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Old 07-11-2010, 10:52 PM   #1
rshosted
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I had a problem in the middle of a brew yesterday. I was using the march pump to push my sparge water up to the sparge arm. I noticed my sparge was a little cold, so I turned up the temperature of the sparge water. It got up to about 190-200 and the water would stop pumping. I took the head apart and everything looked good. I put it back together and the pump did not work. The water cooled to 185 and the pump worked again. It was pushing very strong again. As soon as I turned the water pressure back up, boom no work again.... any ideas on this?

Just a few notes: the pump worked very well below 185. I am using 1/2 line and was not pushing much head (5' or so). Primed the pump well with a good feed line.

 
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Old 07-12-2010, 01:33 PM   #2
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I'm assuming the pump is still spinning, but not moving anything? The pump is probably cavitating at higher temperatures and trying to push steam around doesn't work well. Some times you can restrict the output flow (increasing back pressure) and reduce the cavitation. The other alternative is to mount the pump lower to increase the input pressure.

 
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Old 07-12-2010, 01:57 PM   #3
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You have to limit the flow rate as david mentioned. I can pump up to 210F with a restricted output. Once you hit boiling, you have to kill the flame to be able to pump because boil bubbles will start collecting in your siphon tube and you will lose prime in the pump.

Essentially what is happening is you're creating a slight vacuum on the pump input line and liquid boils at a cooler temp under vacuum.
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Old 07-12-2010, 02:03 PM   #4
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How do people recirculate during the last 15 minutes of a boil then to clean a CFC? I thought this was common practice and one advantage I am really looking forward to when incorporating my 809.
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Old 07-12-2010, 02:07 PM   #5
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The pump is cavitating at the higher temperatures. Increasing the positive head on the suction side of the pump (ie mounting the pump lower) will help to mitigate the problem, but I don't think restricting the output flow would be a good idea at all. I've found that it's best that all hoses and fittings have a minimum ID of 1/2" (equal to or greater than the pump inlet ID). Check the inside diameter of all fittings on the suction side. I would bet that some have less than a full 1/2" clear opening. A fitting for a 1/2" hose will typically use a barb with an inside diameter of only about 3/8" and sometimes less than that. Those can be a major bottle neck and on the suction side it's critical to minimize restrictions of any kind for maximum performance.

 
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Old 07-12-2010, 02:17 PM   #6
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Quote:
Originally Posted by Catt22 View Post
The pump is cavitating at the higher temperatures. Increasing the positive head on the suction side of the pump (ie mounting the pump lower) will help to mitigate the problem, but I don't think restricting the output flow would be a good idea at all. I've found that it's best that all hoses and fittings have a minimum ID of 1/2" (equal to or greater than the pump inlet ID). Check the inside diameter of all fittings on the suction side. I would bet that some have less than a full 1/2" clear opening. A fitting for a 1/2" hose will typically use a barb with an inside diameter of only about 3/8" and sometimes less than that. Those can be a major bottle neck and on the suction side it's critical to minimize restrictions of any kind for maximum performance.
+1 Def try reducing any restriction on the inlet before reducing output. Even tight bends can cause cavitation.
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Old 07-12-2010, 02:44 PM   #7
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Quote:
Originally Posted by IrregularPulse View Post
How do people recirculate during the last 15 minutes of a boil then to clean a CFC? I thought this was common practice and one advantage I am really looking forward to when incorporating my 809.
You can't pump boiling wort due to the cavitation problem You can, however, pump wort that is slightly below boiling temperature. How much below depends on the head pressure on the suction side of the pump. Typically, when circulating in a loop through a CFC and back to the kettle, the kettle will be full which provides maximum positive head on the suction side while doing the circulation thing. This is a little different than say pumping hot water from a kettle to an elevated HLT as the head on the suction side will drop as the water level in the kettle falls. We're talking about a very small pressure change, but when it's borderline to begin with, it makes a noticeable difference as it will often be a go/no go situation. The second thing is that when circulating through a CFC like that, you are mostly just pumping horizontally and not up to an elevated kettle, so there is little head on the output side working against the pump. I can easily pump through the CFC and back to the kettle very shortly after shutting down the burner.

 
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Old 07-12-2010, 02:55 PM   #8
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Quote:
Originally Posted by IrregularPulse View Post
How do people recirculate during the last 15 minutes of a boil then to clean a CFC? I thought this was common practice and one advantage I am really looking forward to when incorporating my 809.
I just run it really slow through the CFC and back into the kettle, nothing like boiling wort to sanitize things But I usually just do the last 5 or so of the boil.

 
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Old 07-12-2010, 03:09 PM   #9
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I gotta be honest, I would not buy another march pump. They are too tempermental. I'm really interested in changing pumps.

 
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Old 07-12-2010, 03:29 PM   #10
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Quote:
Originally Posted by rshosted View Post
I gotta be honest, I would not buy another march pump. They are too tempermental. I'm really interested in changing pumps.
IMO, you could get the March pump to operate just fine if you use short, large diameter hoses on the suction side to minimize the restrictions. That and a bleeder valve I am sure would solve the problems. IOW, I don't think the pump itself is at fault. I use thick walled 5/8" ID hose throughout my system and have no problems at all with the pump. The 5/8" ID allows you to use barbed fittings that have an ID of 1/2", so nothing is less than that anywhere. I really think this is the key. The thick walled tubing resists kinking when used to pump very hot liquids. Often I see people using 1/2" ID tubing without giving any thought to the ID of the connection fittings and that can sometimes cause problems.

 
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