Connections between tank and heater should be made with copper, brass or iron pipe. Lead pipe is unsuitable for hot water connections, as it expands when heated and upon cooling does not contract to its original length but sags when run horizontally, thus forming traps in the pipe. Furthermore, the joints on lead pipe are liable to be melted and pull apart when the temperature of the pipe becomes very high, or should the water be siphoned out of the boiler below the waterback, the heat from the fire would melt off the soldered joints.

Circulation between water heater and tank is impeded by friction, therefore the ends of brass, copper and iron pipe should be carefully reamed to remove the burr formed by cutting, and 45 degree bends or large radius 90 degree bends of recess pattern should be used to connect the heater and tank. Pipe of smaller diameter than 3/4 inch should never be used to connect a waterback or heater to a storage tank, and the larger the pipe used within reasonable limits the better the circulation of water.

The usual method of connecting a heater to a hot water tank is shown in Fig. 132. The circulation pipe, a, from the bottom of the tank is connected to the bottom opening of the waterback, and the flow pipe, b, grades from the top opening of the waterback up to the side connected to the boiler, about one-third distance from the bottom. The coldest water in a tank is always at the bottom and the hottest water at the top ready to be drawn through the hot water pipe. The temperature of the water grades uniformly from the hottest water at the top to the coldest water at the bottom of the tank.

A better way to connect the flow pipe from a waterback to a range boiler is shown by the dotted lines, c. In place of entering the side of the boiler, as in the ordinary method, the flow pipe is connected to a branch in the hot water supply above the boiler. The efficiency of a heater depends upon the velocity of the circulating water, and the velocity depends upon the vertical height of the column of water, therefore with the flow pipe connected to the top of the boiler there would be a greater head, consequently a greater velocity than if the flow pipe entered the side of the boiler.

Fig. 132

Many authorities object to the top connection on account of the possible loss of circulation in case the water is siphoned from the boiler to the level of the hole, f, in the cold water tube, or to the bottom of the cold water tube, d. The reason is not a good one, however, for as long as the waterback remains full of water no damage can result.

If steam is generated it will either condense on the walls of the boiler or escape through the cold water pipe to the street mains. It is only when water is siphoned out of a boiler low enough to empty the waterback that it is damaged. Then, if the fire is continued in the range the waterback becomes overheated, and is liable to crack if cold water is quickly turned into it.

The cold water supply to a boiler usually enters the top and is conducted down through the hot water by a tube, d. If the tube were omitted cold water might short circuit from the cold water to the hot water pipe, as shown by the arrow, h, and cold water would then be drawn from the hot water faucet. If the cold water supply did not short circuit to the hot water pipe, it would mingle with the hot water at the top of the boiler, thus tending to cool it. The tube, d, should be tapped at f with a hole sufficiently large to admit air to break the siphon in case a vacuum is formed in the cold water supply pipe. The size of the hole should vary with the size of the tube, and should have a sectional area of at least one quarter the sectional area of the tube.

The cold water tube in a boiler should never extend below the level of where the flow pipe enters the side of the boiler. If water is siphoned from the boiler it cannot be emptied below the end of the cold water tube, and if the end of the tube is above the flow pipe from the waterback, it provides for circulation through the waterback when the flow pipe is connected to the side tapping in the boiler, and in any event it will ensure the waterback remaining full of water when the siphonage takes place. Boiler tubes for the cold water should be of brass or copper to prevent their rusting off or the vent tube choking with rust.

Many plumbers now connect the flow pipe from the waterback to both the side and to the top of a boiler, as shown by the solid lines, b, and dotted lines, c, in the illustration. Safety Appliances - The most serious result of water being siphoned from a boiler is the liability of the boiler collapsing from atmospheric pressure. To prevent this, a vacuum valve can be placed close to the boiler in a branch to the cold water pipe. The vacuum valve will admit air to the boiler in case a vacuum is formed, and thus prevent the boiler being emptied and then collapsed by external pressure. A vacuum valve should be used whenever a boiler is located at such a height in a building that there is danger of the water being siphoned out when a cold.water faucet is opened at a fixture below, after the water is shut off from the building.

Another way of preventing the water being siphoned from a boiler is to place a check valve in the cold water pipe. This method, however, prevents the water expanding back into the street mains when the water is heated, and might cause the boiler to burst from internal pressure unless some relief is provided. Relief is generally provided under such conditions by means of a safety valve or expansion pipe. A Safety Valve, Fig. 133, consists of a valve that is held closed by means of a spring adjusted so that when the internal pressure reaches a certain intensity it will open the valve and hold it open until the pressure is reduced, so the spring can close the valve again. A safety valve should always be used in connection with a check valve when the water is supplied from a street main. The outlet to the safety valve should be connected to a pipe leading to a sink, so that in case it blows off, the water will not be scattered over the kitchen, and scald anyone.

Fig. 133

Combined safety and vacuum valves are sometimes used to provide safety against rupture from internal pressure or collapsing from atmospheric pressure. An Expansion Pipe is used only with tank pressure. It consists of an extension of the hot water pipe up to and over the cold water supply tank, where it should return so as to discharge steam or water into the cold water tank.

A blow-off cock should be provided with every boiler to draw off water from it when necessary to empty the boiler. In practice it is quite usual to connect the blow-off pipe direct to the drainage system, either to the kitchen sink trap or to the waste pipe below the sink trap. This is bad practice. When a building is closed for any great period of time, the boiler is usually drained of water and the blow-off cock left open to carry off any drip from the pipes or boiler. That provides a direct communication between the house drainage system and the water supply system and possibly the living rooms.

The best place to discharge the water from the blow-off of a boiler is in a trapped and water-supplied sink when there is one at a lower level than the boiler blow-off. When there is not, a compression hose bib connected to a branch of the circulation pipe to the waterback will pro-vide a means of emptying the boiler through a hose or into pails. The blow-off cock should always be located at the lowest part of the water heating apparatus, so it can be completely drained of water. If the waterback is located on one floor and the boiler at a higher level, then the blow-off cock would have to be connected near the water-back.