ovde je zasun = gate valve, slide valve (ref. R. mašinske tehnike, J. Miličević)
okno u ovom kontekstu (vodovod) je chamber
V. sliku ovde:
http://www.ispa-karlovac.eu/en/component/content/article/114...
Završeno je zasunsko okno ispred rezervoara Borlin.

http://www.anchorconcrete.com/valvechamber.htm
Anchor Concrete designs and manufactures a wide selection of economical precast meter and valve chambers as an alternative to cast-in-place structures. Our round chambers include 1200, 1500, 1800, 2400, and 3000mm diameter. Our standard rectangular chambers range from 1200x1200mm (inside) to 2000x4900mm (inside) to large custom sizes.

http://webcache.googleusercontent.com/search?q=cache:UALoUzO...
Tipsko zasunsko okno koje se sastoji od kučišta promjera 2,0 m visine do 2,5 m, okno je izvedeno od centrifugalnog poliestera,

http://www.expertglossary.com/water/definition/gate-chamber-...
All > Science > Water
Gate chamber (valve chamber)
* A chamber in which a guard gate in a pressurized outlet works or both the guard and regulating gates in a free-flow outlet works are located. A room from which a gate or valve can be operated, or sometimes in which the gate is located. Concrete portion of an outlet works containing gates between upstream and downstream conduits and/or tunnels.