Automatic boiler blowdown control

Claim 3

In combination with a steam boiler having a blowdown line and a makeup water connection, means to maintain within the boiler the conductivity of the water between pre-determined limits comprising a valve located in said blowdown line in proximity to the boiler, a motorized switch having a repetitive time cycle arranged to open the said valve for a time approximating one-fifteenth of the time cycle of operation, a conductivity cell inserted in the blowdown line between the boiler and said valve and having electrodes exposed to water flowing through said cell, means to impose an alternating current on the cell electrodes, means to rectify the current passing between the said electrodes, a rectifier and electrical circuit means responsive to the rectified current to close the blowdown valve should the conductivity of the boiler water be found to lie within the predetermined limits and alternatively to keep the valve open if the conductivity of the boiler water exceeds the said limits until dilution of the boiler water from the said makeup feed reduces the conductivity to acceptable limits and thereafter to close the said blowdown valve.

Claim 4

In combination with a steam boiler having a blowdown line and a makeup water connection, means to maintain within the boiler the conductivity of the water between pre-determined limits comprising a valve located in said blowdown line in proximity to the boiler, a motorized switch having a repetitive time cycle arranged to open the said valve for a time approximating one-fifteenth of the time cycle of operation, a conductivity cell inserted in the blowdown line between the boiler and said valve and having electrodes exposed to water flowing through said cell, means to impose an alternating current on the cell electrodes, means to rectify the current passing between the said electrodes, a rectifier and electrical circuit means responsive to the rectified current to close the blowdown valve should the conductivity of the boiler water be found to lie within the predetermined limits and alternatively to keep the valve open if the conductivity of the boiler water exceeds the said limits until dilution of the boiler water from the said makeup feed reduces the conductivity to acceptable limits and thereafter to close the said blowdown valve.

Claim 5

The apparatus as claimed in claim 2 wherein the said blowdown valve is located in the skimmer blowdown line positioned within 6 feet exteriorally of the boiler whereby when the valve is opened, measurement of the conductivity of the boiler water occurs at temperatures approximately equal to the temperature of the water inside the boiler.

Claim 6

Apparatus according to claim 2 wherein the production of false signals is avoided by inserting in the electrical circuits controlling the operation, electrical delay networks adjusted to allow time for entrained bubbles in the blowdown water to pass the said electrodes and move out Of the blowdown measurement zone and thereby avoid activation of the said blowdown valve by a false signal.

Claim 7

The apparatus according to claim 2 wherein the conductivity cell is arranged to measure the conductivity of the boiler water only at a point below the invert of the blowdown pipe, to minimize the possibility of bubbles giving false signals to the said blowdown control.