Re: Intermittent Low Water Level

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Posted by Roger Link on July 11, 2000 at 05:17:20:

In Reply to: Intermittent Low Water Level posted by BC Lee on July 11, 2000 at 01:04:12:

: Hi All. Need some advices on this.

: We have 3 Cochane Boilers (4800 kg/hr) fitted with Grundfos Feed Pump (rated 5.5 hp, 2.2 MPA). The boiler pressure is usually around 8-10 bar.

: The problem is that we experience intermittently low water level in the past 4 weeks or so. We checked the feed pump and the chemicals injection point (right before the pump), the filter and line appeared to be clean. There is some carryover found in the steam (white powder-like), and two of the steam traps were not working properly. We have a feed water tank that is large enough that possibility of low water supply is non-existence.

: Could anyone advice what else should we check and what could have caused the water level to go down ?

: Thank you.

1) Check the operation of the float mechanism for the pump controller to see if it freely working and not in a bind.
2) Check to see if the check valve(s) between the boiler and the boiler feed pump is leaking back thru the pump causing it to cavitate or vapor lock therefore not putting sufficient water in the boiler.
3) Check the chemical content in the water to see if there is an excessive amount of chemical that might cause the water to surge up and down violently thus causing the LWCO to trip.
4) Check to see if there is contanination in the condensate return that is coming from a leaking coil or heat exchanger that might cause the water level to surge.
5) Check the demand vs. supply of the process and boiler. Often there are periods during one's process when there is a greater demand than boiler capacity thus causing water to be "pulled" out of the boiler thus causing wet steam. The remedy is to throttle the main gate or non-return valve at the steam nozzle on the boiler to keep the water from exiting the boiler.
6) Check the steam traps in the plant to see if there is full steam pressure passing thru and returning to the CR tank. This will overheat the water thus causing the cavitation/vapor lock condition mentioned earlier.
7) Check the connection at the feedpump line at the boiler to see if there might be a restriction there.
8) Check to see if the boiler feedpump is putting out sufficient pressure by putting a gauge on the discharge then dead heading the valve at the boiler.
If the pump is running a long period of time , it is probably a clogged line , bad check valve or bad traps.Your promlem(s) might be a combination of any of the above conditions.

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