Within HVAC services, pumps are broadly classified into two types: centrifugal pumps and positive displacement pumps. In this guide, the focus will be on the more commonly used centrifugal pump and some key considerations to keep in mind when selecting the pump for your application.
In today's HVAC industry, centrifugal pumps are widely used for a variety of reasons, including their ease of operation and maintenance, high efficiency, low operating costs, wide range of capacity and head (pressure), availability of a variety of sizes, smooth flow rate, and their simple design.
 |
All centrifugal pumps function by using an impeller, which is an internal rotating wheel that adds energy to a fluid being pumped. When in action, the fluid or liquid being pumped will enter the inlet port at the center of the rotating impeller (or eye impeller). As the impeller is spinning in a counter-clockwise direction, the fluid being pumped is thrust outward radially, which causes centrifugal acceleration. While doing this, the rotating impeller creates a vacuum in its wake and draws even more fluid into the inlet. The faster the impeller rotates, the faster the fluid movement and the stronger its force.
Pumps only provide flow, however, and they don't create pressure. Because of this, the flow that a pump produces depends on the resistance it's working against. Resistance is caused by the friction created by the flow of the fluid through the system's pipes, and the greater the resistance the slower the fluid moves.
Pump Components Vary with Intended Use
Within the HVAC industry, the most commonly used pumps are single stage (one impeller) volute-type pumps that have either a single inlet or a double inlet (double suction). For HVAC applications, there are four primary pump types to choose from and they include:
- Close-Coupled End Suction Pumps or In-Line Circulating Pumps. These are designed for use in low flow (up to 50 gpm) circulating systems.
- Base-Mounted End Suction Pumps. This is a pump ideally used for circulating systems with flow rates between 50 and 500 gpm.
- Horizontal Split Case, Double-Suction Pumps. A pump commonly used for applications with flow rates exceeding 500 gpm.
- Vertical In-Line Pumps. Theseare used for applications with limited floor space. Flow rates can vary.
Here's a look at some of the pump's key components and the impact on its function.
Type of Volute
Single: Features a single lipped volute and is used with low-capacity pumps. These pumps maintain higher radial loads.
Double: The most common design for centrifugal pumps, they have dual lips opposite each other, resulting in balanced radial loads.
Triple: Provides excellent radial thrust balancing with 3 lips at 120° intervals along the perimeter of the volute.
Number of Impellers
Single-Stage: One impeller and used mostly in low head (pressure) applications.
Two-Stage: Two impellers in a series and used mostly in medium head (pressure) applications.
Multi-Stage: Has three or more impellers in a series and used mostly in high head (pressure) applications.
Impeller Suction
Single Suction: Has one suction eye on only one side of the impeller. This design is subject to greater axial thrust imbalance since there is flow coming in on only one side of the impeller.
Double Suction: These feature suction eyes on both sides of the impeller. The design provides for a pump that is better hydraulically balanced. However, if suction piping is installed improperly, uneven flow on each side of the impeller is possible, resulting in poor pump performance.
Shaft Orientation
Horizontal: A very popular option as they're easily accessible for service and maintenance.
Vertical: Often used where space is limited and commonly used in a sump or a pit for pumping.
Additional Considerations in Selecting the Best HVAC Pump
When it's time to select the proper HVAC pump for your application, along with utilizing information already presented here, there are a few additional things to consider to ensure choosing the proper one.
- Determine the location and use of the pump.
- Determine the requirements needed for your application, including the flow rate and head.
- Factor in the size of the pump and how it impacts cost, annual operating costs, and noise level when in use.
- Consider the configuration or footprint of the pump and how it will impact regular maintenance.
By having a solid understanding of a pump's function, you'll be sure to select the right water circulator motor to keep your operation flowing smoothly.
Product Compliance and Suitability
The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.