Will This Damage My Pump?

[AnOldUR]

I look at using a speed control on a magnetic drive pump like pedaling a bicycle up a hill. Throttling back on the output side is like gearing down. The magnetic drive does the same work, only the impeller spins slower. By lowering the power to the pump, you’re staying in the same gear, but moving slower because you’re too weak.

 

[wardens355]

Getting back to pumping through the bottom port, help an old guy understand this in simple terms. In my eyes, if pumping from MLT to kettle on a single tier system, once the volume in the kettle exceeds the volume in the MLT, gravity is pushing fluid back on the pump and increasing the work required. Just as in the early part of transfer, gravity is assisting the flow by pushing wort out the valve. With no pump, the two vessles are trying to reach equilibrium. By pumping higher into the kettle (draping the hose or a higher kettle port) it seems there'd be a more consistent and manageable load. The only work the pump has to do is offsetting the height distance between the current level in the MLT and the highest level of the hose.

The discharge hose is filled with liquid to the discharge point, so that is the pressure on the pump. If the kettle is filled below that point and you are connected below the liquid surface, there is less pressure on the pump. And you are mistaken that once the volume in the kettle exceeds the MLT volume it will push back to the pump. It is the height, not the volume, that drives the hydraulic gradient. You are correct that the flow may be more consistent with a fixed, free discharge point above the liquid surface, but the flow rate will be lower overall.

 

[DNKDUKE]

I pump from my MLT into the bottom valve on my kettle every time. No worries on the pump. Once I'm done transferring I spray Star San into the open end of the valve. A 60 minute boil will kill any other potential 'baddies' in the valve assembly. Never had any gunk getting into fermenter. Once again, no worries.

It may "kill any other baddies" but those baddies can still potentially give you off flavors.
I like BIG-H's reasoning and believe that that is exactly where I picked up some off flavors on a couple batches....FWIW.

 

[augiedoggy]

It may "kill any other baddies" but those baddies can still potentially give you off flavors.
I like BIG-H's reasoning and believe that that is exactly where I picked up some off flavors on a couple batches....FWIW.

I would think it would take quite a bit of gunk to give 5 gallons of beer a noticeable off flavor? Not saying its not possible just that I think a tiny bit in a ball valve would have to be really nasty stuff to do so and if someone flushes the system out after every brew that wouldnt be likely to happen...

 

[AnOldUR]

And you are mistaken that once the volume in the kettle exceeds the MLT volume it will push back to the pump. It is the height, not the volume, that drives the hydraulic gradient.

Guess I made an a$$ of me by assuming that the vessels were the same size (like mine), so the height would be the same at equal volume. (Not to mention how grain absorbsion factors in.)

Regardless, isn't it hydraulic pressure that increases the load on the pump as the kettle level increases beyond that of the MLT? Isn't that hydraulic pressure from gravity much greater from a full kettle than in a half inch diameter hose?

 

[AnOldUR]

I would think it would take quite a bit of gunk to give 5 gallons of beer a noticeable off flavor?...

I have to agree. And since I always drain the first pint or more into a pitcher before sending the rest to my fermenter, it becomes even less of a problem.

 

[wardens355]

Guess I made an a$$ of me by assuming that the vessels were the same size (like mine), so the height would be the same at equal volume. (Not to mention how grain absorbsion factors in.)

Regardless, isn't it hydraulic pressure that increases the load on the pump as the kettle level increases beyond that of the MLT? Isn't that hydraulic pressure from gravity much greater from a full kettle than in a half inch diameter hose?

No. Imagine you have a kettle filled with water, and a tube connected to the bottom couple. Raise the tube up and the water level in the tube is going to be the same as in the kettle. If it were as you describe it, the level of water in the tube would be higher (I assure you this does not happen for an open top, non-pressurized tank). I think I posted a link earlier in this thread that goes to a basic hydraulics page. I suggest reading that if you want to better understand.

 

[dmcman73]

Yes I believe it still generates more heat which is what I was talking about when I mentioned all the magnetic ones I have seen heat up and warp when the filters became partially plugged and restricted flow. in my aquariums and reef tank, Yes it was restricted on the input side and not the output but I dont believe that makes a difference since the plastic actually melted/warped and caused the magnets to seize in some cases.... It is still putting more resistance on the coil that drives the magnet in the pump which I believe = more heat from what I've seen. why else would they heat up and warp? they operate like a big turbine of alternator only instead of producing they are consuming energy...both of them generate different amounts of heat based upon the "load" put on thier magnetic field right?

It makes all the difference in the world! The fluid is acting as a coolant and lubrication for the pump. Restrict the flow on the input and you just restricted the lubricating factor the liquid provides and the cooling of it as well because you are essentially starving the pump, this creates a lot of heat.

Restrict it on the output side and the pump head will always be filled 100% with fluid (if it was primed properly) and will have that required lubrication and the liquid will keep the pump as cool as the liquid is.

These motors were built to handle the amount of force you apply to them by restricting the liquid flow on the output side and the magnet drive prevents the motor from stalling and over heating like a shaft driven pump would do.

 

[AnOldUR]

No. Imagine . . .

So, I was confusing pounds with pounds per square inch. PSI is determined by depth not volume. Makes sense when I think about it.