Plumbing Calculations Practice

A small and repeating set: offsets and travel using right-triangle geometry, grade and total fall, pipe and tank volume, pressure and head conversion, velocity and diameter from flow rate, and fixture unit accumulation. Because the set is closed and every answer can be checked by redoing the arithmetic, it is the most reliably scoreable part of any licensing examination.

Each exercise has a stated tolerance, shown under the input box, so an answer that is right but rounded differently still counts. You also declare the unit you answered in, and your value is converted before comparison: so if the number is right but the unit is wrong, you are told that specifically rather than simply marked incorrect.

One cubic foot of water is 7.48 gallons and weighs 62.4 pounds; one gallon weighs 8.34 pounds; one foot of water column is 0.433 psi, so one psi is 2.31 feet of head. Those four carry a large share of the calculation questions on a plumbing exam, and having them immediate turns three-step problems into one-step ones.

Divide the square of the internal diameter in inches by 24.5. A 4 inch pipe with a 4.026 inch bore holds about 0.66 gallons per foot. The constant comes from the cylinder volume formula combined with the 231 cubic inches per gallon conversion, and deriving it rather than memorising it protects you when a question gives the bore in different units.

Fewer than you would expect, because most of them can be rebuilt from two or three relationships. Velocity, flow and diameter all come out of the continuity equation. Pipe volume and gallons per foot come out of the cylinder formula plus the 231 cubic inches per gallon conversion. Offsets come out of right-triangle trigonometry. What genuinely repays memorising is the small set of constants, since those cannot be derived at the desk.

Usually, but the policy belongs to your board and its testing vendor, and it ranges from a basic four-function calculator supplied at the test centre to your own non-programmable device. Programmable and phone calculators are generally prohibited. The candidate bulletin states the rule, and it is worth practising with whatever you will actually be allowed to use.

Unit errors, by a wide margin, and they split into two kinds. The first is converting in the wrong direction, usually multiplying by 2.31 where 0.433 belongs or the reverse. The second is reporting a correct number in the wrong unit, which scores nothing. After that comes using diameter where radius belongs in an area or volume formula, which puts the answer out by a factor of four. The exercises on this page flag a wrong unit separately from a wrong number so you can tell the two apart.

Travel equals the offset multiplied by the reciprocal of the sine of the fitting angle: 2.6131 at 22½ degrees, 2.0 at 30 degrees, 1.4142 at 45 degrees and 1.1547 at 60 degrees. The shallower the angle, the larger the constant. Using the 45 degree figure on a 30 degree offset is the single most common error on offset questions.