TDH Flashcards
Pump
A mechanical device that converts forms of energy into hydraulic energy.
Pump Classifications
Generally pumps can be classified into two classifications.
Positive Displacement
Centrifugal
POSITIVE DISPLACEMENT PUMPS
Operate by reducing the volume of space within the pump that the liquid can occupy. In a reciprocating pump the piston forces the liquid from the cylinder into the discharge line.
Centrifugal Pumps
Move liquid by increasing their speed rather than displacing or pushing them. The vanes do work on the fluid to increase the velocity without decreasing the pressure. The increased velocity is then recovered in the casing as increased pressure.
Centrifugal Force
According to Webster’s, it is the force which tends to impel a thing, or parts of a thing outward from the center of rotation.
Sump
A hydraulic structure that acts as a reservoir from which single of multiple pumps, arrange in parallel, may draw water.
Vortex
The phenomenon by which air enters a submerged suction pipe from the water surface. Usually a cause of poor pump performance when the suction pipe is not adequately submerged.
Manifold
A hydraulic structure used to distribute water under pressure. Can be used to supply fluid to or receive fluid from a parallel arrangement of multiple pumps.
RECIPROCATING Examples
Single or multiple design Piston Plunger Diaphragm Rotary Gear Rotary Screw Rotary Cam
CENTRIFUGAL Examples
These can be single or multi-stage, open or closed impeller
Radial Flow
Mixed Flow
Axial Flow
ATMOSPHERIC PRESSURE Definition
The force exerted on a unit area by weight of the atmosphere.
Standard atmospheric pressure at sea level is 14.7 pounds per square inch.
ATMOSPHERIC PRESSURE
1 Atmosphere = 14.7 PSI or 34 Feet of Water
ATMOSPHERIC PRESSURE - Higher Elevations
At higher elevations atmospheric pressure decreases because the imaginary square tube become shorter, therefore it’s weight decreases.
ATMOSPHERIC PRESSURE
Below sea level
The atmospheric pressure increases at elevations below sea level.
Equilibrium
Equilibrium Exists at the ocean surface because the atmosphere and pushes down and the ocean pushes up air by an equal but opposite amount.
ATMOSPHERIC PRESSURE
Explained
Let us assume we can create a perfect vacuum by removing all air within the tube. Since the pressure of the air within the tube is no longer present, atmospheric pressure pushing down on the surface of the water surrounding the tube will force the water to rise inside the tube to a height where the weight of the water in the tube creates a pressure equal to atmospheric pressure pushing on the surface of the water outside the tube.
ATMOSPHERIC PRESSURE
Expresses In inches of mercy
Due to the common use of mercury to measure vacuum, units are expressed in inches of mercury.
• 14.7 psi = 30” Hg
• 1 atmosphere is also equal to 30” Hg
• 34/30” = 1.33
Therefore,
25Hg x 1.33 = 28’ Lift
Total Dynamic Head
Is measured in feet, therefore, friction resistance must be converted to it’s equivalent gravity resistance.
What are the physical conditions of a portable pump application?
FLOW. Quantity over time = GPM
LIFT (gravity resistance):
• suction lift from surface to impeller. +
• discharge / length of hose to discharge
Rule 1
Pumps are sized by Flow.
Flow Determines line size
3” = 250 gpm 4 = 500 gpm 6 = 1,000 gpm 8 = 2,000 gpm 12 = 4,000 gpm
Duty Point
On a system curve, a duty point is the intersection between the required flow and requires pressure for a given application.
What to know when sizing a portable pump.
FLOW = Determines line size
LIFT = Determines Pump strength
Distance = Determines if line size should be increased to reduce friction loss.
FLOW
Flow in a line Determines Velocity.
Water moving through a line at greater than 12 feet per second creates significant friction and possible cavitation.
At less than 12 feet per second, water flows in a flat manner called laminar flow.
At greater than 12 feet per second, flowing water is turbulent.
Velocity in feet per second.
The maximum velocity of liquid through pipe or smooth bores hose is 12 feet per second DV range.
14 ft per second HL range.
Velocity greater than 14 feet per second require excessive amounts of energy.
