Bilge Pump Not (Always) Priming

[rmbrown]

I occasionally run the hose in my bilge and let the bilge pump (a Rule-Mate 2000) run in an effort to at least replace the dirty water with clean.

Yesterday, when I did that, i lifted the bilge pump, rolled it over, cleaned the screen, and put it back down.  It started as it should but it was unable to prime itself and start the water moving again.  I've never had this issue before so it surprised me.  I played around long enough to determine that if I rotated it 45 degrees it would burp out a big air bubble, and immediately prime and run.  That makes me wonder if there's some gas vent that normally allows that bubble to escape.  I've vacuumed out the bilge often enough to know that the pump normally works fine after being high and dry.

Any ideas?

[KWKloeber]

  You didn't say whether you have a check valve on the hose.

[rmbrown]

My mistake!

I do have a check valve immediately after the pump.

[KWKloeber]

Mike that's possibly causing the air lock. 
Water above the CV is holding it tightly shut, and trapped air can't get past the CV to let bilge water into the pump body.  I have seen some (home) sump pumps that have a tiny hole in the pump chamber or discharge nipple (you can see a small stream spraying while pumping) so that air doesn't get trapped below the discharge check valve.

k

[Jon W]

Not familiar with the Rule Mate 2000, but other Rule pumps (1500 and 3700) are submersible centrifugal type pumps which "prime" by having a flooded suction. If the submerged impeller can spin freely, and the vanes are clean, it will pump water. If it doesn't pump water, the line or exit from the boat must have a blockage. Your check valves should be checked. Sounds like a real life example of the risk of having in-line check valves in the bilge system.

[mainesail]

Rule pump instructions...

[rmbrown]

MS:

Your short answer prompted me to do more research and read your long answer here...  http://www.sailnet.com/forums/gear-maintenance/93937-bilge-pump-non-return-valve.html

Thanks for the intel!

What confuses me is that I believe my boat has likely been set up like this since it was built in December of 92, and it just now developed this issue.  My guess is that there's either something causing more restriction than is used to or the check valve is getting sticking and is harder to open.  Tipping the pump to the side to let out some air, lets the blades move the water, develop more pressure and open the valve.

All that said, the thing to do here is clearly to remove the check valve on my next visit.

[mainesail]

MS:

Your short answer prompted me to do more research and read your long answer here...  http://www.sailnet.com/forums/gear-maintenance/93937-bilge-pump-non-return-valve.html

Thanks for the intel!

What confuses me is that I believe my boat has likely been set up like this since it was built in December of 92, and it just now developed this issue.  My guess is that there's either something causing more restriction than is used to or the check valve is getting sticking and is harder to open.  Tipping the pump to the side to let out some air, lets the blades move the water, develop more pressure and open the valve.

All that said, the thing to do here is clearly to remove the check valve on my next visit.

Keep in mind that a production boat builder is NOT your friend and is NOT doing you nay favors other than getting you the cheapest product that looks good to the ladies as a boat show. They are far too often more concerned with interior aesthetics than important items such as systems.


Boat manufacturers use check valves on centrifugal pumps because they are being cheap, cutting corners, not following the ABYC standards, or because they 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 & not to prevent siphoning.

I have asked a few of these builders why they blatantly ignore the bilge pump makers instructions and why they choose not to follow the acceptable safety standards even when they slap an ABYC sticker on the stern...? The answers? Blank stares or shoulder shrugs usually...

When I install or design a bilge system the centrifugal pump is designed to not to sit in routine bilge water as the primary pump. The centrifugal pump is for "emergency use only".

I use diaphragm pumps for handling nuisance water so there are no DC components regularly in the bilge water or DC power sitting in water.

Corrosion Issues:

Centrifugal pumps are by far my number 1 source of electrolytic corrosion/stray DC current (electrolysis is what hirsuit women do to their upper lip). This despite the guy 10 slips down being blamed for the "rapid anode erosion" when it is actually being caused by the owners own bilge pump in a large percentages of cases.

You don't even want to get me going on how many centrifugal pumps, wiring and their related dime store level bilge switches I find leaking DC current directly into the bilge water. I've yet to find a single diaphragm pump doing this, because they don't sit directly in the electrolyte / bilge water.

Just last night (11/28/17) I was at an ABYC CEU corrosion course discussing this exact issue with both Ed Sherman (VP / Education Director) and John Adey (President) asking them to discuss the corrosion issues related to centrifugal bilge pumps more often in technical training classes. Ed's response was; "I use a diaphragm pump for nuisance water on my own boat and the centrifugal mounted higher up for emergencies." D'oh, no kidding, that is what any skilled boat owner or builder would do yet not what most production builders do, hence why it needs to be discussed more often...


A "properly" designed bilge pumping system for boats like ours would 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 and set both pump and switch at a higher level, that keeps them out of routine bilge water. This cuts down on the DC corrosion risk tremendously and utilizes a centrifugal pump for what it does best "emergency de-watering"... (IMPORTANT: DO NOT USE CHECK VALVES ON CENTRIFUGAL PUMPS NOT SPECIFICALLY DESIGNED FOR THEM)

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 and fuses should ALWAYS be sized based on manufacturer recommendations..

Manual Pump = Henderson/Whale etc. with no check valve just a strainer & the handle physically and always within reach on a tether.

Check valves on centrifugal pumps, 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 long ago and continue to do so today.

Below is an actual correspondence from a bilge pump maker senior engineer, regarding a customer of mine who had a check valve built into a centrifugal pump fail to open. I did not do the install, the customer did. I'd rip the check valve out of that brand of pump in a millisecond and as the first thing I'd do when I opened the box. This little 1 cent check valve cost one of my customers $1800.00 in batteries and over $12,000.00 in repair damages! Over 14k in damages cause by a flap of rubber that should have never even been there. I have far too many stories that repeat this similar or same scenario and many that go far beyond, including sunk boats. As far as I know my customer, an attorney, had some fun with this one, bad news for the bilge pump maker...

"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."


Wow 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 failing to place a warning in the pump manual about this danger? 

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.

Frustratingly far too many owners will not listen to sound advice on bilge pumping systems nor spend the money to design a proper pumping system utilizing a nuisance water pump (diaphragm) and an emergency dewatering pump or two (centrifugal), and a manual pump. A proper bilge pump system design and installation solves the issue of "hose drain-back" and creates a highly reliable system with significantly less potential for corrosion.

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 this because they stop 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 cheap 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 poorly designed and far too often unsafely installed. The damage numbers resulting from this sloppy work are insanely high. Check valves, poor system design, filthy bilges I'd not even let Kim Jong Un touch, DC corrosion, improperly laid out hose runs, poor hose choices, under sized wire, incorrect fusing, incorrectly made terminations, backwards DC 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.
     

Oh and yes an in-depth article on bilge pumping systems is nearing the top of my to-do list for www.MarineHowTo.com

[rmbrown]

Mainesail...  i'm looking forward to it!

[scgunner]

Jon,

A centrifugal pump does require priming to function. If the pump is sitting in water(bilge)that in effect creates a prime. A piston type, or positive pressure pump is an example of a pump that doesn't require a prime.

[Jon W]

You're right, good catch. These Rule centrifugal pumps "prime" due to having a flooded suction. I corrected the post above.