Artwork: Eight common types of valves, greatly simplified. Color key: the grey part is the pipe through which fluid flows; the red part is the valve and its handle or control; the blue arrows show how the valve moves or swivels; and the yellow line shows which way the fluid moves when the valve is open.

The many different types of valves all have different names. The most common ones are the butterfly, cock or plug, gate, globe, needle, poppet, and spool:

• Ball: In a ball valve, a hollowed-out sphere (the ball) sits tightly inside a pipe, completely blocking the fluid flow. When you turn the handle, it makes the ball swivel through ninety degrees, allowing the fluid to flow through the middle of it.

• Gate or sluice: Gate valves open and close pipes by lowering metal gates across them. Most valves of this kind are designed to be either fully open or fully closed and may not function properly when they are only part-way open. Water supply pipes use valves like this.

• Globe: Water faucets (taps) are examples of globe valves. When you turn the handle, you screw a valve up or down and this allows pressurized water to flow up through a pipe and out through the spout below. Unlike a gate or sluice, a valve like this can be set to allow more or less fluid through it.