Bilge pump behavior

Bilge pump behavior

Post by Bob Berm » Thu, 09 Jun 1994 02:13:13


Whenever my bilge pumps run, they do a fine job of pumping
out nearly all the water in the bilge, however when they
shut off, some residual water drains back into the bilge from
the drain hose. This little bit of water is enough to trigger
the pump on again and this cycling continues forever. Does
anyone have any suggestions on how to break this cyclic behavior?
Is this normal operating procedure? It's my understanding that
check valves in bilge outlet lines are not a good idea, so I'd
like to avoid that route, if possible.

One pump is float controlled and one is electronic, both are
relatively new, but neither one seems to know when to quit.

Thanks for any suggestions!!

 
 
 

Bilge pump behavior

Post by dudl » Thu, 09 Jun 1994 08:54:10


->Is this normal operating procedure? It's my understanding that
->check valves in bilge outlet lines are not a good idea, so I'd
->like to avoid that route, if possible.

Why are they a bad idea?  I had a similar problem which I solved by
installing an in-line check valve near the pump.  It fixed the problem
and I had the added security knowing that water wouldn't be able to siphon
back into the bilge.

dudley
.

 
 
 

Bilge pump behavior

Post by Robert Hanne » Thu, 09 Jun 1994 21:39:36


Quote:

>man) writes:
>->Is this normal operating procedure? It's my understanding that
>->check valves in bilge outlet lines are not a good idea, so I'd
>->like to avoid that route, if possible.

>Why are they a bad idea?  I had a similar problem which I solved by
>installing an in-line check valve near the pump.  It fixed the problem
>and I had the added security knowing that water wouldn't be able to siphon
>back into the bilge.

That would be my first choice.  Alternatively, as appropriate, smaller/shorter
hoses (thru-hull closer to bilge) or a larger-travel float.  If the
float is a rotating float (mercury switch), I've glued a long, sealed,
hollow plastic cylinder on the float to slow the rotation to water height.

-- Bob

 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        Robert J. Hanners                          Carderock Division

        -the dry dB game-                          Annapolis, Maryland

 
 
 

Bilge pump behavior

Post by use.. » Thu, 09 Jun 1994 21:17:50

Quote:

>Whenever my bilge pumps run, they do a fine job of pumping
>out nearly all the water in the bilge, however when they
>shut off, some residual water drains back into the bilge from
>the drain hose. This little bit of water is enough to trigger
>the pump on again and this cycling continues forever. Does
>anyone have any suggestions on how to break this cyclic behavior?
>Is this normal operating procedure? It's my understanding that
>check valves in bilge outlet lines are not a good idea, so I'd
>like to avoid that route, if possible.

>One pump is float controlled and one is electronic, both are
>relatively new, but neither one seems to know when to quit.

>Thanks for any suggestions!!

The problem is the water draining back from the hoses, so the
solution (aside from a check valve) is to arrange the hoses so that
less water stays in them.  One way is to shorten them, another is
to have an initial rise, then a long drop to the discharge point.
A third way is to use smaller diameter hoses.  Might work to put
small hose on one pump, so that it keeps the water down, and if
anything happens that it can't keep up with the incoming water, the
second pump takes over.

In a few cases, the problem is caused by the switch being too close
to the pump, so that the initial wave from the returning water
triggers the cycle.  However, if much water is staying in your bilge,
then you may have a greater likelyhood of blisters.

Good luck,
Mike Laing

 
 
 

Bilge pump behavior

Post by Greg Bullou » Thu, 09 Jun 1994 22:51:47

Quote:

>Whenever my bilge pumps run, they do a fine job of pumping
>out nearly all the water in the bilge, however when they
>shut off, some residual water drains back into the bilge from
>the drain hose. This little bit of water is enough to trigger
>the pump on again and this cycling continues forever. Does
>anyone have any suggestions on how to break this cyclic behavior?
>Is this normal operating procedure? It's my understanding that
>check valves in bilge outlet lines are not a good idea, so I'd
>like to avoid that route, if possible.

>One pump is float controlled and one is electronic, both are
>relatively new, but neither one seems to know when to quit.

The fact is, that they are triggered by the amount of water in
the bilge, and it isn't the pump's fault, but the plumbing.

One solution is to use a separate switch which is placed higher
in the bilge than the amount of water which drains back through
the hose fills the bilge.

Another possibility is to minimize the amount of back-flow by
running the hose up above the level of the outlet as vertically
as possible, so that the volume of water which can flow back
is minimized... ...that is, when the outflow reaches its
highest level, it will run downhill and out the discharge.

If you do this, you MUST ensure that the outflow is above the
water-line at all times, other wise you could, conceivably,
start a siphon when the pump shuts off, thus refilling the boat :-(

So instead of this:

                                                  O
                                                 //
-------------LWL--------------------------------//--------
                                               //
                                              //
                                             //
                      //=====================/
                     //
         |------|   //
         | Pump |  //
         |------|==

Try:

                   ||=
                   || ============\\
                   ||              ===========o
----------LWL------||---------------------------------------------
                   ||
                   ||
                   ||
                   ||
                   ||
         |------|  ||
         | Pump |  ||
         |------|==||

Now, instead of containing the amount of water from end-to-end,
the line will likely only contain the amount of the vertical
portion (in practice, some MAY siphon back from the down-hill
section when the pump goes off, but probably not enough to
cause a problem. Unless your bilge sump is very small. Or
the result, if the down-hill portion is just right, might be
that the existing flow keeps a siphon running in the desired
direction!).

By the way, your pump will work better as a bonus, because the
sheer weight of the column of water it is lifting will be smaller
and, once it turns the corner, gravity, and perhaps some resulting
siphon action, will be helping the pump to do its job.

Also, if the discharge DOES get immersed, the loop will make it
necessary for a siphon to start, rather than a simple down-hill
flow, in order to back-fill the boat.

If you really want to be first-rate, you could install a siphon-
breaker loop (vented loop) on the outflow, but perhaps that is
over-kill.

Greg

 
 
 

Bilge pump behavior

Post by Greg Bullou » Thu, 09 Jun 1994 22:55:39

Quote:


>->Is this normal operating procedure? It's my understanding that
>->check valves in bilge outlet lines are not a good idea, so I'd
>->like to avoid that route, if possible.

>Why are they a bad idea?  I had a similar problem which I solved by
>installing an in-line check valve near the pump.  It fixed the problem
>and I had the added security knowing that water wouldn't be able to siphon
>back into the bilge.

Some  people recommend against them because it is one more place
for debris to get stuck and block the line at a critical moment,
and because a system which depends on one is apt to fail catastrophically
by virtue of a little piece of gunk that is too small to block the
line blocking the valve open.

Non-return valves shouldn't be depended upon to prevent siphoning, and
shouldn't be applied where they are subject to sticking and/or where
sticking would result in disaster.

Greg

 
 
 

Bilge pump behavior

Post by Rod Mc Inn » Fri, 10 Jun 1994 01:37:53

Quote:

>Whenever my bilge pumps run, they do a fine job of pumping
>out nearly all the water in the bilge, however when they
>shut off, some residual water drains back into the bilge from
>the drain hose. This little bit of water is enough to trigger
>the pump on again and this cycling continues forever. Does
>anyone have any suggestions on how to break this cyclic behavior?
>Is this normal operating procedure? It's my understanding that
>check valves in bilge outlet lines are not a good idea, so I'd
>like to avoid that route, if possible.

>One pump is float controlled and one is electronic, both are
>relatively new, but neither one seems to know when to quit.

>Thanks for any suggestions!!

  I would guess that you either have a very long hose or a very small
resevoir (depression) where the bilge pump sits.  For the amount of
water that is contained in the hose to raise the water level enough to
trigger the switch seems a bit unusual.

  As other posters have indicated, a check valve is not all that bad
of an idea.  Just be sure that you have a redundant system (a second
bilge pump) because the check valve will add one more place for the
system to clog.

  If you use a check valve, be sure that it is one made for bilge
pumps and not fresh water systems.  The fresh water valves have far
too much pressure drop across them for use in a bilge pump line.

  You may also wish to consider changing the float switch to one that
has a bit more 'hysterisis'. That means that the water level has to
get a bit higher before it turns on, then it has to pump it down a bit
lower to before it turns off.  This will prevent the amount of water
in the hose from raising the water level up to the switch point.

  You can also buy electronic pump extenders that will continue to run
the pump for a few seconds after the float switch shuts off.  These
will allow additional water to be pumped out, which will also prevent
the water in the hose from raising the water level to the switch on
point.

                Rod McInnis

 
 
 

Bilge pump behavior

Post by Peter D. Enge » Fri, 10 Jun 1994 02:42:18


Quote:


> ->Is this normal operating procedure? It's my understanding that
> ->check valves in bilge outlet lines are not a good idea, so I'd
> ->like to avoid that route, if possible.

> Why are they a bad idea?  I had a similar problem which I solved by
> installing an in-line check valve near the pump.  

Check valves are generally frowned upon in bilge pump lines because
1.  They cannot be relied upon to prevent back-siphoning, as they are
easily jammed open by debris from the bilge.
2.  They are a ***point, as the orifice size is usually smaller that the
hose diameter, thus limiting the volume of water that the pump can remove
in a given amount of time.

When back-siphoning after the pump turns off results in so much water that
the pump turns on again, the cure is to re-think how the hose runs from the
pump.  What you need is a shorter hose, of the same diameter.  Perhaps
there is a loop in the hose, or it is longer than necessary.  Perhaps
either the pump or the outlet point could be relocated to shorten the hose.
 Also, there are automatic turn-on switches which can be adjusted to
increase the hysteresis of the pump, so that the depth in the bilge at
which the pump turns on is always greater than that after the pump is off,
and all the hose has drained back into the bilge.

Pete

 
 
 

Bilge pump behavior

Post by Dave Kinz » Fri, 10 Jun 1994 01:25:35

[Bilge pumps cycle]

There is too much water running back for the size of the sump.  Given
that you do not want to change the sump size, you need to reduce the
water running back (shorter runs or a siphon break) or increase the
hysteresis of the bilge switch (longer float, different brand, whatever.)
Changing the switch is not possible for your electronic pump.

-dave

 
 
 

Bilge pump behavior

Post by Dave Kinz » Fri, 10 Jun 1994 01:33:41

[check valves in bilge pump exit line]

Quote:
>Why are they a bad idea?  

  Depends on the pump type.  Assuming a centrifugal pump (the most common)
any restriction in the line will severely reduce the capacity of the
pump.  These get their high rating by being able to pump large volumes
of water at very low pressure.  Any restriction (even an elbow fitting) in
the line will cause this to occur.  You might not notice that this is a
problem if you are only worried about the occasional drip from the
cutlass bearing, but if you have a through hull fail, it will get
your attention in a hurry.

-dave

 
 
 

Bilge pump behavior

Post by Rick Emers » Fri, 10 Jun 1994 07:16:00


RB> Newsgroup: rec.boats

RB> Organization: J. P. Morgan & Co.
RB>
RB> Whenever my bilge pumps run, they do a fine job of pumping
RB> out nearly all the water in the bilge, however when they
RB> shut off, some residual water drains back into the bilge from
RB> the drain hose. This little bit of water is enough to trigger
RB> the pump on again and this cycling continues forever. Does
RB> anyone have any suggestions on how to break this cyclic behavior?
RB> Is this normal operating procedure? It's my understanding that
RB> check valves in bilge outlet lines are not a good idea, so I'd
RB> like to avoid that route, if possible.
RB>
RB> One pump is float controlled and one is electronic, both are
RB> relatively new, but neither one seems to know when to quit.
RB>
RB> Thanks for any suggestions!!

This is going to sound like a flip answer but, seriously, move the
float switches.  You can also try installing a flapper valve to
prevent the water from returning but any restriction in a bilge pump
discharge line is Not Good.  Also, maybe a shorter hose run, if
possible will return less water and reduce the load on the pumps.

Rick

...
 * ATP/Linux 1.42 * That was then, this is now.

 
 
 

Bilge pump behavior

Post by Rick Emers » Fri, 10 Jun 1994 07:16:00


DU> Newsgroup: rec.boats

DU> Organization: Sun Microsystems, Inc.
DU>

Quote:
DU> Berman) writes:

DU> ->Is this normal operating procedure? It's my understanding that
DU> ->check valves in bilge outlet lines are not a good idea, so I'd
DU> ->like to avoid that route, if possible.
DU>
DU> Why are they a bad idea?  I had a similar problem which I solved by
DU> installing an in-line check valve near the pump.  It fixed the problem
DU> and I had the added security knowing that water wouldn't be able to sipho
DU> back into the bilge.
DU>
DU> dudley

The object of the exercise is to remove water as fast as possible.
Anything impeding the flow is going to be a problem.  Even with the
flapper out of the way, there's some loss of flow and resistance.  You
want as big a hose with the least restrictions possible to get all
that water out before the batteries short out...

Rick

...
 * ATP/Linux 1.42 * Uh, yeah...I MEANT to do that!

 
 
 

Bilge pump behavior

Post by use.. » Fri, 10 Jun 1994 20:23:00

Quote:


>DU> Newsgroup: rec.boats

>DU> Organization: Sun Microsystems, Inc.
>DU>

>DU> Berman) writes:
>DU> ->Is this normal operating procedure? It's my understanding that
>DU> ->check valves in bilge outlet lines are not a good idea, so I'd
>DU> ->like to avoid that route, if possible.
>DU>
>DU> Why are they a bad idea?  I had a similar problem which I solved by
>DU> installing an in-line check valve near the pump.  It fixed the problem
>DU> and I had the added security knowing that water wouldn't be able to sipho
>DU> back into the bilge.
>DU>
>DU> dudley

>The object of the exercise is to remove water as fast as possible.
>Anything impeding the flow is going to be a problem.  Even with the
>flapper out of the way, there's some loss of flow and resistance.  You
>want as big a hose with the least restrictions possible to get all
>that water out before the batteries short out...

>Rick

Seems like bilge pumps serve two purposes.  One, as you said, is to
move as much water as possible as quickly as possible in an emergency.
However it seems to me that most of the time there are really taking
care of the small leaks that occur (packing gland, splilled glass,
etc.) and have the task of keeping the bilge as dry as possible.
This keeps down oder, and by some accounts helps to prevent blisters.

I suspect that you will propbably never get a single pump to do both
jobs.  How about a small pump with a check valve and maybe small hose
that will keep up with the normal daily requirements.  If that pump
cannot keep up with the leaks, or clogs, then when the water level
gets a bit higher, a LARGE pump kicks in and also sounds an alarm.

Mike Laing

 
 
 

Bilge pump behavior

Post by Larry Loh Ka » Sat, 11 Jun 1994 00:35:09

Quote:

>Whenever my bilge pumps run, they do a fine job of pumping
>out nearly all the water in the bilge, however when they
>shut off, some residual water drains back into the bilge from
>the drain hose. This little bit of water is enough to trigger
>the pump on again and this cycling continues forever. Does
>anyone have any suggestions on how to break this cyclic behavior?
>Is this normal operating procedure? It's my understanding that
>check valves in bilge outlet lines are not a good idea, so I'd
>like to avoid that route, if possible.

>One pump is float controlled and one is electronic, both are
>relatively new, but neither one seems to know when to quit.

>Thanks for any suggestions!!

1. Unless you can walk on water, a check valve is not a good idea. They
can and do clog and stick closed.

2. The primary pump ( the electronic one) should go in the lowest spot in
the bilge. The secondary pump should be 3 to 6 inches higher. The primary
pump will do incidental water work, while the other pump will jump in to
help with major failures. My #2 pump has twice the capacity of my primary
one. I figure that if it ever comes on, I'm in deep trouble. You should check
the float switch routienly to make sure if works.

3. All hoses should be as short and straight as possible. The discharge port
should be high enough on the hull to stay out of the water. Having the
secondary pump higher will also cut the amount of back flow under normal
conditions in half. That alone may be enough to keep the electronic pump
from cycleing.

Larry Loh Kamp
M/B Baithog

 
 
 

Bilge pump behavior

Post by Uwe Trode - Philips Broadband Networ » Sat, 11 Jun 1994 05:13:20


Quote:


>[Bilge pumps cycle]

>There is too much water running back for the size of the sump.  Given
>that you do not want to change the sump size, you need to reduce the
>water running back (shorter runs or a siphon break) or increase the
>hysteresis of the bilge switch (longer float, different brand, whatever.)
>Changing the switch is not possible for your electronic pump.

>-dave

If the hose length is the culprit, why not run it in a loop. The
water will collect in the loop as under a sink trap and not
drain back into the bilge. Whadd'ya think?

-Uwe