- The lapped faces that that provide the primary sealing in a
- 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.
- A method of keeping both mechanical seal faces square to the
Self sintered silicone carbide
- Same as Alpha sintered. No free silica present. Can be used in
caustic and higher pH liquids.
- 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.
- The soft packing supplied by pump manufacturers. Most of these
leaking packings are being replaced by mechanical seals.
- Usually refers to the seal elastomer. Buna "N" is the biggest
problem because of Ozone attack.
- 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.
- Silicon carbide. A common mechanical seal face material. A
type of ceramic.
- Formed from a powder as opposed to being melted and poured
into a mold.
- A term used in describing how an impeller slides on the solids
in the bottom of a mixer.
- A non precision bearing. Usually manufactured from carbon,
Teflon. brass etc., Allows too much axial and radial movement for
most mechanical seal applications.
- 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.
- Solids in liquid. It is impossible to define when the quantity
and size of the particles becomes too much for the mechanical
- The tendency for one of the pumps feet to rise when the hold
down bolt is loosened. Very bad for alignment.
- When one liquid dissolves or mixes with another liquid.
- The width of the metal bellows. The distance from the inside
diameter to the outside diameter.
- 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
- Refers to the amount of calories or BTUs required to raise a
quantity of a liquid one degree.
- 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
- 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
- The force on the seal faces caused by the spring
- Alloy steels containing a high percentage of chromium.
- The maximum height the liquid is being pumped as long as you
take into consideration the siphon affect in some piping
- 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.
- A measure of the amount of deformation produced in a substance
when it is stressed.
- 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.
- 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.
- 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
- 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.
- 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
- A measure of the feet per minute the seal face or some other
component is moving.
- Runs with out slippage. Used in elevators and compressors
frequently, but seldom used in pumping. Pumps mostly use induction
or "squirrel cage" motors.
- A description of what the pump is required to perform. The
pump will pump where the system curve intersects the pump
- The head caused by friction in the piping. valves and
For information about my CD,
with over 600 Seal & Pump Subjects
Link to Mc Nally home page