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Boat Forum / Cruising / October 2004Heat exchanger-pump, or pump-heat exchanger
While sitting on my (new to me) boat yesterday, trying to figure out how and where to mount a sea water strainer, it occured to me that the hose routing would be a lot cleaner if I connected stuff like this: Intake-strainer-exchanger-pump-exhaust Any problems I'm overlooking with this arrangement? Also, I noticed the heat exchanger zinc (pencil) is mounted on the bottom. This means that whenever I check the zinc, I'm going to have water in the bilge. Any reason I can't have a new zinc nut welded to the top? Oh, it's a horizontal heat exchanger. Thanks, NormB >Intake-strainer-exchanger-pump-exhaust > >Any problems I'm overlooking with this arrangement? ======================================== I believe these pumps can push more water through a restriction than they can pull. > Intake-strainer-exchanger-pump-exhaust > > Any problems I'm overlooking with this arrangement? Two problems. 1) Usually, the raw water pump is mounted low on the engine which keeps the "head" that it has to prime against to a minimum. In many boats the water pump could actually be below water line which will assure that the pump will prime. If you have to pull the water to the top of the heat exchanger it will mean that the pump has to be capable of drawing water several feet higher before it primes. If the system has been totally drained, either from a small leak or perhaps you removed a hose or similar maintenance item then the amount of dry running the pump will need to do before it gets wet will increase dramatically. 2) Even once the system does prime it is likely that it will produce far less "vacuum" then it will pressure. You might experience a drastic drop in flow rate doing it this way. Rod McInnis Rod, thanks for the input. Those are the factors I was looking for. See my reponses below. NormB >> Intake-strainer-exchanger-pump-exhaust >> [quoted text clipped - 8 lines] >will mean that the pump has to be capable of drawing water several feet >higher before it primes. Actually, the strainer and heat exchanger will be just about the same level, (relative to the waterline) as the pump. In a Yankee 30, the engine is mounted amidship almost in the bilge, i.e., very low. Next to the engine (outboard) is a compartment, or box, which forms the forward dinette seat. The top of the engine and the seat are almost exactly the same. My plan was/is to mount the strainer and exchanger under the dinette seat, so that the hose runs would be pretty much level. The whole works would then be about 12" above the sea water intake. >If the system has been totally drained, either from a small leak or perhaps >you removed a hose or similar maintenance item then the amount of dry >running the pump will need to do before it gets wet will increase >dramatically. Very good point...not only would the strainer have to be filled before the pump saw water, but the exchanger would also have to be filled as well. >2) Even once the system does prime it is likely that it will produce far >less "vacuum" then it will pressure. You might experience a drastic drop in >flow rate doing it this way. Another good point. >Rod McInnis I would put the pump before the heat exchanger. Can you just rotate the exchanger so the zinc port is on the top? The water inlet/outlet should face up anyway, so that the cooling water keeps the exchanger full.  SignatureKeith __ Why is it that if you tell someone there are 6.3 trillion stars in the universe they will believe it, but if you tell them that your teak has wet varnish they have to touch it? > While sitting on my (new to me) boat yesterday, trying to figure out how > and where to mount a sea water strainer, it occured to me that the hose [quoted text clipped - 11 lines] > Thanks, > NormB Keith, The heat exchanger I have is designed to be mounted horizontally, with the expansion tank (and radiator cap) on top. So rotating it is out. Thanks for the response...good idea. NormB >I would put the pump before the heat exchanger. Can you just rotate the >exchanger so the zinc port is on the top? The water inlet/outlet should face >up anyway, so that the cooling water keeps the exchanger full. Heat exchanger zinc location: Yes, with the zinc collar located on the bottom of the exchanger, you'll drip some water out every time you change zincs. That's a nuisance, but there's a good reason for this geometry: as the zinc erodes, it often sloughs off pieces bit and pieces of electrolyzed zinc, and when you install a new one, these pieces will likely be washed out of the exchanger with the draining water. If you rotate the exchanger, so you install the zinc from the top, the eroded pieces will fall to the bottom--and stay there forever. The inconvenience of dripping water is far outweighed by the scavenging of the waste zinc. I suggest you stick with your current setup. Dick Behan LNVT "Annie" > While sitting on my (new to me) boat yesterday, trying to figure out how > and where to mount a sea water strainer, it occured to me that the hose [quoted text clipped - 11 lines] > Thanks, > NormB |
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