Page 23 - Boiler_Operators_Handbook,_Second_Edition

8 Boiler Operator’s Handbook

Unless we use a unit reference for a measurement and the range is the height of the tank.
nobody will know what we’re talking about. How With so many arbitrary choices for level it could be
would you handle it if you asked someone how far it difficult to relate one to another. That could be impor-
was to the next town and they said “about a hundred?” tant when you want to know if condensate will drain
Did they mean miles, yards, furlongs, football fields? from another building in a facility to the boiler room.
Unless the units are tacked on we can’t relate to the There is one standard reference for level but we don’t
number. call it level, we call it “elevation” normally understood
With few exceptions there are multiple standards to be the height above mean sea level and labeled “feet
(units) of measure we can use. Which one we use is MSL” to indicate that’s the case. In facilities at lower
dependent on our trade or occupation. Frequently we elevations it is common to use that reference. A plant in
have to be able to relate one to the other because we’re Baltimore, Maryland, will have elevations normally in
dealing with different trades. We will need conversion the range of 10 to 200 feet, unless it’s a very tall building.
factors. We can think of a load of gravel as weighing a When the facility is a thousand feet or more above
few hundred pounds but the truck driver will think of it mean sea level it gets clumsy with too many numbers so
in tons. He’ll claim he’s delivering an eight-ton load and the normal procedure is to indicate an elevation above a
we have to convert that number to pounds because we standard reference point in the facility. A plant in Den-
have no concept of tons; we can understand what 16,000 ver, Colorado, would have elevations of 5,200 to 5,400
pounds are like. Another example is a cement truck de- feet if we used sea level as a reference so plant references
livery of 5 yards of concrete. No, that’s not fifteen feet of would be used there. It’s common for elevations to be
concrete. It’s 135 cubic feet. (There are 27 cubic feet in a negative, they simply refer to levels that are lower than
cubic yard, 3 × 3 × 3) We need to understand what type the reference. It happens when we’re below sea level or
of measurement we’re dealing with to be certain we un- the designers decide to use a point on the main floor of
derstand the value of it. Also, as with the cement truck the plant as the reference elevation of zero; anything in
driver, we have to understand trade shorthand. the basement would be negative. The choice of zero at
When measuring objects or quantities there are the main floor is a common one. Note that I said a point
three basic types of measurement: distance, area, and on the main floor, all floors should be sloped to drains so
volume. We’re limited to three dimensions so that’s the you can’t arbitrarily pull a tape measure from the floor
extent of the types. Distances are taken in a straight line to an item to determine its precise elevation.
or the equivalent of a straight line. We’ll drive 100 miles An area is the measurement of a surface as if it
between Baltimore and Philadelphia but we will not were flat. A good example is the floor in the boiler plant
travel between those two cities in a straight line. If you which we would describe in units of square feet. One
were to lay a string down along the route and then lay square foot is an area one foot long on each side. We say
it out straight when you’re done it would be 100 miles “square” foot because the area is the product of two lin-
long. The actual distance along a straight line between ear dimensions, one foot times one foot. The unit square
2
the two cities would be less, but we can’t go that way. foot is frequently written ft meaning feet two times or
Levels are distance measurements. We always use feet times feet. That’s relatively easy to calculate when
level measurements that are the distance between two the area is a square or rectangle. If it’s a triangle the area
levels because we never talk about a level of absolute is one half the overall width times the overall length. If
zero. If there was such a thing it would probably refer it’s a circle, the area is 78.54% of a square with length
to the absolute center of the earth. Almost every level is and width identical to the circle’s diameter. A diameter
measured from an arbitrarily selected reference. The wa- is the longest dimension that can be measured across
ter in a boiler can be one to hundreds of feet deep but we a circle, the distance from one side to a spot on the op-
don’t use the bottom as a reference. When we talk about posite side. In some cases we use the radius of a circle
the level of the water in a boiler, we always use inches and say the area is equal to the radius squared times Pi
and negative numbers at times. That’s because the refer- (3.1416). When you’re dealing with odd shaped areas,
ence everyone is used to is the center of the gage glass and you have a way of doing it, laying graph paper
which is almost always the normal water line in the over it and counting squares plus estimating the parts
boiler. The level in a twelve-inch gage glass is described of squares at the borders is another way to determine an
as being in the range of –6 inches to +6 inches. For level area. A complex shaped area can also be broken up into
in a tank we normally use the bottom of the tank for a squares, rectangles, triangles and circles, adding and
reference so the level is equal to the depth of the fluid subtracting them to determine the total area.