Pump Dynamics (Part 2): Fluid Hydraulics

Welcome back to part 2. In Part 1 of Pump Dynamics we learned about industrial pump basics. Now that we’ve covered those, let’s get our hands a little dirty and discuss fluid hydraulics.


Hydraulic pumps are used to pump a vast variety of materials such as oils, fertilizers, fats, etc. To avoid any unnecessary damage to your equipment, or worse, yourself, it’s important that you clearly understand the buildup and breakdown points of pumping these materials. 


Specific Gravity:

Specific Gravity is the ratio of a fluid’s density to that of water. Water has a specific gravity of 1. A fluid with a specific gravity of 0.5 weighs half as much as the same volume of water. Oil, fat and crude oil are all examples of fluids with specific gravity values less than that of water. Just remember — if it floats, it’s lighter!


Vapor Pressure:

Vapor Pressure, also known as the boiling point, is the pressure below which a liquid at a given temperature will become a gas. With water, this occurs when temperatures reach 212 degrees F at 14.7 psi at sea level. Vapor Pressure varies depending on the fluids.


Pressure is the force exerted per unit area, typically per square inch (psi). When pressure is exerted on a liquid, that pressure is transmitted equally in all directions. There are three different types of pressure:

  • Atmospheric Pressure: Is the force exerted by the atmosphere (pressure at sea level is 14.7 psi)
    • Atmospheric Pressure = Absolute Pressure – Gage Pressure
  • Gage Pressure: Is the pressure contained in a vessel not acted upon by the atmosphere (units/psig).
    • Gage Pressure = Absolute Pressure – Atmospheric Pressure
  • Absolute Pressure: the sum of gage and atmospheric pressure (units/psia).
    • Absolute = Gage + Atmospheric



Head is used as a standard measure of pressure. Measured in “feet of liquid,” Head is indicated by the height and weight of a column of liquid being discharged by a centrifugal pump. Keep in mind, a pump with a given impeller diameter and speed will raise a liquid to a certain height regardless of the weight of the liquid.


By educating our customers about the machinery they rely on for their day-to-day operations, C&B Equipment can help increase uptime, while decreasing the need for costly off-site repairs. That’s what we call Uptime Solutioneering™.



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