March pump math - maximum head - Home Brew Forums

 Home Brew Forums > March pump math - maximum head

03-29-2010, 01:00 PM   #1
nostalgia

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No, this isn't posted in the wrong forum you sicko Although this is as much brew science as equipment, I guess.

ANYway, I use my March 809 to pump into my MLT from the bottom - in other words when filling the MLT with hot liquor, I use the outlet as the inlet and the water pumps in through my braid.

It works great, but now I'm designing a new (and larger) brewhouse, so I'm curious about whether this will continue to work as the volumes get larger.

The max head for an 809 is listed as 4.3 feet. What I'm curious about is how the weight of the liquid *above* the end of the hose factors in. I see two possibilities, but I don't know enough to know which is correct:

1: It's just inches of liquid above the hose. E.g. if my MLT's inlet is 3 feet above the pump and there's 6" of water in the MLT, the pump sees a head pressure of 3' 6".

2: The surface area of the water matters, as there will be more water for atmospheric pressure to push down on.

There has to be a point where the pump can't overcome the pressure of the water above it. But if #1 is correct, it won't matter if I pump from the top or the bottom, meaning I need fewer connections.

Thanks!

-Joe
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03-29-2010, 03:14 PM   #2
Catt22
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#1 is correct. Think of the head pressure as the force of the weight of a column of water. The pressure at the lowest point is the same regardless of the surface area. When the fluid is not moving (static head) the pressure will be 0.43 psi per foot of depth (for water). When the fluid is pumped and moving there will be frictional forces to overcome which will increase the head pressure. The positive head on the suction side of the pump (assuming there is some) also comes into play and offsets the pressure head on the output side. With a max head rating of only 4.3 ft spec on the pump, you will be approaching the limit with 3.5 ft + frictional losses so I would expect the flow rate to slow substantially as you fill the MLT. Positioning the HLT relatively high will help a lot.

03-29-2010, 03:18 PM   #3
Whiskey
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What model 809 are you using? The 809 PL-HS that is pretty much the standard sold at HB supply stores has a max head of 12'.

My system has the pump almost on the floor and pumps it about 6 feet vertically and still has enough pressure to cause a whirl pool in my HLT.
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03-29-2010, 03:27 PM   #4
Mista_Sparkle
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The head is the difference in the 2 fluid levels , so if you have 1' of fluid in your MLT, the pump is 1' below that, you could pump the fluid back up that 2 feet, and an additional 4.3' above that. Granted, as you approach max head, your flow rate will suffer.
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03-29-2010, 03:30 PM   #5
Bobby_M
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It really doesn't matter because you'd still be pumping the same head if you extended the delivery hose up to the recirc/sparge port anyway. Wait, actually pumping through the output is probably faster because the head slowly increases as it fills. The other way, the head is higher for the whole cycle.

Sounds like a good thing to test for the heck of it. Time it with just water. I wonder if the gravity of mash will have a significant impact.
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03-29-2010, 03:44 PM   #6
Catt22
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The specific gravity of the mash will have an influence, but it will be rather small. The mash being a slurry of liquid and solids (the grain husks), I suspect that the mash density will be less than that of plain water alone as the husk material is very light.

03-29-2010, 03:54 PM   #7
nostalgia

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Quote:
 Originally Posted by Whiskey What model 809 are you using? The 809 PL-HS that is pretty much the standard sold at HB supply stores has a max head of 12'.
Oops, you're right - I was looking on the 809 page, not the 809HS page. Thanks for pointing that out!

-Joe
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03-29-2010, 03:55 PM   #8
nostalgia

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Quote:
 Originally Posted by Mista_Sparkle The head is the difference in the 2 fluid levels , so if you have 1' of fluid in your MLT, the pump is 1' below that, you could pump the fluid back up that 2 feet, and an additional 4.3' above that. Granted, as you approach max head, your flow rate will suffer.
Ok, so if my HLT and MLT are on the same tier, I just have to make sure my MLT is shorter than 12'. I should be able to handle that

-Joe
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03-29-2010, 05:00 PM   #9
Mista_Sparkle
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Quote:
 Originally Posted by nostalgia Ok, so if my HLT and MLT are on the same tier, I just have to make sure my MLT is shorter than 12'. I should be able to handle that -Joe
Hmm, I'm not sure I'm following that. Something like this

Code:
```       ─┬─── │~~~│
│    │HLT│
4.3' ╔╪   │
│   │   │   ║└───┘
│~~~│ ──┴─  ║
│MLT╪═╗     ║
└───┘ ║     ║
║     ║
║     ║
║     ║
║     ║
pump ══╝```
or whatever you plan on doing
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