The two-pipe system is considerably more expensive to install and is not very often found in the home. The one-pipe system gives excellent service if it is properly installed.
Each radiator in a steam system is equipped with a special valve. The purpose of this valve is to allow the air in the system to be driven out by the pressure with the inner mechanism, the valve closes and prevents any steam from escaping from the radiator.
If one radiator in a steam system fails to heat, it is probably because the valve is clogged with dirt or otherwise out of adjustment. This prevents the air inside the radiator from escaping and, consequently, the steam cannot enter the radiator. The valve should be removed and cleaned, or replaced if it still fails to function. Close the shut-off valve to the radiator before removing the small valve for cleaning or replacing.
A variation of the one-pipe steam system is the vacuum system. Here, a special valve prevents air, forced out by the steam, from returning to the radiator when the steam condenses. The result of this action is the creation of a partial vacuum in the system. When the steam condenses, the air pressure in the system is lowered ; this means that the water in the boiler will turn to steam at a lower temperature, with a consequent saving of fuel.
The boiling point of water decreases as the air pressure decreases. Another advantage of the steam vacuum system is that with less air in the pipes, the steam will reach the radiators more quickly.
The efficiency of this vacuum system depends on there being no leaks throughout the entire system of pipes and radiators. A normal one-pipe system may have several air leaks which will not necessarily cause trouble, but if it is converted to a vacuum system, the leaks will seriously impair its operation.
Many difficulties in a one-pipe steam system are caused by improper installation of pipes. The pipes should be as free from sharp angles as possible. Sharp angles offer resistance to steam just as sharp angles in warm-air ducts offer resistance to the air. Bends make the system sluggish as well.
The pipes must be large enough to allow steam to rise while the water is coming down. If the pipes are too small, there will be a certain amount of friction between the water and the steam, and this will cause the system to work poorly.
Noise in a System. There are a number of conditions which will make a steam system noisy. Dirty water in the boiler is one of these, and causes the familiar rumbling noise.
A knocking sound is often due to the improper pitch of the pipes. All pipes must have a downward slope, in order that the water may flow without difficulty from the radiator to the boiler. If, for some reason, a piece of pipe has sagged, water will collect in this depression and become a serious obstacle in the path of the oncoming steam.
The meeting of the steam and the trapped water results in pounding. When it occurs near a radiator, it can generally be eliminated by putting small blocks of wood under the legs of the radiator.
This will increase the pitch of the radiator, and the pipe connected with it, so that the water will find an easy path back to the boiler. When hammering occurs in some other part of the system, try to find a section of pipe that has sagged, causing a hollow where water can collect.
Another reason for pounding may be the position of the steam valve between the radiator and the steam pipe. This valve should be fully opened or fully closed, but never halfway.