They are easily damaged and must be returned to their country of origin for periodic cleaning.

Its many pieces of glass required periodic careful cleaning and alignment.

The internal parts need periodic cleaning, degreasing and repacking.

The belts needed periodic cleaning and conditioning to keep them in good condition.

Special lifting devices allow for the periodic cleaning of the stars inside and out, removing dust and soot.

"The ones we have will last, with proper periodic cleaning and restructure."

The maintenance of the artificial turf, which normally requires no more than periodic cleaning, is minimal.

On the northern edge is a wide, deep well with a spiral stairway inside (used for periodic cleaning and maintenance of the well).

Modern components are typically required to be designed for ease of inspection of internals and periodic cleaning.

At 8 AM on each school day, students in grades 1-9 begin a periodic cleaning of the campus.