NANTEL Mechanical Engineering

Forced Vibration

A disturbing force is input into the system, causing the system to vibrate at the frequency defined by the input

Incompressible Fluid

A fluid whose density is constant

Specific Weight

A fluids weight per unit volume simply stated as its density multiplied by the acceleration of gravity.

Stress

A measure of the intensity of the forces distributed over a given cross section. This is calculated using the equation at right, where P is the force exerted (lbf or N) and A is the area of the cross section of the component (in2 or m2). The most common units of this are psi or Pa.

Compressive Stress

A negative value of stress.

Rotary Pump

A positive displacement pump consisting of a chamber containing gears, cams, screws, vanes, plungers, or similar elements operated by relative rotation of the drive shaft or casing. These pumps are characterized by their close running tolerances. Examples of these are Gear, Screw, Vane, and Flexible Member

Tensile Stress

A positive value of stress.

Equilibrium

A state of balance between opposing forces or actions that is either static (as in a body acted on by forces whose resultant is zero) or dynamic (as in a reversible chemical reaction when the rates of reaction in both directions are equal).

Throttle Bushing

A stationary part that has a very close fit between the rotating and stationary parts of the pump. These do not fit as closely as packing, so leakage is higher than a packed box.

Pure Substance

A substance whose chemical composition is homogeneous and invariant.

Absolute Temperature

A temperature measured on an absolute scale, where zero is the absolute zero. Absolute zero is defined as the physical limit to how low a temperature any matter can have. Expressed in degrees kelvin or rankine where 0°K = -273°C or 0°R = -460°F.

Vector

A variable quantity that can be resolved into components.

Torque Callout

Also know as torque value, it is a factor in fastener tightening determined primarily by the material and size of the fastener.

Undamped Vibration

Has no components that are capable of dissipating energy and thus, when excited, will continue to oscillate

Shear Stress

If a member is loaded such that the force is no longer along the axis of a component but is acting transversely, the component is under this. This has the same units as normal stress

Newton's First Law of Motion

If there are no unbalanced forces acting on an object it will either remain at rest or continue to move in a straight line with a constant velocity.

International System (SI)

In this system the mass unit is the kg and since the weight is a force - the weight unit is the newton (N).

VI Improvers

Lubricant additives that are used to thicken and lower the viscosity of oils and thus flatten the viscosity/temperature slope to enhance their performance.

Elastic Limit

Most solid objects which are subjected to an applied stress will return to their original shape and dimensions provided the stress is below a characteristic threshold for the material of which they are made. If this limit is exceeded, release in load will not result in full recovery of original form.

Reciprocating Pump

Most useful in high pressure, low flow applications due to their high head capacity. They have three types of moving elements: Piston, Plunger, and Diaphragm

Impulse Turbine

One of the fundamental types of turbines, the steam enters the turbine at the steam chest, it is then expanded through a nozzle where it strikes a turbine blade with an impulsive force causing the turbine to rotate. These type of turbines require high velocity steam for efficient operation.

Reaction Turbine

One of the fundamental types of turbines, these type of turbines utilize a different principle of operation than their impulse counterparts, they use the reactive kick from steam to rotate.

Gage Pressure

Pressure measurments made relative to local atmospheric pressure.

Absolute Pressure

Pressure measurments made relative to zero pressure

Double Shear

Scenario in which a component experiencing a force is sandwiched between two supporting members with a pin or bolt passing through these components.

British Gravitational System

System of units used by engineers in the English-speaking world with the same relation to the foot - pound - second system as the meter - kilogram - force - second system (SI) has to the meter - kilogram - second system.

Newton's Second Law of Motion

The acceleration of an object is proportional to the vector resultant of all forces acting on it, and the acceleration is in the direction of this resultant vector.

Kinetics

The branch of dynamics that describes the relationship between unbalanced forces and the changes in motion that these unbalanced forces produce. This relates the forces acting on a body and the mass of the body and the resulting motion of the body. This is used to predict the motion caused by forces acting on a body.

Preload

The clamping force for bolts or threaded fasteners. To obtain the correct of this on a bolt, you use a torque wrench to determine and control the degree of tightness.

Mechanics

The classical study of Newton's Laws

Density

The fluid's mass per unit volume. This is typically used to characterize the mass of a fluid in a system. The SI unit for this is kilograms per cubic meter and in the BG system, It has the units of slugs per cubic foot.

Newton's Third Law of Motion

The forces of action and reaction between interacting bodies are equal in magnitude, opposite in direction, and collinear.

Tensile Strength

The highest stress a material can sustain before failure.

Overhung Impeller Type

The impeller (or impellers for two stage) is mounted on the end of the shaft which is cantilevered from its bearing support.

Impeller Between the Bearings Type

The impeller is mounted on a shaft with bearings at both ends. These pumps are single or multistage. They also are either Axial (Horizontal) or Radial (Vertical) split case

Slippage

The leakage of fluid from the discharge side of the pump back to the suction side.

Proof Load

The maximum load that a bolt can withstand without acquiring a permanent set, or permanent deformation.

Thermal Conductivity

The measure of the ability of a material to conduct heat.

Torque

The measure of the tendency of a force to produce torsion and rotation about an axis, equal to the vector product of the radius vector from the axis of rotation to the point of application of the force and the force vector.

Saturation Pressure

The pressure existing at a given temperature in a closed vessel containing a liquid and the vapor from that liquid after equilibrium conditions have been reached.

Yield Stress

The pressure which a substance is capable of supporting without fracturing.

Modulus of Elasticity

The ratio of stress to strain in the linear region of a stress-strain curve below the elastic limit which characterizes the property of a material to deform when force is applied to the material and recover its original shape when the force is removed.

Specific Gravity

The ratio of the density of a fluid to the density of water at some specified temperature, usually 39.2° F

Mechanical Seals

The stationary component is fastened to the casing and the rotating component is fastened to the shaft. Both components have highly polished wearing surfaces that accomplish the sealing. The sealing surfaces are held in contact by a spring that is adjusted at installation. This requires some leakage to lubricate the sealing faces; however, this leakage is very small relative to packing and throttle bushing packings

Yield Strength

The stress level which will produce a small amount of permanent deformation in the fastener (usually 0.2% offset is used to define yield).

Dynamic Viscosity

The tangential force per unit area required to move one horizontal plane with respect to the other at unit velocity when maintained a unit distance apart by the fluid. It has units lbf-sec/ft2 pr centi Poise (cP).

Inertia

The tendency of an object to stay in motion.

Specific Volume

The volume per unit mass or the reciprocal of the density.

Turbine or Vertical Impeller Type

This group includes pumps which are built mostly with internal, liquid lubricated bearings, and diffuser casings, are convenient for multistage construction, and discharge through a supporting column

Free vibration

This is the type of vibration that occurs when an object is vibrating at its natural frequency (no energy inputs are needed once it is set in motion).

Superheat

To heat a liquid above its boiling point without converting it into vapor.

Packing

Typically a soft braided graphite packing formed in rectangular sections with butt joints staggered from ring to ring during installation. The sealing is accomplished by compressing the packing around the shaft.

Strain

When a component is subjected to a normal stress, it will deform based on the intensity of the normal stress. This deformation is often normalized as the change per unit length of a component. This dimensionless ratio is called this.

Damped Vibration

When subjected to an initial displacement will vibrate freely with the resulting motion amplitude decreasing with each cycle at a rate that depends on the amount of damping.

Anodic-Cathodic Materials

When these materials are exposed to an electrolyte, a corrosion cell is created where material from the anode releases metal ions to the electrolyte. The cathode receives electrons from the anode and may exhibit corrosion products on the surface.

Zeroth Law of Thermodynamics

When two objects are in thermal equilibrium with a third object, they are in thermal equilibrium with each other.