How many GPM does a Bravo water pump flow?
 

Yes I know there are a lot of variables but approximately how many GPM would a Bravo water pump flow out the exhaust at various RPM? Needing this info to size some bypass and check valves. New design in the works. Just ballpark figures at this point, the valves will have a range to work within.
Tim T.

I researched this extensivly some time ago. The result? Nobody really knows. The best that I could come up with was around 30gpm at full song. Honestly, that was based off of some loose calculations and is really a wild ass guess.

It depends on RPM, speed, and inlet type. Remember it is a floppy vane so the more inlet pressure supporting the back of the vanes, the more output flow potential before the vanes bend and "cavitate". It could be more than 40 GPM depending on those variables.:cool:

I too , did some research last year. The results...Jabscos "Merc replacement " pump is 22 gpm at 2000 rpm. Beyond 2000 the impeller pretty much acts like a blender and just mixes stuff up and the water is forced though by your forward speed.
I don't Imagine the Merc is much different

unless you are going to design something into the system using thermodynamics, flows, heat transfer, energy, chemical equilibrium...yada,yada, yada...mopower looks like he has some data for ya.

heat transfer, and GPM is not our issue....actually most of the time we have too much,,,,which translates into wasted HP...just a little tip.....ANY more flow or pressure than you need is wasted,,,,well at least in our eyes:)..... energy can not be created or destroyed...but what do i know?

there is some prettttay smart M-F'ers that lurk in these here threads!!!!...me and my other brother daryl are not one of 'em!

in short,,,, acutally you can only flow so much through a given orifice.

Yes, that is a given. We are shooting for flow in a system that will have no more than 25 to 30 psi block pressure at WOT. This would requrie the given restriction to not be to small and create excess pressure. If the restriction were large PSI would be low and flow high and vice versa. The question then becomes (with exhast header being the restriction) how many gallons will you flow at 25 psi?

25-30 is too much!

OK what do I want? This was just an example. 502 with B&M 250 at 5psi boost.

15-18lbs @wot

Sheesh,
Sell a guy a blower and he buys a membership, changes names and god knows what else. :)

So right you are, the damn laundry list is starting to get long. Yanked the engine tonight and all looks great inside. Talked to Stainless Marine today and they are in the works of designing roughly the same idea I am working on. 10-psi cracking pressure check valve in the bypass and a backflow preventer on the main lines out from the thermostat housing. I think mine may make it to the water first.

figure out (with your given system) what psi it takes....anything after that is wasted....need more?????????? increase flow not pressure........that what daryel says.

we are experimenting with building a new pump here at work and took the merc pump and tested it to see what kind of output it gets.....heres what we found:

Tests done with a 2hp electric motor running at 3450rpm

-at 3450 rpm with no load restictions and pumping 10' of head the pump puts out 26gpm and 4.3 psi running through a 2 1/4" output hose and was useing just over 1.5hp to run

-at the high end of our test....still 3450rpm pumping 100' of head the pump was outputing @12GPM and generating 43.29psi!! and useing 2.4hp to do it...

I'm scanning a curve we made for it and will post it up here in a few...or if anyone wants it i can email it to you :D

There is one thing that is missing from your test Wally. The pressure and gallonage measurements would be correct with the boat not moving. However, with the boat underway, the inlet side of the pump will be pressurized, thus increasing it's flow.

yes you are correct Cord...this was stictly a bench test to see what the pump can do. :) Unfortunatly we have no way of doing that here at work! :D

What you need is a lap pool big enough to float a boat!

you mean our 5000gal test tank wont do? LOL ;) :D

Tim, so does the Stainless Marine unit have a valve assembly in it, or is it something they are working on?

An interesting topic. I would like to see someone build a better raw water pump. It is unbelievable how short a life the pump has. People change the impellers every 100 hours or so to keep from being towed in, and sometimes that is not good enough. I work in an environment where pumps (thousands where I work) are expected to run 24 hours a day, 7 days a week, for at least 5 years with no repairs and no failures. That is 43,800 hours verses 100! 100 hours of constant operation is just over 4 days. Incredible. And the service? This little pump just pumps water at ambient temperature. In the refinery it is all kinds of nasty hot stuff. Water pumps in an industrial environment can go 10-20 years with no failures, running constantly.

A better pump could certainly be designed and sold for a competitive price, I'm sure.

GO for it Wally!

The Jabsco pump is a vast improvement over the M/C plastic crap. To improve the Jabsco even more we discovered that by using the mercruiser impeller in the Jabsco pump we had better cooling (by more flow and pressure) at higher speeds. It seems that we picked up about 4-5 psi on the top end runs. The difference is that the mercruiser impeller has one less blade and therefore allows for more volume per pump revolution. We also run Imco or Stainless Marine sea strainers with poppet valves set a little above 2-3 psi cracking pressure so as not to blow the strainer tops or preload the suction side of the pump too much.

Hudson

Your industrial pumps are not self-priming.
They run centrifugal bronze impellers (like the circulating pump on the front of your motor which lasts eons until the seal goes bad from sitting too long when you don't use the boat often enough).

Centrifugal pumps are long-lasting for sure. They can be run dry for a while without damage and they can generate a decent flow rate and pressure (multi-stage pumps can generate LOTS of pressure).

BUT
THEY DO NOT SELF-PRIME.
Thus the essential difference...

The rubber impeller pump is a positive displacement pump. It will pump air well enough that it will pull water up the feed line into the pump. A centrifugal will NOT do this.

In fact, a centrifugal can lose prime with even a small air pocket in the intake.

ALSO - a centrifugal pump has a given RPM range that it is efficient. They typically don't work all that well speeding up and slowing down. Too slow and the flow can stall. Too fast and they can cavitate in an air pocket.

A rubber impeller pump will pump well at slow speeds, yet at high speeds the vanes flex enough to allow the pump to unload while still pumping fluid.

If there was a superior style of pump for the raw water application, I figure that we could easily find it on the side of a $100,000 MTU V-16 2000hp diesel.

Guess what kind of pump it has on it???

You got it - a greeeeeeaat biiiiiiig version of the Jabsco style rubber impeller pump...