2 bilge pumpe to one outlet?

purplerobbie said:
Both Johnson 12v pumps.
One is an ultima with a built in level switch the other is a standard pump on a on an off switch.
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Type not make ;)

If diaphragm pumps , which will have outlet valves in them, probably no further action needed. If flexible vane pumps you may get a little back flow through the pump not in use unless you fit check valves.

If plain impeller pumps you will need check valves .

If you'll be operating both together be sure the outlet is large enough for both
 
It depends on the size of the Y-piece and the skin fitting. If it's intended that both pumps will run together then those items should be sized accordingly.
 
I s'pose someone will want to do the same with two or more cockpit drains.... ;)

Akshuly, thinking about it, I want to improve the drainage capacity in my puddle-jumper as the two that are presently fitted are bath-types with a six-part grid which constrains the flow. I've already acquired a pair of proper 'wide open' drain fittings and had intended to replace the original pair. However, might I not be better fitting the 2 new ones in the other corners, and leading the new drain-pipe tubing to appropriate Y-junctions, then into the existing good through-hulls....?

Can anyone see any issues with that?
 
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One warning here. Connecting two pumps to joined outlet is possible, but both pumps should be connected such a way so they are not pumping into each other, unless they have some non-return valves. Normal hand ones have their valves, so they probably won't allow water back. Not so with electrics.
Actually once we had 'water-alarm' and this was all hands to pumps, only to find - hand pump was pumping water back into by way of electric one, also working :eek:
Well, nearest port and no-return valve from plumbing shop.
Just to inform :)

When hoses from two pumps go for joined outlet it was a good rule of thumb for outlet to be double diameter of those; that is with 2' pipes from gushers 30 - 4' outlet. So not to restrict a flow. This may seem too much, but it's about the friction, not pressures.
Less problem if the outlet is onto deck.
 
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I strongly advise against the use of non-return valves with 12v electric submersible pumps, as per the OP's set up, because these pumps are very sensitive to back pressure. The capacity drops off quickly as back pressure increases. Hence the suggestion in the sketch.

Simply discharging pumps towards each other with a T-piece will result, of course, in one pump discharging back down the other pumps outlet pipe. This won't happen with the routing I've shown in the sketch - a system that's always worked fine for me.

Most submersibles have the same size discharge hose, 19mm, from 360 gph up to 1000 gph. At about that rated capacity some switch to 29 mm hose. So, unless both pumps are quite high capacity the short length of combined run hose, and the skin fitting, can be the same size as each individual pump line. In fact, the capacity will be no more than half the rated capacity anyway - that's just the way it is with these pumps.

However, if preferred, an unequal Y-piece, 19mm/29mm and appropriate hose can be used to a 29mm skin fitting if both pumps have 19mm hose. If both pumps have 29mm hose you could go to a 38mm Y-piece and skin fitting although in such a case I'd be looking at separate systems.

All in my opinion, of course, and my opinion might be worth little more than you pay for it!
 
Salty John said:
I strongly advise against the use of non-return valves with 12v electric submersible pumps, as per the OP's set up, because these pumps are very sensitive to back pressure. The capacity drops off quickly as back pressure increases. Hence the suggestion in the sketch.
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a big + 1 for this, any obstruction will cut the output, btw. And the connection of two pump hoses as close to outlet as possible - as in sketch.
 
I'm in favour of minimising the number of holes in a boat. For instance, I like seachests, or manifolds, to bring water into the boat for several purposes using one inlet and seacock. Also for discharging several points to one outlet.
 
Salty John said:
I'm in favour of minimising the number of holes in a boat. For instance, I like seachests, or manifolds, to bring water into the boat for several purposes using one inlet and seacock. Also for discharging several points to one outlet.
Click to expand...

I'd agree generally, but bilge pump outlets are above the waterline and don't pose any leakage problems.
 
Salty John said:
I'm in favour of minimising the number of holes in a boat. For instance, I like seachests, or manifolds, to bring water into the boat for several purposes using one inlet and seacock. Also for discharging several points to one outlet.
Click to expand...
+ 1 :)
and another tip: while installing another pump, emergency one or so, it may be a good idea to make discharge on deck, for instance on outside of cockpit coaming (there is a bit of space to make an upward loop also). No holing the hull, and it'll not be submerged when heeled (this is posing a leakage problems sometimes, actually, like when wave slaps into).
Or when sinking... ;)
 
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Salty John said:
Connect them like this, running down into an unequal Y-piece, and you're less likely to have one pump blow water into the other one:
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I have two pumps installed similar to this. They actually go into the generator outlet. It is a professionally manufactured arrangement and has been like that for 30 years with no problems. Since the outlet is larger than the bore on both pump outlets, both pumps can run together without any loss of flow
 
wanderlust said:
I have two pumps installed similar to this. They actually go into the generator outlet. It is a professionally manufactured arrangement and has been like that for 30 years with no problems. Since the outlet is larger than the bore on both pump outlets, both pumps can run together without any loss of flow
Click to expand...

If they are centrifugal pumps, they will be suffering reduced flow to some extent due to the extra height of the siphon loop and the extra resistance from a longer hose.

It depends why you want two pumps.
Some people have a second small pump which is only there to deal with the small amount of bilge water a bigger one won't lift.
If you are thinking of running both at once to get greater capacity, it may not be a great arrangement.
But it might be OK for a dayboat where you have a pump for each tack with a transom out let.

Having had problems due to a plastic 'y' piece breaking, I think I'd rather have another skin fitting.
If one of the pumps is manual, be aware that the outlet can be at a fair pressure during the pulses, so some water might go to the other pump.

I think you should generally have two independent systems, otherwise there is a single failure point which leaves you with zero pumps.
 
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