Industrial Pumps 101: Understanding the Basics
Industrial pumps are an essential piece of equipment to a wide range of businesses and industries worldwide. They help accomplish many different tasks, and manufacturers design different pumps with specific applications in mind. For you or your operators to use the pumps correctly and safely, you first need to understand the basics of industrial pumps.
The American National Standard Institute
The American National Standard Institute (ANSI) is a private, non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States.
A common misconception is that the ANSI creates the standards that products, such as industrial pumps, need to follow. However, in actuality, they simply oversee the development of such standards.
The ANSI states, “it is the intent of this standard that pumps of all sources of supply shall be dimensionally interchangeable with respect to mounting dimensions, size, and location of suction and discharge nozzles, input shafts, baseplates, and foundation bolts.”
ANSI process pumps are typically preferred because their parts are functionally and dimensionally interchangeable. In other words, you can swap one pump out with another (even if it’s a different brand) because all of the parts should be dimensionally the same.
Classifications of Industrial Pumps
Pumps make up roughly 68 percent of all rotating equipment globally (this includes generators, engines, etc.). There are essentially two different classifications of pumps: centrifugal pumps and positive displacement pumps. Approximately 86 percent of all industrial pumps are centrifugal pumps.
Centrifugal pumps are pressure-creating devices that convert velocity energy to kinetic energy by accelerating liquid to the outer rim of a revolving device known as an impeller. The faster you turn the device, the more pressure you are going to get.
It’s important to note that a centrifugal pump does not create pressure; it only creates flow. Pressure is a measurement of the resistance to flow, and flow depends on the pump system’s characteristics. Centrifugal pumps are perfect if you require high flow rates for low-viscosity liquids.
Positive Displacement Pumps
Positive displacement pumps are designed to create flow by trapping a fixed amount of fluid and forcing (or “displacing”) that trapped fluid into the discharge pipe. Unlike centrifugal pumps, positive displacement pumps are “constant flow machines” and will produce the same flow at a given speed (RPM) no matter the discharge pressure.
A positive displacement pump operating against a closed discharge valve will continue to produce flow until the pressure in the discharge line increases to the point where the line bursts, the pump becomes damaged, or both.
Other Types of Industrial Pumps
Aside from centrifugal pumps and positive displacement pumps, several other less-common types of pumps serve specific purposes.
- ANSI Process Pumps. These pump types incorporate the ANSI dimensional standardization that we discussed earlier. They are easier to customize and adapt to fit multiple applications.
- API Process Pumps. Similar to ANSI process pumps, these adhere to API 610 requirements. These requirements make them ideal for high-temperature and high-pressure hydrocarbon applications.
- Axial Flow Pumps. These pump types are the ideal choice for applications that require high flow rates and low head.
- Booster Pumps. These specialty pumps increase the build-up of pressure to move fluids across long distances.
- Diaphragm Pumps. This pump type is one of the most versatile, as it can handle many sealless fluids, and it can run dry without causing damage to itself.
- Gear Pumps. These pumps feature few moving parts and are easy to build. They are the best choice for clean oil applications.
- Lobe Pumps. Lobe pumps are one of the few industrial pumps that have no metal-to-metal contact within the pump itself. They are ideal for sanitary applications that involve viscous liquids or liquids containing solid bits.
- Magnetic Drive Pumps. This pump type features no mechanical seals, which makes it almost immune to leakage.
- Multistage Pump. This type of centrifugal pump allows for higher flow rates at the expense of higher thrust loads.
- Piston Pumps. This pump type is the best choice for applications that involve abrasive liquids that would damage other types of industrial pumps.
- Progressive Cavity Pumps. These pump types can handle heavy-duty applications that other types of pumps cannot. When it comes to industrial pumps, people see progressive cavity pumps as a “last resort.”
- Screw Pumps. This type of positive displacement pump is ideal for applications that require extremely high flow rates.
- Self-Priming Pumps. As the name implies, these pumps prime themselves, meaning the operator doesn’t have to do it!
- Submersible Pumps. Submersible pumps are designed to be submerged in liquids, particularly water. This feature makes them the perfect choice for areas often subjected to flooding.
Industrial pumps transport various materials, including oils, fertilizers, chemicals, fats, and water. To avoid unnecessary damage to your equipment and harm to you or the pump’s operators, it’s crucial that you clearly understand the buildup and breakdown points of pumping these materials.
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 water. Of course, the volume of the liquid has to be taken into account as well.
Oil, fat, and crude oil are examples of fluids with specific gravity values less than water. Just remember, if it floats, it’s lighter!
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 fluid in question.
Pressure is the force exerted per unit area, typically measured per square inch (psi). When pressure exerts 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 is the sum of Gage Pressure and Atmospheric Pressure (units/psia). Absolute Pressure = Gage Pressure + Atmospheric Pressure.
Head is a standard measure of pressure. Measured in “feet of liquid,” head is indicated by the height and weight of a column of liquid 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.
Shaft Dynamics and Troubleshooting
Industrial pump operators must understand shaft dynamics and know how to solve problems as they arise.
Shaft whip occurs when the shaft shifts 180 degrees from its centerline in every rotation creating a cone shape. An unbalanced impeller is usually the cause of this rotation.
Shaft deflection occurs when a radial load or mechanical imbalance causes the pump shaft to bend down when it is in one position. When the shaft rotates 180 degrees, it still bends downward in a similar way.
Shaft Deflection is a function of four factors.
- Radial force in the impeller
- Length from the impeller to the radial bearing
- Shaft diameter (the smaller the diameter, the more deflection)
- Material properties; different materials have a different flex
The following scenarios are common problems that industrial pump operators face.
- There is no liquid coming from the pump. If the plate is full of green oil, pitch, or tar, no fluid can flow because it completely plugs up the impeller. Thus, nothing will be pumped.
- The suction pipe will not open. The pipe is either unsubmerged or the suction lift is too high. Twenty-five feet is the maximum lift for water before it starts to boil.
- The pump is not producing rated flow. This creates an air leak. When this happens, spray it down with soapy water and see if the water goes into the stuffing box. It will go in if there is a pulling vacuum.
- The pump starts then stops pumping. The pump is improperly primed, meaning it won’t suck in any air.
- The bearings are running hot. This may occur due to improper alignment, lubrication, lube cooling, etc.
- The motor requires excessive power. The liquid is too heavy, requiring more horse-power to pump.
- The pump is noisy or vibrates. This is caused by improper alignment or cavitation.
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