Date: Sun, 05 May 1996 18:17:13 -0700
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: jwakefield@4dmg.net (john wakefield)
Subject: Re: 83 Sink's 12V water pump
First of all, I want to say thanks to Jim of BusBoys@aol.com for his very
instructive discussion of sink water pumps, their history. and current
pricing.
Now I'd like to hear a few words about the trade-offs beyond price between
the immersible water pump (V@L members' price $44.96US) and the
outside-the-tank pump (V@L member's price $35.96US).
Clearly the immersible pump is self priming. Is the outside-the-tank pump
also a self primer?
How about comparing flow rates and your best guess as to which is likely to
have a better life expectancy.
Water getting where it's not intended is another issue. With my old
immersible pump, it got up into the pump motor, even though it's
surrounding case is designed to trap air in its top to keep it dry. I urge
those servicing these immersible pumps to make certain its bottom stays down
and its top stays up, and don't let it lay on its side at your tank's bottom
or you'll allow water to flood the entraped air space where the motor hides
behind an attempt at sealing the rotating shaft. Don't turn it upside down
while it's wet. I could hear water sloshing inside the "sealed" motor
compartment. I remember my "BAR Maid" brand submergible glass washers that
cleaned beer and mixed drink glasses. Their motors ran in an inverted sealed
oil chamber like this. True, the drive shaft seals were good, but the elegant
design feature was the fact that the density of the oil was less than the
surrounding water, so they never got wet and they never introduced a drop of
oil into the "beer clean" (and that's damned clean) water. The speed would
drop, but you'd get tired waiting to wear out one so modified IMO. Also, the
pick-up leading to the impeller must be at the bottom to pump the last
available water from the tank. On the other hand, the immersible pump can't
leak outside because it's inside the tank.
I haven't seen the outside-the-tank style pump nor do I know if it's
identically fead from the tank top. Does it have a "dry on one side wet on
the other" water seal between the motor and pump that's subject to leaking, or
is it a diaphram and check valve design? That's what my Blue Bird Wanderlodge
bus has, and they're supposed to be quite free from leaking problems.
At this point, my options are open and unless I find a good high/low speed
pump, I'll probably go with which ever seems the best, but I still need more
information to decide which I think is best. Thanks for any responses.
John Wakefield
|