two bilge pumps one skin fitting

[richarda]

My boat has a system in which the hoses from both the electric and manual bilge pumps exit through a single skin fitting. While the philosophy is right the plumbing is crude, joining two different size hoses through a modified T piece close to the skin fitting. I am concerned that it has been installed without any real understanding of how the water moves when either pump is activated. Although some water goes over the side it looks to me as if the water from one can simply flow back down the other hose once pump pressure starts to reduce.

Is there a straightforward and agreed way to run the hose from the electric bilge pump (3/4" outlet)and the manual pump (11/2"outlet) through the same skin fitting without backflow or air lock problems?

 

[ruvane]

Non-return valves are the easiest short term answer.

But the installation brings up another question - in the event that both pumps are moving water, will the diameter of the skin fitting be adequate to allow full, unrestricted flow from both pumps?

 

[rogerthebodger]

On my previous boat I had a electric submersable pump at the lowest point in the keel piped 38 mm dia to a henderson MK 5 pump then over a goose neck to the skin fitting. The henderson pump providec the non return valves to stop backflow. Worked very will I would not use both at the same time so capacity was not a problem. The flow rate from the electric pump may have a small reduction due to then small restriction dur to the henderson pump but it was very small and had no real effect on flow

 

[EASLOOP]

Exactly my setup. The riser from the bilge is fitted with a non-return valve as is the outlet from the hand pump. Both pumps are 'T'd at the skin fitting to one outlet. My hand pump is operated from the cockpit so it can be used while single handing if the electric pump gives up. I should have thought that it would be unlikely that both pumps would be in action at the same time. If there is insufficent water in the bilge to activate the electric pump then no problem. If the bilge water fill rate is so great that you need to use both pumps at once then you have a serious leak problem and need to be looking for other emergency solutions. If you anticipate a leak of such magnitude then you need to be using tubing that has a flow rating sufficient to handle the sum of the electric and manual outflow rates/volumes. You would only need this between the 'T' and the skin fitting as the other two pipes will be independant of each other operating in parallel.
Hope this makes sense.

 

[Thistle]

I'd agree that in normal circumstances - emptying a few cupfuls of water every so often - only one pump would be used at a time. But I'd want to know that if I got a significant leak I could use both pumps at the same time to help keep me afloat.

 

[bedouin]

You should consider fitting a non-return valve in the output of the electric pump (assuming it is a centrifugal pump) - but one should not be necessary for the hand pump as that will have valves built in.

How big is the skin fitting?

 

[pete]

Personally I don`t like the idea of any restriction in the outlet from the pumps (not put there by the pump manufacturer) . Can both outlets not be taken seperately well above the water line in a swan neck before dropping into the tee and then through the skin fitting ?.
Pete

 

[markdj]

Don't skimp, get another skin fitting and plumb them all separate. A hole cutter is not expensive nor is some sikaflex. If hardy comes to hardy you will be glad of the full flow going out. All pipes should go in a loop to stop entry of water and can be fitted with a non-return valve if you want.