Figure 3-10. - A typical automatic air vent.

RADIATOR AIR VENTS

There are two types of radiator air vents: automatic and manually operated. A typical automatic air vent is shown in figure 3-10. Air vents are installed to remove air from the radiators, because air keeps the radiator from heating properly.

The type of air vent shown consists of a hermeti- cally sealed bellows, a valve disk and seal, and a vent body. The bellows contains a volatile liquid with a boiling point 10F or lower than that of water. So, when this liquid is heated to a temperature 10F below the steam and water temperature, the liquid volatilizes, expands, and closes the valve. When air surrounds the bellows, the air is cooler than the steam. This causes the bellows to contract, to open the valve, and to allow the air to escape. This cycle then starts over again.

The type that is operated manually is usually a small valve that has a slotted screw incorporated in the stem and a little spout on one side for the discharged air. These manual vents are normally installed in the same place in the distribution system as automatic vents.

STEAM TRAPS

Steam traps are designed to retain the steam in a radiator or other using device until it changes into condensate. After the steam has turned into condensate, the trap releases the water so it can enter the return lines. However, it keeps the steam coming into the radiator from escaping. The trap performs an important function, since the excessive accumulation of water

prevents the proper heating of the radiator or other steam equipment. Also, steam that is permitted to blow through a defective trap results in heat loss.

Types of Traps

Traps are generally classified according to their operation. The most common types of traps are float, bucket thermostatic, float thermostatic, impulse, thermodynamic, throttling, and bimetallic element.

FLOAT TRAP. - The float trap normally consists of a body, float, linkage, seat, and valve. A typical float trap is shown in figure 3-11. As water enters the trap, the float rises, opens the valve, and allows the accumulation of water to flow into the return lines that take it to the boiler. When the water has run out, the float falls, closes the valve, and traps the steam.

The maintenance to be done on a float trap is of a simple nature. One of the most common difficulties is that of the float getting water in it and not rising. In this case, the float must be replaced. The valve sometimes gets plugged or worn and has to be cleaned or replaced.

BALL-FLOAT TRAP. - In a ball-float trap, the valve of the trap is connected to the float so the valve opens when the float rises. When the trap is in operation, the steam and water that may be mixed with it flow into the float chamber. As the water level rises, the float is lifted, thereby lifting the valve plug and opening the valve.

The condensate drains out and the float moves down to a lower position, closes the valve. The condensate that passes out of the trap is returned to the feed system.

Figure 3-11. - A typical float trap.