Plumbing Question

Phanman · #1 06-04-2008, 04:19 PM

I was wondering if I put a ball valve after the return pump to reduce the flow abit if it will burn out the motor or not. Ideally i know you should never restrict the return pump. I bought a mag 18 and i know its going to be too much flow for a 25gal display but i plan on have a 2nd display tank probably 30-50gal once i can find a 2nd tank. At this point I will open the ball valve all the way as the setup idea is to have 2 displays and 1 sump in the basement.

sphelps · #2 06-04-2008, 04:32 PM

All a valve does is add head pressure to the pump, the exact same thing as simply pumping up higher. So obviously adding a valve and restricting the flow will not harm the pump, however it will likely use slightly more power and some pumps can generate a little more noise when restricted.

banditpowdercoat · #3 06-04-2008, 04:52 PM

Acctually, with a centrifugal pump, restricting the flow uses Less power. More water moved = more work, = more power consumed. Just went through this on Saturday with my Firehall and a practice burn. We were using a Gas Honda pump to pump water from the creek up to our porta-tanks. When waterflow was full open, tank of fuel lasted X long( cant remember acctual times) But when we put a gate valve on, and restricted the flow, the fuel lasted alot longer. Like 3/4 of the day to the 2nd tank. This was because the engine saw less load, and throttled back via the govenor.

Now, a Positive displacement pump, power consumed goes up when output is throttled back

Phanman · #4 06-04-2008, 04:57 PM

Thx for the feedback guys. So is a Danner Mag-Drive 1800 Supreme Water Pump a positive displacement pump, or a centrifugal pump? sorry if thats a dumb question...

Delphinus · #5 06-04-2008, 05:00 PM

I was just going to say, bandit beat me to it. It's counter-intuitive but the more a pump has to "lift" water, the less electricity it consumes. It's the speed of the motor that draws the power, and if it's working harder, it's spinning slower. Adding a flow control valve on the output of the pump is thus usually OK and causes you to use less electricity. Only thing is the noise and the heat.

Putting a flow control valve on the **input** side of a pump though is a big no-no. "Pumps push, they don't suck." Ie., having to push harder is OK, but having to suck harder will indeed burn out the pump.

Phanman · #6 06-04-2008, 05:12 PM

thx Tony

Delphinus · #7 06-04-2008, 05:16 PM

Oops, sorry, missed your other question. I think any pump that has an impeller that spins would be considered centrifugal. I don't know what a positive displacement pump is but if I would hazard a guess I would think that we're talking about piston-type or peristaltic-type pumps where a set volume of fluid is drawn in and then physically pushed out.

So anyhow unless I'm way off I would say your Mag drive is a centrifugal pump.

Phanman · #8 06-04-2008, 05:23 PM

thx again Tony

sphelps · #9 06-04-2008, 05:29 PM

Quote:

Originally Posted by banditpowdercoat

Acctually, with a centrifugal pump, restricting the flow uses Less power.

In theory yes, but each style of centrifugal pump will have a different pump curve for both flow and power. As head pressure is initially increased from 0 the pump will actually start to consume more power and as head pressure is further increased the power will reach a max and then begin to decrease. The highest efficiency occurs when the power curve intersects with the pressure curve. So you'll notice I used the word "likely" as it may or may not use more power, you would have to hook up a power meter to figure that one out for sure.

But thanks for clearing that up

banditpowdercoat · #10 06-04-2008, 07:20 PM

Quote:

Originally Posted by sphelps

In theory yes, but each style of centrifugal pump will have a different pump curve for both flow and power. As head pressure is initially increased from 0 the pump will actually start to consume more power and as head pressure is further increased the power will reach a max and then begin to decrease. The highest efficiency occurs when the power curve intersects with the pressure curve. So you'll notice I used the word "likely" as it may or may not use more power, you would have to hook up a power meter to figure that one out for sure.

But thanks for clearing that up

Ya, that is true. But, need a flow meter and a ammeter to truly find the curve. Ammeters I have lots of, but lacking on Flow meters.

BTW Phanman, the Mag 18 is gona have a TON of flow. I tried one on my 45g. had it submersed in the sump. It heated the tank up to 85* just running it alone. Granted, if you run it external, it wont put as much heat into the water, but its still going to. Presently I have a Mag 3.5(50% restricted) and a Quiet one 3000 in my tank and thats putting to much heat into it.