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Old 11-08-2015, 14:48   #106
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Re: Galley Sink Fills With Water

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I'm a believer in very small primary pumps to prevent cycling from run back. I know one fellow who had a very small space to pump and he got cycling from the standard 3/4" discharge hose on the smallest pump. He just adapted it down to 3/8" hose and the cycling went away.
The ideal situation is large capacity primary bilge pumps with a small capacity "dewatering" pump to keep the bilge dry. Different kind of pump of course.
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Old 11-08-2015, 15:08   #107
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Re: Galley Sink Fills With Water

Good points Gordon May! Although I fail to see how a submerged pump can not have water to prime it, regardless of air above the pump. Maybe that applies to those pumps not in the bilge....
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Old 11-08-2015, 15:35   #108
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Re: Galley Sink Fills With Water

Schooner, I think we're saying the same thing. I refer to the little pump as primary because it is the first to come on when water comes in. Of course you would have bigger pumps that would come on if more water was coming in than the little pump could handle.
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Old 11-08-2015, 16:09   #109
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Re: Galley Sink Fills With Water

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Four reasons to avoid check valves on bilge pump systems:

The pump may have some air in it when it shuts off and the check valve closes. The pump can become air locked the next time you want it to run. "Air lock" means that there is air trapped in the pump below bilge water level keeping the impeller from getting traction on the water. Centrifugal pumps are not self priming, meaning they must have water at the impeller to start pumping. An air lock can last long enough to sink your boat (presumably any way), and it does not develop every time. One solution is to drill a small hole in the hose below the check valve. This will eliminate the airlock until the hole gets plugged up with lint. In the mean time, it will also squirt a thin stream of water across your bilge which can be unnerving the first time you see it. The new solid-state augmented float switches extend the pump run time after they actually trip off. This gets the pump trying to suck air at the end of it's cycle and increases the possibility of airlock with a check valve in the system.

The second problem with check valves is that you can trap so much water weight above the valve with a high head that the pump can't open the check valve from a standing start. Centrifugal pumps do not like to be stalled out. With the inevitable air cushion below the check valve, the pump sees a gradually increasing back pressure culminating in complete blockage, The check valve can stick shut a little too. The pump may not develop enough static pressure to open the check valve. The inertia of the water moving through the discharge pipe aids the pumping action, if you think about it. An operating pump is a dynamic system with water moving through it. If you stop the water from flowing, you have changed the system conditions enough that water may not always start flowing again. Bilge pumps are puny little things and do not always tolerate unusual conditions.

The third problem with check valves is they leak. The leakage increases as they age. This means that the check valve you installed to stop your little oscillating pump system now just oscillates with a longer period as the water drains back to the bilge at a slower rate. If the pump only runs every 15 minutes this may be tolerable.

The fourth problem with check valves is that they inhibit a good thing. All that water rushing back down the discharge pipe backflushes the debris screen(s) at the intake to the pump. Mostly these screens do not get clogged and this is why.
Thanks for that. I always knew not to put check valves in as it specifically states it on the mounting instructions but I didn't know why until now. Very helpful
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Old 11-08-2015, 16:26   #110
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Re: Galley Sink Fills With Water

??? How did it get to bilge pump flow back from galley sinks? I must have missed something. Go old school put a float switch higher than the flow back water level. Everybody is happy, no cycling or air lock and pump has prime water. Parallel two switches since they don't have a good reputation.
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Old 11-08-2015, 16:59   #111
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Re: Galley Sink Fills With Water

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...put a float switch higher than the flow back water level...
It doesn't work that way. The problem is that, once the switch shuts off (no matter what level you place it) there is sufficient water remaining in the hose to turn the switch back on.
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Old 11-08-2015, 17:28   #112
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Re: Galley Sink Fills With Water

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It doesn't work that way. The problem is that, once the switch shuts off (no matter what level you place it) there is sufficient water remaining in the hose to turn the switch back on.
I said put the switch higher than the flow back water level. Hell, put a block of wood under it with some Liquid Nails. To be crass it isn't brain surgery. So shim it to what ever is right for your bilge and discharge hose length. I'm not speaking of pump with an internal switch which is somewhat Mickey Mouse.
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Old 11-08-2015, 17:32   #113
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Re: Galley Sink Fills With Water

Let me repeat: It does not work.
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Old 11-08-2015, 17:51   #114
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Re: Galley Sink Fills With Water

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Let me repeat: It does not work.
You need to be more specific about what system when you say "it does not work". Some systems work correctly. For example, pump with a separate switch , (anywhere you want it,) vented loop and a thru hull in the bottom of the hull.
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Old 11-08-2015, 18:07   #115
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Re: Galley Sink Fills With Water

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Let me repeat: It does not work.
Why? Water seeks it's level. It has always worked for me. Maybe I see your point. The switch over travel and the amount of water. Most of those switches are or have been mercury switches that have a cut off delay since turn on and off delay depends on the mercury sliding. We maybe speaking apples and oranges as far as amount of backflow. I will reluctantly cede to your reply.
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Old 11-08-2015, 18:22   #116
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Re: Galley Sink Fills With Water

A vented loop wont work. You need to close the sea cock before sailing.

You could install a suitable ball valve inline in a more convenient location.

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Old 11-08-2015, 18:24   #117
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Re: Galley Sink Fills With Water

Perhaps I could have been more descriptive.

One difficulty with submersible pumps is that they sometimes will cycle just from the amount of water that back-flows into the bilge after the float switch turns the pump off. Raising the float switch will only increase the amount of water in the bilge that cannot be removed via the float switch, as the same amount of water comes back in after the switch shuts off (presuming the size of the bilge remains fairly constant).

One of the best cures for this is the Water Witch style switch with delay.
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Old 11-08-2015, 18:37   #118
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Re: Galley Sink Fills With Water

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A vented loop wont work. You need to close the sea cock before sailing.
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Maybe I'm blowing bubbles because I've already sunk. Having the discharge as low as possible is a good thing, just in case you might heel over, like in a sail boat..
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Old 11-08-2015, 20:45   #119
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Re: Galley Sink Fills With Water

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??? How did it get to bilge pump flow back from galley sinks? I must have missed something. Go old school put a float switch higher than the flow back water level. Everybody is happy, no cycling or air lock and pump has prime water. Parallel two switches since they don't have a good reputation.
You didn't - two overlapping conversations happening here. I've already agreed that I need to not overload the boat so much and/or close the galley sink seacock.

We are now having a conversation on the merits of a putting a check valve in a bilge pump line. I use one because it works in my system and has so for the 27 years on the boat. Then again, we also have a vented loop forward of the check valve, and an exit well above the waterline. I've also noted that the check valve needs replacing about once a year.
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Old 11-08-2015, 21:19   #120
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Re: Galley Sink Fills With Water

This is actually kind of terrifying for me. My 1979 J/30 does not have seacocks on any of the drains (galley sink, head sink, and anchor locker).

I re-did plumbing the in the head last year (NOT fun) and installed a seacock on top of the thru-hull for the head sink. The galley sink and anchor locker, though, remain directly connected to the sea. I've never had a problem with water overflowing into the sink in 3 years of sailing her hard on the bay, though.

It's definitely in my plans to fit proper seacocks on the other two drains, but now I'm feeling like I should definitely prioritize that effort.
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