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.
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.
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.