Bilge Pump Outlet

[Mat-C]

I Have to install a new bilge pump. Can anyone tell me the correct loction for the outlet - ie how high should it be?
Are there ABYC guidelines regarding this?

[Landlubber]

Well maybe you could tel us what sort of boat first please mate, if it sits on a trailer or is ocean going, there is a difference.

[Mat-C]

Sorry... planing powerboat, 30ft long
Coastal cruiser. Though I would not ave thought that ABYC would differentiate, other than maybe for sailboats...

[PAR]

Buy the largest pump you can fit into the space you have available. There's no such thing as too big a pump. Most of the pumps provided by manufactures can't even keep up with a small leak, let alone a good heavy rain.

A typical installation is to put in an "anti siphon" loop. The wise course (big pump, assuming sufficient lift) is to bring the loop up under the side deck as high as possible and place the outlet in a handy location at least 1/4 of the height up the topside flanks.

There's quite a bit of information about pumps from several sources, try a search for "bilge pump testing". Or you can check section 22.5.1.1 (bilge pumps) of ABYC's "Standards and Recommended Practices for Small Craft".

[Mat-C]

Thnaks PAR - just what I was after

[Landlubber]

One thing to remember with long discharfe loops though, is be careful that the capacity of the hose pipe does not trigger the float switch again as it flows back into the bilge from the highest point, I have spent many hours correcting such an occurrence.

The two float switch method or a check valve in that event. Some of the newer pumps probably account for that...

[PAR]

I must admit I assume they'll follow the recommendations of the bilge pump package, which all suggest a check valve.

It's been so long since I have installed one, I didn't know that. In general, Mat, when Par tells you something - thats about what you need to get the job done. ABYC, I believe, states that if there is a thru-hull penetration closer than a foot to the waterline, one needs a valve. It would never come up even if I am right and your outfall is at nine inches...

[Submarine Tom]

Mine are a foot above the waterline (4 pumps in total) but I have half a ton

of buoyancy per inch and 12 000 pounds of displacement. I didn't use a loop

but I did use check valves close to the pump to minimize backflow (float

switch reactivating) but primarily to avoid flooding. I've seen many boats around

here load up with snow an take on water through a bilge pump thru-hull

and sink.

-Tom

And I'm not sure of that valve thing, eh?

[Submarine Tom]

Why not?

[Red Tide]

Originally Posted by PAR

I must admit I assume they'll follow the recommendations of the bilge pump package, which all suggest a check valve.

Why does Rule say "no check valve" for their 2000, 3700, and 4000 gph pumps at http://www.rule-industries.com/files/itemdoct6041.pdf (page 16 in the corresponding pdfs) That doesn't seem to be in the "simple guide" pdfs for their smaller pumps.

[bntii]

Check valves can reduce flow so are not recommended by some.
There is also a danger the a installer will think the back flow preventer (check valve) acts as a anti-siphon.
A check valve should not be used as a anti siphon device. If you need a check valve in a deep small bilge sump, make sure to also place a anti siphon at a high loop as already noted.
By all means never exit a bilge pump to a thru-hull mounted below the water line!

ABYC notes:

22.8.6 The discharge location shall be above the maximum heeled waterline.

22.8.7 The discharge may be located below the maximum heeded waterline if the discharge line is provided with both of the following:

22.8.7.1 A seacock installed in accordance with the requirement of ABYC H-27.
22.8.7.2 a vented loop or other means to prevent siphoning into the boat. A check valve must NOT be used for this purpose.

ABYC further notes to use check valves ONLY when necessary due to cycling of the pump.
I generally place seacocks and anti siphon loops in all installations, as well as a high as practical discharge.

[PAR]

I have no issues with any of the above observations and the reason why I just take the loop up to the underside of the side deck. For what it's worth, you'll loose nearly 10% pump capacity with most check valves and the corrugated hose, sold and/or supplied with pumps will eat another 5%. This efficiency lose will rise dramatically once the lift is over half the pump's capacity, which is one reason to install the biggest pump you can fit. Once you've got this one installed, place another big ass pump near by, with a float switch slightly higher then the first. This secondary pump will hopefully live an uneventful life, but if it doesn't, it'll come on when you need it most, which will about the time you're thinking about removing the raw water intake hose from it's thru hull and using the engine pump to suck the bilge dry.