System Sizing & Design Flashcards

A sediment filter with a 20-micron cartridge is placed before a 5-micron cartridge in a multi-stage system. This arrangement is called:

Answer: Series depth filtration with graded porosity

Graded porosity in series filtration progressively removes larger particles first to protect finer downstream media from premature loading.

For a residential RO system rated at 50 gallons per day (GPD), approximately how long will it take to fill a standard 3.2-gallon storage tank to 75% capacity under typical pressure conditions?

Answer: Approximately 1.4 hours

50 GPD ÷ 24 hours ≈ 2.08 GPH; filling 2.4 gallons (75% of 3.2 gal) takes 2.4 ÷ 2.08 ≈ 1.15 hours, or about 1.4 hours accounting for declining production as tank pressure rises.

Which of the following best describes the purpose of a bypass valve assembly in a water treatment system design?

Answer: To allow service or replacement of equipment without interrupting water supply

A bypass valve lets untreated water flow directly to the home while the treatment unit is offline for service or replacement.

When designing a system to remove nitrates by ion exchange, why must the resin be specifically a strong base anion (SBA) resin rather than a standard cation softening resin?

Answer: Nitrate is an anion and requires an anion exchange resin to be captured

Nitrate (NO₃⁻) is a negatively charged anion, so it can only be exchanged by an anion exchange resin, not a cation resin.

A water system serving an 8-unit apartment building needs to be designed. Compared to sizing for a single-family home with the same total fixtures, what design adjustment is most important?

Answer: Apply a diversity factor, as not all fixtures in all units will run simultaneously

A diversity (coincidence) factor is applied to multi-unit buildings because statistical probability of all fixtures running simultaneously is much lower than in a single unit.

In a twin-tank alternating softener system, what is the main operational advantage over a single-tank system?

Answer: Continuous soft water supply with no hardness breakthrough during regeneration

When one tank regenerates, the second tank remains in service, ensuring uninterrupted soft water delivery with no hardness slip.

A designer is specifying pipe size for a whole-house treatment system. The source water contains high iron and the system will include a backwashing iron filter. What pipe material should generally be AVOIDED in downstream distribution?

Answer: Galvanized steel

Galvanized steel pipe can leach zinc and corrode when residual dissolved iron oxidizes inside the pipe, causing rust staining and flow restrictions.