mag pump problems

[douggiestyle]

ive a mag 9.5. when i do a water change and shut the pump down it restarts with one of two different "powers", let me explain more. i do ten gallon water changes (exact) i remove ten gallons and replace ten gallons. some times when i start the pump up my sump is a couple gallons short. some times its right on. some times its a couple gallons two high. never in between. i am contributing this to either an increase (or decrease) in the power of the pump (maybe due to pump impeller rotation?). when i am a couple gallons short there is a higher level in the tank and vice versa. some times if i shut the pump down and restart it my sump is back to the right level.
is this something that others have experienced?

im all ears
thanks,
doug

 

[reefrunner69]

I can think of several reasons this might occur, for times when the sump is low (pump, pumping very fast...stopping the pump has broke loose dirt in the impeller houseing, or slime in the return pipes, or both, the opposite when the reverse s true. There is also the possibility that it's not the pump (and the most likely as well) and it is the overflow that is the culprit.

 

[Bearfan]

Sounds like you're pumping faster than it can return maybe? I have a globe valve to regulate my return flow.

 

[Brisc0]

Its dirt/sediment accumulation like RR said, or perhaps the head pressure is not equalizing appropriately. I have found that a check vavle on the overflow will cause fluctuations like that after startup sometimes. Do you happen to have one?

 

[douggiestyle]

its definately not dirt or over flow problems. i am sure that it is impeller spin direction.

no check valve on the overflow. how does that work?

 

[Brad]

Check valve

Check valve is a one way pass for water to return to the aquarium. If the pump is off, it prevents water from flowing backwards down the return line back into the sump.

...back to this water level mystery. There is only so much water in the system. If the sump level goes UP...the tank level must go DOWN. If the sump is DOWN, the tank must be UP.

Unless water is going somewhere else (like into the basement!), the speed of the pump can only mildly influence this relationship. Outflow will always equal inflow. If it didn't, you would have a flood.

The overflow of the tank prevents water from rising excessively in the tank. If the overflow uses a siphon, air in the siphon can restrict the flow of the siphon causing the tank level to be higher in order to get equal flow to the sump. This would cause the sump level to fall.

That's my guess...some sort of restriction on the overflow or siphon. Dirty overflow box filter, or air inside the siphon.

 

[douggiestyle]

Check valve is a one way pass for water to return to the aquarium. If the pump is off, it prevents water from flowing backwards down the return line back into the sump

i understand what a check valve is. but cant figure out how you can put one on an overflow?

I have found that a check vavle on the overflow will cause fluctuations like that after startup sometimes

 

[douggiestyle]

inside the mag pump is a rubber flapper of sorts that directs flow. when i disassembled the pump to check for dirt the flapper was bent in the direction indicated in the picture. it is not very flexible. as you can see if the pump impeller spins one way flow will be more restricted than if it spins the other way. it most definitely appears to be a problem with pump design. some that have the same flow problems i am having may be contributing them to the wrong source.