Heat 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

On Thu, 28 Oct 2004 16:55:23 -0700, engsol
wrote:

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.

"engsol" wrote in message
...
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

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.

--


Keith
__
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?
"engsol" wrote in message
...
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

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

On Fri, 29 Oct 2004 06:47:24 -0500, "Keith" wrote:

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.

Rod, thanks for the input. Those are the factors I was looking for.
See my reponses below.
NormB

On Thu, 28 Oct 2004 18:37:09 -0700, "rmcinnis" wrote:


"engsol" wrote in message
.. .
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.

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

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"


"engsol" wrote in message
...
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