The Webster Moderator System is a heating system that utilizes a pulsating steam flow arrangement. This system comprises a central heat control of the pulsating flow type for new or existing steam or hot water systems. It is designed for small and medium size buildings and for zoning of large buildings. It directly controls the operation of burner, stoker, blower, or draft damper motors.

The basic components of this system are:

  1. Outdoor thermostat
  2. Pressure difference controller
  3. Control cabinet
  4. Capillary tubing

These four components work together to open and close a valve in the steam main or to start and stop the automatic firing device at the boiler generally through a relay. The pressure difference controller maintains the correct difference between supply and return piping. In combination with metering orifices, this device gives an even distribution of the steam to all radiators in the system thereby preventing over or under heating.

Control is accomplished by varying the length of intervals during which steam is delivered to the radiators. These intervals are longest in cold weather and shortest in mild weather. The timing is such that the longest off interval is comparatively short so that heat output from radiators is practically continuous.

The timing mechanism inside the control cabinet is powered by a synchronous motor which turns a cam. Timing gears between motor and cam set the length of the operating cycle. Rising on the cam is a roller connected to the arm of a switch. When the roller is on the high part of the cam, the switch is in the position for opening the control valve or starting the firing equipment. When the roller is on the low part of the cam, the switch is on the position for closing the control valve or stopping the firing equipment. The length of the cycle is 30 minutes. Other gears can be furnished for cycle lengths from 12 to 60 minutes.

A variator is included in the control cabinet for manual adjustment of the rate of heat delivery to the building. The variator changes the relationship of the switch lever and roller to the cam by moving the cam itself. This is accomplished by mounting the motor, cam and gear train on a movable carriage.

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