Raw water pump for cruisair reverse-cycle system

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jbrem003
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Raw water pump for cruisair reverse-cycle system

Post by jbrem003 »

So the summer marina i'm in advertised dredged slips, but apparently their definition of "dredged" is vastly different from mine.

Needless to say, my raw water pump for the intake on my Cruisair AC system has now overheated and seized. Now, being a former marine electrician, I was of the opinion that I had this one in the bag. After all - I actually have a medal for fixing raw water pumps when I was in the Navy.

Only problem is, since it's a small March submersible pump, the entire casing for the part that overheated is fully encased in a metal enclosure.

No I could send it off to get it fixed from March directly, but i'm wondering; has anyone heard of a raw water pump that isn't raw water cooled and won't burn up when it isn't able to suck up water from the mud I occasionally find myself in? It doesn't need to be self priming, but I sure would enjoy not having to replace this expensive pump every time the moon decides to take the hudson river estuary out to sea.

I know it's not ideal, but I can't exactly start telling marina's how to run their operations, and this is the second marina i've been in that doesn't dredge properly.

Thanks!
-JB
jbrem003
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Re: Raw water pump for cruisair reverse-cycle system

Post by jbrem003 »

On first digging through, I found this guy from the same company. The water flow and HP is a little higher than the old pump (10 Gpm @ 1/15 HP vs 8.5 Gpm @ 1/20 HP) so an inline variable restrictor probably wouldn't be untoward.

http://www.usplastic.com/catalog/item.a ... oCobPw_wcB

It's air cooled so in theory, it wouldn't burn out from sucking air rather than water, but it's also not self priming. If it's not a submersible pump then I want it to self-prime so I can mount it higher in the engine compartment.

The digging continues...
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prowlersfish
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Re: Raw water pump for cruisair reverse-cycle system

Post by prowlersfish »

I have seen the march Pumps run dry with out issue . I believe they have thermal protection . I would stay with then water cooled pump as I have found them very reliable and very long lasting ( more so then air cooled )

If you feel a air cooled one would serve you better go for it. ( make sure its ignition protected )

Most AC pumps are not self priming do to design . If you find one , you will find you can not run it dry .
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Big D
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Re: Raw water pump for cruisair reverse-cycle system

Post by Big D »

I suspect more that it was simply the pump's time. The pumps are overload protected so I think it just reached its end of life, or you blew the bracket o-ring, or the bracket wasn't fully secured and water got in. I suspect you'd have to be sitting in the mud to ingest enough of it to cause a cooling problem though.

The impellers on these continuous duty pumps are magnetically driven, and because of that, these are not self priming pumps as it's not a tight fit between the impeller and housing like that of an engine’s raw water pump. They are simply designed to move water and must be mounted below the water line as a result. The design allows for no shaft seals to worry about which is the most common failure in water pump housings.

The water cooled units cannot be allowed to run dry. When I say that, I mean they are not in water. Running dry and not pumping are two different things. If they are run out of the water or there’s an impeller failure, the motor will eventually overheat and trip its overload protection. This happens because the impeller needs to push water through the cooling system. The impeller might be pumping water through the cooling side but not necessarily through the output/AC system as sometimes the pump's output needs to be primed. The draw back to these is that you must ensure they are winterized properly or else, but they do usually incorporate frost plugs. On the plus side, they are sealed, so you don't have to worry about them getting wet, and they can be run in a gasoline engine compartment.

The air cooled units of course are not sealed so are susceptible to the elements in an engine compartment and getting wet which will shorten their life drastically. They are typically not ignition protected so shouldn’t be installed in a gasoline engine bay.
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jbrem003
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Re: Raw water pump for cruisair reverse-cycle system

Post by jbrem003 »

Ignition protection- aha!! I knew I was forgetting something. Guess we'll see what March says when Monday rolls around. It's a $300 pump at the end of the day but I'm curious as to why the Overload protection didn't kick in. When I pulled the pump out of the engine compartment about an hour after it stopped working it was still hot enough to burn if held.

The magnets and impeller all look to be in perfectly fine condition though. There were no signs of blockage and nothing was lodged in the intake or exhaust lines leading to and from the pump.
jbrem003
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Re: Raw water pump for cruisair reverse-cycle system

Post by jbrem003 »

Or… Now that I'm reading back my own description of what has happened, maybe the overload protection did kick in, and the motor not operating and just making a soft 'MRRRRR' wasn't it seizing, but rather it being tripped...
jbrem003
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Re: Raw water pump for cruisair reverse-cycle system

Post by jbrem003 »

Big D wrote: The pumps are overload protected so I think it just reached its end of life, or you blew the bracket o-ring, or the bracket wasn't fully secured and water got in. I suspect you'd have to be sitting in the mud to ingest enough of it to cause a cooling problem though.
This was exactly what happened, the pump overloaded and shut off and I just thomas got it had seized- thanks Big D! I reterminated the wires and rebuilt the motor since I had it out and cleaned the inline seastrainer to boot. Powered it back on and everything ran like a dream. After a few minutes all the dirt flushed out and water is flowing clean through the system.

I also now know why the previous owner installed two T valves onboard. One right before the pump, and another right before the freshwater pump and tank for the boat, in a worst are I can just turn on the dock water to feed my water pump and the positive pressure from the hose will overpower and water (or lack thereof) coming from the seacock.

Honestly, I'm super glad this happened in the summer and not the winter. I feel like I thoroughly understand my heating and cooling system now. Thanks guys for all the advice and help!
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