozzle, when if the pump is taking air the stream will snap and crack instead of flowing out smoothly. If it is found that the pump is taking air through the suction, and the leak cannot be located in any other way, it may be found by removing the suction basket and turning the end of the suction up higher than the top of the pump, and then filling it with water. The water will be forced out through the joints wherever loose, and leaks can be found in this way.
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.