====================+===================+================
| Vacuum Chamber is | Air Chamber is
| to contain:— | to contain:—
--------------------+-------------------+----------------
500-gallon pump. | 13 gallons. | 17 gallons.
750 „ „ | 18 „ | 25 „
1,000 „ „ | 24 „ | 30 „
1,500 „ „ | 30 „ | 40 „
--------------------+-------------------+----------------
The air chamber, combined with connections for discharge pipe, relief
valve, and hose valves, should be carefully designed to make the
whole weight as small as possible. Keeping this weight down makes
the pump run steadier and brings less strain on the flanges at high
speeds.
An air chamber of hammered copper and warranted tested under a
hydraulic pressure not less than 300 lbs. per square inch is a little
better than cast iron as it holds air better, and being lighter it
wrenches and strains the pump less when running fast and shaking, but
because it costs from $25 to $50 more than cast iron, it is not often
adopted.
_b._ The vacuum chamber must be attached to the pump in the most direct
way practicable, but provision must be made for attaching it in such
manner as not to prevent readily taking off the cylinder heads.
_c._ Every vacuum chamber should be provided on one side near the top
with a 1/4-inch pipe hole plugged. This to be used for attaching a
vacuum gauge if desired.