What is "return pipe"

Return \Re*turn"\, n.

1. The act of returning (intransitive), or coming back to the same place or condition; as, the return of one long absent; the return of health; the return of the seasons, or of an anniversary.

   At the return of the year the king of Syria will come up against thee.
   --1 Kings xx. 2

2. His personal return was most required and necessary.
   --Shak.

   2. The act of returning (transitive), or sending back to the same place or condition; restitution; repayment; requital; retribution; as, the return of anything borrowed, as a book or money; a good return in tennis.

   You made my liberty your late request: Is no return due from a grateful breast?
   --Dryden.

3. That which is returned. Specifically:

   1. A payment; a remittance; a requital.

      I do expect return Of thrice three times the value of this bond.
      --Shak.

   2. An answer; as, a return to one's question.

   3. An account, or formal report, of an action performed, of a duty discharged, of facts or statistics, and the like; as, election returns; a return of the amount of goods produced or sold; especially, in the plural, a set of tabulated statistics prepared for general information.

   4. The profit on, or advantage received from, labor, or an investment, undertaking, adventure, etc.

      The fruit from many days of recreation is very little; but from these few hours we spend in prayer, the return is great.
      --Jer. Taylor.

4. (Arch.) The continuation in a different direction, most often at a right angle, of a building, face of a building, or any member, as a molding or mold; -- applied to the shorter in contradistinction to the longer; thus, a facade of sixty feet east and west has a return of twenty feet north and south.

5. (Law)

   1. The rendering back or delivery of writ, precept, or execution, to the proper officer or court.

   2. The certificate of an officer stating what he has done in execution of a writ, precept, etc., indorsed on the document.

   3. The sending back of a commission with the certificate of the commissioners.

   4. A day in bank. See Return day, below.
      --Blackstone.

6. (Mil. & Naval) An official account, report, or statement, rendered to the commander or other superior officer; as, the return of men fit for duty; the return of the number of the sick; the return of provisions, etc.

7. pl. (Fort. & Mining) The turnings and windings of a trench or mine.

   Return ball, a ball held by an elastic string so that it returns to the hand from which it is thrown, -- used as a plaything.

   Return bend, a pipe fitting for connecting the contiguous ends of two nearly parallel pipes lying alongside or one above another.

   Return day (Law), the day when the defendant is to appear in court, and the sheriff is to return the writ and his proceedings.

   Return flue, in a steam boiler, a flue which conducts flame or gases of combustion in a direction contrary to their previous movement in another flue.

   Return pipe (Steam Heating), a pipe by which water of condensation from a heater or radiator is conveyed back toward the boiler.