Any official word on what would constitute "too long" to wait for the water level to return after a water column blowdown?

Or is this one of those "reasonable and prudent" kinda things?

I mean, I think that we could all agree that a minute might be too long...

But what about 30 seconds?  15 seconds?

Maybe I'll add another Q here, too...

How are you checking your LWCO?  I  (Unless I've got a pretty good load, and can't stand an interruption) like to secure the feed...and wait and watch---

I'm not aware of an official answer to this, but I can say with confidence that 30 seconds is way too long.  15 seconds is too long as well.

It depends upon the size of the boiler and configuration of the water column piping.  If the water has to travel a longer distance it could take a little longer, but most of the time it should be almost immediate.

The way to be sure about this for your boiler is to test it right after you have the boiler and water column inspected.  If the water column is completely clear and it takes 4 seconds, then 4 or 5 seconds should be acceptable to your boiler.  10 seconds means there is starting to be a problem.  15 seconds means shut it down and take the column piping apart.

Thanks for posting.

-Reed

LWCOs should be blown down daily  with the boiler running to see if the boiler shuts down like it's supposed to (without pressing the LWCO bypass button if you have one).  If you just can't/won't tolerate having your boiler go down during this test everyday, then do it as often as you possibly can.  Our official recommendation is to let it shut the boiler off every day.

If you blow down the LWCO just to get the sludge out, you are only performing half of the test (the other half is to prove the burner will cut out).

Bob - Does this cover the 2nd question?  I'm not sure.

This answer refers to high-pressure boilers.  For low-pressure boilers, do this weekly.

Reed

Bob,

This type of thing would be difficult to enforce, so things like this are ASME recommendations rather than requirements.  Letting the boiler trip is strongly recommended (otherwise it is not a test, it's just removing mud), although an inspector will not come in and force you to do this. 

It is assumed that a good operator will attempt to do this in something like the frequency recommended in the code.

Keep posting!

Reed

Bob,

An evaporation test is recommended once per year.  If your LWCO is a little "sticky" it may shut the boiler down during a blowdown test, but hang up if the water level dropped more slowly like it really would if there were a problem.  An evaporation test is done to make sure the LWCO will work in that type of situation.  However, it is a more involved test and is only recommended annually.

Reed