Circulator on supply, no circulator on return.

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Old 01-06-11, 10:23 PM
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Circulator on supply, no circulator on return.

I recently returned to a website noted in many postings here to refresh my memory on boiler bypass piping and read that "the standard to day is to have the circulator mounted on the return pumping away from the expansion tank"
I am curious why this is so, can someone tell me why this is so. How do you benefit from having the pump(s) on the return side?

Thanks in advance.
 
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Old 01-07-11, 05:43 AM
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that is not a completely accurate rule of thumb.

We normally place the circ. on the supply pumping away from the point of no pressure change (expansion tank, fill point), pumping into the heat emitters. This tends to add PSI to the system and can prevent top floor rads from dropping pressure that will happened if your pump is on the return.

Now boiler pumping is a different story, with most mod-cons being the restrictive little buggers they are, you do not want to pump on the supply side as you tend to drop the pressure on the exit of the heat exchanger and that reduces the boiling point and can create some bad problems.

Does that help ?
 
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Old 01-07-11, 08:42 AM
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If your system is working satisfactorily, there is no benefit to changing the pump position. Best to leave it the way it is. Millions of boilers were installed with the pump on the return, pumping toward the expansion tank (located on the supply), and they worked fine. That is the way B&G recommended for many decades.
 
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Old 01-07-11, 10:29 AM
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I believe that this question came up recently in another thread and it was determined that there is a TYPO MISTAKE on that website... why not contact the author and ask if that is correct ?
 
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Old 01-07-11, 12:37 PM
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I should have worded this differently. Would the circulators be better off after the expansion tank or after the cast iron radiators closer to the boiler?
 
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Old 01-07-11, 12:50 PM
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Forget about where the radiators are. Ideally, the pump(s)' suction should be just downstream of where the expansion tank tees into the main.

You original posting confused me. The title is opposite of the body of the post. But, anyway, forget both - they are misleading.
 
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Old 01-07-11, 12:54 PM
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Let me clear things up....what image below makes more sense?

....or

 
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Old 01-07-11, 01:04 PM
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The first diagram is preferred for the reason TOheating explained.
 
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Old 01-07-11, 01:15 PM
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That's what I thought also. How much of a psi loss can you have if the pumps are to go right before the boiler?
 
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Old 01-07-11, 02:12 PM
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Originally Posted by zizanio View Post
How much of a psi loss can you have if the pumps are to go right before the boiler?
Depends upon where you measure it. At the top of the system, the pressure in the second drawing will drop more. If you are asking for a quantitative answer, we'd need a whole lot more information about your system and probably more time than most of us have.
 
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Old 01-07-11, 05:08 PM
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Ballpark I would say that 5 PSI across the pump is not out of the question.
 
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