- Soft foot - A condition whereby the mounting feet of a machine - motor, pump, compressor, turbine, or similar equipment - are not in the same plane and not in proper contact with their mounting pads on the baseplate. Click on link to read more.
Spalling - bearing damage characterized by breaking out of small splitters or chips on its surface due to improper lubrication, mechanical damage, material defect, or material fatigue.
Specific gravity - Ratio of a liquid density to water density at 39.2 degrees Fahrenheit (4 degrees Centigrade). Also known as relative density.
Speed-torque curve - A plot of the pump speed, ranging from zero to full speed, drawn in the x-axis, versus its corresponding torque drawn in the y-axis.
Standby service - A service where an equipment is in idling mode ready for immediate start-up and continuous operation to switch with, unload, or share the load of, another equipment. A standby unit in hot temperature service should be maintained sufficiently warm to prevent thermal shock when it starts up immediately.
Static 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 single plane balancing.
Stress corrosion cracking - Refers to the brittle fracture of metal under tensile stress and some other specific conditions that are conducive for corrosion cracking to occur. Chloride cracking of austenitic stainless steel and caustic embrittlement of cast irons and carbons steel are examples of stress corrosion cracking.
String test - Test involving the whole pump package, including the driver, baseplate, seal flush system including any oil pots or lube system, and bearing forced-feed lube system. The string test may include the auxiliary piping, instrumentation, gearbox, or variable-drive, if specified in the contract. Read more.
Stuffing box - A part of through which the shaft extends out and in which packing rings, or a mechanical seal, and a gland are placed to prevent the liquid from leaking out into the atmosphere.
A stuffing box may be an integral part of the casing, or a separate part bolted into a casing, cover, or nozzle head. The stuffing box may be cooled, or non-cooled, depending on the process liquid temperature.
When a stuffing box is provided with mechanical seal, it is more specifically referred to as "seal chamber."
Suction bell - A flared tubular section at the bottom of a vertical lineshaft pump for directing the flow of liquid into the impeller inlet. A similar piece on horizontal pump is usually referred to as suction case.
Suction lift - the capability of pump to "suck" liquid into its suction nozzle.
Suction case - A flared piece in a horizontal multistage pump for directing the flow of liquid into the impeller inlet. A similar piece on a vertical pump is usually referred to as suction bell.
Suction specific speed (NSS) - A dimensionless number, or index, that defines the suction geometry, or suction hydraulic characteristics, of a pump.