What is "check valve"

Valve \Valve\, n. [L. valva the leaf, fold, or valve of a door: cf. F. valve.]

1. A door; especially, one of a pair of folding doors, or one of the leaves of such a door.

   Swift through the valves the visionary fair Repassed.
   --Pope.

   Heavily closed, . . . the valves of the barn doors.
   --Longfellow.

2. A lid, plug, or cover, applied to an aperture so that by its movement, as by swinging, lifting and falling, sliding, turning, or the like, it will open or close the aperture to permit or prevent passage, as of a fluid.

   Note: A valve may act automatically so as to be opened by the effort of a fluid to pass in one direction, and closed by the effort to pass in the other direction, as a clack valve; or it may be opened or closed by hand or by mechanism, as a screw valve, or a slide valve.

3. (Anat.) One or more membranous partitions, flaps, or folds, which permit the passage of the contents of a vessel or cavity in one direction, but stop or retard the flow in the opposite direction; as, the ileocolic, mitral, and semilunar valves.

4. (Bot.)

   1. One of the pieces into which a capsule naturally separates when it bursts.

   2. One of the two similar portions of the shell of a diatom.

   3. A small portion of certain anthers, which opens like a trapdoor to allow the pollen to escape, as in the barberry.

5. (Zo["o]l.) One of the pieces or divisions of bivalve or multivalve shells. Air valve, Ball valve, Check valve, etc. See under Air. Ball, Check, etc. Double-beat valve, a kind of balance valve usually consisting of a movable, open-ended, turban-shaped shell provided with two faces of nearly equal diameters, one above another, which rest upon two corresponding seats when the valve is closed. Equilibrium valve.

   1. A balance valve. See under Balance.

   2. A valve for permitting air, steam, water, etc., to pass into or out of a chamber so as to establish or maintain equal pressure within and without. Valve chest (Mach.), a chamber in which a valve works; especially (Steam Engine), the steam chest; -- called in England valve box, and valve casing. See Steam chest, under Steam. Valve face (Mach.), that part of the surface of a valve which comes in contact with the valve seat. Valve gear, or Valve motion (Steam Engine), the system of parts by which motion is given to the valve or valves for the distribution of steam in the cylinder. For an illustration of one form of valve gear, see Link motion. Valve seat. (Mach.)

      1. The fixed surface on which a valve rests or against which it presses.

      2. A part or piece on which such a surface is formed.

         Valve stem (Mach.), a rod attached to a valve, for moving it.

         Valve yoke (Mach.), a strap embracing a slide valve and connecting it to the valve stem.

Check \Check\ (ch[e^]k), n. [OE. chek, OF. eschec, F. ['e]chec, a stop, hindrance, orig. check in the game of chess, pl. ['e]checs chess, through Ar., fr. Pers. sh[=a]h king. See Shah, and cf. Checkmate, Chess, Checker.]

1. (Chess) A word of warning denoting that the king is in danger; such a menace of a player's king by an adversary's move as would, if it were any other piece, expose it to immediate capture. A king so menaced is said to be in check, and must be made safe at the next move.

2. A condition of interrupted or impeded progress; arrest; stop; delay; as, to hold an enemy in check.

   Which gave a remarkable check to the first progress of Christianity.
   --Addison.

   No check, no stay, this streamlet fears.
   --Wordsworth.

3. Whatever arrests progress, or limits action; an obstacle, guard, restraint, or rebuff.

   Useful check upon the administration of government.
   --Washington.

   A man whom no check could abash.
   --Macaulay.

4. A mark, certificate, or token, by which, errors may be prevented, or a thing or person may be identified; as, checks placed against items in an account; a check given for baggage; a return check on a railroad.

5. A written order directing a bank or banker to pay money as therein stated. See Bank check, below.

6. A woven or painted design in squares resembling the patten of a checkerboard; one of the squares of such a design; also, cloth having such a figure.

7. (Falconry) The forsaking by a hawk of its proper game to follow other birds.

8. Small chick or crack.

   Bank check, a written order on a banker or broker to pay money in his keeping belonging to the signer.

   Check book, a book containing blank forms for checks upon a bank.

   Check hook, a hook on the saddle of a harness, over which a checkrein is looped.

   Check list, a list or catalogue by which things may be verified, or on which they may be checked.

   Check nut (Mech.), a secondary nut, screwing down upon the primary nut to secure it.
   --Knight.

   Check valve (Mech.), a valve in the feed pipe of a boiler, or other conduit, to prevent the return of the feed water or other fluid.

   To take check, to take offense. [Obs.]
   --Dryden.

   Syn: Hindrance; setback; interruption; obstruction; reprimand; censure; rebuke; reproof; repulse; rebuff; tally; counterfoil; counterbalance; ticket; draft.

A check valve, clack valve, non-return valve or one-way valve is a valve that normally allows fluid ( liquid or gas) to flow through it in only one direction.

Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves are often part of common household items. Although they are available in a wide range of sizes and costs, check valves generally are very small, simple, or inexpensive. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem. The bodies (external shells) of most check valves are made of plastic or metal.

An important concept in check valves is the cracking pressure which is the minimum upstream pressure at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure.

Heart valves are essentially inlet and outlet check valves for the heart ventricles, since the ventricles act as pumps.