滤床

[机] 滤层

[ noun ]
filter consisting of a layer of sand or gravel for filtering water
<noun.artifact>

Filter \Fil"ter\, n. [F. filtre, the same word as feutre felt,
LL. filtrum, feltrum, felt, fulled wool, this being used for
straining liquors. See {Feuter}.]
Any porous substance, as cloth, paper, sand, or charcoal,
through which water or other liquid may passed to cleanse it
from the solid or impure matter held in suspension; a chamber
or device containing such substance; a strainer; also, a
similar device for purifying air.

{Filter bed}, a pond, the bottom of which is a filter
composed of sand gravel.

{Filter gallery}, an underground gallery or tunnel, alongside
of a stream, to collect the water that filters through the
intervening sand and gravel; -- called also {infiltration
gallery}.