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Old 02-08-2020, 18:52   #1
er9
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raw water pump uses different elbows intentional?

trying to find replacement elbows for my Oberdorfer water pump">raw water pump. the input side is 5/8 hose barb to 5/8 male NPT. on the output side its 5/8 male NPT to 1/2" hose barb.

do they reduce the flow on the output side for a specific reason? seems like the more flow the better but for the life of me there is no such thing on the internet as a 5/8 male NPT to 5/8 hose barb bronze elbow.
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Old 02-08-2020, 19:17   #2
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Re: raw water pump uses different elbows intentional?

5/8 npt in general would be a rare bird - you sure its not 1/2 npt, which measures a bit over 3/4 at the threads.....

Matt
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Old 02-08-2020, 19:24   #3
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Re: raw water pump uses different elbows intentional?

Quote:
Originally Posted by mlydon View Post
5/8 npt in general would be a rare bird - you sure it’s not 1/2” npt, which measures a bit over 3/4” at the threads.....

Matt
I'm not sure. the more i research it the more confused im getting.

this is the inflow elbow.
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Old 02-08-2020, 19:29   #4
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Re: raw water pump uses different elbows intentional?

Quote:
Originally Posted by mlydon View Post
5/8 npt in general would be a rare bird - you sure its not 1/2 npt, which measures a bit over 3/4 at the threads.....

Matt
outflow side...
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Old 03-08-2020, 10:03   #5
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Re: raw water pump uses different elbows intentional?

A local local plumbing supply company sorted out my similar confusion in just a couple of minutes -- and at no charge!
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Old 03-08-2020, 10:12   #6
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Re: raw water pump uses different elbows intentional?

Never heard of 5/8 pipe thread.
Also, is there a taper to those threads? They almost look like straight threads... on your first pics? I guess they must be tapered..
Probably 1/2" NPT. Maybe just buy one 1/2 NPT of any shape and see how it fits. A couple bucks to try.
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Old 03-08-2020, 10:23   #7
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Re: raw water pump uses different elbows intentional?

Quote:
Originally Posted by Cheechako View Post
Never heard of 5/8 pipe thread.
Also, is there a taper to those threads? They almost look like straight threads... on your first pics? I guess they must be tapered..
Probably 1/2" NPT. Maybe just buy one 1/2 NPT of any shape and see how it fits. A couple bucks to try.

thanks. its hard to see but they are tapered. they measure about .02ish larger dia at the other end of the thread.



its looking like thats waht im going to have to do.



still curious though why they reduce the flow on the output. they did the same thing on my Groco sea strainer.
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Old 03-08-2020, 10:27   #8
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Re: raw water pump uses different elbows intentional?

Quote:
Originally Posted by er9 View Post
thanks. its hard to see but they are tapered. they measure about .02ish larger dia at the other end of the thread.



its looking like thats waht im going to have to do.



still curious though why they reduce the flow on the output. they did the same thing on my Groco sea strainer.
Is "they" the previous owner? If so they likely used what they could find. There is nothing gained by using 1/2" hose instead of 5/8" hose. Then again if all they could find at the time was 1/2" and the pump can deliver the required flow rate (at the increased head caused by smaller tube) then nothing was lost by going with 1/2 over 5/8.
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Old 03-08-2020, 10:40   #9
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Re: raw water pump uses different elbows intentional?

Quote:
Originally Posted by Statistical View Post
Is "they" the previous owner? If so they likely used what they could find. There is nothing gained by using 1/2" hose instead of 5/8" hose. Then again if all they could find at the time was 1/2" and the pump can deliver the required flow rate (at the increased head caused by smaller tube) then nothing was lost by going with 1/2 over 5/8.

good question. looks original. yeah i suppose thats a possibility. i guess it doesnt matter so long as i get the flow rate the pumps spec'd to deliver. need to try and figure out what that number is.
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Old 03-08-2020, 12:00   #10
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Re: raw water pump uses different elbows intentional?

The pipe threads are 3/8" NPT, for both suction and discharge. The hose barbs are for 5/8" and 1/2" ID hose.

I have what is probably the same pump series on my A4.

It is VERY common for a pump to have a smaller discharge line than the suction side. Increases pressure/velocity, aids in priming as well.
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Old 03-08-2020, 12:05   #11
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Re: raw water pump uses different elbows intentional?

Forgot to add, it's more than likely that the pump, fittings and hose sizes are all original. Check the manual for your engine.
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Old 03-08-2020, 13:07   #12
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Re: raw water pump uses different elbows intentional?

Quote:
Originally Posted by Brewgyver View Post
The pipe threads are 3/8" NPT, for both suction and discharge. The hose barbs are for 5/8" and 1/2" ID hose.

I have what is probably the same pump series on my A4.

It is VERY common for a pump to have a smaller discharge line than the suction side. Increases pressure/velocity, aids in priming as well.
interesting. yeah i figured if there was a reason it was either to increase pressure or to match the fitting on the heat exchanger. im going to try and clean up the fittings i have although the smaller one has a fair bit of buidup inside it.

i wonder if the smaller fitting exiting the sea strainer is used to build pressure and help with lifting the water up to the pump? its definately a Groco fitting so im guessing original as well.
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Old 03-08-2020, 16:06   #13
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Re: raw water pump uses different elbows intentional?

What is wrong with them, why do you think they need replacing?

You said a local plumbing shop squared you away, Very unlikely their parts are bronze parts and you do NOT want brass, you need bronze.

Lastly it’s very common and a good idea for the intake to be larger then the exit, that’s to ensure that the pump never has to pull much vacuum, if it does then it can cavitate and it will look like you have air in the output line.
That’s also why it’s the same way on the strainer.
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Old 03-08-2020, 17:24   #14
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Re: raw water pump uses different elbows intentional?

If you cant figure this out then take the fitting to a marine hardware store and see exactly what you have.
I work with many different raw water pumps, and most of them below 2hp have larger inlets than outlets.
1.25 x 1 .....1.50 x 1.25...1.00 x .75 all are very common.
I use FF silicone bronze fittings to upsize it all...keeps things flowing smooth.
White brass is dangerous.
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Old 03-08-2020, 18:14   #15
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Re: raw water pump uses different elbows intentional?

Yes, indeed, use silicone bronze ONLY. Quite a few boats have sunk, or tried to, due to exactly that: using brass hose barbs.
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