Generally speaking a packing is a contrivance or a material to close
a joint. Various greasy materials with gaskets, flax, hemp, etc., are
used in joints which are screwed down, also collars of rubber, red
lead, luting, graphite, etc.
[Illustration: “U” PACKING—FIG. 134.]
A most important part in the practical working of nearly all
water-pressure machines is the leather collar, the invention of which
by Bramah removed the difficulties which had been experienced in making
the large ram work water-tight when submitted to great pressure.
It consists of a circular piece of stout leather (see cut page 20),
in the center of which a circular hole is cut. This piece of leather
is thoroughly soaked in water and is pressed into a metallic mould
and so that a section of it represents a reversed ^U^, and is fitted
into a groove made in the neck of the cylinder. This collar being
concave downwards, then in proportion as the pressure increases, the
edge nearest the ram being trimmed down, it fits the more tightly
against the ram plunger on one side and the neck of the cylinder on the
other. It should be saturated with Neatsfoot or Castor oil so as to be
impervious to water.
[Illustration: CUP PACKING—FIG. 135.]
When the least amount of friction possible is desired in the operating
of a hydraulic plunger, there is no form of packing which can surpass
a properly prepared and applied Leather “^U^” Packing (Fig. 134), and
in practice its position is according to conditions, either in a groove
near the upper end of the cylinder, or at the lower end of the ram.
When for any reason it is not desired to use the outer lip of the
packing, the resulting form is known as a Cup Packing, (Fig. 135), and
when the inner lip is used then we have the Hat or Flange Packing. Fig.
136.
[Illustration: FLANGE PACKING. FIG. 136.]
When the water pressure is not over 2,000 lbs. to the square inch, and
a greater allowance for friction is not important, a fibrous packing
can be used, which is easier of application than these for large sized
cylinders.
The loss of power by the best of leather packings is 1 per cent. on 4
in. ram, 1/2 per cent. with 8 in. ram and 1/4 per cent. with 16 in.
ram.
HYDRAULIC
APPARATUS