THis caught my attention, so I too looked-up the SVS series.
https://www.groco.net/media/file/file/s/v/svs-series.pdf
It has the old-school tapered plug style of valve. I have no idea why it would leak-down, or where the water would go, but I agree with Ted's guidance here. Given the amount of futzing the OP has tried with no success, time to hit the reset button.
BTW - I am seeing many people using Groco Flanged NPT>NPS Adapters with a ball valve instead of a traditional all-in-one flanged seacock. Allows the ball valve to be easily replaced needed, which is admittedly rare.
https://www.groco.net/products/valves-seacocks/flanged-valves/ibvf-flange-adaptor
Peter
I have not done it personally but have read of others using aerosol shaving cream looking for vacuum leaks. While underway spray different areas to see if there is a change.
No. But I have lubed it through the drain by putting a zerk there. I lubed it until grease came out the t-handle threads. The boats in the water. I might have a diver cup the hole while I open up the valve but if the rubber cylinder is shot I might be in trouble.
This is not what the Guidi installation guide says. Page 7: https://www.guidisrl.it/wp-content/uploads/2020/06/Water-intakes-and-scoops.pdfIs the scoop facing forward or aft? It's counterintuitive but they are supposed to face aft. Most of them get installed backwards. Facing aft they resist bubbles or anything else but water getting sucked in.
I had a similar issue. It was a blockage right in the input of the strainer. It was not visible until you looked into the water input port and not inside the strainer itself. The very high suction from the raw water pump attempting to keep the volume of water flow normal was pulling in air from the lid.
There was no leakage/drips of water ever. Once the blockage (tight ball of weeds that got stuck in the input) was resolve, all was well. It allowed some water flow through but required the super high suction to do so. The reason it only happens when running was the increased suction from increased RPM. That caused enough suction to start pulling in small amounts of air from around the strainer lid that normally would never do so.
Take a look, maybe it is the same thing. It is an easy fix. It could also be the thru hull partially blocked. If there is an input hose before the strainer it could be internally blocked or partially collapsed inside creating this odd issue.
Good luck
Have the exact same strainers on my GB 49. There is supposed to be a plastic washer.. probably Teflon.. under the big tightening nut on top… do you have one?
Cavitation is not always air mixing with water . It is often pressure change that boils water making air. Also just because you do not see water leaking doesn’t mean you do not have an air leak. Under vacuum air can actually come through a hose and for sure come through a hose barb. We see this often without ever seeing a drop of water .
I'm no physicist but cavitation doesn't "make air", it creates a void or vapor filled cavity, hence the name, and that void collapses the moment the vacuum drops. The voids would only remain if the vacuum remained, and that can't occur at rest, assuming it's happening at all. Lowering the pressure on a liquid does lower the boiling point, but again once the pressure returns to normal, the voids collapse.
This does not occur in any raw water strainer I have ever seen (I have seen it occur in polishing system filters), if the vacuum was high enough to get the water within the strainer to "boil", at the very least the impeller would wear out very quickly, and/or the engine would be overheating because it would be starving for water.
This sounds like an air leak in plumbing between the strainer and the hull, a leak in the strainer housing, or ingestion of air bubbles from the bottom. A scoop will make no difference, it helps with prime but will scoop in water or air bubbles alike.
SteveI'm no physicist but cavitation doesn't "make air", it creates a void or vapor filled cavity, hence the name, and that void collapses the moment the vacuum drops. The voids would only remain if the vacuum remained, and that can't occur at rest, assuming it's happening at all. Lowering the pressure on a liquid does lower the boiling point, but again once the pressure returns to normal, the voids collapse.
This does not occur in any raw water strainer I have ever seen (I have seen it occur in polishing system filters), if the vacuum was high enough to get the water within the strainer to "boil", at the very least the impeller would wear out very quickly, and/or the engine would be overheating because it would be starving for water.
This sounds like an air leak in plumbing between the strainer and the hull, a leak in the strainer housing, or ingestion of air bubbles from the bottom. A scoop will make no difference, it helps with prime but will scoop in water or air bubbles alike.
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About the only thing I can figure is that there is cavitation happening at the intake. Had a diver check it. Couldn't see anything.
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Thanks!
Steve
I'm no physicist either but I do believe that there is a phenomenon that is similar to cavitation called "degassing" where dissolved gases come out of the liquid when the liquid experiences reduced pressure. If not mistaken this is what happens when a carbonated drink bottle is opened. The pressure is reduced and the didolved gas escapes as bubbles. In that case they do not redisolve unless subjected to increased pressure so a vapor pocket is formed and is evident.
Flow through a restriction causes the reduction in pressure.
In the case of the strainer a restriction could be causing dissolved air to come out of the water as small bubbles?
SteveDon:
I thought for a while before writing that response, because I know that dissolved gas can be extracted from liquid, if enough vacuum is present, but I don't know enough about the physics of that to say whether or not it can happen here. You can get water to boil at room temperature if you apply enough a vacuum, but those "bubbles" are water vapor, not dissolved air from the water.
I suppose my 30+ year marine gearhead gut is telling me that just doesn't happen in strainers, I've never seen it, so why is this one different?
Is the scoop facing forward or aft? It's counterintuitive but they are supposed to face aft. Most of them get installed backwards. Facing aft they resist bubbles or anything else but water getting sucked in.
If this only happens while underway I can almost guarantee that you're getting bubbles along the hull that are going up into the strainer. Had the same problem on MOJO. The best solution is to simply drill and tap the top of the strainer for a 1/8" hose barb. Install the barb and run a 1/8" hose up high in the boat (higher than the waterline will ever be even when heeled substantially). Leave end of the hose open to the atmosphere. Any bubbles coming into the strainer will immediately go out the hose on top. Problem solved. I ran MOJO for 20 years with this solution...
STB
You may very well be correct and I'm all wet. Just sort of thinking outloud and writing it down... no strong technical proof behind it.
My only reaction is there must be disolved air or O2... otherwise the fish would all die... right? Wave action, especially white caps keep at least the surface water aerated and it must disperse to keep fish alive at depths?? Now I'm really getting out of my wheel house... lol
Keep us posted.
Glad you got it resolved, congratulations.
The "seacock" looks like a thru-hull fitting with an inline ball valve on top. Strictly speaking that's not a seacock by ABYC standards, as the threads are almost certainly incompatible (unless the thru-hull uses combination threads, it doesn't look long enough to be that style), NPT vs. NPS, and because it lacks an integral flange it is unlikely to pass the 500 lb. 30 second static load test. Did the yard supply the parts?
More here https://stevedmarineconsulting.com/seacock-selection-service-and-avoiding-the-pitfalls-2/
Glad you got it resolved, congratulations.
The "seacock" looks like a thru-hull fitting with an inline ball valve on top. Strictly speaking that's not a seacock by ABYC standards, as the threads are almost certainly incompatible (unless the thru-hull uses combination threads, it doesn't look long enough to be that style), NPT vs. NPS, and because it lacks an integral flange it is unlikely to pass the 500 lb. 30 second static load test. Did the yard supply the parts?
More here https://stevedmarineconsulting.com/seacock-selection-service-and-avoiding-the-pitfalls-2/