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Old 22-07-2011, 20:42   #16
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Re: Check Valves

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Originally Posted by Greg S View Post
Again, as I have them in my boat, I would be very interested in make, model, age and circumstances of the indecent.

In a recent flooding incident, involving a fellow boater that I know, THE major problem was that the bilge that was so full of crud and debris filters on the pumps were clogged instantly. After the first minute there was nothing getting through the pump, let alone any check valve. Afterwards I asked him if he had tasted the water to determine if it was fresh or saltwater. He said no, he wasn't going to taste that slimy s**t! The check valve was the least of his worries. (turned out it was fresh and all ended well) My bilge is very clean, to the point of pressure washing it every now and again, plus I have lock down bilge boards so I guess the check valve, for me, is the greatest concern. Thus the question.

Thx - G
It was an older boat, but the problem was not boat specific.

A check valve, or in fact ANY loop in a bilge pump line or cockpit drain line is very dangerous in cold climates if boats are kept in the water. The water in the loop (or the water held up by the check valve) can freeze, blocking the line completely.

The pump worked fine the next day, pumping like crazy... after the boat slipped under the relatively warm water.
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Old 22-07-2011, 21:56   #17
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Quote:
Originally Posted by Greg S
Bash,

Stuck in the closed position, I presume? And under what conditions, used often or rarely?

Thanks,
Greg

PS - What type, brand and size if you remember.

Thx - G
Stuck closed.

It was a small Rule pump. I've always used a system where I have a small "working" pump at the deepest possible point in the bilge, with a huge "emergency" pump a couple inches higher up. (The emergency pump is always alarmed, and I've never yet had one go off.)

In this case, it was the "working" pump that had the stuck check valve. It just didn't have the guts to force the valve open. We were liveaboards at the time, so we discovered the situation before the pump burned itself out. No damage.

But I pulled the check valves out immediately, and I haven't used them since then.
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Old 22-07-2011, 22:03   #18
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Re: Check valves

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Originally Posted by Maine Sail View Post
It's not just about debris, in fact debris is the least of your worries with a check valve. These valves quite often stick shut especially if the bilge pump does not cycle often. The biggest draw back is the added head pressure that the pump can not overcome. This additional head is caused by the standing water in the discharge hose, and thus, they simply cavitate and do nothing but make some neat little bubbles in the bilge. Fill a grain silo with corn and then try to push a door open into it...... Pretty tough. The check valve creates the same type of resistance to the bilge pump, Centrifugal pumps deal horribly with any added head pressure..

On top of all that the largest maker of centrifugal bilge pumps, Rule, specifically says NOT to use them.

They can be a danger if used on a system with centrifugal bilge pump.
As a preventative measure, I recently replaced my aging Rule 2000 primary bilge pump and USS (Ultra Safety Systems) switch that came with my boat. I replaced them with the same components. In the process of also replacing my discharge hose, I discovered an inline, one-way check valve about 3' from the pump and on about a 2' rise. In doing some research, I discovered the drawback of check valves for this application that MaineSail warns about, found out ABYC disapproves of it, and even had one of the engineers at USS recount several incidents of sinkings where the bilge pump was happily running but failing to pump. So I promptly removed the check valve, only to experience the constant cycling of the pump from the standing water left in the hose. I have a 47' center cockpit with a deep bilge, so I'm estimating approx. 16-18' of 1-1/8" hose from pump to transom, and maybe a 7-8' total rise. There's also a vented loop just inside the transom.

Talk about head pressure! The pump just keeps cycling on & off as the water in the hose is discharged out but then falls back into the bilge. MaineSail -- would not the head pressure issue you speak of be lessened with a check valve that's only 3' from the pump? Is there another solution? The two-pump answer from an earlier post seems somewhat complicated, esp. since I already have a secondary pump that sits higher up but, for safety's sake, has its own discharge hose & thru-hull. Seems like my situation can't be that unique. For the time being, I've installed a new check valve and everything works perfectly, but is there another answer that could eliminate the risky valve but prevent the water in the hose from constantly cycling the pump???

P.S. Thanks for the butyl tape, MaineSail -- it works exactly as you described and also happens to be OEM all over my 25-year old boat with no leakage!
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Old 23-07-2011, 07:57   #19
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Re: Check Valves

Quote:
Originally Posted by thinwater View Post
It was an older boat, but the problem was not boat specific.

A check valve, or in fact ANY loop in a bilge pump line or cockpit drain line is very dangerous in cold climates if boats are kept in the water. The water in the loop (or the water held up by the check valve) can freeze, blocking the line completely.

The pump worked fine the next day, pumping like crazy... after the boat slipped under the relatively warm water.
Excellent point! Thanks. Hope to never be in water that cold again, but you never know, and winterizing the would not do one damn bit of good on that one. OK, definitely no check valves in (very) cold water!



Quote:
Originally Posted by Bash View Post
Stuck closed.

It was a small Rule pump. I've always used a system where I have a small "working" pump at the deepest possible point in the bilge, with a huge "emergency" pump a couple inches higher up. (The emergency pump is always alarmed, and I've never yet had one go off.)

In this case, it was the "working" pump that had the stuck check valve. It just didn't have the guts to force the valve open. We were liveaboards at the time, so we discovered the situation before the pump burned itself out. No damage.

But I pulled the check valves out immediately, and I haven't used them since then.
It would seem then, as Main Sail also indicated, that the smaller pumps do not like check valves. I think I will consider removing the check valve from my smaller pump and work out a different solution for it. The larger two, Rule 2000's, I'll leave for now. One one backs up the other and the likelihood of both having problems at the same time, for the short times I'm off the boat, would seem slim. Still, good food for thought.

Thx - G
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Old 26-07-2011, 09:52   #20
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Re: Check Valves

I have read this thread and am still not clear on what options I have to solve the problem I have with bilge pumps in my boat.

In the Swan 36 there is a 5 foot deep small deep bilge in the back of the keel just below the companion way ladder. I have 2 bilge pumps both pretty large, one quite a bit higher in the bilge than the other. The lower pump discharge hose loops about 6 feet above the pump. Fortunately the bilge usually doesn't fill. The bottom pump cycles on a switch and pumps till it draws the water down as low as the switch float allows and stops then the head back flows. I have set the switch above the pump a bit so the pump pumps out enough water not to keep cycling but that leaves the lower pump completely under water after it cycles (Till I run the pump manually and draw it down lower, as far as the pump can pump). I have been told this is not good but have not been able to figure out how else to set this up without a check valve. I have been told not to install a check valve for several of the reasons described in the thread.

I don't understand how the small bottom pump could be installed in this situation since it will still continuously cycle the same way the current pump I have dose, if I have the switch in the bottom of the bilge.

The only solution I have been able to figure out is to have a long float switch if possible. I have installed the USS (Ultra Safety Systems) switch but it is not nearly long enough it only pumps the water down about 3" before it shuts off. It would need to be at least 12" from switch turn on and turn off points.

Is there a float switch set up that could be that 12 inches long or at least longer than the USS version?

Any other ideas of what I might try?

Thanks

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Old 26-07-2011, 10:48   #21
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Re: Check valves

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Originally Posted by EddieS View Post
A couple of things. It is my understanding that a pump must lift the water to the highest pointin the discharge system be it through head loss or elevation, and will do so unless the pump is weak (or very near its shutoff head), but it has nothing to do with a check valve holding that water in the discharge line. If a check valve is located some distance away from the pump and the portion of line from the pump to the check valve drains back into the sump one may have a priming issue. A check valve does require additional head ussually comparable to several additional feet of discharge tubing/pipe in head loss. A failed check valve (stuck closed) will cause a pump to reach its shutoff head-not pump anything. A failed check valve (stuck open) will cause the discharge line to drain back into the bilge, and possibly cycle the pump, or set up a syphon if the discharge is below the water level.
It is not typically not good for a pump to spin backwards (this is what happens when a submersible pump quits, and the water within the discharge line drains back through the pump, so a check valve holds the water in the discharge line as opposed to allowing it to drain back to the bilge (and possibly cycling the pump on and off).
Thanks
Ed
Yes you're pushing against the same static head, the difference is that it is possible to trap air in the pump. The centrifugal pumps do not pump air or air water mixes very well. Seems to me that a section of horizontal hose would have the best chance of making the problem occur. Picture that the pump comes on and pushes some water into the hose, not yet opening the check valve above. The air returns to the pump in the top of the hose, and keeps an air water mix in the pump. It never reaches a high enough pressure to open and check valve. Only when the pump has no air in it will it reach the speced output pressure and open the check valve.


This shurflow pump with a low outlet shows how easy it would be for air to return, they even say don't mount their pump with the exit hole facing down or have any sags in the hose.

http://www.shurflo.com/files/Educati...00-00%2010.pdf

It doesn't matter if a centrifugal pump spins backward with reverse flow.

John
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Old 26-07-2011, 10:51   #22
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Re: Check Valves

i read my instructions on my new pumps before installing them. they usually say do NOT use a check valve. so i do not. mine are rule pumps.
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Old 26-07-2011, 10:59   #23
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Re: Check Valves

FWIW, Ultra Safety Systems makes a special float switch designed for deep sailboat bilges that addresses this issue of airlock. I think the idea is that the intake holes on the switch are set higher up to insure there is always a few inches of water left at the bottom of the bilge to prevent air getting back to the pump. Thought I'd give them a call and see if I can figure out how to run the pump w/o a check valve. I'll post anything useful.
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Old 26-07-2011, 11:00   #24
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Re: Check Valves

The small pump has a very small discharge hose. The hose is too small to hold enough water to cause the pump to cycle. When the float switch shuts off the small pump, the water in the hose does flow back but the volume is not enough to start the pump again. I had one customer who had to go down to a 3/8" ID hose to avoid cycling. He used a little Rule 360 and adapted it to 3/8" hose. It solved his problem.
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Old 26-07-2011, 16:19   #25
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Re: Check Valves

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The small pump has a very small discharge hose. The hose is too small to hold enough water to cause the pump to cycle. When the float switch shuts off the small pump, the water in the hose does flow back but the volume is not enough to start the pump again. I had one customer who had to go down to a 3/8" ID hose to avoid cycling. He used a little Rule 360 and adapted it to 3/8" hose. It solved his problem.
Exactly.
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