One of the most popular science curriculums on the market, Apologia has colorful and bright pages that kids will love. The upper grades are written in an easy to understand style, which comes in handy when learning subjects such as Chemistry or Biology. Dr. Wile (the author), takes special care in writing the curriculum for homeschooling students.
1 Tap is used in the British Isles and most of the Commonwealth for any everyday type of valve, particularly the fittings that control water supply to bathtubs and sinks.
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. The word is derived from the Latin valva, the moving part of a door, in turn from volvere, to turn, roll. The simplest, and very ancient, valve is simply a freely hinged flap which drops to obstruct fluid (gas or liquid) flow in one direction, but is pushed open by flow in the opposite direction. This is called a check valve, as it prevents or checks the flow in one direction.