The volume of water which is used intermittently for the purpose of
operating presses—draw-benches for brass and copper tubing and the
like is replaced by a pump or pumps which are started and stopped
automatically by a connection between the accumulator and the throttle
or belt shifter of the pump. The accumulator is used for a double
purpose of maintaining a constant pressure and to store up any surplus
force of the pumps. The friction loss in the transmission of power
by water through mains is very small, as for example: _It has been
found that water under a pressure of 700 lbs. per square inch may be
transmitted through well proportioned mains, one mile with a loss of
only two per cent._
The useful work stored in an accumulator may be calculated by the
following rule: _Multiply the area of ram in square inches by the
length of the stroke in inches by the pressure m pounds per square inch
divided by 33,000 lbs. the equivalent of one H. P._
This represents the work done by one full stroke of the accumulator ram
in descending from its highest position to its lowest.
Example. Required the work done by one stroke of a ram twelve inches in
diameter, and a stroke of twenty-two feet, under a pressure of 750 lbs.
to the square inch. Area of 12 ram = 113·097 square inches. No. of ins.
in 22 ft. = 264. Then
113·097 × 264 × 750
------------------- = 678·582 H.P.
33,000
Mr. Tweddel designed the accumulator shown in Figs. 147 and 148 to
furnish the varying demand for water where only one appliance of this
kind is used in connection with a hydraulic system of shop tools more
especially where these tools are numerous.
The ram or spindle _A_ is fixed top and bottom and acts as a guide for
the cylinder _B_ which slides up and down upon it.
[Illustration: