A pump is a mechanical device that converts mechanical forms of energy into hydraulic energy. Generally pumps can be classified into two classifications – positive displacement pumps and centrifugal pumps.
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 liquids by increasing their pump speed rather than displacing or pushing them. The vanes of the pump impeller do work on the fluid to increase the velocity without decreasing the pressure. This increased velocity is then recovered in the casting as increased pressure.
Typical Centrifugal Pump Impeller - In centrifugal pumps, water enters the pump and travels into the impeller through the impeller eye. In general, the larger the impeller eye, the greater the volume in gallons.
Portable Pump
A portable pump is a package that consists of a pump including drive and frame or canopy. A portable pump has a lifting device and forklift sleeves and is therefore easy to move. Developers strive to minimize the weight of portable pumps. Additionally, they can be mounted onto trailers for added convenience.
Pump Curve Chart
Each centrifugal pump has its own pump curve chart. It's basically a graph showing the pump's performance across its entire operation range, including NPSH (Net Positive Suction Head) requirement and horsepower needs.
Pump Flow
The pump flow refers to the real delivery of the pump, indicating the volume of liquid pumped per unit of time. Typically, flow is measured and specified in gallons per minute on the pump curve chart.
Pump Head
The vertical height of a static column of liquid corresponding to the pressure of a fluid at that point. Head can also be considered as specific work necessary to increase the pressure, velocity or height of a liquid to some value.
Shut-off-head - Is the head generated by a pump with the discharge valve closed (pump running at zero capacity).
Statis Pressure Head - (energy per pound due to pressure). The height to which liquid can be raised by a given pressure.
Total Head (Formerly called Total Dynamic Head). Equal to the total discharge head minus the total the total suction head or plus the total suction lift.
Static Suction Lift - The vertical distance in feet, when the source of supply is below the pump, from the surface of the liquid to the pump centerline.
Static Suction Head - When the liquid supply is above the pump. The vertical distance from the pump centerline to the surface of the liquid.
New Positive Suction Head Required
The losses from the suction connection to the point in the pump where energy is typically added, usually via the impeller blades. These losses are determined through testing and are dependent on factors such as pump design, size, and operating conditions.
New Positive Suction Head Available
The energy, above the vapor pressure of the fluid, available at the pump suction to push the fluid into the pump. NPSHA depends on the system layout and must always be equal to or larger than the NPSHR.
Cavitation
A result of insufficient NPSHA. When pressure in the suction line drops below vapor pressure of the liquid, vapor forms and travels along with the liquid flow. These vapor bubbles or ‘’cavities’’ collapse when they reach regions of higher pressure on their way through the pump. The violent collapse of vapor bubbles forces liquid at high velocity against the metal, producing surge pressures of high intensity on small areas. These pressures can exceed the compressive strength of the metal, and actually blast out particles, giving the metal a pitted appearance.
Pressure
The force exerted per unit area of a fluid. According to Pascal’s principle, if pressure is applied to the surface of a fluid, this pressure is transmitted undiminished in all directions.
Atmospheric Pressure - The force exerted on a unit area by the weight of the atmosphere. The standard atmospheric pressure at sea level is 14.7 psi.
Absolute Pressure - The sum of atmospheric pressure ad gauge pressure. The absolute pressure in a perfect vacuum is zero. Absolute pressure of the atmosphere at sea level is 14.7 psi (0 psi gauge).
Vapor Pressure - The pressure exerted when a solid or liquid is in equilibrium when its own vapor. Vapor pressure is a function of the substance and of the temperature.
Vacuum
Commonly used in referring to pressures below atmospheric. Vacuum is commonly expressed in inches of mercury. At sea level, 14.7 pounds per square inch (psi) of atmospheric pressure is equivalent to 30 inches of mercury.
Static Suction Head
When the liquid supply is above the pump. The static suction head is the vertical distance from the pump centerline to the surface of the liquid.
Static Suction Lift
When the liquid supply is below the pump. The static suction lift is the vertical distance from the surface of the liquid to the pump centerline.
Pipe Friction
The system loses pressure when the water flowing through the piping encounters resistance. For instance, friction arises due to the roughness along the pipe walls. Additionally, pressure loss happens due to turbulence caused by valves, fittings, and variations in the pipe's section.
System Curve
A graphical representation of the relationship between the total head and the flow rate for a given fluid system.
Most common pump abbreviations
Q
Capacity, actual pump flow in gallons per minute or m³/hour
H
Head, vertical height of a static column of liquid in feet or psi or mwc
n
Pump speed in revolutions per minute (rpm)
η
Efficiency in percentage %
P
Power required in brake horsepower bhp or kilowatt kW
Hp
Horsepower(1 Hp= 0,745 kW kilowatts)
TDH
Total Dynamic Head = Sum of Static Height, Static Suction Lift and Friction Loss
Static Height
The maximum height reached by the pipe after the pump - measured from the center line
Friction Loss
The loss of pressure due to the flow of the liquid through pipes and fittings (resistance)
NPSHr
Net Positive Suction Head Required in feet or mwc
NPSHa
Net Positive Suction Head Available in feet or mwc
Cavitation
Process in which small bubbles are formed and implode violently; occurs when NPSHa < NPSHr
BEP
Best Efficiency Point
BSFC
Brake Specific Fuel Consumption in lb/hph or g/kWh
dB(A)
Sound level in decibels (A) stands for the A-scale
V
Velocity in feet/sec or m/s
ρ
Density is the mass per unit volume of a substance
