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Old 07-14-2010, 11:44 AM   #1
DustinHickey
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Default 3 questions regarding march pumps....

I am about to buy a march pump model 809hs to pump my hot wort out of my morebeer kettle, through a counterflow chiller, through a venturi valve, and into my fermentor. My kettle is kind of low and this isnt a loop system so i have the following questions:

1) what is the net suction head pressure for this pump at boiling?

2) my chiller is 3/8" copper, do you think there would be a problem if i ran all 3/8" tubing upstream of the pump to the venturi valve?

3) in most march pump systems where the pump is below everything, is the beer that remains in the line after pumping just figured as a loss or does it usually siphon out?

Thanks for your help.
Dustin hickey

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Old 07-14-2010, 02:44 PM   #2
Catt22
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Here's my best guess at the answers to your questions:

1. Go here for info on this: http://www.engineeringtoolbox.com/boiling-point-water-d_926.html
When the liquid is at the boiling point, vapor bubbles will form in the kettle and when they reach the pump head it will lose prime. Just below the boiling point the pump can still cavitate, but at what point depends on the pressure head on the suction side of the pump among some other things such as the speed of the impeller, flow rate, restrictions in the suction line, etc IIRC. The bottom line is that you won't be able to pump boiling liquids at all and generally not until the temps fall somewhat below 200F with the common home brewing configurations we typically use. I'm not proficient enough with pump calcs to take it any further than that and I may not have this exactly right, but I think it's fairly close to the way it works.
2. The 3/8" tubing will work, but only marginally so. Assuming it's tubing that you are using, then that would be the outside diameter. The inside diameter would be something like 1/4" which is on the small side and quite restrictive. This will inhibit the flow rate considerably. Whether or not that could be a problem I cannot say without more information. I'm not clear on the purpose of the venturi valve. Is this for aeration or what?
3. Yes, in most systems this wort is just chalked up to a loss. In any case, the volume is likely very small and not worth worrying about or trying to recover. You can easily calculate the volume in the line and when you do so, you will realize that it is rather trivial. It will be much less than you think.

Hope this was of some help. I'll defer to others for refinement and corrections.

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Old 07-14-2010, 03:01 PM   #3
DustinHickey
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Thanks Catt22,
Further comments..

1) Understood. I will not be pumping boiling liquids since I am pumping from my kettle just to cool the wort. My main question is how much net suction head pressure is required at the pump inlet, or in other words ( how much lower than the kettle does the pump have to be? )

2) The tubing I will be using is 3/8" inside diameter on the upstream side of the pump. Sorry I should of specified.

3) Ok. sounds good.

Thanks
Dustin

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Old 07-14-2010, 03:08 PM   #4
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1. A good rule of thumb for this is about 1 foot of drop to the pump head. You can get by with less, but it will be harder to prime the pump. So long as you can get a gravity flow to completely flood the pump volute, you will be good to go. A bleeder valve on the output side of the pump makes this a snap.
2. 3/8" ID is better. Still somewhat restrictive which will inhibit the flow, but as long as you are happy with the flow rate it's OK. Go to larger tube if you want to improve the flow rate, but that's really the only issue.

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Old 07-14-2010, 03:11 PM   #5
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1) ok that should be no problem. I will be approximately 1'-0" below the bottom of the kettle.

2) It is only going to be about 3' of 3/8" tubing and then my 25'-0" counterflow chiller which is also 3/8" copper tube. If it wasnt for the chiller i would stay all 1/2" but at the moment I have no choice in the matter i guess.

Thanks for our help Catt22.

Have a good day.

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Old 07-14-2010, 03:22 PM   #6
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Quote:
Originally Posted by Catt22 View Post
The bottom line is that you won't be able to pump boiling liquids at all and generally not until the temps fall somewhat below 200F with the common home brewing configurations we typically use.

Catt, I have no problems pumping boiling wort with my March. I circulate though my coil for sanitation before I turn off the burner.
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Old 07-14-2010, 03:40 PM   #7
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Quote:
Originally Posted by arturo7 View Post
Catt, I have no problems pumping boiling wort with my March. I circulate though my coil for sanitation before I turn off the burner.
Then it ain't boiling. With enough positive head on the suction side, it's possible to mitigate the cavitation problem. If it's actually boiling and vapor pockets are forming, the pump will lose it's prime. At least that's what has happened in my experience. Perhaps you know a trick that I don't to overcome this problem. You can pump liquids that exceed the standard boiling temperature of 212F if it's a closed pressurized system, but there again, the liquid is not actually boiling due to the increased pressure. The hotter the liquid, the higher the pressure would need to be. A good example of this is the cooling system on a car. The radiator cap typically keeps the pressure at 15 psi above atmospheric so the coolant can be above 212F without actually boiling. We aren't dealing with a closed system, so our limit is the atmospheric pressure plus whatever minor positive suction head we have and that is usually only about 1 or maybe 2 psi depending on the liquid level above the pump head. I can pump through my chiller and back to the kettle at just under boiling temps, but I can't pump to any significant height, such as my elevated HLT (5-1/2 ft +) at anything above 200F. There are more than a few variables that can affect this such as the flow rate, hose sizes, fittings and restrictions on both sides of the pump, so as usual, YMMV as with most everything else brewing related.
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Old 07-14-2010, 04:05 PM   #8
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My pump is about a foot below the kettle, after the pump there is 4' rise to the top of the coil. Maybe there's enough head pressure to make it work? Maybe it's not at boiling temp going through the coil?

Either way, I can maintain a boil in the kettle while I'm pumping through the coil. I'm supposing this is enough to sanitize the coil.

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Old 07-14-2010, 04:35 PM   #9
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Quote:
Originally Posted by arturo7 View Post
My pump is about a foot below the kettle, after the pump there is 4' rise to the top of the coil. Maybe there's enough head pressure to make it work? Maybe it's not at boiling temp going through the coil?

Either way, I can maintain a boil in the kettle while I'm pumping through the coil. I'm supposing this is enough to sanitize the coil.
I'm confident that the hot wort will effectively sanitize your chiller coil (and mine too). It is important to flush it out with clean water immediately after use and then run some hot Oxyclean or PBW through it at the earliest opportunity to clean it well, but you already knew this I'm sure. That's my standard procedure and I have had zero contamination problems so far. I sure hope I never do.
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Old 07-14-2010, 05:06 PM   #10
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Hey guys,
That brings up another good question. What is your procedure for cleaning your pump and lines? I am not running a loop so what do you think would be the best way to clean everything?

My system will be as follows.

More beer kettle w/ ball valve through high temp silicone beer line to pump. then from pump through silicone beer line to chiller. then from chiller directly to venturi valve and fermentor.

What i mean is that there will only be one pass through the pump and chiller. When you say hot PBW, what temperature would that be and do you think one pass through would be enough?

-Thanks,
Dustin Hickey

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