When it comes to selecting the right pump, it’s essential to understand some fundamental concepts. While factors like Head (H), Flow Rate (Q), and Fluid Characteristics (such as density, viscosity, and temperature) play a significant role in pump performance, one concept often misunderstood is the relationship between Head and Pressure. Though closely related, they’re not the same—and understanding this distinction can make all the difference in choosing the right pump, especially if you’re considering regenerative turbine pumps like those from MTH Pumps.
Defining Head and Pressure
- Head is the height a pump can raise a liquid and is measured in feet or meters of liquid column. Notably, head remains constant regardless of the fluid’s density, meaning that a pump can lift fluids like water, oil, or other liquids to the same height.
- Pressure, by contrast, depends on the density of the fluid. The same height of fluid will produce different pressures based on the liquid’s density. For example, while water and a denser fluid like sulfuric acid might rise to the same height, they exert different pressures due to their density difference.
How Pressure and Head Are Measured
- Head isn’t measured directly. Instead, we measure Pressure at the pump’s suction and discharge points using gauges, typically in PSI (pounds per square inch). To convert this pressure to head, we must account for the specific gravity of the fluid.
Conversion Example
Let’s consider a pump that operates at 33 gallons per minute (GPM) with a head of 33 feet, moving both water and sulfuric acid (H₂SO₄):
- For water (specific gravity = 1.0), the pressure is about 14.7 PSI.
- For sulfuric acid (specific gravity = 1.8), the pressure is approximately 26.5 PSI.
The relationship between head and pressure can be expressed as:
P [PSI] = 0.433 × H [feet] × γ [specific gravity]
Where:
- 0.433 is the conversion factor from feet of water column to PSI.
- H is the head in feet.
- γ is the specific gravity of the fluid.
Power Consumption Considerations
Power consumption also depends on pressure, and the power formula is as follows:
N [kW] = (γ [specific gravity] × Q [GPM] × H [feet]) / (3956 × η)
Where:
- Q is the flow rate in gallons per minute.
- H is the head in feet.
- η is the pump efficiency.
For more information on optimizing power usage, visit our efficiency and performance page.
Practical Tips for Pump Technicians
- Fluid Viscosity: These relationships apply mainly to low-viscosity fluids like water. Higher-viscosity fluids may require adjustments to pump performance.
- Head and Flow Rate: A pump’s head at a fixed speed depends on the flow rate and follows its characteristic performance curve.
- Determining Required Head: Calculating the head a pump needs involves more than the vertical distance. Be sure to consider: Geodetic head: The height difference between suction and discharge. Pressure differences at suction and discharge. Friction losses from the piping system.
The Bottom Line for MTH Pumps’ Regenerative Turbine Pumps
With a solid understanding of head versus pressure, you’ll be better equipped to choose the right pump for your specific application. MTH’s regenerative turbine pumps are engineered to deliver precise fluid handling across industries, accommodating a wide variety of liquids while maintaining efficiency and reliability.
