CHAPTER XXXI =. i 
SOME HYDRAULIC PRESSURE MACHINES 
449. Packing for Hydraulic Rams and Pistons.—To prevent — 
leakage of the water between a ram, plunger, or piston and the — 
cylinder various forms of packing are used. The U-leather packing 
shown in Fig. 828 has been extensively used. The water leaks past 
the ram as far as the packing, and, entering its interior, presses one side 
against the recess in the cylinder and the other against the ram. The 
greater the pressure of the water the greater is the tendency to leak, but 
in the U-leather packing the force with which the leather is pressed — 
against the ram and against the recess in the cylinder to prevent 
leakage is proportional to the pressure of the water. ‘This is one great 
merit of the U-leather packing. 
The U-leather packing is made from a disc or flat ring of leather, 
which is moulded between two cast-iron blocks, as shown in Fig. 829. 
The leather is softened in hot water and placed between the blocks, 
which are then pressed together in a hydraulic press or by bolts and nuts, 
the bolts passing through the blocks. The leather is kept in the mould 
for about twenty-four hours, when it is removed, and after it is dried, it 
is trimmed to the form shown in Fig. 828. 
The hat-leather packing is shown in Fig. 830. This is more commonly 
used for small rams, valve spindles, ete. 
The cup-leather packing is mainly used for pistons. A piston packed 
with two cup-leathers is shown in Fig. 797, p. 499. A cup-leather 
packing on a ram is shown in Fig. 839, p. 526. | 
Hat- and cup-leathers are moulded in a similar manner to the 
U-leather. 
The leather for hydraulic packings should be the best quality oak- 
tanned, sole leather. It is planed to a uniform thickness of about 
three-sixteenths of an inch. The flesh side of the leather is made the 
rubbing side of the packing. 
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