Loss of AC Pump Prime

[JD5652]

Since we have been running the 58 LRC up the ICW since 6/2/19... we have lost the prime on the air conditioning pump about a dozen times. Only happens while underway. Checked and cleaned the strainer... strainer was "mudded up" a little..... tightened all hose clamps... none were really "loose".... hose from thru-hull to pump appears to be in very good condition with no cracks.....

Anyone expernece this on similar Hatteras or have any thoughts on other possible thigns to check??

Thanks in advance!

 

[CTdave]

I had a similar situation a while back. I replaced the impeller and the problem was solved. I'm not saying this is the problem that you're experiencing but it sounds like it. Even after being hauled out of the water, I've never had to prime the pump.
Good luck!

 

[jim rosenthal]

Could the passage of seawater across the external strainer be sucking the prime out of the inlet hose?I believe this could happen with a mushroom type strainer. With a scoop strainer, not so likely.

 

[Pascal]

I don’t think an LRC can go fast enough for flow to be disrupted or Air to be ingested assuming the pump is in good condition

What kind of pump do you have? Some of the Cruisair branded pumps or Scott Punp have metal impeller that will either corrode or erode with time resulting in a weaker pump which may not be able to suck water under way

Also check for obstruction inside the seacock and outside the scoop. If it only happens underway I doubt that s the problem but you never know. So many times I have open a strainer lid and gotten a healthy flow yet under pump suction something would just clog flow

 

[SKYCHENEY]

I loose prime after a run but not while underway. I replaced my Oberdorfer pump with a March. Still have the same issue.

 

[Pascal]

That s weird. What kind of TH cover do you have? Scoop?

 

[JD5652]

The pump I have is a Scot Model 68 and it does indeed have a bronze impeller. I talked to Scot Pump Company this morning and they stated that the impeller life is equivalent to running continuously for two years. The pump itself is about 4-5 years old and has spent a significant amount of time in Florida... so the AC pump ran a lot. They stated it is very likely a worn impeller. So I ordered an impeller (~$80) and a seal kit (~$30)... they should be here by end of the week... just in time for my arrival in Mystic.

FYI.... I do NOT believe I have a scoop on the AC thruhull.... it's simply the mushroom end of the thruhull.

Thanks for everyones suggestions and help!!

 

[Pascal]

We have a large Scott pump on the 84 Lazzara i run. About a year ago i notices water flow out the discharge wasn’t quite what it used to be and the upper chiller shut down on high pressure. Turned out to be the impeller being eroded. I had a spare pump so I was able to swap it right away

That s why I prefer March pumps. No erosion. I ve had a couple of the plastic impeller break over the years but you swap it in 5 minutes. Don’t even have to pull the hoses off

I really like external South Bay Stainers for air con and water makers. The wedge sale eliminates issues underway and block debris from getting in

 

[JD5652]

Pascal-

Thanks for the feedback.... I will likely put a Southbay or some style on the 58 LRC next time I haul.... what about a scoop thruhull??? … since I'll mostly be doing 10 knots or so all the time would that be advised??

Thanks!

 

[Pascal]

What i like about the South Bay strainers is that nothing will go thru the screen unlike slotted scoops

 

[racclarkson@gmail.com]

When my centrifugal pumps start to lose it, it's usually from too much impeller end-play on the shaft. A thin copper or nylon washer that reduces that play has always seemed to get them pumping like new.

 

[Pascal]

No, with metal impellers (Scott, Cruisair etc) you get erosion on the impeller leaving a stump. No vanes = no flow