_ diameter than the upper part AB. The 
lower end of the ram is fixed in the base 
_ shown, and the upper end (not shown) is 
rigidly held by a bracket attached to a wall 
cylinder which slides up and down on the 
ram. The lower and upper ends of the 
cylinder fit the larger and smaller parts of 
the ram respectively, leakage being prevented 
by packings, as shown. The cylinder is 
amount of the load depending on the water 
pressure required. Water enters or leaves & 
the accumulator by the pipe E, and passes 
| along a central hole in the larger part of the { 
ram ; this central hole communicates with the YJ 
| 
water space in the cylinder by transverse 
holes in the ram at B. When at the bottom 
of its stroke the cylinder rests on the 
props F. - 
If W=total moving load, d,=larger f 
diameter of ram, d,=smaller diameter of 
ram, and p=intensity of water pressure, 
then, neglecting friction, "(d] — d})p=W. 
From this it will be seen that if the difference 
between d, and d,, be Small, p will be large for 
a comparatively small value of W, but the 
capacity of the accumulator is small. 
than the differential accumulator. 
or in any other convenient way. D is the > 
loaded with cast-iron weights as shown, the // 
BA 
Wd 
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Yj, 
G 
a 
Frq@. 835. 
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HHH 2 
SOME HYDRAULIC PRESSURE MACHINES 
~ 452. Tweddell’s Differential Accumulator.—In this accumulator 
there is a fixed ram ABC (Fig. 835), the lower part BC being of larger 
SRS 
| 5 
523 
If d is the diameter of the ram of an ordinary accumulator carrying 
the same load W under the same pressure p, then d= ,/(d}—d:). 
ordinary accumulator would therefore have a much more slender ram 
The 
_ The differential accumulator is usually comparatively small, say 
d, =6 inches, d,=5 inches, and a stroke of about 4 feet. 
_ The differential accumulator is used in connection with one hydraulic 
machine only, such as a hydraulic riveter, where the force exerted at the 
beginning of the operation is comparatively small, but at the end it must 
be large. The capacity of the differential accumulator being small, the 
load descends rapidly and with increasing speed, and as the operation of 
the hydraulic machine approaches the end, the falling load is brought 
quickly to rest, with the result that there is a considerable rise 
in the pressure of the water, and therefore a considerable increase 
in the force exerted by the hydraulic machine at the conclusion of its 
operation. 
453. Intensifying Accumulator.—An accumulator in which the 
load on the ram is produced by low pressure, water, say from the ordinary 
water supply; acting on a piston, is shown in Fig. 836, This is called an 
