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  #1  
Old 10-12-2009
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My kingdom for a good bilge pump and an honest manufacturer!

I have never posted an incendiary message anywhere, but today is the day:

Thirteen month ago I installed a new Attwood V500 bilge pump in my Southern Cross 31. Last night, while at anchor, a seeping seacock admitted enough water to trip the bilge pump at 3 a.m. The odd noise woke me, and, on investigation, I saw the pump running, but moving no water off the boat. Turns out that the pump is incapable of moving any water up the seven-foot gradient from the bottom of the bilge to the outlet of the plumbing on the topsides. Now, a Southern Cross 31 is neither big nor deep of draft (4 foot, 7 inches). I still have the instructions and the sales receipt for this pump, and the specifications state that it should move 200 GPH at a 6.7 foot head of pressure. Baloney! It moves nothing! If I had not been aboard, the pump would have run until it had killed the batteries, at which point the water level would have risen until the boat sank. I note that this specification is based upon performance at 13.6 volts for the 12 volt model. Where the **** does Attwood get 13.6 volts = 12.0 volts? Not my math class. Apparently, this is an ABYC specification. In any event, it is a moronic specification.

Having dispensed with Attwood as a manufacturer of quality equipment, I visited the local marine supply store and then Rule - ITT (at least Rule claims that their pumps are not manufactured in China - who wants to buy something as critical as a bilge pump from China?). Rule's specifications for bilge pumps are similar to Attwood's, except for the addition of this caveat: "Output is based on 10 hour break-in period and at 13.6V (12V models)". Again, the same ******** about 13.6 volts = 12.0 volts, but with the addition of nonsense about a 10 hour break-in period. In the history of the known universe, how many bilge pumps have been run for 10 hours prior to installation? Zero? Less than zero?

As a professional pilot, this is precisely the kind of crap that really scares me about the boating world. If these pumps had been installed aboard an aircraft, some engineer at the FAA would have taken a look at the specifications and said, "Nah, this is a bunch of crap. Say something meaningful." But in the free-for-all of the boating world, manufacturers can actually sell at a profit an item as critical as a bilge pump that can't actually move any water whatsoever in a real-world application. So:

1. Dump some water in your bilge and see if any water actually comes out the fitting on the topsides. I bet none does.

2. Are you aware of the make and model of a bilge pump that actually pumps bilge water overboard?
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Old 10-12-2009
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Rule pumps aren't bad... but I prefer a diaphragm type pump to an centrifugal impeller based one. The Flojet type pumps are pretty good and with the right type of float switch, quite reliable. Diaphragm pumps create far more pressure and deal with lift and running dry issues far better than do centrifugal based pumps.
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Last edited by sailingdog; 10-13-2009 at 07:32 AM.
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Old 10-12-2009
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Firstly, REMOVE ANY CHECK VALVE AND TROW IT AWAY!!! Secondly, make sure you have SMOOTH walled hose. The specs are usually for smooth hose not corrugated. Thirdly, make sure your pump will not kick on until the water is above the hose discharge level of the pump. It your float switch kicks it on below this level the pump will cavitate, suck air, and do nothing but make noise.

Centrifugal pumps are what they are, a joke, no matter who's pump you buy. If you want a real bilge pump spend the money and get a Par Max diaphragm pump.

As far as bilge pumps go I think we need to be very careful taking any centrifugal pump at face value, as many do, because items like a check valve can reduce the pumps capacity dramatically. Having two large pumps a wise idea with centrifugals!

Flow rates, as rated by bilge pump makers, can be quite misleading. They should serve only as a rough guide of a pumps "best case" capacity compared to others of similar design.

Bilge pump capacity is usually rated as “open flow” or what's called “open bucket” rate. This means the figures account for no, nada, zero vertical lift and also no discharge hose friction, radius bends, check valves or discharge outlet restriction.

Actual flow rates, under real operating conditions, can be drastically lower. Water must be lifted up and out of the bilge and then be pushed through lengths of hose to the discharge point. This resistance is called head. Head pressure is basically the weight of the water and the frictional resistance of the hose, bends, check valve and outlet.

Most centrifugal pumps, like the ones made by Attwood, Rule or Johnson Pumps, have large internal tolerances to allow the passage of bilge crap. Sadly because of this design their flow rate decreases dramatically with increases in head pressure. Unlike a vane pump, or diaphragm pump, which would be less affected by head loss, the pumps rotor or impeller does not come in direct contact with the pumps walls. Impeller/vane pumps and diaphragm pumps are less affected by head pressure than a centrifugal pump is and they may actually be more effective, and move more water, despite a lower "labeled" GPH rating. Some of the vane/impeller pumps can handle 60+ feet of head pressure with ease. Because of the large tolerances in centrifugal pumps it can lead to, and create, cavitation if the head pressure is extreme enough like in the case of a check valve.

I'm sure many of us have seen the bilge pump kick on and then not actually suck any water but instead just create noise and bubbles in the bilge. This can usually be eliminated by removing those ridiculous head boosting check valves and the crappy corrugated bilge hose and replacing it with smooth walled hose..

The output of many centrifugal bilge pumps can diminish by as much as half with only a few feet of head and can stop entirely at between 13 and 20 feet, depending on the size of the bilge pump. Remember head is not just the peak height/lift of the hose it is the friction, height, bends and fitting restrictions all added together.

Another serious consideration is voltage. What is your pump rated at? Is it 13.6, 14.2 volts or 12 volts. This will and can make a difference as the pumps motor increases and decreases output based on voltage.

There have been a few tests like the ones conducted by West Marine. They rated pumps based on voltage and head pressure. Most manufacturers ratings (open bucket / no head ratings) were off between 10-50%. the output on average was reduce by about
5% for every foot of head pressure. With voltage the drops from 13.6 volts to 12.2 volts were another 15-30% off on top of the head pressure loss. So your 800 GPH centrifugal pump may not even deliver 1/3 of that rating in a real word situation and these numbers are still without a check valve..

I guess what I'm getting at is this; unless you have a "monster truck" grade bilge system, do not count on anywhere near the face value rated capacity from your bilge pump and please, what ever you do, remove that check valve..

Some other things to consider:

- Use smooth walled discharge hose as it has significantly less head resistance than does corrugated.

- If the discharge outlet is close to the waterline you must use a high loop in the discharge hose to prevent siphoning. It is advised to add a siphon break at the highest point to ensure it won't back siphon. Even with a high loop a bilge pump can still siphon without a siphon break. I have been on more than one boat that self siphoned when under sail and power.

- Do not succumb to the temptation of using a "check valve" with a centrifugal pump. If you have 5' of height, in a 1" hose, the pump will most likely cavitate before it can throw open that check valve with that standing water behind it..
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Last edited by Maine Sail; 10-12-2009 at 08:04 PM.
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Jabsco Diaphragm pump

I have a Jabsco Diaphragm pump and it pumps out the bilge just fine, my lift is around 4 feet. I also have been told to use the smooth walled hoses, even though they spec the reinforced hoses for the bilge.

cheers
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Old 10-12-2009
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Attwood V500 bilge pump is no longer available. I found some for sale on the web for as low as $10. Apparently this pump sucks in all the wrong ways.
I installed a Rule pump in our bilge this past spring and have been quite happy with it. Our head to outlet is about 4'. Many models to choose from.
I don't think any product in the marine industry would stand up to FAA standards, except, perhaps the toilet paper.
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Old 10-12-2009
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Maine Sail is right. 10000% right. The PO on my boat had a check valve and it killed the batteries trying to move 2" of water uphill 24". I ripped it off, installed a vented loop and have been good ever since. Your problem sounds very much like what I had. Took me a while to figure it out because it's not intuitive. The pump LOOKS so powerful (2500GPH), but these pumps can move lots of water but are NOT powerful enough to push uphill.

Use a loop. Toss the checkvalve.

I'm betting that's your problem.
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Old 10-12-2009
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I also agree with Maine Sail.
CapnRon - you can buy reinforced hose that is only corrugated on the outside and has a smooth wall inside.
wnor - Where should your bilge pump be made if you live and sail in China?
Brian
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Old 10-13-2009
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I have 2 electric bilge pumps, both Rule, both 1000gph (I think), both centrifugal and both work a treat. The only down side for me is that the centrifugal pumps always let some water back down the pipe when they are switched off so the bilge is never totally empty.

The plus is that when the shockingly bad level switches available (EVERY ONE OF THEM) leave the pump running and they will, the pump rarely gets damaged. I have had one of my pumps running possibly for a whole week (luckily I was on shore power then ) and it was moderately warm but still works today, a year later.

I also have two smaller centrifugal pumps running in my shower sumps to evaucate the water from the shower stalls. They have always work without a murmur and I have no idea how old any of the above pumps are.

So once again, if you have the bucks for top-of-the-range pumps, go for it. But if you don't, don't feel bad, the affordable ones work too.
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Old 10-13-2009
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I love the judgment of Chinese products. So base and emotional! More more! More dramatic hatred!
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Old 10-13-2009
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The other problem with check valves, especially in a bilge pump line, is that if there is water sitting in the line, which is often the case, the pressure from the water column in the hose can prevent the check valve from operating properly.

The reason many use check valves with centrifugal pumps is the back flow that happens when the pump shuts down. This generally doesn't happen with a diaphragm pump setup.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
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