56. PRIMING - A violent intermittent action resulting in the throwing of slugs of
boiler water over with the steam, similar to the agitation when water is boiled in an
open vessel.
The filling of the liquid end of a pump with liquid to remove vapors present and
eliminate the tendency to become vapor bound or lose suction.
57. PUMP - A machine for moving a liquid by taking energy from some other source
and transferring it to the liquid. Common types are as follows:
a. CENTRIFUGAL - A pump in which fluid movement is developed
primarily by the action of centrifugal force (whirling action). No
valves.
b. MULTI-STAGE - A centrifugal pump which has two or more impellers
mounted on the same shaft. The discharge from one impeller is
conducted to the suction eye of the next impeller. This type is used to
obtain high differential pressure between suction and discharge.
c. RECIPROCATING - A positive dis-placement type of pump consisting
of a plunger or piston moving back and forth within a cylinder. Liquid
is pumped with every stroke of a double acting pump. Liquid is
pumped only when the piston is moving in one direction (every other
stroke) in a single acting pump.
d. DUPLEX - A reciprocating pump that has two or more liquid cylinders,
each having its individual drive. Duplex pumps have a more steady
discharge pressure than do simplex pumps.
e. SIMPLEX - A reciprocating pump that has one liquid cylinder on a
single drive. Usually used on lubricators, chemical injectors, etc.
f. ROTARY - A positive displacement pump with a fixed casing
containing the rotating element or elements consisting of gears, cams,
screws, vanes or modifications of these elements. Suitable for pumping
viscous liquids or where high vacuums are required.
58. CAVITATION - A condition inside a pump wherein the liquid being pumped
partly vaporizes due to temperature, pressure drop, etc. It can be identified by
noisy operation and erratic discharge pressure. It can cause excessive wear on the
impeller and case. This can often be remedied by increasing the pressure on the
pump, usually by raising the level of liquid being fed to the pump, or else by
decreasing the flow rate through the pump.
59. REACTOR - The vessel in which all or at least the major part of a reaction or
conversion takes place. On most units this will be the vessel in which the catalyst
is located.
