The use of compressed air has become very general through the use of
small hand pumps; the cylinder of these must be smooth, and the plunger
is usually packed with a cup leather packing.
[Illustration: FIG. 340.—Gas Fitter’s Proving Pump.]
Fig. 340 shows a _gas fitter’s air proving pump_. The gauge is attached
to any opening into the system of pipes to be tested, with a rubber
hose leading to the pump. By working the pump the air is forced into
the pipes; upon stopping the pump if the hand upon the gauge remains
stationary there are no leaks in the system. If there are leaks the
hand of the gauge will gradually return to the zero mark.
NOTE.—Before putting the pressure on it is customary to put some
ether into the small cup—near the gauge as shown—this has a cock
which must be opened and closed at the proper time so that the ether
will be forced into the pipe system and disclose by the sense of
smell the location of the leak.
Fig. 341 shows a _Portable Tire Air Pump_, which can be used by hand
or affixed to a wall or bench; it is of the lever type, with 2 × 8
cylinders, fitted with check valve and extra heavy rubber tubing.
As the leverage on the piston-rod increases the resistance on the
piston also increases, thereby securing the powerful leverage of the
well-known “toggle-joint” principle as the piston finishes its stroke;
thus the best possible results are obtained.
Fig. 342 illustrates a _Hand Lever Air Pump_ with cylinder 3-1/4″
× 6-1/4″; its capacity—one stroke—is 36 cubic inches. The greatest
pressure it is intended to operate against is 150 lbs. to the square
inch. In operation this design has the advantage of the leverage of the
toggle-joint indicated above.
Fig. 343 exhibits a Hand Air Pump which has the same dimensions as that
just described, screwed to the floor. Its particular advantage is the
fact that the motion of the lever is natural and easy being horizontal
and still retaining the advantages of the toggle-joint.
[Illustration: FIG. 341.—Hand Pump.]
[Illustration: FIG. 342.]
[Illustration: FIG. 343.]