AC raw water pump?

Skybolt

Skybolt

Well-Known Member
Nov 11, 2014
6,425
Kent Narrows, MD
Boat Info
Reel Nauti
460 EC
Engines
Detroit 6v92TA
(Low profile's)
Alison Gears
Westerbeke
12.5kw Genset
I currently have a March MD5LC 870GPH ( https://www.defender.com/product.js...870-gph&path=-1|51|2234226|2234240&id=2205849 ) It usually does ok but I need to barnacle bust twice a season, other's on my dock don't do that ever and only clean the strainer. MY water flow compared to there's is about half.

I have two AC units which are 5/8 inlet/outlet the standard size. The boat came with the March pump and is 3/4 inlet and 1/2" outlet. I have it plumbed with 1" inlet and 3/4 outlet hose but that drops to 5/8 and feeds both AC units with 5/8 lines. I have put in 5/8 brass Y where they split. I want to change to 3/4 line but can't get through the firewall/floor area and is quite the project to do so. I am thinking for now to upgrade the pump to a lager flow rate such as the one ( https://www.defender.com/product.js...536-gph&path=-1|51|2234226|2234240&id=2552150 ) which is 1536GPH.

Just checking what the guys in the hot climates are using? Two pumps individually plumbed I am guessing?
 
My 16k btu requires 500 g/h and the front 8k takes 250ish, so pump should do the job. I have similar setup, seems to do fine, except all lines are 5/8”.

May a bad/worn impeller? On some march pumps, the impeller/head is replaceable separate from the motor.
 
Remove the head end, should be maybe 4-screws. The impeller is a small round fluted disc that rides on a small ceramic shaft. Clean the shaft with a very fine piece of emory cloth maybe 4-500 grit and clean the impeller good. Make sure it spins very freely as in you can blow on it and it will spin. Put back together and see if it is any better. Takes 10 min max….I had one where the impeller was too tight to the shaft for some reason and cleaning the ceramic shaft fixed it. Maybe nothing, but worth a try.

Bennett
 
Have you checked the through hull fitting intake for growth? A single small oyster can severely cut down your flow.

BTW, if that Y fitting you are using is really brass and not bronze, you are asking for trouble in salt water.
 
My units are 16 and 12 and my original Taylor made pump is just shy of 1000gph.
950 I think.
 
985
56F07266-9509-4FE5-BBAE-EDABC276AFC3.jpeg
 
Orlando - this is the pump that I have for the three units in the cabin. Two 18K BTU and one 27K BTU.
It's a very good pump that would probably solve your flow issue and provide enough pressure/flow to keep sediment from settling in the system.
https://citimarinestore.com/en/ober...dorfer-centrifugal-pump-104m-06-10f36bj.html#
Regarding the Y fitting - rather install a 1/2" NPT X 3/4" NPT bushing on the pump discharge then thread a 3/4" NPT tee onto that adapter. Then install 3/4" NPT X 5/8" Hose adapters in the tee and connect the AC supply hoses to those. You will net much better flow.
Tom
 
@my3sons Yeah, that's what mine are as well, 16 and 12. But I am guessing another 80GPH isn't going to change the flow that much. Probably need to BB again and see where that goes.

@dtfeld Yep mine are the same 5/8 line then 5/8 Y to units. The output of the pump is 1/2" Seems small to me.

The AC gets cold and seems ok, but struggles on the 90+ days (like today), but then who's doesn't. Does keep it at 68 though so I guess I shouldn't complain.
 
ttmott said:
Orlando - this is the pump that I have for the three units in the cabin. Two 18K BTU and one 27K BTU.
It's a very good pump that would probably solve your flow issue and provide enough pressure/flow to keep sediment from settling in the system.
https://citimarinestore.com/en/ober...dorfer-centrifugal-pump-104m-06-10f36bj.html#
Regarding the Y fitting - rather install a 1/2" NPT X 3/4" NPT bushing on the pump discharge then thread a 3/4" NPT tee onto that adapter. Then install 3/4" NPT X 5/8" Hose adapters in the tee and connect the AC supply hoses to those. You will net much better flow.
Tom
Click to expand...

Thats what I have on the pump head 1/2 x 3/4 barb then is reduced to 5/8 because I couldn't get the line into the cabin through the firewall/floor. I guess I need to try harder on that one. But your saying run the 3/4 line to the Y adapter? That was my intention, I even have the 3/4 braided hose but ran into issues getting the line through the fire wall/floor.
 
SKybolt said:
Thats what I have on the pump head 1/2 x 3/4 barb then is reduced to 5/8 because I couldn't get the line into the cabin through the firewall/floor. I guess I need o try harder on that one. But your saying run the 3/4 line to the Y adapter? That was my intention, I even have the 3/4 braided hose but ran into issues getting the line through the fire wall/floor.
Click to expand...
1/2" NPT is larger that 5/8" ID hose. You don't want the fittings to adapt to the 5/8" hoses to be the restriction like the Y fitting is.
Here is the Oberdorfer installation on my boat - The hose arrangement is the old configuration that I have changed but it gives you an idea what I'm trying to describe.
IMG_5478.jpg
IMG_2706.JPG
 
Last edited:
Here is the current arrangement; I found a pic.
Note that I have added garden hose couplers for easy BB/flushing disconnect. You can see that I have a cap on one of the discharges - Flushing one of the units and still operating all of the others. offsetting the FL heat...
IMG_4943.jpg
 
ttmott said:
Orlando - this is the pump that I have for the three units in the cabin. Two 18K BTU and one 27K BTU.
It's a very good pump that would probably solve your flow issue and provide enough pressure/flow to keep sediment from settling in the system.
https://citimarinestore.com/en/ober...dorfer-centrifugal-pump-104m-06-10f36bj.html#
Regarding the Y fitting - rather install a 1/2" NPT X 3/4" NPT bushing on the pump discharge then thread a 3/4" NPT tee onto that adapter. Then install 3/4" NPT X 5/8" Hose adapters in the tee and connect the AC supply hoses to those. You will net much better flow.
Tom
Click to expand...

+1 with Tom, that is the same set up I went with and it works awesome....

upload_2022-6-13_21-18-9.png
 
@ttmott and @ocgrant - you guys sold me. I have a similar setup except the feed to the manifold (What I call the Y). My manifold is in the floor of the salon, so I have a 20' run to the manifold that I need to change over to 3/4 instead on the 5/8 there now. But I see what you are talking about. Great setup for sure.
 
Personally we fought an Oberdorfer for years on our boat. Would always develop pinholes in the face plate. We switched to a March pump, 2000 gph and have not had an issue other than cleaning the magnetic impeller. 6 plus years.
 
bahamabreisus said:
Personally we fought an Oberdorfer for years on our boat. Would always develop pinholes in the face plate. We switched to a March pump, 2000 gph and have not had an issue other than cleaning the magnetic impeller. 6 plus years.
Click to expand...
Didn't we discuss that previously? Bonding vs AC grounding and galvanic corrosion? It wasn't a problem with the pump. Or was that someone else....
 
That’s a lot of pump. Those guys are running more and much larger units, so it might be overkill for your application. I haven’t looked, but might require some AC electrical upgrades as well maybe something like a new breaker, but potentially all new AC wiring. One minor downside is the mechanical shaft seal…it will eventually need service.

One way to increase your flow from the existing pump is to reduce the “head”. Every fitting , change in hose diameter etc increases the head, and reduces flow. 90* elbows are the worst, but transitioning back/forth to different diameters will also degrade flow rates. Sounds like you have a lot going on. Mines not much better, but cleaning up your plumbing might get you what you need.
 
dtfeld said:
That’s a lot of pump. Those guys are running more and much larger units, so it might be overkill for your application. I haven’t looked, but might require some AC electrical upgrades as well maybe something like a new breaker, but potentially all new AC wiring. One minor downside is the mechanical shaft seal…it will eventually need service.

One way to increase your flow from the existing pump is to reduce the “head”. Every fitting , change in hose diameter etc increases the head, and reduces flow. 90* elbows are the worst, but transitioning back/forth to different diameters will also degrade flow rates. Sounds like you have a lot going on. Mines not much better, but cleaning up your plumbing might get you what you need.
Click to expand...

Yeah, my issue is the boat only has one 5/8 line going into the cabin under the floor then splits into two for each AC unit. I was trying to upgrade that line to 3/4 this past winter but could not get the existing line out from where it was and did not want to "Rip" it out in fear of wiring being tied to that line. So my other though was just run a second line and make a manifold such as Tom and Grant did. But in trying to get fish tape through and under my floor was next to impossible and it only has to go four feet. I think I need to just BB the lines and deal with it this year, but run a second new lines in the fall and see how that does. The pump will be the last thing that gets replaced.
 
ttmott said:
Didn't we discuss that previously? Bonding vs AC grounding and galvanic corrosion? It wasn't a problem with the pump. Or was that someone else....
Click to expand...
Had the discussion with someone. Got different advice from local AC guy and from Sea Ray. Neither seemed to make a difference. Went with March, no issues since. Another dock mate had same issues with Oberdorfer and just switched to March also.
 
dtfeld said:
That’s a lot of pump. Those guys are running more and much larger units, so it might be overkill for your application. I haven’t looked, but might require some AC electrical upgrades as well maybe something like a new breaker, but potentially all new AC wiring. One minor downside is the mechanical shaft seal…it will eventually need service.

One way to increase your flow from the existing pump is to reduce the “head”. Every fitting , change in hose diameter etc increases the head, and reduces flow. 90* elbows are the worst, but transitioning back/forth to different diameters will also degrade flow rates. Sounds like you have a lot going on. Mines not much better, but cleaning up your plumbing might get you what you need.
Click to expand...
We run 3 units, 1-16K, 2-12K longest run is almost 50ft. We have replaced hose with 5/8 on the longest run. Another reason for big pump is a bunch of growth in the lines, the faster we can move the water the slower the growth inside the hoses.
 
My .02, a PVC manifold connected directly to the pump will snap off eventually and a boat could sink, even if the pump is not running. These impellers will not stop water flow like a seawater pump impeller. I believe this is also an ABYC directive.
 
LMBoat said:
My .02, a PVC manifold connected directly to the pump will snap off eventually and a boat could sink, even if the pump is not running. These impellers will not stop water flow like a seawater pump impeller. I believe this is also an ABYC directive.
Click to expand...
You are correct if below the waterline. On my 500DB where the pump is mounted it is just barely above the waterline. It's a curse and blessing as the pumps are not self priming and end up being a PITA getting to operate after cleaning if above the water line. However, in my case, I wanted to take no chances and that is why I moved the manifold off the pump and above.
If on the other hand that manifold did break off the AC units would go HI-PS and shut down the pump.
 
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