FELT CONDITIONERS	199
means of raising the nap and cleaning it by suction is bound to be more or
less destructive.
The Vickery Adjustable Friction Type Felt Conditioner—Tins is an improved
type which has recently been introduced, and whereas in the case of the
standard conditioning unit the felt is drawn across the fixed top of the box,
so creating friction and consequent wear, in the case of the adjustable
friction type the box is divided into three suction chambers, the first and
last of which are operated at a very low vacuum, while the centre chamber
is operated at a higher vacuum.

[Vtixrp
fig. 77.—felt conditioner designed joa mould and boajd machines

Friction between the felt and the conditioning unit is reduced to the
minimum necessary for efficient conditioning by means of revolving members
in the box itself, and travelling bands at each edge which carry the felt across
the face of the box.
Further, there are means for adjusting the degree of scraping action on
the face of the felt
Some installations which have already been made dhow a remarkable
increase of efficiency and an increased felt life averaging up to as much as
50 per cent
The suction roll is now quite commonly used as a wet-felt cleaning device.
Usually it is made smaller in diameter than the suction press roll. To get