Air conditioning losing prime

[cenger]

After a trip my air conditioning pump loses prime. It takes a wile for the system to push water when back at the dock which makes me nervous. When I have not taken the boat out, the pump is instant shooting water out with good flow. Any thoughts for what I should look at ?

 

[racclarkson@gmail.com]

After a trip my air conditioning pump loses prime. It takes a wile for the system to push water when back at the dock which makes me nervous. When I have not taken the boat out, the pump is instant shooting water out with good flow. Any thoughts for what I should look at ?

AC pumps are centrifugal meaning they’re mounted below the waterline to gain prime. So three things to look at. It’s possible the intake picked up some air underway. A centrifugal pump won’t catch prime in air. You may have a restriction on the supply side (sea strainer) or the pump impeller is showing it’s age. Bet it’s number one. Check supply hose and make sure it stays low in the bilge. Finally, centrifugal pumps can run dry without harm.

 

[rsmith]

When we first got the boat we’d loose prime on the ac pump backing down hard on a fish. We mounted the pickup lower closer to the keel and put a forward facing strainer on it solved the problem now if idiots would stop letting their ice bags melt on the docks and the bags blow in the water it be all good. Seems my intake finds ice bags at 3am and the ac starts cycling

 

[Pascal]

A few things

What kind of pump? Pumps with metal impellers suffer from impeller erosion over time and will be less effective
What kind of pick up? Scoop? This should prevent any issue. Personally I prefer the South Bay Strainers with mesh outside.
Make sure your hose runs straight uphill from the sea cock to the strainer and to the pump. Any high point will cause an airlock.
Make sure the pump is low enough below waterline. If it cycles while the boat is on plane it could loose prime

 

[cenger]

It is an Orberdorfer pump. I let it run and it’s working now. Thank you for the input. Feels good to be boating in the North East.

 

[Captain Ralph]

There has to be a uphill route from the thru hull past the pump. Usually air gets trapped around the pump and it can not clear.
Pump discharge must point up and below water level.

Send in some pictures of your install and we can better isolate the issue?
Also, is this a new symptom? Pascal has a good point.

 

[Pascal]

It is an Orberdorfer pump. I let it run and it’s working now. Thank you for the input. Feels good to be boating in the North East.

How old is it? I ve seen impellers errode in 6 to 8 in some cases.

 

[oscarvan]

Install a bleed valve in the line?

 

[cenger]

Enclosed is the pump setup. I’m not sure the age of the pump but the boat is in fresh water. This is a new occurrence so I think I’ll replace the pump side.

 

[oscarvan]

Looks like there already IS a bleed nipple on that "T" in the high spot. Did you open it? Wonder if it was put there for just this reason?

 

[Pascal]

Looks like the strainer is above the pump inlet. Any air trapped in there will be hard to purge.

 

[Captain Ralph]

Yep, what an air trap.
That bleeder is your mission till you raise the pump or lower the plumbing before it.
Don't feel special, lots of us have to vent some A/C pump after a run.

Where is your water line. You may just be able to raise the pump up a few inches.

 

[racclarkson@gmail.com]

Looks like there already IS a bleed nipple on that "T" in the high spot. Did you open it? Wonder if it was put there for just this reason?

Enclosed is the pump setup. I’m not sure the age of the pump but the boat is in fresh water. This is a new occurrence so I think I’ll replace the pump side.

Looks like you could eliminate all those BS fittings and take the rise out of that hose from strainer to pump intake. Looks like a March pump. You can add a thin copper washer behind the impeller and see if that brings it back to normal ops. If so, you’ll need an impeller in another year or two. Try it before you knock it.

 

[cenger]

Thanks for all the input. I'll start with the easy things by raising the pump and taking out the rise in the hose. I had not opened the bleeder but that my also be a short term trick.

 

[oscarvan]

I had not opened the bleeder but that my also be a short term trick.

May well be possible that this was the solution by those that came before you.

 

[Boatsb]

Don't raise the pump. It's not going to help. It will make it worse.

Check the pump impeller for wear. If it's got a lot of use get it rebuilt and resealed before you find out it's worn out.

Don't play games with washers or hacks. Just fix it right the first time. Consider it maintenance.

 

[Pascal]

That’s a band aid. You shouldn’t have to bleed every time you run at speed. Check the waterline but as long as you can keep It below WL, raising the pump to remove the high point may work. East to test

 

[Bob Bradley]

I pretty much solved the problem on my 43C by installing a TEE on the outlet side of the pump. I run a small hose off it to a point between the engines where its easily accessible. Put a ball valve with a barbed nipple at the end of the hose. When the AC vapor locks (frequently when offshore drift fishing at night and snap rolling) I just go down between the engines and open the ball value at the end of the line. It usually reprimes itself, but on occasion I have to suck on it a bit. Salt water isn't that bad. Certainly better than siphoning gas or diesel.

 

[racclarkson@gmail.com]

If you pull the output line off the pump and you’re not getting a small geyser (with the pump off) your install has been altered from the factory. I’ve rolled and planed as much as anyone and never had to worry about any of this. Raising pumps to fix a hose problem is wrong, IMO.

 

[rsmith]

Get rid of the strainer it’s just a sink risk.