+-----------+-----------------+----------------------------------+
| | Absolute | |
| | Pressures in | Mean Velocities for Tubes |
| | lb. per sq. in. | of a length in feet. |
+-----------+--------+--------+------+------+------+------+------+
| | p0 | p1 | 1000 | 2000 | 3000 | 4000 | 5000 |
+-----------+--------+--------+------+------+------+------+------+
| Vacuum | 15 | 5 | 99.4 | 70.3 | 57.4 | 49.7 | 44.5 |
| Working | 15 | 10 | 67.2 | 47.5 | 38.8 | 34.4 | 30.1 |
| | | | | | | | |
| Pressure | 20 | 15 | 57.2 | 40.5 | 33.0 | 28.6 | 25.6 |
| Working | 25 | 15 | 74.6 | 52.7 | 43.1 | 37.3 | 33.3 |
| | 30 | 15 | 84.7 | 60.0 | 49.0 | 42.4 | 37.9 |
+-----------+-----------------+------+------+------+------+------+
_Limiting Velocity in the Pipe when the Pressure at one End is
diminished indefinitely._--If in the last equation there be put p1 =
0, then
u´_mean = 0.708 [root](d/[zeta]l);
where the velocity is independent of the pressure p0 at the other end,
a result which apparently must be absurd. Probably for long pipes, as
for orifices, there is a limit to the ratio of the initial and
terminal pressures for which the formula is applicable.