J. R. S. writes:

"I am a reader of your valuable paper and you will confer a favor by giving the whys and wherefores of the following difficulties a brother plumber experienced not long since with a range boiler and back. He asks me, Would leaving the sediment cock open burst the back when the supply was sufficient to keep the boiler full, regardless of waste through sediment cock. He gives me a sketch as follows:

"Boiler is in basement. A is a supply pipe and connected in the bottom of a tank on the fourth story of the building. B is a check valve to keep water in tank from washing back into the main. C is sediment cock. Our brother came to repair a burst in pipe D, and in order to do this he shut off the supply and emptied boiler through sediment cock C; wiped the joint, turned the supply on, and left the job as being all right, forgetting to close sediment cock. In a few hours he returned to see how the job was, and found a hot fire, but boiler and circulating pipes cold and a fearful water hammer in the boiler. On dumping the fire he found the water-back had cracked and then discovered the sediment cock open. On putting in a new back and closing the sediment cock the job proved to be all right.

"I explained the cause of the trouble to my friend as follows: That the escape of the water through pipe E and sediment cock C created a vacuum in pipe D. making a downward flow of cold water in circulating pipe F, through back and pipe D, and out at sediment cock. The flow of cold water on the hot back cracked it, and also caused the water hammer in boiler. Am I right? If not, please favor us with a correct reason, and oblige."

[If there were a downward flow of water in the pipe F, thence through the water-back and pipe D, and out through the sediment cock, the chances are the back would not be injured, unless, indeed, this flow suddenly started when the back was red-hot.

If the boiler and circulating pipes F and D were cold, when the condition of things was first noticed, it is likely the water was passing as you say, otherwise they would be very hot.

The water hammer you mention certainly cannot be caused by steam formed in the back (as you say the pipes and boiler were cold), therefore the rumbling or water hammer must be caused by air in a partly filled boiler; or you may be misinformed about the boiler and pipes F and D being cold, and the water hammer may have been really caused by steam, as we assume it was by water running into the back through pipe D and then being driven violently from the back through both pipes in the form of steam.

If enough water remained in the boiler (when the sediment cock was open) to cover the upper end of the pipe F, the back would not be cracked or burned.]