boiler, feedwater heater, or surge tank. Usually, the vacuum pump is supplied with a float switch as well as a vacuum switch, and it can be operated as a condensate pump unit. The float switch should be used only when the vacuum switch is defective, and then only until the defects can be repaired or corrected.

This system can be used in all types of buildings, and it is of particular advantage for the satisfactory operation of indirect radiation units, heating coils, and ventilating units, and for other units that requires close automatic control. Indirect radiation is a term applied to warm-air heating systems that receive their heat from steam supplied to their heat exchanger coils.

Maintenance

When considering the subject of maintenance on a two-pipe vapor distribution system having a vacuum pump, you will find that most of the troubles that have previously been discussed also apply to this system. In this distribution system, however, keeping air from leaking into the system is more of a problem than in the other distribution systems. Excessive air leakage often causes the pump to run all the time, or the leakage can cause the system to fail to heat altogether. To eliminate -air leakage, you must find the point where air is leaking and repair it, so air cannot get into the system. Rusty spots and water seepage usually indicate the points at which air is leaking into the system.

Q4. On a gravity, one-pipe, air vent system, the return of condensate to the boiler depends on what factor?

Q5. Air in a one-pipe system has what adverse effects?

Q6. What is the major difference between a two-pipe system with a return trap and a two-pipe system with a condensate pump?

Q7. What is the function of the vacuum pump on a two-pipe vapor system?

STEAM DISTRIBUTION SYSTEM COMPONENTS

Learning Objective: Recognize different system components and understand their basic operation, application, and maintenance.

In previous sections of this chapter, you read about various components as you studied the various distribution systems. The components were only mentioned, however, and not explained in detail. Therefore, in this section, we are going to discuss these components, their purpose, operation, and maintenance.

RADIATORS

Steam radiators. are normally classified into two categories. One is the fin-tube radiator, which consists of a metal tube that has metal fins attached on the outside to increase its total heating surface. It generally has a valve at one end and a trap at the other end. This radiator has been used more extensively in the past 15 years. It is readily adaptable to areas where floor space is limited, since the radiator is normally mounted on the walls. The second category is the cast-iron radiator, which is made in sections. A typical cast-iron radiator is shown in figure 3-9. These radiators are similar to those used in hot-water heating systems. The cast-iron radiator is generally used in the one-pipe distribution system. In this system, there is only one distribution pipe connected to the radiator. This pipe delivers steam to the radiators, and it also returns water from the condensed steam to the boiler. For this reason, the radiators must be tilted slightly toward the distribution pipe.

The radiators in a two-pipe steam distribution condenses into water. prevents steam from leaving the radiator until it system are connected to the boiler by means of a distribution pipe as well as by a condensate return pipe. Since the steam and condensate in this system flow in separate pipes, the pipes are smaller than those required for the same size radiator in a one-pipe system. The radiator outlet is usually equipped with a steam trap that

Figure 3-9. - A typical cast-iron radiator.