TWL: RE: Bilge Hose Check Valves
I don't like check valves in bilge pump hoses. It's very easy to get caught
on a simple problem that can prove disastrous. Assuming the check valve is
close to the pump, which it would be in your description, the pump starts
and pumps out against the check valve. But then the pump stops and the
check valve closes. The pump can easily overcome the backpressure of the
check valve ball, but can it overcome the backpressure of the check valve
ball, with 2 feet or 6 feet or more of water column above the check valve
holding the ball down? Often, our little Rule style pumps cannot force the
ball off the seat against this weight of water. Use a vented loop instead
and run the vented loop straight from the pump to a location above the
waterline and then out to the discharge throughull. You will still have a
back flush of water the distance of hose from the pump to the top of the
vented loop, but I think it's a better solution than a check valve.
Joe Engel
-----Original Message-----
From: John & Judy Tones [mailto:jtones@home.com]
Sent: Wednesday, August 09, 2000 3:59 PM
To: Trawler World
Subject: TWL: Bilge Hose Check Valves
While I agree with the principle behind not having check valves in your
bilge pump discharge lines, at times they are very valuable.
<SNIP>
Don't understand the difference, Joe. The water column weight against the pump
is the same with or without the check valve. The check valve ball should add
very little to the pump load unless it sticks.
But apparently you are saying they aren't independent as I describe it -- that
instead the ball in the valve is harder to open when there's a column of water
on it than the water itself would "weigh". ?? Does it stick against its seat or
something? Seems it shouldn't work against you this way.
I know check valves are generally condemned, but I like a proper check valve
installation. I had to install one in a bilge pump line once because of the way
the boat was built. It was a 1 1/2" gate flapper, not a ball valve. I had no
problems with its pumping, which used one of the biggest of the Rule pumps, as
it made the water disappear (past the check valve) in my tests so fast I
couldn't believe it.
I think a bigger pump with a check valve will always be the better choice, and
the combination is a winner.
--
Regards --- Don Dement
M/V Merrymar -- DeFever 48 -- Annapolis
Joe Engel wrote:
I don't like check valves in bilge pump hoses. It's very easy to get caught
on a simple problem that can prove disastrous. Assuming the check valve is
close to the pump, which it would be in your description, the pump starts
and pumps out against the check valve. But then the pump stops and the
check valve closes. The pump can easily overcome the backpressure of the
check valve ball, but can it overcome the backpressure of the check valve
ball, with 2 feet or 6 feet or more of water column above the check valve
holding the ball down? Often, our little Rule style pumps cannot force the
ball off the seat against this weight of water. Use a vented loop instead
and run the vented loop straight from the pump to a location above the
waterline and then out to the discharge throughull. You will still have a
back flush of water the distance of hose from the pump to the top of the
vented loop, but I think it's a better solution than a check valve.
Joe Engel
Maybe I have missed something regarding vented loops but every one that I
have seen was ABOVE the water line. In our case that would mean that there
would essentially be no change in what was there originally, before I
installed the check valve. It is about 4 feet from the level of the pump to
the waterline with about 6 feet of hose so how can a vented loop help reduce
the back flow.
The pump in this case is a little Rule 500 GPH and it has been doing a great
job for just over two years now, with the check valve. Before the valve I
burnt a Rule 500 GPH pump out in about two months due to the almost constant
running / cycling during my leakage problems.
Just so you don't think that I am relying on a "little biddy" pump to keep
us afloat the following is a bilge pump list as installed on Penta;
a) bilge sump Rule 500 GPH with float type switch (and check
valve)
b) bilge - mid vessel Rule 3700 GPH with float type switch and NO
check valve
c) bilge - forward Rule 3700 GPH with electronic water sensor
with check valve
d) back-up #1 Jabsco power take-off 62 GPM / 1-1/4" "Y'ed"
to [c] The nature of this pump eliminates the need for a valve.
e) back-up #2 good old manual "pump like hell" 1-1/2"
It probably seems as though my boat is nothing but thru-hull fittings but
since I did the conversion from its fish boat set-up I actually removed and
filled 3 thru-hulls. In her original set-up I believe that the existing
power take-off pump was actually set up as a wash down pump and there was a
second one (another 1-1/4") plumbed into the same 2-1/2" thru hull on the
intake sides, probably also for wash down use.
I hope that you can see where I am coming from Joe, not arguing but just a
trifle confused. I have a system that is working great for my situation but
I would like to understand more about "vented loops".
Cheers
John Tones
Sidney, BC
MV Penta