High pitched squeal coming from vent loop on Heat Pump heating system.

Hi,
Very recently a high pitched squeal sound started coming from a vent loop that I think is used by the heating system (Cruisair heatpumps), the sound comes on when the circuit for the pump is turned on. I have 3 circuits, one for each zone and then 1 for the main pump.

Any ideas what would cause a vent loop to make a sound like that?

Thanks!
Arthur

Greetings,
Mr. A. Three things come to mind...Some sort of obstruction in the hosing or a failing vent loop and the most unlikely BUT possible is a failing bearing in the pump/motor telegraphing the noise up the tubing.

Ok thanks, I was thinking about an obstruction. I’ll let you know what I find.

Air in the system. Look for leaks. It would appear that the vented loop is doing exactly what it was designed to do. Also check the reservoir and make sure you have enough coolant.

Ok so after some investigation here is what I have found.
The loop that’s making the noise is one of two that exit saltwater as part of the heat pump cooling system. The salon unit has its own exit point and the forward and pilothouse share one. They are fed off the same pump which is located closer to the salon unit.
Visual inspection of the pump and strainer seem ok.
When I turn off the valve at the throughhull that’s connected to the noisy loop it goes away, but I think that’s normal. Turning off the other throughull quiets the noise but it’s still there...

Water output in both seem fine when open.
Also there is no leak, bilges are dry.

So based on all of this I doubt it’s the pump or strainer as flow seems fine and turning off the throughhull near the pump doesn’t help much.
Could I possibly have a blocked line to one of the two heat pumps up front and would that cause something like this?
Or could the vent have failed?

Also on a side note since it’s an above water line exit why would there be enough pressure to make sure a loud sound, what’s the purpose of the vent loop?

Thanks
AC

The vented loop lets air in when the raw water shuts down so a syphon isn't created bringing water back in from the thru hull. There is a little valve at the top of the loop that does this and maybe it is whistling because it is partially blocked. You can usually remove the valve part at the top of the loop and clean it out.


David

I cleaned out the vent loop (was nothing to clean) but when i hold my finger over it I can feel the water going through but there is lots of gurgling and it feels like it’s pulsing a bit.

The loop may be aspirating air from the vent. As the water flows past the fitting for the vented loop, it creates a venturi and the pressure drop is creating enough of a vacuum to pull air through the duckbill. That would be my guess. A change in the pump volume or pressure could have an effect on that. I'd look for a strainer/inlet obstruction, particularly if this just started. Does it stop if you temporarily block the air inlet to the loop vent? If the answer is yes, then that's the cause of the noise. Remedy is a different story.

The entire water circuit for a water cooled AC is sealed from the bilge, so I don't understand why a vented loop is needed?
I don't have one on my boat for the heat pump.

No sea water can backflow into the bilge to sink the boat.

You could even run the outflow under the water. My outflow through hull is about 8 inches above the waterline.

That’s exactly what I was thinking, I have no idea what purpose this vent serves.
After more troubleshooting it is indeed creating a vacuum and pulling air in, not pushing air out.
Based on that I struggle to see how a low flow or air in the system could cause the noise so reliably. Or... could the vent just be bad and if the seal failed it would naturally do this as the water creates a Venturi effect and sucks in air?
Noise goes away when I put my finger over the vent, and water flow is the same no matter what I do.

Thoughts?

Check if it is one of the Forespar vac breaker fittings with the little joker valve. These make a high pitched squeal on our boat when the bilge pumps shut off. BTW, it is easy to put the little rubber valve in backwards.


I agree that, if this is a closed system that can't let water into the boat, the vac breaker is not needed and apt to cause more problems than it prevents.

Greetings,

Mr. A. You may have isolated the source of the noise by putting your finger over the vent. IF the valve is easy to get to, why not take it out for a test? Again, IF the unit IS the source, you can opt to leave it out or replace it.

This is what the vent looks like if it is a Forespar fitting:




BTW, the joker valve fits in a 1/4" compression fitting like it was made for it. I've made my own vac breakers for fuel polishing system header tanks and bilge lines where I didn't want to use the whole Forespar return bend. You can buy just the cap and valve from West Marine or Forespar.

I have also used the Forespar vented loop on a head line for neat appearance but didn't need, or want, the vac breaker function so I just replaced the valve with a small disk of thick rubber gasket material.

sdowney717 said:

The entire water circuit for a water cooled AC is sealed from the bilge, so I don't understand why a vented loop is needed?
I don't have one on my boat for the heat pump.

No sea water can backflow into the bilge to sink the boat.

You could even run the outflow under the water. My outflow through hull is about 8 inches above the waterline.

Click to expand...

Agreed. There is no vented loop in my system. Easiest solution to the noise--remove the vented loop.

So it does look like a forespar fitting, and I’m pretty sure it’s not on backwards as it started out of the blue.
I think I’ll try a replacement to see if it failed (pure curiosity) then just cap it.

I was worried about a larger problem in the system but it sounds like that’s unlikely.

Thanks everyone!

Arthurc said:

I think I’ll try a replacement to see if it failed (pure curiosity) then just cap it.

Click to expand...

Don't bother. I just put one in brand new because our boat didn't have a vent in the high loop. It squealed the very first time I tested it. Every one I have ever installed has made a noise when draining down.


Just cut a piece of that red gasket material (about 1/8" thick) you can get at a hardware store to a disk that just fits in the cap and replace the joker with that.


Some jokers are louder than others. The new one I just put in will probably wake us up the first few times the bilge pump runs in the middle of the night. I may swap it to the second bilge pump which is installed just above the normal bilge high water level so it will stay dry and unused in case the extra pumping capacity is ever needed.

Thanks all, I’m just going to block this one with gasket material.