When you find that the individual radiator fails to heat, either an inoperative steam trap or a radiator that is not installed correctly can cause the trouble. Repairing or replacing the steam trap or correcting the improper installation of the radiator can eliminate these troubles.

When it is the whole distribution system that fails to heat, clogged or closed receiver vents can cause the trouble, a flooded return line, the lack of pump capacity, or air binding the system. These troubles can be remedied by opening the vents, checking and adjusting the pump cut-in, replacing the pump, or repairing inoperative rerun traps.

One common trouble that occurs in this type of distribution system is the overflow of water from the receiver vent. An inoperative pump usually causes this condition. The pump may be causing the flooding because of its inadequate capacity or because it is unable to handle the volume of condensate required. This condition can be corrected by either repairing or replacing the pump.

Another cause of overflow of water from the receiver vents is an obstruction in the line between the condensate receiver and the boiler. The trouble can be remedied by eliminating the obstruction, regardless of whether it is a closed valve or a clogged line.

TWO-PIPE VAPOR SYSTEM WITH A VACUUM PUMP AND A CONDENSATE RETURN

The two-pipe vapor distribution system with a vacuum pump and a condensate return, as shown in figure 3-8, is similar to the two-pipe vapor system with a condensate pump. The piping in this system includes separate steam and return mains.

Installation

Most vapor distribution systems with vacuum pumps and condensate returns are similar. However, it is seldom that two steam distribution installations are alike in detail. When installing vapor-heating distribution systems, it is advisable to refer to the manufacturer's recommendations, civil engineer mechanical drawings, and specifications for the proper installation procedures.

Operation

When this type of distribution system is operated, the steam is supplied at the top of the radiator and the air and condensate discharged through a thermostatic trap from the bottom of the opposite end of the boiler. All returns are dry and terminate at the vacuum pump. The vacuum pump is usually a motor-driven unit, although low-pressure steam turbines have been successfully used to a limited extent. The vacuum pump returns the condensate to the boiler and maintains the vacuum or subatmospheric pressure in the return system. The maintenance of a vacuum in the return system (3 to 10 inches of water) enables almost instantaneous filling of the heating units at low steam pressure (0 to 2 psi) since air removal is not dependent upon steam pressure.

The vacuum pump withdraws the air and water from the system, separates the air from the water, expels the air to the atmosphere, and pumps the water to the

Figure 3-8. - A two-pipe vapor system with a vacuum pump.