Although all gravity, one-pipe, air-vent systems are alike in design, it is seldom that two installations are alike in detail. Since the details differ with the make and model of equipment, it is recommended that the manufacturer's installation procedures be followed. Also, you should follow the mechanical blueprints for a particular installation. There is some general information in this section that applies to most heating systems of this type.
To prevent water hammer and re-evaporation of the water, drain all condensate from the lines. The necessary internal drainage can be obtained by sloping the lines down, in the direction of condensate flow, at least one-fourth of an inch for every 10 feet of pipe. The radiators must also be tilted, so the condensate flows out of them into the same pipe through which the steam is entering.
Air vents are installed in the steam lines and radiators to eliminate air in the system. Air in the system tends to block the flow of steam, and it consequently acts as an insulator by preventing the emission of heat from the heating surface. Therefore, the air must be quickly and effectively vented from the heating equipment and steam lines to get quick and even heating from the steam-heating system. Most steam distribution systems are now fitted with automatic vents that permit the air to pass but which block the passage of steam. Figure 3-5 shows air vents in the radiator and the distribution system.
The operating instructions for gravity, one-pipe, air-vent systems vary from one installation to another. The manufacturer of the equipment usually furnishes the specific operating instructions for the equipment.
Generally speaking, most steam systems have a main steam stop valve located on the top of the boiler. The purpose of this valve is to hold the steam in the boiler until you are ready to let it out. When you are ready to turn the steam into the distribution system, you should only crack (open very little) the valve. The reason for doing this is to allow the system to warm up slowly and avoid any thermal shock to the lines and fittings. After the system has warmed up, the main steam stop valve should be opened slowly. While opening the valve, you should check often to ensure that the proper water level is maintained in the boiler.
You will also note that the radiator valves in one-pipe steam distribution systems should be either completely open or completely closed. Partial opening of the valve interferes with the proper drainage of water from the radiator.
In this portion of the text, the common problems you are most likely to encounter in the field when maintaining a gravity, one-pipe distribution system are discussed. The most probable causes of these problems and the remedies for them are considered.
When a radiator fails to heat or water hammer occurs, there are several probable causes. One is the failure of the air vents to function, thereby causing the radiator to become air bound. A second cause is that the radiator valves are not completely open. Another cause is that the radiators and lines are not correctly pitched. To remedy these causes of heat failure, you should inspect the operation of the air vents and the positions of the radiator valves to make sure they are open. You should then check and correct, if necessary, the pitch of the radiators and lines when the other checks do not correct the trouble.
A fluctuating waterline in the boiler can be caused by an excessive pressure drop in the supply lines, which, in turn, is usually caused by partial stoppage in the pipes. This, of course, can only be remedied by removing the cause of the stoppage. Uneven heat distribution is another trouble that you may encounter. This can be caused either by inoperative radiator vents, improperly vented steam mains, or incorrectly pitched mains. To eliminate this uneven heat distribution, you should check and clean the air vents at the radiator and those in the steam mains. Then check and correct, as required, the pitch of the steam lines if the other remedies have not corrected the trouble.
The two-pipe vapor system with an alternating return trap, as shown in figure 3-6, is an improvement over the one-pipe system. The return from the radiator has a thermostatic trap that permits the flow of condensate and air from the radiator. It also prevents steam from leaving the radiator. Because the return mains are at atmospheric pressure, or less, a mechanical return trap is installed in the system to equalize the condensate return pressure with the boiler pressure. The mechanical return trap is primarily a double-valve floatContinue Reading