An unusual arrangement.....

[KenMcCulloch]

We inherited a system with two Henderson MkV bilge pumps in series on the same hose. One electric, one manual in the cockpit. This arrangement seemed to work OK until when the diaphragm on the leccy one split we realised that a failure of either pump could mean a failure of both. Not quite as stupid as it sounds, there is another entirely separate manual pump. Work is in hand to separate both the suction and discharge of these two pumps.

What's the strangest arrangement you have found yourself questioning a previous owner's sanity over?

 

[robmcg]

Electric bilge pump too. Wired to fused bilge pump switch, so why hide another inline fuse for it in a hidden away place? Why have a 30A fuse in that fuse holder?

 

[lpdsn]

We inherited a system with two Henderson MkV bilge pumps in series on the same hose. One electric, one manual in the cockpit.

In series? Or in parallel?

 

[theoldsalt]

In series? Or in parallel?

The clue is in Ken's post:encouragement:

 

[NUTMEG]

Sons boat, manual bilge pump in cockpit, discharged into cockpit which drained....into bilge!

Needless to say he sorted it out

 

[lpdsn]

The clue is in Ken's post:encouragement:

You mean the bit of his post I quoted where he said in series but then went on to add a description that makes more sense if he was describing a parallel arrangement, causing me to ask whether he really meant in series?

 

[DickieT]

I seem to remember seeing a diagram for the system suggested by Lavac regarding the electrification of their loo. It consisted of the original pump placed in series with the electric pump. The idea being the manual pump was still available should the electric one fail. More an inconvience (!) feature than a safety issue of course. Would not fancy it myself, another potential source of blockage. Perhaps that is where the last owner got the iidea from ? But agree, would prefer two separate pumps.

 

[milltech]

A post title like that's more normally associated with some unusual marital set-up, I was quite disappointed. But then it would have been in the lounge, stupid of me.

 

[ianj99]

A post title like that's more normally associated with some unusual marital set-up, I was quite disappointed. But then it would have been in the lounge, stupid of me.

We now know who to ask for advice on this type of 'unusual arrangement'...

 

[andygc]

You mean the bit of his post I quoted where he said in series but then went on to add a description that makes more sense if he was describing a parallel arrangement, causing me to ask whether he really meant in series?

If the pumps are in series and the diaphragm splits on the first pump, the second will pump air. If the diaphragm on the second splits, the first one will pump water through the split. Either way, the pumps won't empty the bilge. If they are in parallel you need at least two failures for the system to fail because the pumps have both inlet and outlet valves.

 

[milltech]

We now know who to ask for advice on this type of 'unusual arrangement'...

Regrettably I have found one-at-a-time about the best I can manage.

 

[Daydream believer]

A post title like that's more normally associated with some unusual marital set-up, I was quite disappointed. But then it would have been in the lounge, stupid of me.

What!!!!1 Did you think it was 2 women in parallel
Been tried ,but normally goes wrong at some stage, needing an expensive repair possibly involving maintenance

Bit like the OP's pumps I suspect

 

[Dave_Seager]

The benefit of Lavac's approach is that if one pump blocks you can use the other to clear it.

 

[lpdsn]

If the pumps are in series and the diaphragm splits on the first pump, the second will pump air. If the diaphragm on the second splits, the first one will pump water through the split. Either way, the pumps won't empty the bilge. If they are in parallel you need at least two failures for the system to fail because the pumps have both inlet and outlet valves.

Thanks. That makes sense.

I've only ever had pumps fail by ceasing to actually pump water rather than spraying it out or letting air in.

 

[KenMcCulloch]

If the pumps are in series and the diaphragm splits on the first pump, the second will pump air. If the diaphragm on the second splits, the first one will pump water through the split. Either way, the pumps won't empty the bilge. If they are in parallel you need at least two failures for the system to fail because the pumps have both inlet and outlet valves.

Which is exactly what happened last season. The diaphragm on the electric pump, under the quarter berth, split and so any attempt to use that just made some sucking sounds and deposited water in the locker under the bunk. Trying to use the manual pump just sucked air through the split diaphragm. We now have two independent pumps with separate suction pipes. They share a single skin fitting but that shouldn't be a problem.

 

[Chalker]

As someone said earlier, the two pumps in series is a standard Lavac arrangement. Faulty joker and flap valves are common and the series arrangement solves the problem. How the h..l do you break a Henderson MkV daphragm, they are nearly bulletproof!

 

[charles_reed]

As someone said earlier, the two pumps in series is a standard Lavac arrangement. Faulty joker and flap valves are common and the series arrangement solves the problem. How the h..l do you break a Henderson MkV daphragm, they are nearly bulletproof!

I understand, from the post, that the electric pump diaphragm split.
All the electric bilge pumps, across which I have come, are centrifugal - however I do note that diaphragm shower-tray pumps are commonplace.
I have 3 centrifugal electric and two manual diaphragm pumps - two of the electric pumps empty through a common pipe to the outlet with one-way valves to prevent refilling bilges.
Works well - especially for the engine bilge - I'm still trying to visualise the original - obviously others are far more imaginative than I.

 

[prv]

All the electric bilge pumps, across which I have come, are centrifugal - however I do note that diaphragm shower-tray pumps are commonplace.

Centrifugal bilge pumps have to be immersed in the bilge. No problem in a shallow sump above a solid fin keel, but in our old boat with a long keel the bottom of the bilge was a narrow and inaccessible pit about four feet deep. I didn't want to consign a pump to the depths, so I had an electric diaphragm pump mounted in the cockpit locker and a hose reaching down into the bilge with just a small strum box on the end.

Pete