Here's a strange one. It appears that I have a thru hull leak in my refrigeration raw water pickup. The strange part is that it only appears to leak when I am running the refrigeration and am drawing water in through the thru-hull. Fridge pump on / original thru-hull open -> definate leak. Fridge pump off / original thru hull open or closed -> no apparent leak. Fridge pump on using alternate thru-hull, original thru-hull closed -> no apparent leak. There were recent repairs to this thru-hull and I suspect that something was not installed correctly when they re-installed the thru-hull, but I cannot understand why this leaks only when water is being pulled in. I do not understand the physics of this problem. So far the boat has not sunk.
- Status
The leak
may be so small that it needs to have water under vacuum (when the pump is running)which forces it though the opening into your boat. With the pump off, you may still have a leak but it may be so little and so slow that it isn't noticable. Think of a hose with a pinhole in it. With water in the hose line, not under presure, nothing comes out. When you turn on the hose and put it under pressure. Not exactly the same concept, but it is in reverse. Jack Manning s/v Victim of Fate Atlantic City, NJ
may be so small that it needs to have water under vacuum (when the pump is running)which forces it though the opening into your boat. With the pump off, you may still have a leak but it may be so little and so slow that it isn't noticable. Think of a hose with a pinhole in it. With water in the hose line, not under presure, nothing comes out. When you turn on the hose and put it under pressure. Not exactly the same concept, but it is in reverse. Jack Manning s/v Victim of Fate Atlantic City, NJ
Surely a vacuum or lower pressure
would cause air to enter the hose, not liquid to come out. Perhaps the leak is from higher up and is running down the outside of the hose till it gets to the though hull and then drips off?
would cause air to enter the hose, not liquid to come out. Perhaps the leak is from higher up and is running down the outside of the hose till it gets to the though hull and then drips off?
Ball valve hydrodynamics
The ball is actually a restriction in some ball valves. The ball hole is not the same size as the fitting hole. This could cause some local pressure increases as the water is sucked through the valve due to the water hitting the ball restriction. This would tend to force the water between the ball and the valve housing and could be causing a leak. I agree this is an odd one as the vacuum side would normally leak air in not water out while water is flowing.
The ball is actually a restriction in some ball valves. The ball hole is not the same size as the fitting hole. This could cause some local pressure increases as the water is sucked through the valve due to the water hitting the ball restriction. This would tend to force the water between the ball and the valve housing and could be causing a leak. I agree this is an odd one as the vacuum side would normally leak air in not water out while water is flowing.
Maybe a Crack...
...in the thru hull housing. That would account for only leaking when drawing water. Check it out before it's too late!
...in the thru hull housing. That would account for only leaking when drawing water. Check it out before it's too late!
It is a suction leak.
If you you are using the same intake hose with the original and the alternate through the hulls then the leak is most likely due to a bad valve which leaks under pressure. Replace. Suction leaks are very hard to find but it looks like you have done your homework.
If you you are using the same intake hose with the original and the alternate through the hulls then the leak is most likely due to a bad valve which leaks under pressure. Replace. Suction leaks are very hard to find but it looks like you have done your homework.
self healed or wrong diagnosis
Thanks all - I brought the boatyard mgr down to see what I discovered, and of course the mystery leak failed to occur. Either I was lulled by a poor diagnosis (and I still have a leak to track down elsewhere in the boat), or temporarily opening/closing/disconnecting the thur-hull (permanently?) cured the problem. Interested in that ball valve / hydrodynamic leak comments, but no water apparent around the valve. I might try a half-open valve and see what happens.
Thanks all - I brought the boatyard mgr down to see what I discovered, and of course the mystery leak failed to occur. Either I was lulled by a poor diagnosis (and I still have a leak to track down elsewhere in the boat), or temporarily opening/closing/disconnecting the thur-hull (permanently?) cured the problem. Interested in that ball valve / hydrodynamic leak comments, but no water apparent around the valve. I might try a half-open valve and see what happens.
- Status