EAR TEST METHOD. - Hold one end of a metal rod to the trap body and place the other end in the ear, or use an engineer's stethoscope. If the trap is operating properly, you will hear the regular opening and closing of the valve. If operation is defective, you will hear considerable rattling or the continuous flow of steam.

PROTECTION AGAINST FREEZING - Pro- tect traps from freezing in cold weather. If the steam is shut off during freezing weather, drain the traps and piping of all condensate. Make certain insulation is in good condition. The inverted bucket is especially prone to freezing because, in normal operation, it is half filled with water.

Figure 3-19. - A typical unit heater installation.

WATER TANKS

A boiler plant and heating system cannot be operated so the flow of water and the flow of steam are always in balance. The demand for water by the boiler may exceed the rate at which water is being returned from the heating system, or the water may be returning at a rate that is greater than the requirements of the boiler. One or more tanks can be installed to compensate for uneven flows and for differences between the demand and supply of water. These vessels are called surge tanks.

Sudden reductions in pressure may lead to violent steam formation. Flash tanks help eliminate disturbances in the piping system caused by this process. These tanks are usually small and are located near the traps where the pressure release occurs.

Unit steam heaters are convection heaters in which the air is circulated by means of a fan. The unit heater is similar to an automobile radiator. It is enclosed in a sheet metal case with the fan mounted at the rear. A typical unit heater is shown in figure 3-19. The steam enters the unit at the top and the heat is transferred to the fins of the heater. The fan blows the air over the fins and out into the space to be heated. When the steam condenses, the steam trap, usually a float thermostatic type, allows the condensate to drain into the condensate return line. A strainer is installed just ahead of the trap to help keep foreign matter out of the trap.

Unit heaters are usually suspended from the ceilings of shops, offices, dining halls, and warehouses. This type of installation saves on floor space, provides for rapid heating, and gives wide distribution of heat.

Unit heaters should be taken down periodically and cleaned, because dust and lint collect between the fins and reduce the flow of air.

WATER HEATERS

Steam-operated water heaters are used to supply hot water for laundries, dining halls, latrines, and other facilities. There are two general types of these heaters: storage and instantaneous.

Storage Type

The storage type of water heater is used to provide potable (drinking) water. The steam-operated storage type of water heater consists of a steel tank that contains a steam-heating coil like that shown in figure 3-20. The hot-water tank is connected to the base water supply system and remains full of water at all times.

The steam is circulated through the heating coil or "bundle," as it is sometimes called. The heat from the steam is transferred through the walls of the coil to the water in the tank. Because of the difference in weight between hot and cold water, the hot water rises and the cold water goes to the bottom of the tank where the

Figure 3-20. - The storage-type water heater.