Glossary S1


Sealless pump - belong to a special class of pumps that do not require a sealing
element to prevent the pumped liquid from leaking into the atmosphere because
its internal rotor, assembled with the impeller, do not extend outside of the
pressure containment casing.

Seal flush piping Plan 11

Second critical speed - see first critical speed for explanation.

Self-priming pump

Self-venting pump - a pump whose casing can be flushed of entrained gas by
simply opening its suction and discharge control valves and rotating the shaft
manually prior to starting. The pump casing does not have a vent connection. In a
multistage pump, only the first stage volute needs to be self-venting.

API Standard 610 considers a pump to be self-venting "
if the nozzle arrangement
and casing configuration permit adequate venting of gases from the first-stage
impeller and volute area to prevent loss of prime during the starting sequence
."

Semi-open impeller - a single suction impeller with no front or suction shroud but
has a back shroud enclosing the impeller vanes. A semi-open impeller is typically
used when pumping dirty liquid, or liquid containing slurry or small solid particles.

Series operation - a set-up whereby two or more pumps operate in a manner
where one pump discharges into the suction of the next pump (and so on into the
next pump.) The capacity of each pump is the same for all pumps in the series,
but their total head is the sum total of the heads of the individual pumps which
could be different from one another. (see parallel operation.)

Shaft - the part of the pump on which the impeller is mounted and through which
the input power is transmitted from the driver to the impeller, or impellers.

Shaft flexibility factor (SFF) - an index  or dimensionless number indicating  the
relative shaft flexibility of one pump with another pump of similar size and design.
SFF is calculated using the formula SSF = (L^
3 ) / (D^4). A lower SFF value means
that a shaft is likely to have less deflection, less vibration, and will have a better
mean time between failures (MTBF).

Shaft sleeve - a thin cylindrical sleeve placed on a portion of a shaft to protect it
from wear and corrosion. When used on the destaged portion of a shaft it is used
to protect the keyway from damage. Shaft sleeve is also used as a positive lock to
prevent a part, such as an impeller, from moving axially along the shaft.
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Shuttling - see ball shuttling.

Similarity Laws - same as Affinity Laws.

Single plane balancing - the correction, or reduction, of residual unbalance to
comply with specified or acceptable unbalance limit by removing (preferred
method) or adding weight in one correction plane only. Also referred to as
static
balancing
.

Single stage pump - a pump designed with only one impeller. See two-stage and
multistage pumps.

Single suction pump - a single stage pump with a single suction impeller, or a
multistage pump with a single suction first stage impeller. See
double suction
pump
.

Single suction impeller - an impeller with a single inlet, or suction, and where the
liquid enters the impeller from side  only, as opposed to a double suction impeller
where the liquid enters from both sides of the impeller.  A radial flow impeller can
be either single or double suction, but mixed flow and axial flow impellers are
always of single suction type. See
double suction impeller.


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