Elements of Plumbing

by Samuel Edward Dibble

[Fig. 69] shows a thermostatic control valve attached to the bottom of a heater coil, and at the side of storage tank. The best arrangement is at the bottom, for it does not shut off the gas supply until the boiler is full of hot water.

Connecting Tank and Coil Gas Heater.—The boiler and the coil gas heater have a different connection. The bottom of the tank and the bottom of the heater are connected. The top of the heater and the top of the boiler are connected. The accompanying sketch shows how this connection is made. If the tee on the top of the boiler into which the gas-heater connection is made is not the first fitting and placed as close to the outlet as possible, the water will not circulate freely into the boiler. This connection according to the drawing should be studied and memorized.

Instantaneous Gas-heater Connections.—An instantaneous gas heater is placed in the basement. The copper coil in it is connected at the bottom with the cold-water supply and the top outlet of the coil is connected with the hot-water system of piping. There is no need of a storage tank with this heater. When a faucet is opened in any part of the hot-water piping system, the water passing through the water valve at the heater causes the gas valve to open so that the whole set of burners in the heater is supplied with gas, and the burners are lighted from a pilot light. When the faucet is closed, the gas supply is shut off and the burners are put out. The pilot is lighted all the time. Space will not permit going over these connections in detail. It is a large field and requires considerable thought.

Safety and Check Valves.—When a meter is used on a water system, the water company demands that a check valve be placed on the hot-water system to prevent the hot water from being forced back into the meter in case the pressure got strong enough in the boiler. If a check valve is used for this purpose, or for any other purpose, a safety valve must be placed on the boiler piping system to relieve any excessive pressure that may be caused by having the check valve in use. There is today, with meters of modern type, no reason to use a check valve or a safety valve. If an excessive pressure is obtained in the boiler, it is relieved in the water main.

When water is heated, it expands. If the heat becomes more intense and steam is formed, the expansion is much greater, and some means must be provided to allow for it. This expansion can be allowed to relieve itself in the water main as explained above. When a check valve is placed on the piping, this means of escape is shut off and a safety valve must be employed. Without these reliefs, the pressure would be so great that an explosion would result. When steel pipe and steel boilers are used for storage tanks and connections, the pipe and tank will shortly start to rust and parts of the piping are stopped up with rust scales. The water also becomes red with rust when the water becomes hot enough to circulate. When the pipes are stopped up, steam is formed and a snapping and cracking sound is heard. To avoid these conditions, the piping should be of brass or lead and the storage tank should be of copper. The installation cost of brass and copper is greater than steel, but they will not have to be replaced in two or three years, as is the case with other material. A valve should be placed on the cold-water supply to control the entire hot-water piping system. A pipe with a stop cock should be placed underneath the boiler and should extend into a sink in the basement so that the boiler can be drained at any time for cleaning or repairs.

Connecting with Fixtures.—To have all fixtures properly supplied with hot water it is necessary to run what is termed a circulating pipe. This circulating pipe is a circuit of pipe extending from the top of the boiler to the vicinity of the fixtures and then returning to the boiler and connecting into the pipe leading out of the bottom of the boiler. From this circuit all branches are taken to supply all fixtures requiring hot water. This circulating pipe has hot water circulating through it all the time. Therefore the fixtures are supplied with hot water very quickly. The circulating pipe and its branches are run without any traps or air pockets.

Fig. 73.—Expansion loop. Four 90° ells.

Fig. 74.—Expansion loop. Five 90° ells.

Fig. 75.—Expansion loop. Six 90° ells.

When running the piping, it should be borne in mind that not only does the water expand when heated, but the pipe expands also. Therefore due allowance must be made for this expansion. The long risers should have an expansion loop as shown in Figs. [73], [74] and [75]. There are installed on some jobs what is known as an expansion joint. This will allow for the expansion and contraction of the pipe. The writer's experience with these joints has not been very satisfactory. After a while these joints begin to leak and they must have attention which in some cases is rather expensive. An expansion loop as shown in the sketch, made with elbows, will prove satisfactory. If the threads on the fittings and pipe are good, no leak will appear on this joint.