Two Output Fittings on new Dynamo Pump... What is the 2nd?

kristof

Active member
Jun 8, 2009
37
Pittsburgh, PA
My new Pentair Dynamo arrived yesterday. According to the drawing below from Pentair's website the output should be a 1.5" female NPT. There are female NPT threads on the output port but there are male threads around the outside of the port as well. There's no indication of them on the mechanical drawing. Are these mystery threads 2" male NPT?

EDIT: I've established that it's not 2 inch NPT by comparison with a known 2 inch male NPT fitting. My current thinking is that it's a thread for one of these "1/2 union" things. I don't quite know what they are though!

I was also surprised to find that the motor came with a (low-off-high) switch backplate. Like the mystery port, there was no indication of this in any of the Pentair literature I've seen. It was a pleasant surprise since I'm already wired for a plug-in pump and I was expecting to have to direct wire and do my own speed switch.

 

kristof

Active member
Jun 8, 2009
37
Pittsburgh, PA
I used digital calipers to measure the mystery port. The diameter measured around the outside threads is about 2.443 inches at the threads' peak. The threads themselves are 0.126 inches from peak to peak.

I forgot to mention that there was no documentation of any kind accompanying the pump. Unbelievable! No manual, not even a single sheet of 8.5x11 with basic information.
 

kristof

Active member
Jun 8, 2009
37
Pittsburgh, PA
Rangeball said:
I believe your assumption is correct.
I was wrong. It's not a 2 inch male NPT port. I had forgotten that I have a 2 inch male NPT fitting left over from the old pump hookup. The two are completely different. The 2 inch NPT fitting has a slightly small diameter. The threads on the NPT fitting are symmetric whereas the threads on the pump are a ramp shape. The NPT threads on the fitting are also much finer. They're closer together and not nearly as high as those on the pump port.

What in the world is this thing?
 

kristof

Active member
Jun 8, 2009
37
Pittsburgh, PA
Ok, my current thinking is that it's for a "1/2 union." Are "1/2 unions" standard (can I buy at Home Depot?) or do I need to get a special Pentair branded one?
 

kristof

Active member
Jun 8, 2009
37
Pittsburgh, PA
Rangeball said:
Sorry, I have no idea, but pentair has always been very responsive and helpful when I call. You might give that a shot.

Here's the owners manual from their site. It shows the threaded collar you are talking about.

http://www.pentairpool.com/pdfs/DynamoOM.pdf
I never thought of calling them! :-D I guess it's no matter. I've called every pool store in the area and no one has the right fitting. It would be a special order. I've decided to go with the 1.5 inch NPT since I want to get things up and running ASAP. I can get standard NPT stuff off the shelf from Lowes.

Thanks for your help Rangeball.
 

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