MODIFIED SYSTEMS OF STEAM HEATING.
It is beyond the scope of this course to go into the details of the various modified or patented systems of steam circulation, yet it seems advisable to point out the essential features of certain of these systems. The Webster and Paul Systems will be found described in Part III of the Instruction Paper on Heating and Ventilation.
Thermograde System. With this two-pipe system air valves are omitted; the supply valve on each radiator is of a special designed to be set to admit quantities of steam under different condi- tions—to fill the or entirely full of steam. On the end of each radiator is placed a auto-valve, designed to permit the escape of air and water into a return pipe open to the atmosphere at the top. In the case of large buildings the water flows by gravity to a tank, from which it is pumped to the boilers.
Some of the advantages claimed for this system are :—Absence of air-valves and air-lines; control of the heat emitted, by means of the special controlling valve at the supply end of each radiator. The pip ing is the same as for ordinary gravity systems.
Vapor System. This system is designed, as its name implies to work on a very low pressure. The radiators, preferably of the hot water type, must have considerably more surface than with low-pres sure steam heating. A special valve is placed at the supply end of each radiator, designed to admit any desired volume of steam.
A little trap or water-seal fitting is connected with the return end of each radiator, a small hole being provided above the water line to permit the escape of air. All returns are joined in the basement and discharge to an open water column alongside the boiler, any steam in the returns being condensed by passing into a coil provided for the purpose.
No safety valve is required with this sys tem. In case of an ex cess of pressure in the boiler, the water is back ed out into the column above mentioned; a float is raised; and dampers are closed.
The advantages claimed are:—Com plete control of the heat given off by the radiators by means of the special regulat ing valve on each; absolute safety; small pipes; absence of air-valves.
Mercury Seal Vacuum Systems. In one of these systems, commonly used with gravity-return apparatus, air-valves similar to those shown in Fig. 55 are placed on the radiators, and the air-lines connected with a main line discharging through a mercury seal or column, the function of which is to seal the end of the pipe and prevent the en trance of air after the air from the system has been expelled by raising the steam pressure. In another mercury seal system, air valves are omitted and "retarders"—so called—are placed at the return ends of radiators.
With a tight job of piping when the air in the system has once been got rid of, the plant may be run for some time—or until air leaks in again—at a pressure less than the at mosphere and with radiators at tem peratures corresponding to those of hot-water radiators.
Among the claims made for this system are:—Wide range of tempera ture in the radiators, secured by vary ing the degree of vacuum; the advantage of a hot-water heating sys tem without large radiators, since steam under pressure can be car ried in the radiators in cold weather.