Grundfos CRN 1-3 Head: Check It at Your Flow Before You Order a Replacement

If a Grundfos CRN 1-3 fails at your plant and you need a replacement fast, here’s the part that sounds wrong: don’t ask for quotes yet. The model number is not your specification, and the lowest price is not your lowest cost. Before anything else, find two numbers: the flow your process needs, and the head it needs at that flow. A Grundfos CRN 1-3 doesn’t have “a head.” It has a head curve, and the curve falls as flow rises.

I’ve spent nine years at a regional pump distributor that handles Grundfos, doing the job nobody envies: taking the call when a pump dies and there’s no spare. I’ve processed more than 200 rush orders in that time, including same-day turnarounds for plants where every downtime hour cost more than the replacement pump. I’ve also made expensive mistakes of my own. After all of it, what I’m surest about is this: sizing a Grundfos replacement starts at the duty point — never at the model number on the old pump, and never at the price list.

“Grundfos CRN 1-3 head” is not a single number

Search for the Grundfos CRN 1-3 head online and you’ll find a range of figures. Most websites quoting them aren’t lying. They’re quoting different points on the same curve. At zero flow the pump reaches shut-off head — the highest pressure the hydraulics can produce. It looks good on paper and tells you almost nothing about your application. At the flow your process actually needs, head will be lower, sometimes much lower. So when a supplier answers “what head does a CRN 1-3 give?” without asking what flow you need, treat that answer with suspicion.

What the model number actually tells you

CRN 1-3 breaks down like this:

• CRN — Grundfos’s vertical multistage pump range. The N designates acid-resistant stainless steel wetted parts, common in food, beverage, and water-treatment duty.
• 1 — the pump size, roughly the flow in m³/h at the efficient operating area.
• 3 — the number of stages. Stages add head: more stages, more pressure, about the same flow.

Those last two digits are the ones that matter when someone quotes you a “bargain.” If the duty needs more head, you should be looking at more stages, not a different price. If it needs more flow, more stages won’t help — the pump size has to go up. And any quotation that lists only “CRN 1-3, $X,XXX” without a duty point is missing the single most important line on the page.

The night a “same pump” wasn’t the same pump

In March 2024, a food-processing plant called me at 4:15 p.m. on a Thursday. Their washdown pump — a CRN 1-3 running through a variable-speed drive — had tripped and wouldn’t restart. The motor was gone, and it had taken the drive’s output module with it. Cleanup ran the next morning; no spare pump existed.

The maintenance manager asked three suppliers for a replacement CRN 1-3 plus a drive. Our quote included both. A competitor quoted “the same pump” for $230 less — pump only. Under pressure to get the line running, the manager bought the cheaper option and wired the pump directly to the mains. Same pump model. Wrong system. Without speed control, the pump made more pressure than the washdown piping was rated for. The relief valve cycled, the pipework hammered, and the plant spent roughly $1,150 on two emergency service calls and repairs over the next nine months. Then it paid for the drive retrofit anyway.

I’m not telling you this to make us look smart. A few months earlier, my own team had shipped a rush order based on a model number alone, with no duty check, because the customer was shouting at us. We got lucky — the mistake was caught at startup. That’s when we made it policy: no rush quote leaves our desk without a duty point written on it. Pumps follow physics, not invoices.

The German engineering term for the whole process is Pumpenauslegung — pump sizing. When you see “Grundfos Pumpenauslegung” in technical documentation or sizing tools, that’s what it means: start from flow and head, compare with the curve, then pick the pump that lands on your operating point. It works the same in every language.

A faster way to size a CRN 1-3 replacement

If the pump is already dead, do this while your supplier is preparing the quote:

1. Get the full model code from the nameplate. Not just “CRN 1-3” — motor power, voltage, shaft seal, elastomer and material variants. Take a photo and send it. The nameplate is a map, not the destination.
2. Fix your flow. Use a flowmeter if one exists. If not, use tank fill timing or the original process specification.
3. Fix your head. If a discharge pressure gauge is installed, read it while the system is running. Remember that 1 bar equals roughly 10.2 metres of head, and account for suction pressure if it isn’t open to atmosphere.
4. Compare that point against the official curve. Ask the supplier directly: “At my flow, what head does a CRN 1-3 produce, and does it cover my required head with margin?” Use current data from the Grundfos Product Center rather than an old PDF from a third-party site. As of January 2025, the official curve data is still available free through Grundfos.
5. List what else was part of the old system. A variable-speed drive, pressure transmitter, or control panel is part of the specification, not an optional extra. So are seal and material choices. If a quote ignores them, you haven’t actually compared prices yet.

A competent distributor should return a quote with the duty point on it. If you only get a model number and a price, ask why. And if the answer is “it’s what you asked for,” find another distributor. That’s not rudeness. It’s the thing that prevents the kind of failure that dairy plant learned about the hard way.

When you should ignore this advice

This shortcut assumes you’re replacing an existing system whose duty hasn’t changed. It does not apply when you’re designing a brand-new system from scratch, when water chemistry demands special materials, or when there’s no operating history to copy. Those jobs need the full calculation: static lift, pipe friction, fittings, valve losses, NPSH, and a margin for future changes.

And a note of honesty: I deliberately didn’t give you one flat “CRN 1-3 head” figure to order from, because the right figure depends on your flow and on the exact variant. Anyone who gives you a single number with no flow attached is oversimplifying. My rule after 200+ emergency replacements is simple: trust the curve, verify the duty point, and let the price fight for second place.

A great price on the wrong pump is not a deal. It’s an expensive reminder that pumps don’t care how much you paid for them.