There is a serious objection to the closed system that makes its use inadvisable under any condition with a Diesel engine. The discharge, being closed, is not under the observation of the opera tor. The circulation can be broken without the knowledge of the operating force; this has resulted in broken cylinder head and jackets in a number of cases. As a safeguard, a check valve with an outside lever connected to a bell-ringer is recommended.
Open Cooling 166 is the schematic layout of the open cooling system with a storage tank. With this system, the water is stored in the overhead tank and enters the cylinder jacket at A; after cooling the engine, the water discharges into the open funnel at B, flowing into the sump C. A centrifugal pump D lifts the water from this sump and discharges it in the top of the cooling tower E. In dripping down this tower the water is cooled and, collecting in the catch basin F, is lifted by the pump G and forced into the overhead tower. This system is frequently used without the overhead tank. With this plan the pump G forces the water through the engine jacket. It is at once appar ent that this latter plan is objectionable since it is dependent on the pump G for the steady flow of water. If the suction is stroyed, the system at once becomes dangerous. Low-pressure engines are often installed with this system, but the cost- of a Diesel plant is entirely too great to ignore the overhead tank. A 30,000-gallon tank with a 30-foot steel tower can be installed at a pre-war cost of approximately $3000. The interest on the investment ($180) is a low premium on the insurance of protection against engine damage due to lack of cooling water.
With a few engines the cooling water, after passing through the engine, is used to cool the exhaust header. With others the water is first passed around the air compressor and inter-and after-cooler before entering the engine jackets. Results from these cooling methods are fairly satisfactory. The proper cooling pipe layout embodies individual lines to the air compressor. and coolers, to each engine cylinder jacket, to the valve cages and to the ex haust headers. All these lines should have brass cocks in the intake side, and the discharges should all lead to a common discharge funnel. Each discharge line may well be fitted with thermometers, while a single thermometer on the intake line before the lines branch to the various parts is sufficient.
Water Pipe.—All the water lines in the engine room are best laid in pipe chases. This places the piping out of sight and provides more room in the plant. The pipe should be extra heavy galvanized pipe; though the pressure is small, this thick ness of pipe prolongs the life of the system. The threads in all fittings must be clean and sharp, while the pipe ends should be fully threaded. Red lead or other dope must be avoided, while the unions should have either ground joints or copper gaskets; rubber gaskets are at best of short life, and a pipe line should be made up in such a way that it will never give trouble. In those engines where water is admitted direct into the exhaust pipe, the drip line from the exhaust should not discharge into the cooling-water discharge; due to the carbon in suspension, it is advisable to run this drip to the sewer. Frequently the fuel contains enough sulphur to eat iron pipe if employed in the drip line; consequently brass drips can be more profitably used.
Cooling Towers and Tanks.—As has been already explained, an overhead tank is advisable in every Diesel installation. A steel tower and tank of from 25,000 to 30,000 gallons capacity is sufficient for any installation under 3000 h.p. since in this maximum case a 30,000-gallon tank would provide, in the event of pump failure, cooling water for one and one-half hours. Plants of 300 h.p. or less will find a wooden tank on a wood tower quite satisfactory, Fig. 167. A 12X12 ft. tank of 2-inch cypress staves will hold close to 12,000 gallons and can be erected on a 30-foot tower at a cost of $1200. A tower made of 8 X 8 in. yellow pine with the joints reinforced by steel plates and braced by diagonal steel rods is amply strong for this tank.
Regulating Floats.—Every overhead tank should be fitted with some form of high- and low-water alarm. Such a device appears in Fig. 168. When, due to faulty circulation, the water level in the tank becomes dangerously low, the float strikes the lower collar on the shaft A. Its weight overcomes the resistance of the spring E, and the point F contacts with H, causing a bell to ring and lighting up the red globes. If the level becomes high, the green lamps light and the bell rings. In either event the engineer has ample warning that the water tank demands attention. This is a positive safeguard against damage due to a pump failure.