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Old 03-07-2022, 17:40   #1
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Bilge joiner has vent

I was working on my bilge hose at the weekend.

There is a joiner, and the join has a very small hose coming out from the side. The house is only a few mil in dia and about 2 inches long (it doesnt go anywhere - just vents)

In the picture below I have one end of the bilge hose off, but it shows the joiner and this random vent hose as I call it.

Anyone seen the vent hose before and any ideas what it does?
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Old 04-07-2022, 04:14   #2
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Re: Bilge joiner has vent

I'm not clear about what I'm looking at here. What is the square plastic thing with the 4 bolts actually doing there? Is it some sort of check (one way) valve? Normally a "joiner" wouldn't look like this. It would just be a round piece of plastic with hose barbs on each end.

When you say "bilge hose" do you mean a hose that goes into the bilge and is connected to some sort of pump?
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Old 04-07-2022, 05:22   #3
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Re: Bilge joiner has vent

I believe, but am not certain, that what you're looking at is a check valve to prevent water from above the valve from flowing back down into the bilge.



If you have a check valve well above the pump, and the discharge well above the check valve, after the pump stops pumping, the water below the check valve drains back through the pump into the bilge. At this point you have, starting from the bottom: the pump, then a length of hose with air in it, then the check valve, then a length of hose with water in it, then the discharge.



The pump has a hard time priming. The slug of air is trapped by the slug of water above the check valve. The pump is not designed to pump air very efficiently, so it can't push the air hard enough to lift the slug of water above the check valve out of the way.



One solution is to have a tiny vent hole *below* the check valve. This allows the trapped air to escape when the pump is trying to prime. The downside is that when the pump is running, of course, a tiny percentage of the discharge flows out through this vent hole rather than through the main discharge. It's usually piped so that this "wasted" discharge runs harmlessly back to the source.
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Old 04-07-2022, 16:22   #4
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Re: Bilge joiner has vent

good explanation
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Old 04-07-2022, 23:39   #5
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Re: Bilge joiner has vent

Quote:
Originally Posted by ChrisOwens View Post
I believe, but am not certain, that what you're looking at is a check valve to prevent water from above the valve from flowing back down into the bilge.



If you have a check valve well above the pump, and the discharge well above the check valve, after the pump stops pumping, the water below the check valve drains back through the pump into the bilge. At this point you have, starting from the bottom: the pump, then a length of hose with air in it, then the check valve, then a length of hose with water in it, then the discharge.



The pump has a hard time priming. The slug of air is trapped by the slug of water above the check valve. The pump is not designed to pump air very efficiently, so it can't push the air hard enough to lift the slug of water above the check valve out of the way.



One solution is to have a tiny vent hole *below* the check valve. This allows the trapped air to escape when the pump is trying to prime. The downside is that when the pump is running, of course, a tiny percentage of the discharge flows out through this vent hole rather than through the main discharge. It's usually piped so that this "wasted" discharge runs harmlessly back to the source.
+1 for the excellent explanation. I believe that is exactly what I am looking at. The small vent hose has broken off and the new pipe might be covering the vent hole, so I will need to check that.
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Old 05-07-2022, 09:47   #6
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Re: Bilge joiner has vent

Quote:
Originally Posted by BigAl.NZ View Post
I was working on my bilge hose at the weekend.

There is a joiner, and the join has a very small hose coming out from the side. The house is only a few mil in dia and about 2 inches long (it doesnt go anywhere - just vents)

In the picture below I have one end of the bilge hose off, but it shows the joiner and this random vent hose as I call it.

Anyone seen the vent hose before and any ideas what it does?
You mean a limber hole?
Joining the bilge compartments?
And that little hose goes to nothing?
There seems to be a bellows of some sort like used on "dripless" systems.
Right in the front.
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Old 05-07-2022, 17:48   #7
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Re: Bilge joiner has vent

Quote:
Originally Posted by Boatyarddog View Post
You mean a limber hole?
Joining the bilge compartments?
And that little hose goes to nothing?
There seems to be a bellows of some sort like used on "dripless" systems.
Right in the front.
Boatyarddog
Could it be that we are looking at a decommissioned propshaft log?
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