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How To Design And Install Plumbing
UPFEED AND GRAVITY RETURN SYSTEM
The upfeed and gravity return system shown in Fig. 240 is commonly used in small residential and industrial installations. Its working efficiency depends on the accuracy of its construction.
Circulation of water is an action governed by laws of physics. In constructing a hot-water system the slightest mistake on the part of the installing mechanic may interfere with me operation of natural laws and thus cause unsatisfactory service. The proper style of valves and fittings and the correct sizing of pipe are essential to efficient function of the system.
The purpose of a gravity return and upfeed system is to permit a constant circulation of hot water within the piping arrangement. The circulation allows the building occupants to draw an immediate supply of heated water at any plumbing fixture. A circulating return offers an economy in that waste of water is eliminated.
The principle on which a gravity return system functions is provided in the unequal weights of two columns of heated water of uniform height. The inequality of weight is the result of a variation in temperature in the two columns. A mechanic can do much to help insure a temperature variation in a circulating system.
Construction of an Upfeed and Gravity Return System. On an upfeed and gravity return system the heating unit and storage tank must be placed lower than the distribution piping. They should be located so as to serve the piping system conveniently and efficiently.
The distribution main is connected to a tapping on the top of the storage tank close to the flow from the heater. It is suspended from the basement ceiling at a slight grade upward from the storage unit, and various risers are taken from it. On large installations the distributing main should be equipped with a valve. The intervals of suspension are determined by the diameter of the pipe.
The hot-water riser should be connected to the distributing main by means of a 45-degree connection. Fig. 241. This practice may vary according to the length of the risers. It is a common occurrence on this system to have one riser circulating faster and more thoroughly than the others. This is often due to the fact that the connections to the distribution main are improperly made, as for example, where three risers are connected to a distributing main, one being taken from a main with a tee set vertically, another tee being set at a 45-degree angle, and a third tee set horizontally. The vertical tee affects the circulation of water at the 45-degree connection and almost completely stops the circulation of water at the horizontal connection. This is true because heated water has a tendency to rise, and a riser which particularly manifests this tendency naturally interferes with the circulation of the others.
