[f. EXHAUST v.] The process or means of exhausting.
1. a. Steam-engine. The exit of steam from the cylinder after having done its work in propelling the piston; the passage through which this takes place; = EDUCTION 5. (Also in similar sense with reference to water-power and gas engines.)
Etymologically, this is appropriate only to the case of a low-pressure engine, in which the steam is literally ‘exhausted’ from the cylinder by opening communication with the condenser; but when high-pressure engines were introduced, the word continued to be used as a synonym of EDUCTION, which it has almost superseded.
1848. Pract. Mech. Jrnl., I. 44/2. I have before seen double valves with the duplex steam passages, but in all of them the exhaust was single.
1865. Burgh, Slide Valve, 71. In some instances an increase is deemed necessary to allow a more free exhaust.
1875. R. F. Martin, trans. Havrez’ Winding Mach., 76. Back-pressure in the exhaust, owing to the large masses of steam which are suddenly let out through contracted … passages.
1887. J. A. Ewing, in Encycl. Brit., XXII. 487. If during the back stroke the process of exhaust is discontinued before the end.
1889. Blackw. Mag., Sept., 322. The rapid pulse-like beats of the exhaust [in a locomotive].
1890. Engineer, 30 May, 441/2. No choking of the exhaust can prevent an increase of speed.
b. The process of exhausting (a vessel) of air; the degree to which exhaustion is carried.
1880. De La Rue, in Nature, XX. 33. The greatest exhaust that we have produced, 0·000055 millim. Ibid. As the exhaust is carried further it becomes a pale milky white.
2. a. The production of an outward current of air by creating a partial vacuum. b. Any apparatus for effecting this. Cf. exhaust-fan.
1852. Pract. Mech. Jrnl., V. 54. A free and copious exhaust is secured on both sides of the cylinder [fan].
1884. Bath Herald, 27 Dec., 6/4. An exhaust [in a flour mill] carries away the lightest particles.
1887. W. Emden, in Pall Mall Gaz., 11 Oct., 11/1. There are two great exhausts to draw off smoke and heat from the stage.
1889. Daily News, 2 Jan., 2/4. A steam exhaust, which produces an artificial air current.
3. attrib. and Comb., chiefly in sense 1 a, as exhaust-passage, -pipe, -valve; also exhaust-fan (= earlier exhausting fan), a fan for producing a current by creating a vacuum; exhaust injector, an injector for feeding a steam-boiler with water, worked by exhaust steam; exhaust-port, the opening in the slide-valve of a steam-engine for the escape of exhaust-steam (= exhaust-passage); exhaust-steam, the waste steam discharged from the cylinder of a steam-engine.
1874. Knight, Dict. Mech., I. 815/2. *Exhaust-fan.
1882. Walsall Observer, 24 June, 7/5. An exhaust fan for drying hay and corn in the stack.
1890. Engineer, LXX. 473/2. We have for years made *exhaust injectors that … utilise waste steam.
1848. Specif. Varley’s Patent No. 12,238. 2. *Exhaust-passage.
1854. Pract. Mech. Jrnl., VI. 115. As the exhaust passage [in a water pressure engine] is open to the pipe, the waste water passes off through this pipe. Ibid. (1848), I. 44. The central *exhaust port of the slide valve.
1848. Pract. Mech. Jrnl., I. 80/2. The *exhaust steam from the cylinders.
1890. Engineer, 7 Nov., 386/2. (title of paper), Treatment and Utilisation of Exhaust Steam.
1848. Specif. Varley’s Patent No. 12,238. 2. The two *exhaust valves.
