extent
without throwing a strain upon the pipe. The eduction pipe is attached to
the condenser by a flange joint, and the bolt holes are all made somewhat
oblong in the perpendicular direction, so as to permit the pipe to be
slightly lowered, should such an operation be rendered necessary by the
wear of the trunnion bearings; but in practice the wear of the trunnion
bearings is found to be so small as to be almost inappreciable.

624. _Q._--Will you describe the valve and valve casing?

_A._--The length of the valve casing is 16-1/2 inches, and its projection
from the cylinder is 3-1/2 inches at the top, 4-1/4 inches at the centre,
and 2-1/2 inches at the bottom, so that the back of the valve casing is not
made flat, but is formed in a curve. The width of the valve casing is 9
inches, but there is a portion of the depth of the belt 1-1/2 inch wider,
to permit the steam to enter from the belt into the casing. The valve
casing is attached to the cylinder by a metallic joint; the width of the
flange of this joint is 1-1/4 inch, the thickness of the flange on the
casing 1/2 inch, and the thickness of the flange on the cylinder 5/8ths of
an inch. The projection from the cylinder of the passage for carrying the
steam upwards, and downwards, from the valve to the top and bottom of the
cylinder, is 2-1/4 inches, and its width externally 8-5/8 inches. The valve
is of the ordinary three ported description, and both cylinder and valve
faces are of cast iron.

625. _Q._--What description of piston is used?

_A._--The piston is packed with hemp, but the junk ring is made of
malleable iron, as cast iron junk rings have been found liable to break:
there are four plugs screwed into the cylinder cover, which, when removed,
permit a box key to be introduced, to screw down the piston packing. The
screws in the junk ring are each provided with a small ratchet, cut in a
washer fixed upon the head, to prevent the screw from turning back; and the
number of clicks given by these ratchets, in tightening up the bolts,
enables the engineer to know when they have all been tightened equally. In
more recent engines, and especially in those of large size, Messrs. Penn
employ for the piston packing a single metallic ring with tongue piece and
indented plate behind the joint; and this ring is packed behind with hemp
squeezed by the junk ring as in ordinary hemp-packed pistons.

626. _Q._--Will you describe the construction of the cap for connecting