How to Read a NETZSCH NEMO Pump Curve: 7 Checks Before You Sign the PO

Reading a NETZSCH NEMO pump curve seems straightforward. That's the problem.

If you're ordering a NEMO progressing cavity pump and using the curve to justify your selection, this checklist is for you. I've been handling pump orders for 9 years, mostly for chemical dosing and polymer processing applications. I've personally made—and documented—6 significant mistakes, totaling roughly $24,000 in wasted budget. That doesn't count the delays and the awkward conversations with plant managers.

This is the checklist I now run before every pump purchase. It's 7 checks, and each one has caught at least one real problem in the past 3 years. If you're new to reading curves from the NETZSCH progressive cavity pump catalogue, this checklist will also walk you through the basics of what a curve does and doesn't tell you.

Check 1: Lock Down Your Fluid Data Before Opening the Curve

The curve is only valid if the starting conditions are right. The standard NETZSCH NEMO pump curve is based on water at 20°C. If you're pumping anything else—and you almost certainly are—you need these four numbers before you look at any graph:

• Viscosity at the operating temperature
• Specific gravity
• Solids content, including the maximum particle size
• Suction pressure, or whether the pump is flooded

In 2017, my first year on the job, I skipped this step. I ordered an NM045 for what the datasheet described as a "medium viscosity" fluid. It turned out to be 2,500 cSt at the actual line temperature. The pump delivered roughly one-third of the rated flow. We spent $6,800 on a pump that was wrong for the application, and the vendor's return policy didn't cover a custom elastomer construction.

Checkpoint: Fluid data sheet completed, verified, and attached to the requisition?

Check 2: Confirm the Curve Matches Your Exact Pump Version

Not all NEMO curves are the same. A single-stage pump has a different flow-to-pressure characteristic than a multi-stage version. The rotor diameter, stator pitch, and even the elastomer material all shift the curve.

This is where the NETZSCH progressive cavity pump catalogue earns its keep. The NM code tells you the pump model, and the suffix letters tell you the configuration. I've seen two "NM076" pumps that looked identical from the outside but had completely different stator geometries and performance characteristics.

Always match the curve header to the exact catalogue page and pump version you intend to specify. The curve you received via email might be for a different revision.

Checkpoint: Curve header information matches the catalogue page and the pump version in your inquiry?

Check 3: Read the Curve at Your Operating Pressure, Not the Maximum

This sounds obvious. It's amazing how often it gets overlooked.

A progressing cavity pump curve is a near-flat line with a slight negative slope—flow drops as differential pressure increases, mostly due to internal slip. But the line is only part of the picture. The curve also defines the operating window, and the flow at the maximum pressure point may be nowhere near what you need.

I almost lost a $12,000 order in 2023 because the spec sheet highlighted the max pressure, and nobody checked the flow at that point. It was 30% below what we needed. We caught it after I highlighted the pressure/flow intersection on the curve and sent it back to the sales engineer.

Checkpoint: Flow at your expected operating pressure meets the required flow plus a 10% margin?

Check 4: Apply the Viscosity Correction Before You Fall in Love with the Curve

Here's the thing about NEMO pumps and viscosity: higher viscosity actually improves volumetric efficiency because slip decreases. But it also changes the power requirement, and very high viscosities can increase the NPSH demand. We'll get to NPSH in a moment.

The curve you see in the catalogue is water-based. NETZSCH provides viscosity correction charts for their pumps, and they typically appear in the technical section of the catalogue. If you ignore them, your flow estimate might be wrong, and your motor sizing certainly will be.

This is the mistake I still kick myself for. In September 2022, I ordered a NEMO pump for a polymer dosing application. The fluid was listed as "heavy liquid" on the datasheet—hardly a specification. I skipped the correction factor because the standard curve looked fine. When the pump started up, the motor tripped on overload within 15 minutes. The stator was smoking. $5,100 of damage and a 3-week delay.

Checkpoint: Viscosity correction factor applied to the curve and to the drive sizing?

Check 5: Verify NPSH on the Suction Side

Honestly, I'm not sure why NPSH gets ignored so often. My best guess is that it looks like a technical footnote rather than the thing that determines whether your pump works at all.

The NEMO curve includes the required NPSH at various speeds. You need to compare that to the NPSH available in your system. A simplified version of the calculation looks like this: NPSH available = suction head + atmospheric pressure − vapor pressure − friction losses. If that number is below the curve's NPSH requirement, you're in trouble.

The classic mistake—which I made in year two—is placing the pump above the tank without accounting for static lift and vapor pressure. The pump cavitated constantly. We changed speed, swapped stators, even tried different suction piping. The real problem was the installation, not the pump. $3,200 in replacement parts and a month of headaches, and the actual fix was restructuring the suction line to flood the pump.

So glad I checked the NPSH calculation before the last polymer order. Almost approved a smaller model, which would have cavitated on startup.

Checkpoint: NPSH available ≥ NPSH required + 0.5 m at all operating conditions?

Check 6: Check the Power Curve Before You Approve the Motor

Most NETZSCH pump curves include an absorbed power line. Ignore it at your own risk.

The absorbed power depends on differential pressure, speed, fluid properties, and density. If you're working from a water-based curve, the power figure will be too low for a viscous fluid or a high-density slurry. Specific gravity multiplies everything, so a dense liquid like caustic soda or lime slurry can push the actual power far beyond the curve's line.

My rule of thumb: take the absorbed power from the curve at the worst-case operating point, then multiply by 1.25 for motor selection. The margin covers viscosity swings, density changes, and the extra torque needed during startup.

In 2021, I approved a motor that was sized exactly at the curve's power limit. "Budget optimization," we called it. The motor ran hot, tripped regularly, and we spent more on diagnostics than we saved on the motor. That $3,200 order became a 4-week headache over a $200 motor upgrade.

Checkpoint: Motor power ≥ absorbed power from the curve × 1.25 at all operating points?

Check 7: Respect the Speed Limits for the Stator Material

This is the check that most people miss entirely.

The speed lines on the curve tell you what the pump can do mechanically. They don't tell you what the stator elastomer can handle over time. Different stator materials have different maximum peripheral speeds, especially when abrasive media is involved. With abrasive fluids, you may need to run at half the maximum speed the curve implies, or you'll be replacing the stator every few months instead of every couple of years.

NETZSCH publishes recommended speed ranges for the different stator materials in the technical section of the catalogue. It's not front-and-center, but it's there. Look it up for the media you're pumping.

Checkpoint: Selected speed is within the stator material's recommended range for your media?

Final Notes: The One Thing I'd Tell My Younger Self

If I could redo those early orders, I'd invest in better specifications upfront. At the time, I didn't know enough about pump curves to ask the right questions. Given what I knew then, my choices were reasonable. But they weren't smart.

Keep a copy of the curve with the purchase order. Highlight your operating point, the correction factors, and the limits you verified. It sounds bureaucratic, but it saves you when the pump arrives and someone asks, "Wait, why did we order this version?"

We've caught 47 potential errors using this checklist in the past 18 months. Maybe 45, I'd have to check the log—but it's definitely over 40. At least, that's been my experience with NEMO pumps in chemical dosing applications. That said, every application is different, and if you've found additional curve-reading pitfalls, I'd genuinely like to hear about them.

I'd rather spend 10 minutes explaining a pump curve than deal with mismatched expectations after installation. An informed customer asks better questions and makes faster decisions. That's good for you, and honestly, it's good for us too.

If you take nothing else from this checklist: the pump curve is a promise under ideal conditions. Your job is to check it against real conditions—viscosity, NPSH, speed limits—before you sign.