OPEN (ATMOSPHERIC) VAPOR SYSTEMS

OPEN (ATMOSPHERIC) VAPOR SYSTEMS

A vapor system with a return line open to the atmosphere without a check, trap, or other device to prevent the return of air is sometimes referred to as an open or atmospheric system.

An open vapor system is frequently used when the steam is delivered from its source under high pressure. When this is the case, pressure reducing valves should be installed in the system to reduce the pressure of the steam to a suitable operating level. An open vapor system is also used when there is no need to return the condensation to the boiler (i.e. when it is wasted within the system). A condensation-return pump should be used when the system design requires the return of the condensation to the boiler.

In an open vapor system, the pressure at the boiler is one to five ounces or enough to overcome the frictional resistance of the piping system. The pressure at vent is zero gauge or atmospheric. In operation, steam is maintained at about five ounces pressure in the boiler by the action of the automatic damper regulator. The amount of heat desired at the radiators is regulated by the degree of opening of the supply valve. Steam enters at the top of the radiator and pushes out the air through the outlet connection which is open to the atmosphere. The condensation returns to the boiler by gravity. This system has the advantage of heat adjustment at the radiator, but the divitalizing effect in the air is somewhat greater than in the vacuum systems because the steam entering the radi­ ators is at a higher temperature than the steam of lower pressure in the vacuum system. It is, however, simple.

The success of a vapor steam heating system depends upon the proper working of the automatic damper regulator in keeping the boiler pressure within proper limits. To accomplish pressure regulation, the dampers are controlled by a float working in a float chamber in communication wi,th the water space in the boiler, as shown in Fig. 19.

When the pressure in the boiler is the same as that of the at­ mosphere (i.e. zero gauge pressure), the water level in the float chamber (Fig. 19) is the same as that in the boiler and the index hand points to zero.

As steam generates, the steam pressure increases and the water level in the boiler is forced downward. The latter action causes the level in the float chamber to rise until the pressure due to the difference (AB) (Fig. 19) of water levels balances that in the boiler.

The float in rising, connected as it is by pulleys and chains to the dampers, closes the ash pit damper, thus checking the draft and preventing a further increase of steam pressure.

In this system, the steam feed is connected to the top of the radiators and the air and condensation is taken from the bottom, because steam is lighter than either air or condensation. Accord­ ingly, when steam is admitted it floats on top of the air, •thus, driving the air out through the lower connection.

The chief feature of a vapor system is that the amount of heat given off by each radiator may be regulated by the steam valve. Thus, in Fig. 19, the valve of radiator (C) is opened just a little, which will admit only just enough steam to heat a larger portion of the radiator; with valve wide open on (E), the entire radiator is heated.

The kind of radiator used is the downflow type in which steam enters at one end at the top and the air and condensation passes out at the other end at the bottom.

As steam enters a cold radiator it forces the cool air in the radiator out through the trap into the return piping. The operation of a typical downflow radiator is shown in Figs. 20, 21 and 22. Fig. 20 shows the steam entering, air passing out through thermo­ static retainer valve. Fig. 21 shows more steam entering and con­ densation and the balance of the air passing out through ·the trap, the action progressing until (as in Fig. 22) the radiator is full of steam.

As the radiator warms up, the steam gives off heat and in so doing condensation takes place. The condensation being heavier than steam falls to the bottom of the radiator and flows to the trap through which it passes into the return piping. After the air is forced out, the steam fills the radiator and follows the condensation to the trap. The trap closes when the steam enters it because the steam is hotter than the water. This excess heat expands the valve control element, closing and holding the valve against its seat with a positive pressure, ·thus preventing the steam from flow­ ing into the return piping.

The trap closes once the radiator is completely filled with steam, and heat is given off as the steam condenses. The conden­ sation thus formed, which is cooler than the steam, flows in a steady stream to the trap which it slightly chills, causing it to open and allowing the condensation to pass out into the return piping (Figs. 23 and 24).

When properly working, the trap adjusts itself to a posHion corresponding to the temperature of the condensation just as a thermometer does to the room temperature, and permits a con­ tinuous flow of condensation from the heat emitting units (Fig. 25).