If those of you using check valves in centrifugal pumps could only see the tens of thousands of dollars in ruined batteries or damaged cabin
soles or engines etc. that I have seen as a result of improperly installed check valves you may think twice about ignoring the manufacturers advice.
In a well designed bilge system you would install a diaphragm "nuisance pump
" to deal with nuisance water
and let the Rule/centrifugal pump deal with oh $hit
This was from the Rule
Pump web site before the changeover to Xylem.
"The Rule Pumps FAQs:
Q: Can I install a check valve on the pump discharge?
Check valves are not recommended
Why doesn't Rule Pumps want check valve on the pump's discharge?
Check valves are prohibited by the American Boat & Yacht Council for use as an anti-siphon device-and with good reason: They're notorious for failing in both the open and the closed position, which respectively leads to flooding or failure to pump. If the valve is close to the pump, the pump may not be able to overcome the weight of the water on the other side of the valve, rendering the pump ineffective.
Q: Why does my automatic Rule Pump turn off if I install a check valve on the discharge of the pump?
The automatic bilge pump turns on about every two and a half minutes to "check" for high water. If water causes resistance on the pump, it continues to pump until the resistance lowers. With the check valve installed at the pump, it can't feel the weight of the water, and shuts off, allowing the bilge to fill with water!"
Rule does not recommend a check valve on their centrifugal pumps. You can always do what you want on your boat but you would be ignoring the advice of the manufacturer of the pump, and creating a potential safety issue
. The first priority of a good bilge pump system design is to design a good system
that is safe.
Just because DIY's and builders do it, to save money
, does not make it a correct
or necessarily safe installation
A prudent installation
on a sailboat, where you want to prevent flow-back, is to either to install a diaphragm pump
, the ideal solution, or to get a float switch with a delay or install a smaller "nuisance water pump
". The delay will not always solve the problem however so a diaphragm pump, that can
handle a check valve, or has the check valve feature built in, is the proper & safe solution to prevent flow-back.
A check valve in a centrifugal pump is not a good solution to flow-back, it is a potentially dangerous installation.
If you want to solve the problem in the correct manner
then you'll want to install a diaphragm pump
. If you want to go against the sage advice of the manufacturer, by all means, use a check valve....
Other than what I posted above. Here's one of the responses Rule sends out when you ask this question. This was sent to one of my customers who chose not to believe me. He then got really angry when his cabin sole
was ruined and tried to blame it on Rule sending them a rather terse letter. I had already warned him not to install the check valve but he ignored the installation instructions and my advice based on experience.. The whole shebang cost him nearly 4k for a new cabin sole
Originally Posted by Rule Pumps Tech Support
Both Rule and our competitors' centrifugal style bilge pumps have very little air vacuum pressure because there is a large gap between the centrifugal impeller and the impeller housing (depending on the pump, it could range between 1/16"-3/16") which allows high flow and some bilge debris to flow past the impeller without damaging the unit.
The negative side of having the large gap between the housing and the impeller is the impeller needs to come in contact with water to pull the water out of the bilge (water being a lot thicker than air).
A check valve in the bilge hose seals
air in the hose and will not allow the water to come in contact with the impeller. The pump may be in a few inches of water (or completely submerged) but because of the air pocket, the pump cannot remove the water from the bilge.
If you wanted to remove as much water as possible, you could try installing a diaphragm style pump. The diaphragm pumps have internal check valves and are self priming to at least 6'. The only drawback is that the diaphragm pumps do not have as much flow as the centrifugal pumps. If you mounted the centrifugal pump switch higher than the switch for the diaphragm pump, the diaphragm pump could be used for the daily water seepage and the centrifugal pump could be used for emergency pumping.
In that last sentence Rule nails it
.... That is a proper bilge pumping system
which has no check valve in the centrifugal pump discharge....
If you want to prevent back-flow use a two pump system a "nuisance pump
" (diaphragm) and a "emergency" pump
(Centrifugal) you could even go further with engine driven oh $hit pumps too... If I had a dime for every bank of batteries a stuck check valve has murdered on a centrifugal pump......................
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, or air locks, and to push open a sticky check valve. Most small boats can't swing the loads of a rotary vane pump so a diaphragm pump is the way to go.
Centrifugal pumps with check valves often just make neat little bubbles and the water remains in the bilge. Seen this far too many times to count and the damaged or sunk boats that go along with it..
I am the guy replacing the batteries that the bilge pump killed when the check valve stuck and the float switch remained ON.........
That said you can
design a bilge pump system safely
but it would not include a check valve on a centrifugal pump that is not specifically designed for one.