Two Bilge Pumps on the Same Hose

[GordMay]

Originally Posted by delmarrey

You are right!
I just like to compensate for the reduction of hole size for a bronze thruhull fitting and all restriction of the other fittings, with room to spare. The inside of a hose is not necessarily the smallest orifice in a system.

You’re also right, to allow for fitting & other constrictions etc. However, I believe that 1-1/4" may be overdoing it for 2 x ½" pipes.
The 3/4" I cited includes only a 6% fudge factor; so perhaps a 1" diameter combiner hose might be better.

To clarify the arithmetic:

To double the area (capacity) of a circle (pipe or hose), multiply its diameter by the square root of 2, which is 1.414, rounded off.
Hence, 2 x ½" pipes = 0.5 x 1.414 = requires One pipe at minimum 0.707".

Conversely, to divide the area of a circle by 2, divide the diameter by the square root of 2; or equivalently, multiply by 0.707.
Hence, a 3/4" pipe = (0.75 x 0.707) = will handle Two pipes at 0.53".

[psneeld]

Originally Posted by daddle

Ummm...manual bilge pumps and some electric pumps have two check valves built into them. So how bad can they be? Just saying. Such are rules...

However, I agree that one should not share outlets on bilge pumps that are expected to keep the boat floating when something goes wrong. There's always room for another hose. Get out the SawsAll.

Check valves provide resistance and ANY head on a centrifugal bilge pup starts to decrease it's pumping capacity dramatically.

Most marine stuff is built to crap specs anyway...bilge pumps are in the "worst" category of bad advertising in my book.

[Ziggy]

Originally Posted by belizesailor

Aside from other problems pointed out, this also reduces your potentially pumping capacity. You won't BOTH pumps fully functional at all times. You might just need them both.

Actually, there were no problems pointed out in this thread so far with using a manual Y valve to connect two pumps to a single hose. Although with this arrangement only one of the pumps is functional at any one time, there is no loss of either pump's capacity, neither pump can back feed the other, and there are no check valves to get stuck. I agree that it is not as desirable as two independent pumps, each with its own hose and through hull, but just like the OP, I have no way to run two 1.5" hoses from my bilge. A manual bilge pump is primarily a backup for a large capacity electric pump. If the electric pump fails, it will take me about 15 seconds to turn the Y valve.

[David M]

Given all the potential problems along with the seriousness of the potential consequences, it's not worth taking the chance for the small amount of convenience.

[delmarrey]

Originally Posted by GordMay

You’re also right, to allow for fitting & other constrictions etc. However, I believe that 1-1/4" may be overdoing it for 2 x ½" pipes.
The 3/4" I cited includes only a 6% fudge factor; so perhaps a 1" diameter combiner hose might be better.

To clarify the arithmetic:

To double the area (capacity) of a circle (pipe or hose), multiply its diameter by the square root of 2, which is 1.414, rounded off.
Hence, 2 x ½" pipes = 0.5 x 1.414 = requires One pipe at minimum 0.707".

Conversely, to divide the area of a circle by 2, divide the diameter by the square root of 2; or equivalently, multiply by 0.707.
Hence, a 3/4" pipe = (0.75 x 0.707) = will handle Two pipes at 0.53".

I understand the math! I'm just one that over builds everything, unlike the aircraft industry, and now the new boating indu$try, cutting materials costs where ever they can.

[bewitched]

Originally Posted by Ziggy

Actually, there were no problems pointed out in this thread so far with using a manual Y valve to connect two pumps to a single hose.

I appreciate that some may not have space to run two separate systems, but it is definately desirable. There is a big problem with using a Y valve over separate systems.

Example: 1 manual pump with a capacity of 25 gpm and one electric pump with a capacity of 25 gpm. With separate hoses you pump 50 gpm, with a Y value you pump half this.

[Ex-Calif]

Originally Posted by amarf

I do not have place for another hose for bilge pump (manuel). so my question is if it is possible to mount electric bilge pump on the same hose as manuel pump is mounted on?

I was stongly advised against this on the forum 4 years ago.

I ended up putting the submersable electric pump in series with my manual wobble pump.

4 years later all is well. The electric pumps through the wobble pump and the wobble pimp has no problem "pulling" through the electric.

I have a small boat. YMMV...

[Ziggy]

Originally Posted by Ex-Calif

The electric pumps through the wobble pump and the wobble pimp has no problem "pulling" through the electric.

That's interesting. I'm surprised the manual pump can suck through the electric... What kind of electric do you have?

[Ziggy]

Originally Posted by bewitched

I appreciate that some may not have space to run two separate systems, but it is definately desirable. There is a big problem with using a Y valve over separate systems.

Example: 1 manual pump with a capacity of 25 gpm and one electric pump with a capacity of 25 gpm. With separate hoses you pump 50 gpm, with a Y value you pump half this.

Yeah, I get it. But without the Y valve I get only one pump pumping 25 gpm, with no backup. Which do you think is better? By the way, a Rule 3700 electric pump with a 1.5" port can probably do close to 50 GPM all by itself.

[bewitched]

Originally Posted by Ziggy

But without the Y valve I get only one pump pumping 25 gpm, with no backup. Which do you think is better?

For sure manual plus electric and a Y valve is better than an electric alone. And if you cant fit more than one pipe through the bilge, that may be your only option.

Is it possible to have a stored hose connected to the manual that you could unroll and throw out the companion way in an emergency? Is it worth moving the manual so this could be possible?

The important thing is that you are comfortable with what ever system you go with.

For the record, I do have a Y valve in my system...which is: 2no. alarmed electric pumps, one manual inside, one manual outside. Inside manual goes through the same pipe as one of the electric pumps, selectable by the Y valve.

[Ziggy]

Originally Posted by bewitched

Is it possible to have a stored hose connected to the manual that you could unroll and throw out the companion way in an emergency?

Of course it is. One could board-mount a manual pump and store it in a locker with a few coils of hose.

Originally Posted by bewitched

Is it worth moving the manual so this could be possible?

I don't think so. If the electric pump is functioning and water is flooding in, I'm better off occupying myself with damage control than sitting at the manual pump. Even with adrenaline flowing, I could only operate the manual pump for a limited time anyway.

[Ex-Calif]

Originally Posted by Ziggy

That's interesting. I'm surprised the manual pump can suck through the electric... What kind of electric do you have?

Rule 5600(?)

[Ziggy]

Can't find that one on their web site but it should be easy enough to try with the other models. Thanks!

[Ex-Calif]

Originally Posted by Ziggy

Can't find that one on their web site but it should be easy enough to try with the other models. Thanks!

For sure it is not a positive displacement pump. I'll look next time I am on the boat. Its been a while since I was in the bilge...

[witzgall]

We have one of our two manual pumps in-line with and electric pump. Works great.

Chris