| Low Water Cutoff | Stops the burner on a low water condition. Burner restarts when normal water is achieved. | Feedwater modulating control valve (steam) | On signal from level controller, modulates open/close to allow condensate to flow into boiler. |
| Aux. Low Water Cutoff | Stops the burner on a low water condition. Burner restarts when normal water is achieved, and manual intervention is involved (manual reset). | Quick opening blowoff valve (steam) | Lever handled valve piped to bottom of boiler to allow quick discharge of condensate and contaminants. |
Optional: Boiler Level Controller (steam) | Signals feed water valve to modulate open/close as necessary to maintain proper water level. | Slow opening blowoff valve | Wheel handled valve piped to bottom of boiler to allow slow discharge of condensate and contaminants. |
| Optional: Boiler High Water Alarm (steam) | Signals the operator of a high level in the boiler. If desired, could stop the burner as well. | Continuous blowoff control valve (steam) | Position indicating hand wheel needle valve to meter the discharge of condensate at the top of the boiler. |
| Operating Limit Controller | Restricts the boiler from over pressure or temperature. Stops the burner on high condition, restarts when boiler returns to normal. | Continuous blowoff control valve (steam) | TDS manual control. Position indicating hand wheel needle valve to meter the discharge of condensate at the top of the boiler. |
| High Limit Control | Restricts the boiler from over pressure or temperature. Stops the burner on high condition, restarts when boiler returns to normal and manual intervention is involved (manual reset). | Automatic continuous blowoff system (steam) | TDS automatic control. Controller, electric valve and conductivity probe. Controller opens/closes valve on basis of input signal from probe. |
| Modulating press or temp. controller | Signals burner to adjust firing rate on the basis of the boilers current operating pressure/temperature. | Steam non-return valve (steam) | Combination stop/check valve to isolate and back flow prevention. |
| Pressure or combination press altitude gauge | Direct reading gauge located close to the limit controls. Boiler monitor. | Steam stop valve (steam) | Stop gate valve to isolate boiler. |
| Low Fire Hold limit control | Restricts the burner from firing above “low” prior to water temperature achieving set temperature. | Sight glass | Visual indication of water level. |
| Safety Relief valve(s) | Boiler shell mounted device to vent excess steam/water when boiler pressure/temperature is exceeded. | Tri-cocks | When opened, gives secondary indication of water level. |
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