valve

Pluralvalves

Formsvalves, valving, valved

1. 1
   nouncountable

   A device that controls the flow of a gas or liquid through a pipe, manifold, or other enclosed passage.

   The plumber shut off the main valve before replacing the cracked pipe.

   Pressure-relief valves on the boiler opened automatically as the steam built up.

   Note

   The name comes from a door: Latin valva was one leaf of a double door, and a valve still opens and shuts a way through. The verbs follow the picture, so a valve is opened, closed or shut off, and a qualifier usually says what it guards or does, as in a main valve or a pressure-relief valve. The same picture runs through the valves of the heart.

2. 2
   nouncountable

   A membranous flap, fold or partition, or a set of them, that lets the contents of a vessel or cavity pass one way while stopping or controlling flow the other way.

   The surgeon replaced the patient's damaged aortic valve with an artificial one.

   Leaky valves in the leg veins let blood pool and swell the veins.

   Note

   The body names its valves by where they sit: the atrioventricular valves between the heart's chambers, the ileocecal valve where the small intestine meets the large. When one fails, doctors say it leaks if it cannot close fully, and call it narrowed, or stenotic, if it cannot open fully.

3. 3
   nouncountable

   In an internal combustion engine, a device that admits fuel and air into a cylinder or lets the burned gases escape.

   Each cylinder in the engine has two intake valves and two exhaust valves.

   A burned exhaust valve can rob an engine of much of its power.

   Note

   In nearly all internal combustion engines the valves are of the poppet type, so poppet valve is the precise name when the kind matters. Mechanics name them by job, intake or exhaust, and count them per cylinder, which is where descriptions like two intake and two exhaust valves come from.

4. 4
   nounBritishcountable

   An electronic vacuum tube, a sealed tube with the air removed.

   Guitarists still favor valve amps for their warm tone.

   He spent the weekend hunting for a replacement valve for his 1950s television set.

   Similartube

   Note

   Here British and American English part company: what a British speaker calls a valve, an American calls a vacuum tube. The split carries into compounds, so a valve radio or valve amplifier in Britain is a vacuum-tube radio or amplifier in the United States.

5. 5
   verbtransitive

   To control or regulate a flow by means of a valve.

   Engineers valve the coolant through the system to hold the reactor at a steady temperature.

   The technician valved the steam into the turbine in short bursts.

   Similarregulate, meter

6. 6
   nouncountable

   One of the separate pieces that make up a bivalve or multivalve shell.

   Only the left valve of the fossil scallop was preserved in the rock.

   A chiton's shell is made of overlapping valves that let it curl into a ball.

   Note

   The word gives the bivalves their name: a clam, mussel or oyster lives inside two valves joined by a hinge. Shells built from more pieces, like a chiton's row of overlapping plates, are multivalve, and paleontologists speak of a left or right valve when only one half of a fossil survives.

7. 7
   nouncountable

   One of the separate panels that make up a folding door or a window sash.

   Each valve of the folding door was carved with climbing vines.

   The carpenter rehung the window's valves so that they met neatly in the middle.

   Similarleaf, panel

8. 8
   nouncountable

   One of the pieces into which certain fruits naturally separate when they split open to release their seeds.

   As the capsule ripens, its valves pull apart and the seeds spill onto the ground.

   Each valve of the dried bean pod twisted sharply, flinging the seeds across the path.

   Note

   A pea pod is the familiar case: its two halves are valves, and so are the walls of a lily's seed capsule. How many valves a fruit opens into, and how they part, can help botanists tell related plants apart, which is why plant descriptions count them.

9. 9
   nouncountable

   Either of the two similar halves that together make up the shell of a diatom.

   The pattern of pores on each valve helps scientists identify the diatom species.

   When a diatom divides, each daughter cell keeps one of the parent's valves and builds a new one.

   Note

   A diatom's two valves are not quite equal: the larger overlaps the smaller like the lid of a box, and together they make its glassy shell. When the cell divides, each daughter keeps one parent valve and builds a new, smaller one inside it, so a line of dividing diatoms tends to shrink over the generations.

10. 10
    nouncountable

    A small part of the anther in certain plants, such as the barberry, that opens like a trapdoor to let the pollen escape.

    In the barberry flower, each anther sheds its pollen through a little valve that lifts upward.

    Under the lens, the anther valves had curled back, each holding a sticky load of pollen.

    Note

    Botanists keep the old Latin picture of valva, a door that swings: here the door is a tiny hinged flap on an anther, lifting to let the pollen out where most anthers simply split along their length. The same idea of a part that opens gives the segments of a splitting fruit and the halves of a shell.

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