{{unreferenced, date=December 2012 A pressuretrol is a control used to control a steam

boiler A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central h ...

, by setting when the boiler should begin and end firing based on steam pressure. The pressuretrol is generally secondary to another control, such as a thermostat(generally in smaller buildings) or outdoor-reset controller- If this controller is not calling for heat, the pressuretrol will not activate the boiler.

Settings

Pressuretrols have 2 settings: A main cut-in or cut-out setting (depending on model), and a differential setting (which is either additive or subtractive, and usually stated on the controller). The main setting is accessible from the outside of the controller, but the differential is often located inside the controller box, and typically the cover must be removed by removing a screw to access the differential control. If the main setting is a cut-in setting, then the differential setting sets the cut-out setpoint by adding to the cut-in setting(additive), and if the main setting is a cut-out setting, then the differential sets the cut-in by subtracting from the cut-out setting (subtractive).

Domestic hot water

Note that in systems in which the boiler provides

domestic hot water Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating. In industry, hot water and water heated t ...

as well as steam, the pressuretrol does not control the DHW temperature. This is controlled by an

aquastat An aquastat is a device used in hydronic heating systems for controlling water temperature. To prevent the boiler from firing too frequently, aquastats have a high limit temperature and a low limit. If the thermostat A thermostat is a ...

which can control the boiler independently of the pressuretrol to meet DHW demand.

References

Control devices Boilers