Page 261 - Boiler_Operators_Handbook,_Second_Edition

246 Boiler Operator’s Handbook

apparatus when you get back to the test bench. Note that happen if you clean it up right away.
the sample line in Figure 36 is shown long enough to To make it easier to clean and limit breakage of
submerge it in a sample bottle. That’s necessary to pro- glassware many plants have rubber mats under the test
vide a representative sample for testing sulfite content. equipment. I regularly tell someone “you can get white
Once the sample is exposed to air some of the sulfite will rubber.” The entire test stand should be white. It’s a
start reacting with the water in the air. lot easier to see color changes and other things with a
To minimize contamination of your water sample white background. I would like to have a picture of a
with air insert the sample line to the bottom of the sam- test stand after regular use to hold up as a good example
ple bottle, leaving it submerged as the bottle fills, and but I haven’t seen one yet. I can’t say too much because
allow the bottle to overflow for a couple of seconds to I know I never kept the ones I used that clean; now I
eliminate mixing of air with the sample and displace all know better.
the air from the sample bottle, flushing off the surface so If I’m watching an operator running water tests I
you have a sample that wasn’t in contact with air. can tell quickly if he’s up to the task, even when they’re
If you’re drawing from a remote sampling point nervous with me standing there watching them. They
take another bottle for rinsing your apparatus. Unless know what the results should be and add most of the
you’re testing the sample for sulfite immediately you reagent quickly to get to the point where it should be
should cap the flooded sample bottle. That’s the right added drop by drop. That saves time in the process and
way to draw a sample even if you’re not testing for sul- has no effect on the outcome. Holding the sample con-
fite. Always draw at least twice as much as you’ll need, tainer up so its lip is above the reagent spout prevents
that small amount of sample is negligible compared to spilling but you can get awful tired if it takes too long
the cooling water you’re wasting, see the section on wa- to add the reagent until the color change is evident. Oc-
ter consumption. casionally you’ll overshoot. No big deal, just measure
I seldom find a water test bench closed up. Most of up another sample and do it over. That’s one reason you
the time everything is setting out and the stand is well drew a large sample to begin with.
illuminated. Didn’t anybody ever read the instructions Speaking of measuring; you do know you’re sup-
for the test reagents that state they degrade when ex- posed to measure to the meniscus right? That’s the level
posed to light? A good bench will be closed up and dark. inside the glass (Figure 8-2) not the line at the edge of
Also, the extra reagents and other test chemicals will be the glass where the water tries to climb the sides. There’s
stored in their shipping containers in a dark area that less than 99 milliliters in the cylinder of the figure, not
has a reasonably constant temperature. Stacking them 100. There’s very little liquid in that edge so you don’t
on shelves leaning against the sheet metal outside wall want to read the level there.
that’s cold in the winter nights and heated by the sum- Write it down as soon as you read it. Make it a
mer sun is not the right place to put them. habit. No matter how good you think you are at remem-
It’s also a little dumb to order a ten-year supply of bering numbers the time will come when you can’t re-
reagents (yes, I’ve found bottles with ten year old expi- member them long enough and you’ll have to repeat the
ration dates on them setting in a plant’s storage locker). test to get the results right. Also, never assume you’ll get
It’s a pain to order stuff at regular intervals but some of
it has a short shelf life. You want to be confident of the
results you get when testing your water so make sure
you have fresh reagents. If the expiration date is before
next week, throw it away and get new.
Most test stands I see are kept clean but I do re-
member one in a poultry processing plant that had…
you got it, chicken droppings all over everything. Part
of the cleanliness is associated with operating the test
bench because some reagents can damage or discolor
paint if they’re spilled. The automatic filling burettes
will spray reagent out a little hole in the back if you
force too much reagent up. Those spatters on the back of
the test cabinet are an indication of carelessness. If you
do accidentally pump some out the discoloration won’t Figure 8-2. Meniscus