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-   -   Bilge pump non return valve. (http://www.sailnet.com/forums/gear-maintenance/93937-bilge-pump-non-return-valve.html)

H and E 11-09-2012 09:01 AM

Bilge pump non return valve.
 
Someone recommended that I install a non return valve on my automatic bilge pump. As a result I ordered one and installed it. BIG MISTAKE. The first time I tested it the valve stuck and would not allow the water to pump out. Its now gone. After I pumped the bilge there was no flow back through the pump back into the bilge.

Maine Sail 11-09-2012 09:22 AM

Re: Bilge pump non return valve.
 
Quote:

Originally Posted by H and E (Post 945874)
Someone recommended that I install a non return valve on my automatic bilge pump. As a result I ordered one and installed it. BIG MISTAKE. The first time I tested it the valve stuck and would not allow the water to pump out. Its now gone. After I pumped the bilge there was no flow back through the pump back into the bilge.


Yep.... Big mistakes on centrifugal type pumps....

Sabreman 11-09-2012 09:29 AM

Re: Bilge pump non return valve.
 
As Maine Sail says, it's a mistake to install a check valve in line with a centrifugal bilge pump (e.g., Rule pumps). The pump can move a lot of water but doesn't have much power. Think of it as high voltage, low amperage. Use a Vented Loop instead.

The PO of our boat installed a check valve and the bilge pump never really worked. I fussed with it for the first few months of ownership until the bilge filled and the battery drained when the pump ran in a vain attempt to move the water. I installed a vented loop and haven't thought of it in 7 years.

Brewgyver 11-09-2012 06:05 PM

Re: Bilge pump non return valve.
 
It's not quite as simple as no check valve on centrifugal pumps. A great many centrifugal pumps MAY use a check valve (or foot valve, as they are called when installed directly into the pump outlet. Most sump pump and condensate pump installations use a check or foot valve.

It's just that the typical 12 volt bilge pump for small boats has very low head capacity. The tradeoff is between flow and head, as it is on all centrifugal pumps. Higher head = lower flow, and vice versa.

Maine Sail 11-09-2012 09:59 PM

Re: Bilge pump non return 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, a centrifugal pump will simply cavitate and do nothing but make some neat little bubbles in the bilge.

For boats stored in-water during cold weather the water in the bilge hose above bilge level can freeze when the bilge water is not frozen. This present an impossible situation to pump into.

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..

Check valves on rotary vane pumps or diaphragm pumps do not suffer the issues they do on centrifugal Rule style pumps. I have seen everything from ruined interior cabinetry, cabin soles and engines due to stuck check valves. I have also seen boats that sank because of a stuck check valve..

The largest maker of centrifugal bilge pumps, Rule, specifically recommends not to use them.

They can be a danger if used on a system with centrifugal bilge pump. Bilge pumps are safety items anything that can prevent the pump from pumping becomes a potential danger.

Rule Pump Instructions
http://www.pbase.com/mainecruising/image/136622304.jpg

Classic30 11-11-2012 08:58 PM

Re: Bilge pump non return valve.
 
Quote:

Originally Posted by Maine Sail (Post 946215)
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, a centrifugal pump will simply cavitate and do nothing but make some neat little bubbles in the bilge.

For boats stored in-water during cold weather the water in the bilge hose above bilge level can freeze when the bilge water is not frozen. This present an impossible situation to pump into.

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..

Check valves on rotary vane pumps or diaphragm pumps do not suffer the issues they do on centrifugal Rule style pumps. I have seen everything from ruined interior cabinetry, cabin soles and engines due to stuck check valves. I have also seen boats that sank because of a stuck check valve..

The largest maker of centrifugal bilge pumps, Rule, specifically recommends not to use them.

They can be a danger if used on a system with centrifugal bilge pump. Bilge pumps are safety items anything that can prevent the pump from pumping becomes a potential danger.

Maine, there are instances where you might need to install a check valve (I needed to) and ways to do so that doesn't give rise to the "standing water in the discharge hose" you mention (install it high up near the discharge point - not in the bilge with the pump itself).. I guess exactly what you do depends on the specific circumstances and the type of boat.

I've known check valves to fail open (bits of rubbish preventing the flap closing), but I've never heard of one sticking closed.. but then we don't get the freezing weather you get. I've known of boats that sank because there was no check valve fitted when they needed one..

IMHO, the bottom line is: Don't install a check valve unless your particular installation means you have no other alternative.

BTW, the other thing that can prevent the pump pumping is lack of a strum box.. make sure you use one. :)

BubbleheadMd 11-13-2012 09:02 AM

Re: Bilge pump non return valve.
 
Quote:

Originally Posted by Sabreman (Post 945884)
As Maine Sail says, it's a mistake to install a check valve in line with a centrifugal bilge pump (e.g., Rule pumps). The pump can move a lot of water but doesn't have much power. Think of it as high voltage, low amperage. Use a Vented Loop instead.

The PO of our boat installed a check valve and the bilge pump never really worked. I fussed with it for the first few months of ownership until the bilge filled and the battery drained when the pump ran in a vain attempt to move the water. I installed a vented loop and haven't thought of it in 7 years.

If I install a vented loop in my discharge line, should be closer to the pump, or to the point of discharge?

Maine Sail 11-13-2012 09:17 AM

Re: Bilge pump non return valve.
 
Quote:

Originally Posted by Hartley18 (Post 947055)
Maine, there are instances where you might need to install a check valve (I needed to) and ways to do so that doesn't give rise to the "standing water in the discharge hose" you mention (install it high up near the discharge point - not in the bilge with the pump itself).. I guess exactly what you do depends on the specific circumstances and the type of boat.

I've known check valves to fail open (bits of rubbish preventing the flap closing), but I've never heard of one sticking closed.. but then we don't get the freezing weather you get. I've known of boats that sank because there was no check valve fitted when they needed one..

IMHO, the bottom line is: Don't install a check valve unless your particular installation means you have no other alternative.

BTW, the other thing that can prevent the pump pumping is lack of a strum box.. make sure you use one. :)

If you want to use a two pump system a "nuisance pump" and a "primary" pump then a check valve can be fitted to the lower nuisance water pump. they still stick and kill batteries though... I would NEVER, and I don't use the word never often, recommend a check valve on a single pump installation when a centrifugal pump is being used. If you want a check valve please use a rotary vane or diaphragm pump that has the ability to deal with the head pressure of the standing water and to push open a sticky check valve... Centrifugal pumps often just make neat little bubbles and the water remains in the bilge.

It is your boat, you can do as you wish, but check valves on centrifugal pumps are a danger waiting to happen. You would be horrified at the number of "check valves" I see that fail to open. I am the guy replacing the batteries that the bilge pump killed when the check valve stuck and the float switch remained ON.........

MastUndSchotbruch 11-13-2012 09:46 AM

Re: Bilge pump non return valve.
 
Quote:

Originally Posted by Maine Sail (Post 947659)
... Centrifugal pumps often just make neat little bubbles and the water remains in the bilge...

I experimented a bit with a check valve (NOT on a boat, actually, long story...). My experience was exactly what you describe, it got stuck in the 'closed' state at the drop of a hat.

BUT: I had never thought of doing what Hartley suggests:

"install it high up near the discharge point - not in the bilge with the pump itself"

In that case, you do NOT have the water column keeping the valve stuck in closed. That seems to me the smart way to do it (why didn't I think of that?).

Next time I have a chance, I will try that on my installation.

Maine Sail 11-13-2012 09:59 AM

Re: Bilge pump non return valve.
 
Quote:

Originally Posted by MastUndSchotbruch (Post 947668)
I experimented a bit with a check valve (NOT on a boat, actually, long story...). My experience was exactly what you describe, it got stuck in the 'closed' state at the drop of a hat.

BUT: I had never thought of doing what Hartley suggests:

"install it high up near the discharge point - not in the bilge with the pump itself"

In that case, you do NOT have the water column keeping the valve stuck in closed. That seems to me the smart way to do it (why didn't I think of that?).

Next time I have a chance, I will try that on my installation.

But that pretty much defeats the entire purpose of the check valve. A siphon break is still a choice that won't stick closed. If you are not preventing hose drain back then there is little point for a check valve...... Bilge pump hoses should always be installed to prevent back siphoning which includes a high loop and a siphon break....


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