mislim da je greška u tekstu, "šiber" je sprava za računanje, "slide rule":
https://www.google.rs/search?q=šiber&client=firefox-a&hs=zSe...
Ovde bi trebalo da bude "šuber", tj otvor ili poklopac/vratanca koji taj otvor zatvaraju;
šuber -hatch, ref. Građevinski rečnik, B. Vukičević

https://www.google.rs/search?q=hatch definition&ie=utf-8&oe=...
1. An opening of restricted size allowing for passage from one area to another, in particular.

http://www.thefreedictionary.com/hatch
a. An opening, as in the deck of a ship, in the roof or floor of a building, or in an aircraft.
b. The cover for such an opening.

Od konteksta zavisi da li se misli na sam otvor ili na vratanca/poklopac tog otvora

http://www.narvi.fi/en/products--/fireplace-products--/other...
Cast iron kitchen stove and coal hatch doors

Serbian term (edited): šiber (deo peći na čvrsta goriva)

"šiber" jeste sprava za računanje, "slide rule", ali se isto koriste i za klizna vratanca na pećima "sliding door"

"Puštanje kotla u rad
….
.
2.7. Kontrola i sigurnosni elementi
Sistem za regulaciju promaje reguliše ulaz vazduha u komoru za sagorevanje ispod kotlovske rešetke. Njega kontroliše regulator promaje ili ručno podešavajući zavrtanj na vratancima regulatora promaje na kotlu. Drugi regulator promaje (za dimenzije 8 – 10 članaka) reguliše protok vazduha na zadnjim vratancima. Šiber na vratima za loženje se koristi za ulaz sekundarnog vazduha u komoru za sagorevanje. Šiber u zadnjem delu kotla koristi se za ulaz tercijalnog vazduha, i mora da bude blago otvoren 3 - 5mm (u slučaju potrebe, ovaj otvor se može povećati) .
[http://www.portal-doo.eu/portalwps/wp-content/uploads/2010/0...]

"The improved chulha has a sliding firebox doors and chimney dampers to control air supply for combustion. During field trials, fuelwood savings of the order of ..."
[http://www.teriin.org/index.php?option=com_casestudy&task=de...]


"An exhibition quality model of a 3 ½" inch gauge Lord Nelson Class E Southern Railway 4-6-0 Locomotive and Tender 'Lord Howe' No 857, built by Mr A W G Tucker the copper boiler with fittings including water and pressure gauges, blower, injector, brake, whistle and clack valve. Cab detail includes twin arm regulator, reversing wheel, drain cocks, lever operated sliding firebox doors, folding doors and polished mahogany plank flooring Chassis details include twin outside cylinders with Walschaerts valve gear and twin inside cylinders, drain cocks, lubricator, eccentric driven feed pump and bypass, whistle, brake gear. Tender of double bogie design with fittings including hand operated feed pump,water cock, brake, steps, handrails and tool boxes.
The locomotive is finished in malachite green and black livery with 'Southern 857' to tender and having polished brightwork. Length 52 ½" Cab Width 6 ½" "
[http://www.dnfa.com/search.asp?view=keyword&keyword=||&noperpage=20&auction=13538&catname=Steam%20%26%20Model%20Engineering]



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Note added at 3 hrs (2013-08-14 18:18:16 GMT)
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jedan primer kamina s providnim kliznim poklopcem, slično "šiberu" na krovu automobila (Version with vertical sliding door with flat glass....)

http://www.archiexpo.com/prod/edilkamin/wood-burning-closed-...

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Note added at 3 hrs (2013-08-14 19:01:21 GMT)
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"Šiber u zadnjem delu kotla koristi se za ulaz tercijalnog vazduha, i mora da bude blago otvoren 3 - 5mm (u slučaju potrebe, ovaj otvor se može povećati)"
Mislim da ovo ukazuje na to da je "šiber" klizni poklopac (=> ovaj otvor se može povećati); klapna (koja se otvara oko osovine) je ili privremeno otvorena ili potpuno zatvorena, tj. klapne se ne ostavljaju trajno otvorene par milimetara.

Ako je pitanju manji otvor, moguća je i varijanta "sliding hatch".