These gauges are apt to get out of order for various reasons namely,
there is no theoretical method of determining the motion of the pointer
due to a given pressure; this is done by tests in which known pressures
are employed, and accordingly the divisions on the graduated scale are
usually unequal, hence these instruments are tested by attaching them
either to a mercury column, or to a dead weight safety valve having for
its seat an exact square inch surrounded by a knife edge, or a piston
of standard area loaded with weights. This sharp edge is covered by a
fibre washer of leather for moderate pressures, say 150 lbs. per square
inch, or vulcanized fibre or its equivalent for higher pressures.
[Illustration: FIG. 451.]
Fig. 451 represents a pump that can be used for pressures up to 10,000
lbs. per square inch. The Hand-Lever Pump shown at the right in cut is
used for filling the Pressure Pump cylinder and connections with oil or
glycerine, and may also serve for testing gauges of low pressures up
to 15 or 20 lbs. The suction pipe _a_ is connected with the reservoir
containing the oil or glycerine, which after being used is discharged
by valve _d_ and returned into the reservoir by pipe _c_.
In filling the pump the cylinder spindle has to be screwed all the way
out, and the valves _b_ and _d_ closed before it is put under pressure.
[Illustration: FIG. 452.]
“SUGAR-HOUSE” PUMPS.
The handling of semi-liquids, commercially known as _thick stuff_, has
always been considered more or less of a serious problem, and many
designs of mechanism in the form of pumps have been invented for that
purpose.
_For pumping tar the improved forms of rotary pumps_ have recently come
largely into use. These will be described later under their proper
heads. Fig. 212, page 232, Part one, represents a very satisfactory
design of plunger pump for handling the heavy stuff alluded to.
_The Deane single sugar-house pump_ is shown in Fig. 452. These are
largely used for pumping molasses, syrup, cane-juice, melter-pan
products, etc., and are fitted with linings, valves, etc., to best suit
the condition of the fluid to be pumped.
The valves are very large and the motion of the pumps is somewhat
slower than for water. By removing one set of bolts all the valves are
uncovered.
These products of the sugar-house when of a high temperature can be
pumped nearly as fast as water; the following list gives the approved
proportions of these pumps.