Restricting pump flow - damages pump?
 

I am going to put a ball valve on the output of my mag-drive pump to restrict flow. Will this hurt the pump? Should I be diverting the flow instead with a 3 way outlet?

I have read that restricting the flow on the output is OK, but restricting the flow on the input of the pump is not good for the pump. I have been restricting my return pump flow for about two years on my present pump with no issues.

above poster is correct, but greatly reducing it will result in increased noise

My understanding on restricting flow on a Mag pump is to use a T fitting with a ball valve to diverting the flow back into your sump. This way you are not creating any back pressure on the pump which can be hard on them. I found this image to help explain.

I restrict the output on my mag12 and it gets quieter. You can search my username for the question that I asked.

I used 1" return lines on my 75g, as this was more than enough using the Headloss Calculator. The issue I was having was when the ball valve was wide open, it sounded like the pump was cavitating, even though it is completely submersed in the water.

I couldn't figure it out and it was weird that on my 50g, using 3/4" return lines, it is wide open without any noise.

Turns out, without enough head pressure, the pump will be noisy. I turned the gate valve back to about 75% now, restricting the flow, and the pump is basically dead silent.

Why not use an appropriately sized pump? Are use making use of a pump you already own?

There's no difference between restricting the flow by using a valve on the output and restricting the flow by having to pump the water higher. Both just increase the head pressure and won't damage the pump.

Restricting flow by putting a valve on the input can cause cavitation, which can damage the pump.

Just follow the above posts......do not put a ball valve on the inlet, either put one on the outlet or t off and put some back into your fuge area or skimmer section.

-Steve

I read somewhere that restricting the pump increases electric consumption (not sure if this holds for mag type pumps) even if this is falls the way energy prices are heading it would pay to downsize pump

75% open will not hurt pump, you can get cavitation with going too low of a flow. Wont save money as pump has to make more pressure to get through restriction. If you need to cut back more than half i would downsize pump.

I would just divert it off the main. On a plus side you could also use that bypass feed to run a TLF/BRS reactor.

You do not get cavitation from restricting the output of a pump, but from either not having enough flow through the pump(on the suction side,) or restricting the suction too much with a valve.

I restricted or reduced a Mag 9 .5 and Mag 12 on freshwater tanks for several years and never had a problem. I decided to redirect some flow on a current Eheim 1262 I'm using now in saltwater. I think either way you're good. I put a gate valve on both the DT return line and the sump refugium return line so I can throttle either way. I like having the excess flow created in a little more power (moderately oversized) so I don't have to worry about not having "enough". I can always find somewhere to direct it.

neat thing about restricting the outlet, as flow goes down, so does the power bill

I think you have that backwards

If you think you might ever want to use any kind of reactor, as mentioned earlier, go ahead and T off the return line and with a couple ball valves, create a small manifold that you can use to plumb in the reactors.

You might eventually want to use calcium/carbon/gfo reactors (or add a fuge, or add another tank to your system, etc.) and this is the perfect opportunity to prepare for them for very little cost $$. Until you add reactors, the outlet from the manifold can be controlled by the valve on it and directed to flow back into the sump just below the water line so no splashing occurs.

As said already though, valve restriction is just like head pressure, so it shouldn't hurt the pump, to a point.

nope.

Example my Reeflo Barracuda full open 262 watts, where I normally run it valved back for reduced flow through the sump, 240 watts.

This is an all new setup. I have the overflow rated at 300gph. Ideally, I'd like the return pump to be able to flow 300gph at the tank level. This means some amount higher than 300gph rating to get the proper flow into the tank. I will lose some pressure in the pipes, radius's and outlet not to mention losing something more as the pipes get growth inside them and as the pump ages. I think I will always need to have a ball valve to match the pump to the conditions and I don't see any way to have an "appropriately sized pump" unless I am ok with always running below the overflows rated capacity as I will always want my overflow to be at or greater than the return pumps flow capacity. So the next best solution is to get a pump rated higher and crank it down as needed. Which is what I am doing with my 700gph mag pump.

As the head increases, the pump is pumping less, therefore doing less work. So it generally- in most cases- uses less power.

I had a sicce syncra on a kill a watt, and could watch the watts go down the more I closed the ball valve. It went from its rated 47 watts down to 31 pretty easily.

it must work different then on a magnet driven motor than a regular (wired motor) Because I saw a demo with a motor and a amp meter when a load was put on the motor the amps shot up.
thats why I stated "(not sure if this holds for mag type pumps)" in the above post thanks for the info

What kind of motor are you taking about?
If the motor has the capability to produce X amount of force constantly (to a limit), even if the “load” varies, then yes it will consume more energy to push/move a higher load. Just like a car engine, it can achieve x mph but the more weight the car has the more gas it will use to achieve that speed.

Most water pumps in this hobby will produce less GPH the higher the head pressure gets hence reducing the energy consumed.