A somewhat similar system can be arranged to operate the starting box of the pump motor as well as to ring an alarm bell.
Cooling Towers.—If a supply of cooling water can be secured from a shallow well, the best plan is to install a power well pump and allow the discharge to waste into the sewer. Unfortunately such a supply is seldom available, and some form of cooling tower whereby the discharge water can be cooled for reuse becomes a necessity. This, in most installations, consists of an upright wooden tower filled with slats down which the water trickles and is cooled by the upward current of air. Like all structures, the tower may be constructed at an expense ranging from a few hundred to several thousand dollars. The former cost covers a simple tower for a small plant, while a large installa tion demands the more expensive construction.
Plants of 300 h.p. will find the tower in Fig. 169 fairly economical in first cost and amply large for the required cool ing. This tower can be erected at a total material and labor charge of $300. The sump under the tower is 24 inches deep but can easily be deepened at slight expense. The X16 in. foundation bolts should be inserted at the time the concrete is poured. The frame of 4X6 in. timbers, resting on 6X6 in. sills, is large enough, especially since the ship-lap sides further strengthen the structure. The sides are sealed with the ship-lap with the idea of haVing the air currents enter the tower under the bottom row of baffles and pass out at the top. If the sides are open, practically no circulation is set up.
The discharge from the engine first flows into the main trough and, passing through a series of holes in the trough sides, enters the distributing troughs. The latter are notched to allow the water to overflow before completely filling the trough. This feature is of advantage when the troughs settle. The holes in the main trough can be plugged, thereby offering means of con trolling the distribution of the water.
Figure 170 shows a somewhat similar design for an installa tion of 1000 h.p. In the particular plant where this tower was used a cooling pond with spray nozzles was originally employed. In erecting this tower, the pond was retained as the sump. As
the drawing shows, the tower was placed on the pond bank, and a drip surface E of 1 X10 in. ship-lap covered with three-ply rub beroid roofing was placed under the tower. In this drawing the tower sides are boarded tight with ship-lap. However, this was not carried down below the bottom baffles. On windy days the water was blown out the open sides at the bottom, caus ing a washing of the bank and a settling of the tower sills. In erecting a tower, the sides should always be well down below the bottom baffles.
For having a capacity of 1500 to 2000 h.p. the more elaborate tower design in Fig. 171 will prove more suitable. This tower has the sides covered with louvres while the top is carried above the trough, forming a chimney. This construction pro vides an increased volume of air passing through the sides while the chimney gives the necessary draft.
Circulating the small one-engine plants where a single operator cares for the machinery, the most approved type of circulating pump is either an outside packed triplex pump or a horizontal plunger pump. A large percentage of plants have centrifugal pumps, but this type is dangerous in the small plant. If an overhead tank is a part of the installation, the centrifugal pump offers no objectionable feature. In those plants not possess ing the protection of the overhead tank, the loss of the pump suction, as often occurs with this pump, is dangerous. The pump, in small plants, should, if possible, be chain-driven from the engine shaft since a broken belt is to be avoided at all costs.
Large installations usually employ motor-driven centrifugal pumps. With the overhead storage as a plant protection, this pump is by far the best for large plants.
In placing the pump, the suction line should be made as short as possible and the lift kept at a low value. In discharging into the overhead tank the pipe should run to the top of the tank rather than enter the tank bottom. This places a constant head on the pump, and, in case the pump suction valve leaks the entire tank will not empty. A by-pass line from the tank bottom can be run into the pump discharge for priming purposes.