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Old 11-12-2015, 19:34   #1
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Raw Water Pump - only 3/8 npt?

I'm having trouble figuring something out.

How do I get from 3/4 npt on the raw water intake to 3/8" npt-female on the oberdorfer water pump">raw water pump, then from 3/8" npt female out of the raw water pump to 5/8" barb on the heat exchanger without using brass reducers or nipples (i.e. bronze only)? Currently, whole setup is pieced together using bronze and brass nipples and reducers plus a few brass 90 degree elbows.

Both Moyer Marine's oberdorfer replacement pump (MMI 502 flange pump ) and an oberdorfer N202M-7 only have 3/8" npt female input/output

Here's the problem.

Raw water intake is 3/4", goes from thru hull 3/4" barb off the thru hull to perko bronze strainer (3/4" input and output), to the V-drive (in 3/4" pipe thread and out 3/4" pipe tread). From V drive with 3/4" hose for 10' to the raw water pump, were the input port is only 3/8" npt female. Then out from the raw water pump's 3/8" npt female to 5/8 barb on the heat exchanger. I'm having a hell of a time finding the necessary parts in bronze. to make all these connections with a 3/4" hose to the raw water pump, then 5/8"hose from pump to Hx.

I'm trying to redo the PO's work and get rid of the brass fittings and minimize the number of connections/fittings.

Engine is Universal M-50/5444 (that's the 4 cyl, V1902 Kubota block) with a Walter RV26 v drive. Engine freshwater cooled, v drive raw water cooled.

If the raw water pump is only 3/8" npt, do I really need the 3/4" hose from v drive to the input of raw water pump? If not, I can bush the output of the walter V drive from 3/4 npt female to 3/8" barb and run 3/8 ID hose to the raw water pump. I haven't figured out how to deal with the 3/8 output form the pump to the 5/8" barb on the Hx. PO used brass reducer.

If the pump ports were 1/2", problem would be solved. I just don't understand why 3/8" npt is used; there are no fittings for that size in bronze. Well, ther are fittings, but not the ones I need go step up to 3/4 and 5/8" hose.

I redrilled and tapped 1/2" npt on an old spare oberdorfer and it worked, but the I realized that every replacement pump will have to be drilled and tapped for 1/2".

There is probably a simple solution that I just can't see right now.

If anyone can help me figure this one out, let me know.

scherzoja is offline   Reply With Quote
Old 12-12-2015, 03:14   #2
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Join Date: Nov 2010
Location: UK, Croatia
Boat: Fountaine Pajot Athena 11.6m Rapa Nui II
Posts: 426
Re: Raw Water Pump - only 3/8 npt?

Use plastic reducers in-line in the hose. I.e. 3/4 hose, reducer 3/8 hose or whatever. Double clip each hose connection.
Rapanui is offline   Reply With Quote

raw water, raw water pump, water

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