What causes water fluctuation on a small steam boiler? 3

[Serrot]

The water level on the low water cutoff fluctuates and causes boiler to cut out on low water. I am told that it is caused by the water conductivity level which doesn't sound true to me. Can you please share your thoughts on this matter?

 

[willard3]

When does the water level fluctuate, on boiler start-up?

 

[RossABQ]

I think what the person telling you this means is, poor water quality can result in frothing or carryover problems that result in a trip on low water. Water quality can be inferred from conductivity. Blow down thoroughly (from both skimmer and bottom drains) and see if it improves. Watch conductivity change as you blow down.

 

[MintJulep]

A high water level can cause level fluctuations. If it is a really small boiler the difference between too little and too much can be small.

 

[TBP]

What kind/size of boiler is it?

 

[rmw]

Is your load fluctuating? If so, then shrink and swell as the boiling (bubbling) rate changes. The level will swell on load increases as the lowering pressure induces boiling due to flashing of the saturated fluid down the the reduced pressure caused by the load fluctuation.

When the load lessens, the pressure rises in the boiler and the boiling is suppressed so the level drops like a rock.

If your water level controls are not sophisticated, they will see the level increase due to swell as high level and will stop feeding the boiler when in actuality, the boiler needs water to make up for the steam leaving and when the swing stops, then the level falls for two reasons, one due to the shrink as mentioned earlier and two, because the level controls have been starving it for water during the period of swell.

Two element and three element feedwater controls are designed to overcome that phenomenon.

rmw

 

[imok2]

The most common measure to prevent foaming and priming is to maintain the concentration of solids in the boiler water at reasonably low levels. Avoiding high water levels, excessive boiler loads, and sudden load changes also helps. Very often contaminated condensate returned to the boiler system causes carry-over problems. In these cases the condensate should be temporarily wasted until the source of contamination is found and eliminated.

 

[Keith53]

Also.....Are you operating the boiler well below designed pressure and at high loads? If so, install a pressure reducing valve at the outlet and set it to maintain desired line pressure, then increase boiler operating pressure to design specs.

Operating at too low a pressure from design will cause same problem when loaded.