COLUMN | Guest Column
Beyond the Spec Sheet: The Dos & Don’ts of Submersible Pump Selection
Alex b. Hitsman | Kerr Pump & Supply
If you work in municipal and industrial wastewater management, you know the submersible pump is a workhorse, and the market has been moving in the direction of using more submersible pumps. However, a pump is only as good as the system it is designed for. Often, we see engineers and operators trying to solve hydraulic problems with a pump and upgraded features or by listening to manufacturer "upsells" that add complexity and cost without adding value.
Whether you are retrofitting an existing lift station or designing a new one, the goal is reliability and efficiency at the best value for the municipality or company.
Consider a situation I run into often: I am on-site with an operator reviewing a lift station retrofit and a set of discontinued alternating current (AC) pumps from the 1970s. Almost immediately, the request comes in to replace them with dry pit submersibles. Naturally, I ask the critical question, “Do you have an issue with this lift station flooding?” When they admit it has never flooded, the disconnect becomes clear. This insistence on installing flood-proof technology in a dry station is a prime example of “shiny object syndrome”—prioritizing new equipment over the actual needs of the application.
Here are some dos and don'ts to consider during the selection process.
| IMAGE 1: Impeller options for submersible pump (Images courtesy of the author)
DO: Adhere to Standards (10 State & UL)
Regulatory compliance isn't optional, but it is often misunderstood.
- The 10 state standards: Even if your specific state hasn't fully adopted the recommended standards, adhering to them is the gold standard for liability protection and design integrity.
- Explosion proofing: Know your hazardous location classifications. Does your state or local code require explosion-proof motors for this application?
- The rule: If there is a chance of methane buildup (common in raw sewage lift stations), an Underwriters Laboratories (UL)-rated explosion-proof motor is a nonnegotiable safety feature, not an upgrade.
DON'T: Fall for the 'Upsell' Features
Manufacturers love to bundle features that look great on a brochure but offer little return on investment (ROI) in the field. Be wary of:
- Proprietary smart monitoring relays: Unless your supervisory control and data acquisition (SCADA) system is set up to talk to a specific brand's proprietary protocol, these often end up being expensive paperweights. Stick to standard thermal and moisture sensors that integrate with universal controls.
- Exotic materials: Standard materials are usually sufficient for municipal wastewater. Unless you are pumping highly acidic industrial waste, paying more for a stainless steel pump generally is not necessary.
- Unique features: If only one manufacturer offers a unique feature that no one else in the industry does, ask yourself if this is really an advantage for your system or a want that will tie you to this one manufacturer and limit competition.
DO: Fix the System
DON'T: Over-Engineer the Pump
This is the most common mistake in the industry. If a station is struggling, throwing a larger pump at the problem is rarely the answer.
- Analyze the force main: Is the head pressure high because the pipe is scaled up? Are there broken pipes letting sand and grit into the system?
- The philosophy: You cannot pump your way out of a bad system design. Fix the restrictions and breaks in the piping first and purchase the pump you need, not the pump that is designed to compensate for the problem, because you will still have the problem.
DO: Design for Fewer Than 10 Starts per Hour
Heat is the enemy of electric motors. The most stress a motor endures is during startup (inrush current).
- The guideline: Size your wet well and set your floats/transducers to ensure the pump cycles fewer than 10 times per hour.
- The benefit: This allows the motor windings to cool between cycles, extending the stator's life.
| IMAGE 2: Mechanical seal chamber
Do: Select Features for a Lift Station
Avoid the copy/paste engineering mentality. Every lift station is its own unique system. A pump at a wastewater station has different needs than one at a grinder station at a cabin.
- Review the influent: Does this station handle high grit? High rags? Chemical runoff? Select the pump hydraulics (vortex vs. solids handling vs. chopper) based on the specific media, not a generic preference.
DO: Select Hardened Parts Only When Called For
Hardened materials are expensive.
- When to use them: If you are pumping sand, grit or slurry, high-chrome iron impellers and volutes are worth the investment to prevent abrasive wear.
- When to skip them: For standard sanitary sewer applications, standard cast iron or ductile iron is perfectly adequate. Don't pay for "rock crusher" specs on a station pumping wastewater.
DO: Match Mechanical Seals to the Application
The mechanical seal is the gatekeeper of your motor's safety.
- Standard service: Carbon/ceramic is often the default but can be weak; it is only recommended for the motor side.
- Wastewater standard: Silicon carbide vs. silicon carbide (SiC/SiC) is recommended for the lower seal. It resists abrasion and corrosion better than tungsten carbide.
- The recommendation: Always specify a double mechanical seal arrangement. If the primary fails, the secondary protects the motor while the moisture sensor alerts you.
Additional Recommendations: The Pro Tips
- Cable entry protection: The number one failure point for submersible pumps is water wicking down the cable. Specify pumps with a capillary barrier or a distinct terminal block that prevents cut-cable water intrusion from reaching the stator.
- Check the best efficiency point (BEP): Don't just look at the max flow. Select a pump where your operating point falls within the preferred operating region (POR) of the curve. Running too far left or right of the BEP causes cavitation and vibration, shortening the life of pump components. If you can't find a pump that is near best efficiency, it might be worth considering system design changes.
- Variable frequency drive (VFD) considerations: If using VFDs, make sure the pump is rated for VFDs and make sure your curve selection is steep and allows a versatile operating range of the pump and VFD.
Another scenario I commonly find myself in is reading a spec that calls for hardened impellers, specific control monitoring and VFDs built into the pump. Then I get phone calls from the engineer and end user asking if I am going to quote the project. My answer is “no,” because they didn’t create a pump spec; they created a manufacturer spec, and now only one company can quote the project.
Remember, the best pump is not the one with the most features; it is the one matched to its system. By focusing on system hydraulics first, adhering to safety standards and refusing to pay for unnecessary upgrades, you ensure an efficient system that keeps the maintenance crew happy.
Alex B. Hitsman is a sales engineer for Kerr Pump and Supply. His combined experience as an operator, maintenance man and salesman has given him a unique insight into mechanical equipment and troubleshooting. Hitsman has a degree from Delta College in chemical technologies. He may be reached at alex@kerrpump.com. For more information, visit kerrpump.com.
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