Boiler Blowdown Controller Settings

Lakewood has two dedicated boiler controllers, the Model 150 and Boiler NexSys.  We also have two controllers (Models 1575e and 3175) that can be used for cooling tower applications as well as boilers.  Let’s talk about the controller settings that are specific to boiler blowdown.

Boiler Blowdown Methods and Timers

All four of the controllers mentioned above can perform “Continuous” and “Sample/Cycle” boiler blowdown methods.

The Model 150 and Boiler NexSys have the additional method option of “Sample/Hold.”

Check out a detailed description of the boiler sample methods here.

It is very important to have appropriate timers when using “Sample/Cycle” or “Sample/Hold” sample methods.  The correct intervals depend on the specific system.  Please note the sample time is entered in minutes and seconds (MM:SS) while the cycle time is entered in hours and minutes (HH:MM).  The hold time on the Model 150 and Boiler NexSys is set at 45 seconds.

As the name implies, there are no timers associated with the “Continuous” sample method.

Ball Valve Delay

Cooling tower blowdown valves typically require power to open and close automatically when power is removed by means of a spring or on-board capacitor.  Note that there is only one power connection along with the neutral.

In contrast, boiler blowdown systems use motorized ball valves, which require power to open and power to close.  There are separate power connections to the valve actuator for each.

It takes a certain amount of time for the valve to “stroke” fully from one position to the other.  If the valve is commanded to close before it completes the process of opening, or vice-versa, it will end up in a half-open state.  The ball valve delay feature prevents this from occurring.  To use this feature, determine how many seconds it takes to open and close the valve.  Use the longest time and add 1 second.  Use this value as your BALL VALVE DELAY.  This delay time will also be observed when manually operating the blowdown relay.