3. Vapor Steam Heating System. Flashcards
- How is the boiler operating pressure controlled in a vapor steam heating system?
Vaporstats are used to control boiler operation. They are calibrated in ounces of pressure.
- How does a vapor steam heating system work?
The steam explodes out of the boiler pushing the air and condensate through the steam traps into return piping. The radiator quickly fill with steam and the call for heat is satisfied. In this system the air flows back towards the boiler and is eliminated from the system by an air eliminator. Some vapor system utilize vacuum air vents to rid the system of air. Vacuum air vents permit air to leave the system but when the system cycles off air can not reenter the system through the vacuum air vents.
- What is the purpose of an air eliminator?
Remove air from the system rapidly, and at as low a pressure as possible.
- How does an air eliminator work?
A ball check is mounted with 45* street ell so that a very low pressure will move the ball to one side along the very slightly inclined valve seat. At the same time any reversal of flow will quickly seat the valve. This sensitivity to reversal the pressure permits the building up of a vacuum in the return even when the boiler is under the pressure. This valve assembly would also pass steam and water if they reached it, but any small amount of flash steam on return side of the thermostatic traps is quickly condensed. The condensate would back up in the return. The float would seat the liquid valve preventing the escape of water through the air vent.
- Describe the operation of a boiler return trap?
- Condensate from the heating units flows to check valve that is closed by the boiler pressure.
- The water rises upward and antlers the boiler return trap, filling it and raising the float which operates the valve mechanism.
- When the trap is full, the weights that operate the valve mechanism are tripped, vent valve is closed and steam valve is opened, admitting steam that is at boiler pressure to the trap. The pressure in the boiler, in the boiler return trap and in that part of the return line on the boiler side of check valve A are equal, permitting the head of water between boiler line and the level of water in the boiler return trap to force the condensate through check valve B into the boiler.
- As the level of water in the trap falls the float ball drops and reverses the action of the valve, closing off steam valve and reopening vent valve. At this point one cycle has Benin completed, one trap full of condensate has been returned to the boiler.
- How does the condensate flowing through the drips from the supply main return to the boiler in vapor system?
It does not have to pass through the boiler return trap because the pressure differential is small.
- How does boiler that use coal to fire work?
- As the outside air temperatures drops and the system thermostat calls for heat, the boiler’s draft damper is fully open and the coal fire has maximum air flow.
- When the thermostat is satisfied or high-limit cutoff, the draft damper is closed. The diminished air flow decreased the amount of heat the coal fire is capable of producing. A coal fire is not immediately extinguished. It will continue to generate heat but at a diminished capacity. When the fire starts to die out the steam in the radiators begins to condense. The boiler continues to make steam but there are fewer pounds of it in the system and its in a low temperature.
- If the outside air temperature drops the thermostat signals the damper regulator opening the damper. The increased air flow will result in additional heat and higher steam pressure and temperature.
- How does vapor system work?
- When the thermostat has reached the high-limit cutoff, the draft damper will close.
- When the fire in the boiler start to die out the steam in the radiators begins to condensate. There are no standard air vents on this system, so no air will be readmitted into the system. Since no air is readmitted, a vacuum begins to form. When the system drop into a vacuum the boiling temperature of the water drop, the temperature of the steam decrease and the amount of space a given amount of steam occupies increases. The boiler continues to make a steam but there are fewer pounds of it in the system and its at a low temperature.
- If vapor systems are so great, why are they not installed anymore?
- When the system cycles off and air flow into the furnace was stopped the coal fire continued to generate heat for a long period of time. The system cooled slowly and the vacuum formed slowly. Any air that was trapped in the radiators expanded slowly and did not expand back into the supply mains.
- In oil or gas fired boilers, once the thermostat is satisfied and the fuel valve shuts the flow of fuel, the furnace rapidly cools down. The system quickly goes into a deep vacuum. The trapped air quickly expands into supply mains. This slow down or stops the flow of steam, when there is a call for heat and the system cycles on.
- How can you get the replacement part for are eliminators and boiler return traps?
They are no longer being manufactured. A vapor system shall be modified so it will work without these components.
- How can a vapor system be modified?
- Before work on repiping the system begins, it is a good idea to tag all the steam supply and condensate return piping.
- Some types of vapor system did not utilize radiator traps. Thermostatic radiators and F&T traps must be installed.
- On systems which require the use of high operating pressures, the vaporous tar must be replaced with a pressure trol.
