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How To Design And Install Plumbing
The mechanical devices which make up an overhead feed system of water supply are as follows:
1. An open storage tank equipped with an overflow pipe and a condensation pan.
2. A twin set of centrifugal or piston pumps.
3. A float and electric control switch.
The pump usually is located in the basement of the building and is mounted on a well-insulated and substantial footing. The inlet side of the pump is connected to the city water supply and is equipped with a gate valve, A.
The outlet side of the pump is connected to the overhead storage tank just below its overflow rim and must be provided with two check valves and a gate valve, installed as close to the pump as is practical, B. To provide for shut off in an emergency, a valve should be placed close to the tank as well. The tank is placed above the highest installed fixture which requires water, usually the roof penthouse.
The supply of water to the tank is controlled by an electric float switch installed within the tank close to its overflow rim. When the water in the tank recedes and rises to established levels, the float switch starts and stops the electrically driven pumps, C.
Whenever a water system depends on a mechanical device, suck as a float switch, the installation must be protected. Should the control device become defective, overflow of the tank would occur and damage would result. This possibility can be averted by connecting an overflow pipe of adequate size to the tank at a point below the top rim. The overflow should be drained onto the roof of the building and be run just as direct as possible. If this cannot be done, it may be connected indirectly to the storm sewer. Should the building be without a storm sewer, the overflow may terminate indirectly into the sanitary sewer.
The condensation which occurs on the outside surface of the tank is dripped into a condensation pan. The pan is provided with a drain pipe, which discharges separately onto the roof. Should the tank overflow pipe be taxed to its capacity, backflow into the pan would cause flooding of the building, therefore, cross connection of the two wastes is inadvisable. The indirect connection of both drains serves to prevent contaminated wastes contained in the storm or drainage system from backing up into the water tank.
The fixture riser supply main should be connected to an opening near the bottom of the tank. The main usually is suspended from the steel framework between the ceiling of the top floor and the roof of the building. The main is pitched from the tank to the risers and should be well suspended to avoid sagging of pipes. The risers are connected to the main at right angles. Inverted 45-degree connections are advisable. Each riser must possess a valve located close to the main.
