bilge pump plumbing

[Lennie]

I want to install another electric bilge pump and want to know if I can just plumb the output to the intake of the manual pump? Will it pump through it?

Thanks,

Lennie

[NSboatman]

You may be able to pump through it, depending on the arrangement, but it is not a good idea for many reasons:

- the flow restrictions imposed by the valves in the manual pump will reduce your electric pump output significantly.
- redundancy between manual and electric bilge pumping is usually desired.
- any debris picked up by your electric pump will get pushed through the manual, and possibly clog it, thereby taking out both pumps.
- the efficiency of the manual pump will also suffer, since now you're sucking through a less-than-ideal 'strum-box' (the electric pump).
- in real flooding situations, you are already using up the discharge capacity of both pumps with the electric - even if you have extra hands available to wag the handle of the manual, you won't be able to push more water through that single line and increase the ability to dewater.

In short- don't do it.

One thing you can do is plumb it into a cockpit drain line if you have one... this saves a thru-hull sometimes; but it too can have undesirable side-effects.

Really, all bilge pumps should have their own suction and discharge lines, all the way from bilge to overboard.

[Lepke]

Someday you may need both the electric and manual. I've been around docks all my life and seen a few boats sink and a number come close. Most often it was the bilge or shower pump. Even a 100' tug once.
Many people screw up bilge pump installations. Some sink their boats. You need a loop with a suction break so the line can't siphon water back into the boat if the outlet is forced underwater. Check valves aren't reliable because bilge debris can hold them open. New bilge pumps usually come with a diagram of a proper installation.

[Lennie]

Thanks for the replies, I'll plumb it in as a stand alone unit