4.3.2 Continuous TDS Blowdown
The new TDS blowdown operation will hold the valve at a calculated value for the duration of the top
blowdown. The top blowdown will not operate if the burner is not firing or if the water is within the
allowed TDS threshold. The following procedure takes place during the continuous TDS operation:
1. From a closed position, the TDS valve fully opens to gain a fresh sample.
2. The valve then fully closes, allowing a settle time; the sample is then measured.
3. If the TDS value is above the target TDS value, the valve will use a PI loop to calculate a fixed
angle for the blowdown; it will hold this position for the duration of the blowdown timing.
4. Once the top blowdown time has elapsed, the sequence shall start again.
5. Once the TDS value has been reached or decreased to below the target TDS value, the valve
shall remain closed for the duration of the blowdown timing.
6. This PI loop control will continue to maintain the target TDS value.
4.3.3 Solenoid Valve TDS Blowdown
The sampling and control sequence of the top blowdown using the solenoid valve is detailed below:
1. If the boiler water sample is above the required TDS value the system will open the top
blowdown control valve for 5-300 seconds. This time duration is user variable and is
designated blowdown time.
2. After blow down the system invokes a 5 second settlement interval.
3. After the settlement period a 5 second measurement routine is carried out to establish the
current TDS level.
4. If the boiler water sample is still above the required TDS value the system will repeat the top
‘Blowdown Time’ routine as detailed above in 1) BDT.
5. When the boiler water sample is measured as below the required TDS level, the system will
then take a sample every 60-300 seconds. This sample time interval is user variable.
6. The duration of the sample time is 3-10 seconds. This is user variable.
7. The system then repeats this cycle.
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