Bilge Pump Cycling

[Mark Elkin]

I've noticed my bilge pump cycling on and off regularly -- sometimes.  A little investigation showed that this happens when the bilge has filled enough for the float switch to start the pump.  The water level then drops and the pump turns off.  What happens next is the real cause -- the water in the pump's exhaust hose drains back into the bilge and that re-triggers the float switch.  And the whole cycle starts all over.

I traced the hose from the pump.  The next stop is the manual bilge pump behind the cockpit, and then down the drain hose to the thru-hull at the bottom of the transom.  Apparently, there is nothing to prevent the water in the hose between the automatic and manual pumps from flowing back down and refilling the bilge.  Does anyone else have this problem?

I'm considering adding a check valve in the hose, but an article in Sail magazine a couple months ago suggested that anything that even partly obstructs the bilge pump output is a bad thing.  What do you other C34 owners think?

FYI, my temporary solution is to get into the bilge with a big sponge and a bucket and remove the excess water.  But the water eventually returns -- however, that is another subject.

Mark

[This message was edited by Yorkshire Rose on June 07, 2001 at 10:07 AM.]

[bobdl2]

I solved this problem by placing a check valve in the bilge pump hose.  It is an inexpensive check valve from Home Depot which may need to be replaced every other year as the spring will eventually rust, so the valve does not close.

[dave davis]

I had the same problem a few years ago and I tried two different check valves. One was a cheepy plastic thing and the other was a top line bronze $. Both did not work because the water in the hose had too much of a head presure aginst the spring in the valve keeping it closed. Another way of looking at it was the bilge pump did not have enough power to overcome the pressure of the water in the hose. I also made things worst because I put a riser loop in the aft lazorat(sp) because I was getting water siphoning back from the following sea. This adds to the height of the water and adds head pressure.
I did the same as you, I sponged out the bilge and made a nise cozy home for a family of spiders in the nice dry summers we have in San Francisco. But they take off during the rainy season because I get water comming down inside my mast. I'm looking forward to your respones to see if there is another answer out there. It just occured to me that a bigger stonger bilge pump$ might solve the problem. Raising the float valve will prevent it from cycleing on and off, but will not get you any lovely spiders. I miss my Spell Check...I should have written this in my Words Program and pasted it to this MB.
Good luck!

[jentine]

Change the float switch.  Over time it has become too sensitive.  It should not come on with so little water in the bilge.

[msenko]

I have successfully installed check valves in bilge pump hoses in some pretty deep bilges, much deeper than what is found in Cat 34's regardless of vented loops. On my previous installations, I would guess the "head" would be 7 to 8 feet, and a ribbed hose which isn't all that great for flow. The valve I used was a plastic one commonly found at the nearest marine supply store.

Perhaps the pump you are using is rather small for the job and doesn't have enough power to overcome the head pressure. The one I installed was a Rule 3700. Granted the bilge is small in a Cat 34 for this size pump if it would even fit. On the other hand, should a through-hull fail you would probably want a larger pump ;-).

Back to the valve, it was just an internal flapper valve which should offer minimal resistance. The valve was made of rubber/neoprene which can never corrode, making this a one-time project. (I hate doing projects like this more than once!

[Mark Elkin]

Mike,
The pump I have is fine overcoming the head pressure.  The issue is when the pump stops.  All the water still in the exhaust hose is now free to flow back down the hose, thru the pump, and refill bilge.  When enough water has done so, the float switch activates the pump and the water goes back into the hose; the bilge water level drops and the float switch turns off the pump.  And the cycle starts all over again.

Anyway, I found an inexpensive flapper type valve at Home Depot.  It does not provide a perfect backflow stop, but it greatly slows the backflow.  So now the bilge pump cycles on maybe once to twice an hour verses every 5 minutes.


Mark Elkin
Yorkshire Rose, #133

[Mark Elkin]

Dave,
You mentioned moving the float switch higher.  That may cure the spiders, but not the pump cycling on/off.  I do remember seeing an circuit that used 2 float switches and an extra relay to control the pump.  Only the upper switch activated the relay and pump.  Only the lower switch deactivated them.  The bilge does fill higher before being emptied, but the backflow of water from the exhaust hose won't raise the blige water level enough to trigger the pump again.  Of course, the drawback is the extra complexity and cost of this system.

BTW, I just found some spider webs in my bilge last week, after I sponge dried the bilge.  I guess they like the dry Southern Calif summers as well.

Mark Elkin
Yorkshire Rose, #133

[Exile]

Nigel Calder says there's no solution to the problem of water backfilling from the outlet hose.  This from a Cruising World article sometime in the last 6 months.

[Dave Veenhuis]

The newer Rule automatics come on at a depth of about 2" and pump down to about 3/4".  The backflow is not enough to turn the pump back on.  I had the same pronlem until I installed the new  pump this year.