Bilge pump outlet issue

[wiekeith]

I’ve an issue with my bilge pump system that’s really baffling me - hope you guys can help.

The problem. I developed a fresh water leak into the bilge (which clearly needs addressing, of course), and noticed that the bilge pump, a Sahara 750, with built-in float-switch, would operate but sometimes not pump out any water. I stripped it down and all looked OK, but it still occasionally did it, so I assumed the pump was faulty and replaced it with a Whale Supersub Smart 650. However, I’m still getting the same problem with the pump sometimes running but not extracting any water. And it can occasionally run for up to an hour or so like this when it happens, if I'm not down below to notice it!

If I ‘wiggle’ the Whale pump around a bit when this happens it will sometimes start pumping, then turn off when done. Incidentally, the inlet to the pump is submersed when this happens, so it’s not a case of it taking-in air.

The plumbing. The pipe from the pump is ¾”. I’m not sure of the length of the run as it disappears into the structure and pops-out under the floor of the starboard cockpit locker, then into the transom area. But, the pump is about in the middle of the boat, so it would be 20’ if it was a straight run, therefore it must be more than that as it meanders a bit and it rises about 3’ as well. If I blow down the pipe, from the pump end, it takes quite a bit of puff before water in the pipe eventually exits (so the pipe must be going downhill at some point, then back up again, hence holding water), but there’s no resistance when the water has eventually been blown out.

When the pump is pumping-out water, the stream from the through-hull on the transom is about 12”, which I think is healthy.

Oh, one other bit of information. The shower sump system, which is self-contained, is also in the same bilge area, is about 18” higher than the bilge pump, and also uses a Sahara 750 pump. I’m not sure of the extraction pipe route, which is initially different to the bilge pump pipe, but I believe it joins the bilge pump pipe with a Y connector about 6” from the through-hull in the transom. I don’t get any problems with this, which is used daily.

Looking through the forum archives I see that somebody has previously reported a problem with the Smart 650 randomly operating, so it could be coincidence that I replaced a faulty pump with a troublesome pump, but I think my problem may be a bit different.

I obviously need to stop the freshwater leak into the bilge at some point, but it’s my ‘friend’ at the moment as it has highlighted a potentially greater problem.

Sorry this post is so long, but I thought I’d try and give as much information as possible upfront - I know you guys will otherwise be asking lots of questions.

Any thoughts on what could be going-on here would be greatly appreciated as it’s got me baffled…

[Lepke]

I had a similar problem that came down to a thin piece of clear plastic laying in the bilge and occasionally being sucked up to the pump pickup. The pump would run, even getting hot. When I noticed and shut it off, enough water would back wash the plastic away for next time. But the time I got to the bilge everything looked normal.
I have also had zero luck with any bilge pump that has a built in sensor. They either fail with the pump on or off. My boat has 5 WT bulkheads and 6 bilge areas so I have a bunch of pumps. Also 3 shower/sink sumps.

[model 10]

With all the twists and turns in the plumbing, maybe it would drive an automatic pump crazy. A separate switch mounted so the pump has a bit of head before it starts might be more dependable, if you have some sort of keel of course.

[wiekeith]

Great thought Lepke, but alas, just checked and there's nothing there. :-( Whatever the outcome I think I'll ditch the auto pump though - it does seem to have a mind of its own.

Guy, I do have a keel, and could quite easily mount a float switch a few inches higher than the pump. In fact, I think I'll dump a bucket of water into the bilge with the existing pump to see if the extra head makes a difference.

Thanks for the responses.

[cal40john]

Did the pump ever work reliably? If not the ups and downs in the hose could be the problem. The pumps I have bought the manual states that the hose cannot have any low spots to trap water. While the pump has some air trapped in it, it is possible for it to not develop enough pressure to push the water in the low spot out.

[wiekeith]

Originally Posted by cal40john

Did the pump ever work reliably? If not the ups and downs in the hose could be the problem. The pumps I have bought the manual states that the hose cannot have any low spots to trap water. While the pump has some air trapped in it, it is possible for it to not develop enough pressure to push the water in the low spot out.

Yes, the original pump did work reliably. Well, until it recently stopped working reliably, that is!

[Terra Nova]

Never combine bilge pump plumbing. Eliminate any traps in the outlet hose.

[HopCar]

Cal40john hit on what I was thinking. Water is trapped in the discharge hose holding air in the pump. With air in the pump it can't create enough pressure to push the water out of the hose. Eliminate the low spot in the discharge hose and the problem will go away.
I think

[zeehag]

anti backflow valve into sump system, check all hoses for integrity, then test.

[Terra Nova]

Never install a check valve in a bilge pump line.

[zeehag]

sump pump is different system than bilge pump and if there is backflow, there is a problem, as you are siphoning back into boat the showersump water and bilge water, both.
never put the anti backflow valve on a bilge pump.

[wiekeith]

Thanks for all the useful responses – much appreciated.


I have tried two things, as well as giving your responses and suggestions great thought. I dumped a bucket of water into the bilge to create more head – the pump primed in a second or so and extracted all the water. I also checked that the shower sump water was not back-flowing into the bilge pump line.


So this is where I am:
1. I accept that there is clearly an issue with water/air trapped in the line that’s causing a problem – need to re-route the pipework, and fit a dedicated through-hull (presently 5 lines share 2 through-hulls!).


2. The ‘automatic’ bilge pump was probably not a good investment as too temperamental – replace with a ‘traditional’ one.


3. Use a separate float switch mounted slightly above the pump to ensure there’s a head of water when the pump operates. This will probably also mean that residual water in the pipe that runs back into the bilge when the pump stops will not cause cycling, hence a check valve will not be required.


Once again, thanks guys.