This is how I solved it: Assuming a burner control of some sort is used, so boiler pressure can be considered "constant" (it does not really matter HOW constant, because any variations in that pressure also are determined by the position of the steam control valve, therefore repeatable), the steam consumption is determined by the steam control valve. Which means, water supply should follow the position of that steam valve.
I have a transmitter with decent programming possibilities WRT slaved channels and curves.
I installed a feedpump with speed control (in my case the "electronic" version of the Regner feedpump), and slaved that channel to the throttle.
Then I did four runs, each run at one constant speed, and of course each run at a different speed (test basin recommended for close observation of the boiler level), and adjusted the pump speed curve for each of those power settings.
It keeps my boiler level absolutely stable for the duration of a full feedwater tank, without ANY form of control, or additional subsystems.
One of the reasons why I prefer simplicity over "control systems" is that the waterlevel in the boiler is affected by load changes, and a feedwater control cannot do anything but respond to those immediate and sudden level changes, while in reality it should NOT: it should only respond to trends in the water level.
For example: if after a period of low speed steaming the steam control is suddenly opened, the water level will show a quick increase due to the intensifying of the boiling process caused by the pressure drop. The pressure drop will cause the burner control to open fuel supply, boiling intensifies even more. At that point in time an active feedwater control will reduce or even stop the feedpump temporary because it sees a high water level, while in reality the boiler still contains the same amount of water, but needs MORE water, not less, because it is delivering steam at a higher rate.
Opposite is also true: Coming from a period of full speed steaming and the throttle valve is closed, the boiler level will initially drop, leading to increased activity of the feedpump.
Like in all controlled systems, time is a factor here, and depending on how often the throttle valve setting is changed, this can lead to "oscillation" of the waterlevel.
In itself, this will usually NOT lead to any problems with the boiler itself, usually the water level margins will be wide enough. But it will affect the "quality" of the steam the engine receives (wetter or drier), which can cause issues with irregular lubrication in case of a displacement lubricator, and also the oil separator (assuming one is fitted) might fill up quicker than necessary.
The latter especially became an issue for me when the operating time of the system as a whole started to exceed the safe operating time of the oil separator: I had to come in for "slops disposal" halfway, which was annoying.
Based in real life engineering experience, I am a strong believer in striving for an as stable operation as possible. Each factor in and of itself has not that much effect, but all factors combined can result in very significant improvements, even in small scale installations.
And isn't "optimizing" an important part of the fun we have?
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Topic: Live Video for Boiler Water Level Monitoring (Read 3487 times)