Plumbing Question

[Phanman]

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]

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]

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]

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]

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]

thx Tony

[Delphinus]

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]

thx again Tony

[sphelps]

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 :biggrin:

[banditpowdercoat]

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 :biggrin:

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.

[Phanman]

damn... well water is going in tonight so ill be able to test it out. Worse comes to worse Ill move the Mag18 to my 150gal setup which will happen in about a weeks time and look at buying a smaller pump. The tank is in the basement so hopefully it wont get too hot. Im currently trying to setup 3 display tanks at once so I have a little work ahead of me, haha..

thx for the advice thou.