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Grundfos Pump Orientation


Jim Katen
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Originally posted by Jim Katen

Can anyone tell me why it's important to have a Grundfos circulating pump oriented so that its motor shaft is horizontal?

What bad thing happens if the shaft is vertical?

- Jim Katen, Oregon

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Interesting question. May have to do with loads as they consider it a continuous duty motor. May also have something to do with forces of water flow. Let us know if you find the answer.

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There may be no thrust wear surfaces. (thrust bearing)

Also, the seals are flat surface seals, that is they don't seal around the shaft, but rather against a flat on the housing with a mild spring load. The installed height of the seal is critical because that's what determines the spring load; too short an installed height equals a high spring load and premature wear. Too tall an installed height equals too light a spring load and possible leaks.

If the armature is hanging from the spring load on the seal it could create premature wear.

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When I had my house built I had a dedicated hot water loop installed and the plumber installed the circulation pump with the shaft vertical. After some discussion and them reaching the conclusion that it didn't matter I gave them the installation instructions and they were happy to comply.

I don't know why the shaft orientation makes a difference because they will work correctly vertical.

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Originally posted by Chad Fabry

There may be no thrust wear surfaces. (thrust bearing)

Also, the seals are flat surface seals, that is they don't seal around the shaft, but rather against a flat on the housing with a mild spring load. The installed height of the seal is critical because that's what determines the spring load; too short an installed height equals a high spring load and premature wear. Too tall an installed height equals too light a spring load and possible leaks.

If the armature is hanging from the spring load on the seal it could create premature wear.

Yes, it's got to be something along those lines. But in each of those cases I'd imagine that the normal action of the pump -- regardless of its physical orientation -- would exert forces on the bearings or the seals that are comparable to those exerted by gravity.

That is, even if it were installed in the horizontal position, I'd imagine that the action of the pump would exert some thrust on the shaft that might be equal to the thrust that gravity would exert on such a light part.

Or am I full of beans?

- Jim Katen, Oregon

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Originally posted by Jim Katen

Originally posted by Chad Fabry

There may be no thrust wear surfaces. (thrust bearing)

That is, even if it were installed in the horizontal position, I'd imagine that the action of the pump would exert some thrust on the shaft that might be equal to the thrust that gravity would exert on such a light part.

Or am I full of beans?

- Jim Katen, Oregon

Try this: I am not sure a "circulator" has sufficient power to "pump". It helps move water that is heated from the boiler which is already causing movement in the pipes because the water is expanding on the outlet side. The motor may only have adequate power to assist that movement without putting excess load on the seals.

I have a taco circulator stored somewhere in my basement and will dig it out to see if there is a better explanation.

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I dug out the taco. It states that the motor must be horizontal, except that if you want to install it vertical you must run the system pressure at a minimum of 20 lbs. There is no other explanation so unless someone has access to an engineer at one of the circulator companies we can only guess it to be a load thing. It further states that the "bearings" are lubricated by water so the vertical installation may need the pressure to keep the bearings lubricated. Sounds good to me anyway.

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Hi Jim,

I suggest calling Grundfos and asking one of their tech reps. You could also call Kolyn Marshall at Watts Radiant at 417-447-8031, tell him the guys at TIJ told you to give him a call, and ask him if he can explain it to you; he's an engineer and Watts Radiant's National Training Director.

ONE TEAM - ONE FIGHT!!!

Mike

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Originally posted by hausdok

Hi Jim,

I suggest calling Grundfos and asking one of their tech reps. You could also call Kolyn Marshall at Watts Radiant at 417-447-8031, tell him the guys at TIJ told you to give him a call, and ask him if he can explain it to you; he's an engineer and Watts Radiant's National Training Director.

I may do that on Monday. In the meantime, I found this on the web:

It is preferable to install Grundfos circulators in a vertical pipe

pumping upwards. This position ensures that the pump shaft

is horizontal, which reduces the thrust bearing load and ensures

positive air purging from both the rotor chamber and impeller

housing.

Pumping downwards in a vertical pipe is not recommended as

this may lead to air locking of the pump, with resultant loss of

performance. However, pumping downwards is acceptable

provided an effective air vent is incorporated in the system,

before the pump.

Where pumps can only be installed in horizontal pipework, it is

imperative that the pump shaft is horizontal, or slightly higher

at the vent plug end.

The shaft must not fall below the horizontal plane, even by a

few degrees, as this causes premature wear of the top bearing

and shaft.

Pumps should not be installed with the shaft in a vertical plane,

as this may lead to dry running of the top bearing, noise and

possible pump failure.

To avoid cavitation noise and risk of damage to the bearings the

minimum pump inlet pressure should be 1.4m at 82°C (water

temperature).

So, in addition to the bearing issues that Chad & Scott brought up, it seems that Grundfos is concerned with air becoming trapped in there. I had never considered that.

- Jim Katen, Oregon

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I walked into a house about a year ago, and the woman who owned it explained that the hot-water circulating pump wasn't working, but that a plumber was scheduled to come repair the thing several days later.

Just to be polite, really, I asked if the plumber had any idea about what had happened to the pump. She said the guy apparently thought it was mismanufactured at the factory.

So a couple of hours later, I'm down in the basement, stairing at the pump, and realizing the only way I'd have known it was faulty--without really cold water issuing from the faucets for a long time when I checked the plumbing fixtures--was the lack of whirring the pumps make.

Anyhow, the installation instructions were sitting on top of the water heater, so I took a look to see if I could learn something. Honest to God, the pump was installed wrong, just like the first diagram in Jim's photo of the instructions.

My nature being what it is, I circled the photo with the big X on it and slid it, along with one of my business cards, into the pipes so the plumber couldn't miss it. Unsurprisingly, I never heard from the guy.

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  • 2 years later...

In hot tub applications, if the Grundfos pump is installed vertically, water WILL enter where its not supposed to. I speak from experience. They unlike their competition "Laing" HAVE to be horizontal. Experiment with it, install it vertically and its guaranteed to fail within 72 hours. When it fails, remove the wiring cover, then the capacitor retaining clip, and unplug the wiring harness, water will run out of the winding compartment. The pump, once failed, is trash.

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