Seal faces
The lapped faces that that provide the primary sealing in a mechanical
seal.
Seal life
Seals should run leak free until the sacrificial face (usually
carbon/ graphite) is worn away. More than 85% of the mechanical
seals in use today fail prematurely.
Seal only pump
The pump does not have a conventional stuffing box so it could
not be supplied with soft packing.
Self align
A method of keeping both mechanical seal faces square to the
rotating shaft.
Self sintered silicone carbide
Same as Alpha sintered. No free silica present. Can be used in
caustic and higher pH liquids.
Series operation
The pumps are connected with the discharge of the first pump
discharging to the suction of the other. The speed and impeller
widths must be the same or the difference in capacities could
cause cavitation or over heating problems.
Shaft packing
The soft packing supplied by pump manufacturers. Most of these
leaking packings are being replaced by mechanical seals.
Shelf life
Usually refers to the seal elastomer. Buna "N" is the
biggest problem because of Ozone attack.
Shore "A"
A scale used to measure elastomer hardness.
Shut off head
The maximum head that the pump can generate with a given impeller
outside diameter and horsepower driver.
SiC
Silicone carbide. A common mechanical seal face material. A type
of ceramic.
Sintered material
Formed from a powder as opposed to being melted and poured into
a mold.
Skidding
A term used in describing how an impeller slides on the solids
in the bottom of a mixer.
Sleeve bearing
A non precision bearing. Usually manufactured from carbon, Teflon.
brass etc., Allows too much axial and radial movement for most
mechanical seal applications.
Slenderness ratio
Another name for L3/D4
Slip stick
An alternating slipping and sticking of the seal faces caused
by a poor lubricant between the faces. Will cause vibration problems
at the seal face unless the vibration is dampened.
Slurry
Solids in liquid. It is impossible to define when the quantity
and size of the particles becomes too much for the mechanical
seal.
Soft foot
The tendency for one of the pumps feet to rise when the hold
down bolt is loosened. Very bad for alignment.
Soluble
When one liquid dissolves or mixes with another liquid.
Span
The width of the metal bellows. The distance from the inside
diameter to the outside diameter.
Specific Gravity
A measure of the weight of a liquid. Fresh water at 4?C (39?F)
is given a value of one. If the liquid you are questioning will
float on water the specific gravity is less than one. If it sinks,
it is higher than one. Density is a better term.
Specific heat
Refers to the amount of calories or BTUs required to raise a
quantity of a liquid one degree.
Specific speed
A formula that describes the shape of a pump impeller. The higher
the specific speed the less N.P.S.H. required.
Speed of sound
In air it is 1090 feet per second, in water it is 4800 feet per
second.
Spool piece
Usually refers to a seal and bearing combination that is supplied
for some mixer applications. It depends upon the application,
but this is not a good idea if there are already two anti-friction
bearings already installed on the shaft
Spring force
The force on the seal faces caused by the spring compression.
Stainless steel
Alloy steels containing a high percentage of chromium.
Static head
The maximum height the liquid is being pumped as long as you
take into consideration the siphon affect in some piping systems.
Stationary seal
The spring loaded or moveable portion of the seal does not rotate
with the shaft. Must be used when the seal surface speed exceeds
5000 fpm. or 25 meters per second.
Stiffness ratio
Another name for L3/D4
Strain
A measure of the amount of deformation produced in a substance
when it is stressed.
Stress
A measure of the intensity of the load applied to a material.
Stress is expressed as the load divided by the cross-sectional
area over which it is applied.
Stress relieve
To take residual stress out of an object. This is very important
with lapped seal faces; especially those that have been inserted
into a metal holder.
Stuffing box
That portion of the pump that held the packing and now holds
the mechanical seal.
Stuffing box pressure
Between suction and discharge pressure but closer to suction
pressure.
Suction head
The head on the suction side of the pump. You subtract it from
the discharge head to determine the head being produced by the
pump. It is a sum of the static, pressure and friction heads.
Suction recirculation
Piping from the bottom of the stuffing box back to the suction
side of the pump. Used to lower pressure and circulate liquid
in the stuffing box.
Suction specific speed
A formula that will predict one of the types of cavitation. Pumps
should be purchased with a number below 8500 (10,000 metric)
Surface speed
A measure of the feet per minute the seal face or some other
component is moving.
Synchronous motor
Runs with out slippage. Used in elevators and compressors frequently,
but seldom used in pumping. Pumps mostly use induction or "squirrel
cage" motors.
System curve
A description of what the pump is required to perform. The pump
will pump where the system curve intersects the pump curve.
System head
The head caused by friction in the piping. valves and fittings.