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Old 30-05-2012, 12:25   #1
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double / piggyback circulation pump?

Does anyone out there have on their engine, or have experience with, a double water circulation pump?
I have a keel-cooled Volvo MD 17. The original pump was a simple raw water impeller pump. (Johnson AB F4B 10-24124-1) This pump circulates water and glycol through the engine, and out to the keel pipes for cooling.
Piggy-backed on this pump is another identical unit, which just pumps fresh water to the exhaust elbow and cutless bearing.
The shaft, which is 4 9/16" in length is worn and needs replacing, and I need new seals. None of the suppliers I have contacted know anything about this arrangement, and can't find any part numbers for it on their computers. They can't even find that shaft when I give them the Johnson number (01-45206)
Anybody have the same arrangement?
Know a supplier with the parts?

I could simply go back to a single pump for engine coolant circulation, but then what do I do about the exhaust water injection? Seems to me this function should be tied to engine speed, so a separate electrical pump would be less than ideal.
Do I have the only marine engine with a double water pump?
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Old 30-05-2012, 12:37   #2
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Re: double / piggyback circulation pump?

I've seen them, been a while though. Wierd they cant reference it with the number....
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Old 30-05-2012, 12:41   #3
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Re: double / piggyback circulation pump?

This is what the beast looks like:
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Old 30-05-2012, 12:45   #4
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Re: double / piggyback circulation pump?

I have never really liked the arrangement (wicked fun trying to check/replace the inner impeller in the bowels of the engine room!) - but it has worked well for almost thirty years.

There are lots of other keel-cooled boats out there - how is the exhaust water injection handled on yours?
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Old 30-05-2012, 12:51   #5
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Re: double / piggyback circulation pump?

I'm thinking... why doesnt the engine fresh water pump circulate thru the keel cooler, and one impeller pump cool the exhaust with raw water...?
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Old 30-05-2012, 13:05   #6
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Re: double / piggyback circulation pump?

Thanks, Cheechako. Hope I am not missing your point, but the main engine water pump is the first of the two impeller pumps, and it does indeed circulate the water/antifreeze mix through the engine block and the keel cooler. It cannot, of course, also pump raw water to the exhaust, so they added a piggy-back pump on top of the first pump, to accomplish that task.

I know I am a bit thick at times, but I really can't see any other way of doing this, yet the marine suppliers say they have never heard of such a thing!
So how do others solve this problem?
No other keel-coolers out there?
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Old 30-05-2012, 13:10   #7
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Re: double / piggyback circulation pump?

OK, so that engine has no cast iron centrifugal pump like most engines have I guess. Wierd. Is there a spot on the front of the engine where a plate is bolted on... where a normal FW pump might be added? Not familiar with that engine... maybe most were just raw cooled thru the engine and out the exhaust like my old MD2B was.... so the only way to fresh cool was to add the double pump. You may have to have a machinist make a new shaft... arghhh

OK.... I googled a pic of your engine. It loks alot like my old MD2B. Yeah no facility for a FW pump. I also found a Forum for your engine... didnt save it though. If you Google it , maybe someone there can help with the double pump... Is your pump just mounted on a bracket? possible to work out a two pump arrangement?
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Old 30-05-2012, 13:30   #8
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Re: double / piggyback circulation pump?

That is correct - no cast iron centrifugal water pump. The original engines, MD 17 C & D, used the impeller pump driven directly off the engine. I'm sure many, if not most, were raw water cooled, so the one pump did everything.

With the advantages of indirect cooling came the disadvantage of requiring a second pump for raw water to cool the exhaust.

If nobody is making shafts for this double pump anymore, there must be an alternative solution. If I use a separate pump to deliver water to the exhaust, how do I regulate it so that it does not deliver too much water at idle, yet not enough at cruising rpm's?
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Old 30-05-2012, 13:38   #9
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Re: double / piggyback circulation pump?

well.... if it was also a bronze impellor driven by the belt or a second belt that would be automatic. Or you could go the electric on the keeel cooler side. We built a number of diesel boats with large keel coolers. One requirement was that it had to be able to be run on the trailer for 15 minutes out of water. We came up with a hose driven spray system, but discovered that we could run without it for a long time and the engine didnt heat up! Must have overdesigned the keel cooler! Is yours just a pipe or or a real cupro nickel keel cooler...? If I had to choose, I'd rather have the keel cooler pump go bad than the exhaust pump. (fire danger) I think the best is the two bronze/ two belt solution. One pump might not even have to be engine mounted. I had a friend who had his refrigeration pump attached to the hull and it worked fine. Belt doesnt have to be very tight at all to run one of those bronze impellor pumps.... Dont you love redesigning things that have worked great in the past! Askif you can locate a pump on a Volvo or diesel engine forum..... some old mechainc has one laying on a shelf somewhere....
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Old 30-05-2012, 14:44   #10
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Re: double / piggyback circulation pump?

Keel cooler is just a single "pipe" (1" angle iron), one running down each side of the keel. When I first got the boat I thought that didn't look like enough cooling surface area, but it has worked just great for thirty years!

I'd rather not go to the belt-driven solution in this case. Thinking of following up on your suggestion of using the single original pump, but for the engine cooling function. Then use a separate electrical pump to squirt water into the exhaust. This pump could be manually regulated, and I would have to figure out what speed is necessary to provide adequate quantities of water to the exhaust at the various speeds. I should add an exhaust temperature warning horn anyway.
Thanks for the input!
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Old 30-05-2012, 14:46   #11
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Re: double / piggyback circulation pump?

Hey! I just got three stars!

Am I now a somebody?
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Old 30-05-2012, 14:53   #12
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Re: double / piggyback circulation pump?

Take the shaft to a machine shop and have one made.
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Old 30-05-2012, 15:05   #13
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Re: double / piggyback circulation pump?

Always an option, but I am guessing, in my neck of the woods, it would be cheaper to buy an entire new pump!
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Old 30-05-2012, 18:43   #14
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Re: double / piggyback circulation pump?

Quote:
Originally Posted by nitpik View Post
Keel cooler is just a single "pipe" (1" angle iron), one running down each side of the keel. When I first got the boat I thought that didn't look like enough cooling surface area, but it has worked just great for thirty years!

I'd rather not go to the belt-driven solution in this case. Thinking of following up on your suggestion of using the single original pump, but for the engine cooling function. Then use a separate electrical pump to squirt water into the exhaust. This pump could be manually regulated, and I would have to figure out what speed is necessary to provide adequate quantities of water to the exhaust at the various speeds. I should add an exhaust temperature warning horn anyway.
Thanks for the input!
The advantage of going the other way around then what you state is you wont burn up your exhaust and/or boat AND it self regulates the amount of flow to engine speed.
You could sketch the shaft if you get it out and send for prices. it's small enough to mail for sure..... Maybe Johnson pump would be wiling to give you the drawing... LOL! It's probably what... a 3/8 dia shaft with a couple of flats and snap ring grooves in it? I t also could be electroplated and reground to repair worn grooves....
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Old 31-05-2012, 14:27   #15
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Re: double / piggyback circulation pump?

Using an electrical pump is doable but controlling it to supply the needed water at differing rpms adds a whole new layer of complications. Adding an additional mechanically driven pump won't be cheap when you factor in the price of the pump, sheave, belt and whatever else you need to hook it up. As was said by Cheechako the shaft is probably a stock size and would need minimal machining to get you going. How far are you from Sudbury or the Sault?. I would think there would be no shortage of machine shops in either location.
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