Page 190 - Know and Understand Centrifugal Pumps

Pump Shaft Packing

Packing
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The new increased demands on the stuffing box and stopa of the steam
engine are obvious. The old rudder shaft of the ancient boat only
moved sufficiently to change the direction of the boat. The
reciprocating shaft of the steam engine is in constant movement, with
more velocity and friction. Compare the temperature of seawater with
the temperature of steam. On a sailboat rudder, the stopa had very little
pressure to hold back (2.31 feet of depth is 1 psi). With refinements
and improvements in steam engines, the pressures rapidly climbed
through 10, 30, 50, 100 and 200 psi.

The industry stopped using the word ‘stopa’, and adopted the word
‘packing’. The new packing stuffed into the stuffing boxes on
reciprocating steam rods could withstand the temperatures, abrasion,
and pressures generated by steam. Asbestos, which comes from mines
in rocks and mineral fibers, became a popular component of braided
packing for high temperature applications. New lubricants, mineral and
petroleum based, could survive the frictions and temperatures present
with the constantly and rapidly moving shafts. Packing construction,
braided tightly like a square rope, with surfaces designed to seal against
the shaft, and the stuffing box wall, could contain the higher steam
pressures.
Shortly after the development of the reciprocating steam engine, the
positive displacement pump was born. These pumps could seal and
generate pressures but with one weakness. The flow, or quantity of fluid
that could pass through the pump, is a function of two factors: first,
the size of the pump casing, and second, the motor’s speed. The
reciprocating steam engine is powerful by design, but slow. With the
existing steam engines, it was necessary to increase the size of the pump
in order to pump more. The reciprocating pump is only able to capture,
move, and expel a fixed quantity of fluid according to the size of the
casing. Fabricating large pumps brings its own problems of raw
material, the mold construction, the heating and melting of the iron,
the weight, transportation and maintenance.

Rotary action

Reciprocating action in engines and pumps was again converted back
again into rotary action at the beginning of the last century. First, the
rotary turbine was perfected. Shortly afterward, the internal
combustion engine appeared. In the marine industry, the propulsion
paddlewheels evolved into propellers. Ship design was greatly simplified
with a direct drive shaft from the motor to the propellers. The weight

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