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Bizarre bilge pump mystery

Apr 20, 2016
coastal recreation Inc. Balboa-Aquarius 23 washington nc
That's how the rule pump in my fishing skiff acts, it cycles on intervals seeing if there is water to be pumped. It has been bullet proof for nearly a decade.
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Jan 13, 2015
Hunter 34 Deep Bay, BC
Actually this is backwards. With a DC motor, such as a bilge pump, as voltage goes down so does the current, even stall or in-rush current is dictated by the voltage the motor sees. High resistance at the fuse can actually serve to melt the fuse but this is not because of an over current situation just high resistance and the heat developed..

A bilge pump blowing fuses likely has a leak and the bearing surfaces are becoming sticky. As a bilge pump or any typical DC motor stalls or has a load applied the current of the motor goes up. Bilge pump makers size the fuse to intentionally trip if the rotor is over loaded and drawing too much current so the pump does not catch fire.. With a constant power source, such as an inverter, as voltage goes down the inverter draws more current to maintain the same output but with a DC motor as voltage goes down so does current.

Why do you have a float switch on a Rule automatic pump? First you need to get the wiring correct.

Battery positive terminal>fuse (within 7") > AUTO-OFF-MANUAL switch > BROWN wire to AUTO POSITION > BROWN W/WHITE trace to MANUAL POSITION > BLACK to BATTERY NEG.

No float switch...

Once the float switch is removed the scenario I would start with is that the pump may be suffering from drain back cycling due to a poorly designed bilge pumping system.

As a marine electrician customers can't even pay me to install any of the "auto-sensing" bilge pumps. I simply will refuse the work unless they decide to do it correctly. I will also refuse to install any current Rule float switch.

A "properly" designed bilge pumping system for a boat over 25' will look like this.

Emergency Pump = Largest Rule or other centrifugal pump you can physically fit. Pair it with an Ultra Safety Systems Junior or Senior float switch set at a higher level. (IMPORTANT: DO NOT USE CHECK VALVES ON CENTRIFUGAL PUMPS)

Nuisance Water Pump = Diaphragm pump (check valves are okay on diaphragm pumps) and an Ultra Safety Systems Junior or Senior float switch set for lowest desired water level. Note: All wiring for electric pumps shall be sized for no more than a 3% voltage drop.

Manual Pump =
Henderson/Whale etc. with no check valve just a strainer.
I think the blowing fuses (this was with the RuleMate 750, the second of the three pumps, right before I replaced it) were because the pump had actually failed. It was not heat build-up blowing the fuses because it happened far too fast (probably less than 5 seconds). I assumed the real problem caused the failure, and the failure caused the blowing fuses, although I still can't see how. As you pointed out, with a DC motor if the voltage is low, the pump will just run slower (unlike an AC induction motor, where the amps will increase in proportion). My first thought was that the impeller had jammed, but as I said before it turned very freely.

And the wiring is exactly right, just as you describe, except that the fuse is in the Auto/Off/Manual switch which is about 18-24" from the battery (close enough, I figure).

Removing the check valve isn't an option without significant alterations to the boat. The volume in the line is greater than the volume in the bilge, and it's in the original design of the boat (it's on the original plumbing diagram). Might be a stupid design, but that's where we are. Since I live in a place where it very rarely (almost never) freezes, it's not much of a risk.
Jul 7, 2015
Hunter 33_77-83 Kemah
Have you tried to run the pumps with a stand alone 12 VDC power supply like is used to jump a car with a dead battery?
You may find that all of your pumps are still good.
A ground wire going south because of corrosion causes some weird behavior.
I replaced 2 pumps back to back. First one pulled out was a rule 500 with a float switch.
Found it running down the battery with a slow ineffective constant pump cycle.
Put in an Attwood with internal float. Found it quivering in death throes a few weeks later. It had worked great for the couple of weeks since first installed.
Bought the 1100 gph Rule with computer sensor.
Worked fine.....for 2 weeks.
Found in death throes draining batteries.
Dim light went on.
Grabbed portable car jumper/air compressor 12 vdc power supply and hooked it to the pump.
Pump worked fantastic.
Ran new ground wire all the way from the bus bar to the pump.
Problem solved.
Feb 6, 1998
Canadian Sailcraft 36T Casco Bay, ME
As I said elsewhere, the (current) issue isn't that the pump doesn't run when it should, it's that it runs (very briefly) when it shouldn't. Neither the level nor the manual switch is calling for it to run.

Rule "automatic" pumps cycle on every 2.5 minutes to check for water. If they "sense" water they continue to pump until they sense less resistance and stop pumping. Rule "mate" pumps use a high and low sensor for on & off. These sensors are certainly not the most reliable I have seen especially in dirty bilges.
Oct 12, 2015
Hunter 34 Channel Islands Harbor
My Hunter 34 came with a check valve in the discharge hose. That this valve is working correctly is very important as it is fairly long and is elevated to the discharge hole in the hull. If it is totally non functional your bilge pump will recycle forever because the water runs back downhill into the bilge and sets off the pump again. After re-checking your wiring that would be my next step to replace the check valve.


Apr 22, 2009
Ontario 32 Pender Harbour
I just had my fancy Rule switch fail. I actually have an "automatic" bilge pump (that does the 2.5 minute turn-on thing to test for physical resistance). I installed a check-valve and gave it a try. It worked properly when there was no water (turned on briefly for a few seconds), but if there was water, it pumped it out but did not stop when the water was gone. It would eventually turn off if I cycled the power a few times.
There's NO WAY I'll have a system where the pump does not turn off - that will burn the pump out in no time. So I went back to a simple (Rule) float-switch mounted above the pump so it turns the pump off before all the water is pumped out. I can run the pump manually to get the last bit out if I want.
Moral of this: these "automatic" pumps are crap, at least the automatic part. Mine has a separate wire to attach an external switch - I'd recommend you use that if you have it.
As for these switches, Yeah the old ones seemed to last forever, the new ones, not so much. I don't understand it: we use float switches in Industrial Control in crap that makes bilge-water look like Perrier, and they last forever. I think if this one fails I'm going to someone like Johnson Controls and get a REAL one.

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Oct 12, 2012
Catalina 36 East Greenwich
This is my first response to an item, but this one struck me so I had to share a bit of our experience.
Like the writer, I had a Hunter - 31, but also irrelevant - and replaced our bilge pump with an automatic, environmental friendly self-contained pump, with the same exact, random issues he describes.
I replaced it with a separate bilge pump and float switch and never a problem since with that boat. Since this is a Catalina forum, I will add my present setup in our 2001 36 MKII: two separate 1100gpm pumps; separate float switches (one set a few inches higher than the other; each connected to a separate battery. And, while we are on this fun topic, NEVER install a check valve on a bilge pump discharge hose. I know never is a strong word, and it would seem like a logical thing to do, BUT - in my opinion, by the time the discharge hose is long enough to hold enough water to force the pump to cycle it is holding so much water (which is really heavy) that the pump cannot overcome the static pressure of the water column behind the valve. In this case, I would elect a shorter route and suffer the aesthetics of another through-hull fitting.
Sail on!
Jan 13, 2015
Hunter 34 Deep Bay, BC
Rule "automatic" pumps cycle on every 2.5 minutes to check for water. If they "sense" water they continue to pump until they sense less resistance and stop pumping. Rule "mate" pumps use a high and low sensor for on & off. These sensors are certainly not the most reliable I have seen especially in dirty bilges.
These were (the first two) Rule Mate pumps with the internal electronic high/low sensor, and I couldn't agree more that they aren't reliable in a dirty bilge. I think the original "won't start when it should, won't stop when it's empty" problem was these sensors and a dirty bilge. The ones I had are not the pumps that start every 2.5 minutes to check for water, and the current Attwood Sahara doesn't do that either. Besides, the interval now is between 10 minutes and an hour (or maybe more; I'm not always listening for it). Nowhere near as frequent as 2.5 minutes. If it were that often, I'd have tried the multimeter test long ago.

I'm convinced after all the help here that the current issue is in the wiring between the Auto switch and the pump. The only thing I can think of that fits all the facts is an intermittent short between the brown Auto positive wire (normally 12V) and the brown/white Manual positive wire (normally 0V). This would explain everything except for the timing; but maybe it is the boat rocking that makes a contact, and then the heat of a high resistance connection breaks it again after a couple of seconds?

In any case, the test will be the long alligator clips CaptnRon suggested. If that confirms the issue, I'll pull new wire from the switch to the pump and unless some higher power is really having fun with me on this, that will be that.

Thanks to everyone for all the feedback. I now think I know everything that could possibly go wrong with a bilge pump. And seem to have experienced most of those personally.


Sep 20, 2016
Cal 21 Michigan
And, while we are on this fun topic, NEVER install a check valve on a bilge pump discharge hose. I know never is a strong word, and it would seem like a logical thing to do, BUT - in my opinion, by the time the discharge hose is long enough to hold enough water to force the pump to cycle it is holding so much water (which is really heavy) that the pump cannot overcome the static pressure of the water column behind the valve. In this case, I would elect a shorter route and suffer the aesthetics of another through-hull fitting.
Sail on!
That's sort of correct, though mostly incorrect. Were the pump unable to overcome the static head pressure within the discharge line, it wouldn't be able to overcome that head pressure under any circumstances. What actually happens to a pump under the circumstances you describe is that the closed check valve, with the head pressure sitting atop it, prevents the volute (pump body) of the pump from filling with water, and a centrifugal pump which is air-bound in that manner cannot pick up prime. (I can, and have, create exactly the condition of describe within a water well where the pump sits with 50 feet submergence, which is why you're sort of correct, though for the wrong reason.)

There's a lot of confusion about check valves on bilge pumps, with precious little by way of explanation for admonishments that they should never be used. There isn't a commercial vessel which operates without a check valve on its bilge pump, which should give one pause before making a blanket statement against them. MaineSail got to the heart of it in noting centrifugal pumps, even though all those commercially used pumps are centrifugal. The problem with them can be where they're located, and the inadvertent error of locating them directly at the pump discharge, which is standard practice for most pump installations other than, for instance, bilge pump installations. The reason every commercial vessel has a check valve on its overboard discharge lines is because that line can flow water both ways without one, and should the discharge port be submerged for any reason, it quickly becomes a hull fill line, which is not a good thing.

To purposes of illustration, consider taking a straw, placing your finger over the end of it, so that no air can escape it, and then placing it in a glass of water. (Your finger is acting like a check valve with head pressure on it.) You'll note that water does not rise up the straw very far. That's because, while air is compressible, it's not compressible enough to let other than a bit of water to rise up within the straw. Now, imagine that you've got a pump on the end of that straw. You'll get some water into the pump's volute, but not enough for a centrifugal pump to prime itself. You'd have an "air-bound" pump in that case, regardless of any hooey about the pump's capability of being self-priming. Someone will say, "use a positive displacement pump then". While positive displacement pumps will pump air almost as well as they'll pump water, they don't make for good bilge pumps because the nature of their design makes them low volume pumps and, if you've got water in the bilge for other than benign reasons, you want a pump that can pump a large volume of water rapidly, and that's the forte of centrifugal pumps. (Positive displacement pumps are perfect for pumping out that last bit of water which a centrifugal pump doesn't get and can be installed as low as possible just for that purpose, but in addition to a centrifugal bilge pump. Consider it a stripping pump, which is an actual thing.)

The solution is to place the check valve as close as practicable to the overboard discharge for the bilge line. That prevents not only any significant head pressure sitting atop it, while also providing a longer "straw", which allows the air within the line to compress enough for the pump to pick up prime as it normally would. The check valve doesn't have to be right at the through-hull, though that may offer an undeniable convenience which should not be ignored, and it can be located near it, but more accessible to access. If you use a good quality check valve, especially of the type I'll describe below, it will still prevent the water within no matter how long a discharge line from draining back into the bilge, holding it within the line on vacuum alone. (Ships use swing check valves, but their discharges are below the water line and, more importantly, those swing check valves get "exercised" regularly. That is to say, they're used enough that they do not set up in either an open or closed position, which is a weakness of swing checks, along with the fact that they're not usually the best sealing of check valves, because they depend upon head pressure against them for good seating (sealing).

I recommend a spring check valve, commonly called a "line-check", for use on a boat. And I recommend a specific type of construction line check valve which I'm going to simplify describing by telling you what brand to buy and be done with it. There are a lot of cheap, and pricey, line check valves out there which are not worth your time or money in the installing. Buy a Maas-Midwest and be done with it. I've used them in water well work, from 1" up to 3", under all manners of abusive use, and never seen one fail. I see around 50-75 failed line check valves every year, year in and year out, none of them ever having been a Maas-Midwest. It's the only twenty year old check valve which is still superior to lesser designed ones brand new. It's principle advantage is the design of its poppet. Instead of a conventional disc seat, it uses what looks like a cage, which prevents the poppet from not seating squarely. That cage seats by either head pressure or via its spring, though vacuum will seat it equally well. (I can stand 42' of pipe with one atop it, full of water, and have no more than a drop or two drip out.)

Because bilge pumps use an open impeller design, they can pump some crud, with the suction strainer filtering out the heavy stuff the impeller cannot pass. Obviously, a clean bilge is an asset. A Maas-Midwest check valve will pass anything which the pump will, and it will still seat (seal) at pump shut-off. If you're somehow pumping something which could foul it, you're probably going to foul your pump first and, in any event, the solution is better straining at pump suction. Bilge pump strainers aren't optional, while being well designed for you to get your hands on them to clear them of any debris. Nevertheless, I'm big on overkill approaches, so I recommend a check valve "one size over". If you've a 1" discharge hose, I recommend an 1-1/4" line check valve, bushing it down upon either end to fit your hose. The benefit is in increased passage size within the check valve, though it is a bit of overkill given the cage design poppet within a Maas-Midwest valve, which are bronze, by the way. (I'm pretty sure stainless is available, as well.) Again, I'm not a fan of swing check valves, particularly in salt water applications, simply because of their propensity to have the swing pivot freeze up from lack of use. The more freely they pivot, the more likely they are to leak back also.

Those who are religiously anti-check valve should answer why boat manufacturers use them, as well as answering why they do not object to their use within vented loops on things like their head toilet. (The vent is a check valve.)
Feb 6, 1998
Canadian Sailcraft 36T Casco Bay, ME
Those who are religiously anti-check valve should answer why boat manufacturers use them, as well as answering why they do not object to their use within vented loops on things like their head toilet. (The vent is a check valve.)
Boat manufacturers use them because they are cheap, cutting corners, not following the ABYC standards, or refuse to design and install a proper bilge pumping system. They do this despite the bilge pump manufacturer telling them not to. The ABYC does allow check-valves, for certain situations, (eg: it would be fine on most diaphragm pumps) but not when a manufacturer says not to.

Perhaps the better question would be to ask the builder why they blatantly ignore the bilge pump makers instructions and why they choose not to follow the acceptable safety standards?

Good builders do not use check valves on submersible Rule type pumps and there are builders who do install proper bilge systems. A check valve on a centrifugal marine pump, not specifically designed for one, is simply a Band-Aid for an improperly designed cost-cutting system.

Unless the bilge pump was specifically designed for a check valve, and they will have this physically built into the pump, please do yourself a favor and do not add one. It is not a matter of "if" but when it will cause issues.

Check valves creating problems is not a new story, I have been removing incorrectly installed check valves since I was a 12 year old kid working in a boat yard. They were causing issues with centrifugal pumps in the late 70's & early 80's and continue to do so today.

Below is an actual correspondence from a bilge pump maker senior engineer, regarding a customer who had a check valve built into a centrifugal pump. I did not do the install the customer did. I rip the check valve out of that brand of pump as the first thing I do when I open the box. This little check valve cost one of my customers $1800.00 in batteries and over $12,000.00 in repair damages. I have far too many stories that repeat this similar or same scenario and many that go far beyond including sinking boats. As far as I know he is still in legal proceedings with the manufacturer over the design and the lack of warning in the manual regarding the check-valve.

"The check valve in our XXXX Bilge Pumps, depending on application, may simulate an air-lock situation. Under these conditions the check valves are recommended to be removed. Unfortunately I do not see where we have listed this in our manual or brochures. After our discussion it is clear the application you have is not suitable to have a check valve in your pump."

How about a question for a bilge pump maker who KNOWING SELLS a product they know damn well can create a situation that can 100% prevent the bilge pump from doing its job? How about knowing this and then refusing to place a warning in the pump manual about this danger?

We absolutely can not compare a submersible well pump to a cheap centrifugal bilge pump. These pumps can't deal with much head at all static or frictional, and unlike a 240V well pump, then they can be dramatically affected by voltage fluctuations and voltage drop in the wiring as well as the installation.

Heck our old well at our last house was almost 300' deep. Even without a check valve, there is no 12V centrifugal bilge pump I know of that could even get water to the top of the well cap. The results of an improper bilge installation can result in tremendous damage expense.

The reason that a check valve inside a vented loop does not affect the performance of the pump is because the "check valve" or duck-bill or Scott type vacuum breaker, is not in the path of the water being discharged and a vented loop is not a check valve.. It is simply at the high point to allow air into the hose, at the high point, in order to break a siphon event. The vented loop is also far enough away so the pump can actually prime and begin moving water. The other issue with check valves, that you won't have on a well pump, is hydrocarbons and gummy oily bilge water. This causes the valve seat to become "gummy" and sticky or deteriorate over time and bilge contaminates can actually serve to nearly "glue" the check valve shut and make it significantly more difficult to open.

Using a check valve as a means to prevent water ingress is strictly against the ABYC standards. If we go by the CFR for ship construction electric submersible pumps, like we use, are not even allowed on ships larger than 65' so any discussion comparing the use of check valves on large ships is simply not comparable to the puny/wimpy centrifugal pumps we use on recreational boats.

Sadly boaters are often overly tight with their money and often choose illogically, especially when it comes to doing something in a proper fashion vs. cutting corners to save money. With regards to bilge pumps this is not entirely their fault because far to many boat builders have blatantly ignored manufacturer installation instructions and essentially ripped off the customer by installing what can be considered unsafe and unreliable bilge pumping system.

Boat buyers always tend to think the builder actually knows what they are doing, sadly this could not be further from the truth, so check-valves must be okay, right? Round and round we go and and we have a Catch 22.

Sadly most will not listen to sound advice and spend the money to design a proper pumping system utilizing a nuisance water pump (diaphragm) and an emergency dewatering pump (centrifugal). A proper bilge pump system design and installation solves the issue of "drain back" and creates a highly reliable system.

Heck I know far too many boat owners going on 4 or 5 failed Rule pump switches, which have far exceeded the cost of an Ultra Switch, yet they keep replacing them. I know because they see me on the dock and ask me what switch I recommend because theirs just failed "again".. I tell them to buy an Ultra Junior or Senior, they go to Hamilton and compare price, and come away with another Rule switch. They then ask me the same darn question a few months later and I tell them the same thing...... It is often not until that switch costs them 4-5 figures, in damages, that the light bulb actually goes off.. I tell them the same story with check valves on centrifugal pumps and see murdered battery bank, after murdered battery bank as a result. I also see other damages too that can often far exceed the cost of batteries. How about two 3 month old Honda 250HP outboards.....! Cha-ching $$$$... Yep stuck check-valve on a centrifugal pump. His deductible, 2%, cost him multiples beyond what a diaphragm pump and Ultra Switch would have..

The vast majority of the bilge pumping systems I come across are improperly and rather unsafely installed. The damage numbers resulting from this sloppy work are insanely high. Check valves, poor system design, improperly laid out hose runs, poor hose choices, under sized wire, incorrect fusing, incorrectly made terminations, backwards wiring and the use of low quality poor reliability float switches etc. all lead to damages, ruined batteries, ruined soles, ruined engines and sinking events...
Aug 2, 2011
Newport 30 MKIII Madeira Beach, FL
The Rule 3700 is a large submersible pump with an electronic sensor. It is known to act erratically due to air locks that form in the lines. Perhaps the problem extends to other models. If using an electric bilge pump best to have a float switch and better to have a second manual pump as back up.


Sep 20, 2016
Cal 21 Michigan
The key to understanding MaineSail's quote from the senior pump engineer is an understanding of the proper use of a supplied product. (Which is why most "racing" components, for any sport, come with not only no warranty, but no warranty for suitability of application.) Manufacturers are reluctant to supply their products only to authorized, trained technicians, though they'd certainly have fewer head aches, if lower profits, in doing so. Which is also why I wouldn't hesitate in recommending someone take their boat to MaineSail, simply because, contrary to popular belief, you're paying for experience versus just equipment and labor, with experience being the more valuable of the three. Nevertheless, this is the internet, and there are a lot of boats which not only came with no bilge pump, that will also only be worked upon by their owners, and given that most of those owners are men, I believe it worthwhile to be as expansive as possible in considering design characteristics and factors affecting the projects they decide to tackle themselves, before they do something foolish like putting a check valve directly atop a bilge pump or a sump or sewage pump, for that matter. (Submersible well pumps are almost a sole exception where the check valve belongs directly above the pump.)

Thanks to MaineSail for the usual spirited conversation.


Jan 20, 2005
Nauticat 321 pilothouse 32 Erie PA
pumps like the rule submersibles may cycle because the h 2 0 in the pump outlet line flows back into the bilge when the ump s tops pumping water out. . to cure this problem, we went to a par jabsco belt drive bilge pump ($375 or so) mounted high and dry above the bilge , with an Ultra pumpswitch sealed unit in the bilge. expensive, but worth it.
Jan 30, 2012
Nor'Sea 27 - "Kiwanda" Portland/Anacortes
As to any purchase boat or not -- Safety, reliability, price

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