Circulators Push or Pull

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  #1  
Old 08-09-02, 11:41 AM
PipeBender
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Question Circulators Push or Pull

What is the current feeling on the "best" way to install heating circulators? On the Feed side or the Return side of a loop system.
 
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Old 08-09-02, 11:54 AM
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Cool

If you're talking about water heating, here is an illustration from Laing:

Looks like it's on the Pull side to me.
Good luck!
Mike
 
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Old 08-09-02, 12:06 PM
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Question Re: Circulators Push or Pull

I am talking about a Hot water Heating System (loop system using zone valves ). There seems to be professionals on both sides of the issue but none can give a good reason for their choice. I would welcome a discussion about this issue. Is it becuase of pressure in the boiler (good or bad), air getting into the system (from where?) and / or cooler temps on the return side ?
 
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Old 08-09-02, 12:22 PM
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Cool

You might get a faster answer about that over in the Heating & Cooling forum, but maybe one of the pros in here (I'm not one) can give you their opinion, too.
Good luck!
Mike
 
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Old 08-09-02, 05:12 PM
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Pulling water and discharging into the cold water inlet side of the heater.
All the factors you mentioned are taken into account along with the size of the system.
Heat loss can be surprisingly large on systems (not hydronic heating systems, but just domestic hot water systems) and the recirc system puts a large load on the building cooling system.
Don't know about the air problem you listed, but do know about gases released from cold water while heating take place. This is a natural occurance in tap water with systems using surface water from river or lakes during winter conditions and the water can "hold" much more dissolved gases.
 
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Old 08-11-02, 10:49 AM
SNAKEMANN233
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Originally posted by notuboo
Pulling water and discharging into the cold water inlet side of the heater.
All the factors you mentioned are taken into account along with the size of the system.
Heat loss can be surprisingly large on systems (not hydronic heating systems, but just domestic hot water systems) and the recirc system puts a large load on the building cooling system.
Don't know about the air problem you listed, but do know about gases released from cold water while heating take place. This is a natural occurance in tap water with systems using surface water from river or lakes during winter conditions and the water can "hold" much more dissolved gases.
sounds like it is air locked one way to get rid of air is to install two shut off valves one at each end to shut the flow from either side than install a tee on the out take side the tee is to put a water hose to feed line on the intake side shut valve so you can force the air out.
 
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Old 08-11-02, 12:13 PM
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System has not yet been installed so it's not air locked. I am just trying to figure best way to install circulators.

I am getting some feedback that the main reason to put the pumps on the "feed" side is to reduce/prevent air introcuction. So far it is a toss up. Some say put the pump on feed (before air scoop and expantion tank) other say put the pump on the "return" lines to reduce the heat on the pump and gaskets.

I will keep everyone posted as I get more feeback from this and other forums.
 
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Old 08-12-02, 09:48 AM
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I'll add my comment based on a bit of theory - cavitation at the pump impeller. The higher the water temperature, the more likely the pump will cavitate - all else being equal.
 
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Old 08-12-02, 06:09 PM
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The pumps used for hot water recirc have a temperture range for recommended usage. On the average domestic, residential system, water temperature is not an issue. Heating systems using high temp and high pressure (commercial - industrial), totally different story.
You can install air reliefs on high points if you are real concerned about air introduction into the system. I have installed systems with and without them, depending on what was designed.
 
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Old 08-13-02, 08:25 AM
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I understand that the circulators are "spected" for the temperatures we are talking about (~190 deg F) but what do these temperatures do to the life span of the unit?

It is interesting (disappointing) that we have not heard from any Technical Reps from either the boiler or circulator manufacturers on this issue.
 
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Old 08-13-02, 05:20 PM
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Not as much as you would think. Motors are built for higher operating temps. (Stardard ambient temp is 40 C on most pump motors)
When you start getting into higher temp and pressure range (say 350 PSI @ 375 F - still classified as hot water, not steam) you will need greater clearances and positive ventilation for large motors (have seen water cooled electric motors on applications over 1000 HP) but the pumps themselves are not really affected as the seals or packing are built for this application.

I am interested in the pressure aspect of this original question. I have seen dozens of pull systems on strictly domestic (tap) hot water recirc. Have seen push on boiler loops, with push to building loops, then push to indivual buildings (this was a heating system) and the return the residual pressure on the building loop back to the boiler loop.

I'd like to ask someone who designs these systems about the check valve after the pump where the recirc water is pushed back into the cold water inlet side of the heater. Have seen it with and without, it doesn't look like it matters. In theory it should, in the real world.....just a thought.
 
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Old 08-13-02, 06:34 PM
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I sent a note off to Buderus and Taco to get their thoughts. The Buderus folks said that it did not matter. Haven't heard from Taco yet.

It may be that no one wants to show their lack of knowledge but there has to be an engineering reason for preferring one way over the other, especially when considering the possibility of a failure in another system component.
 
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Old 08-13-02, 08:37 PM
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My experience with circulating pumps is that they run more efficiently when pushing water through a restriction than when pulling. Considering that the boiler would offer resistance to the flow of water, especially a tube boiler, the pump should be before the boiler.
This logic also applies to blower fans. They are always installed before the system's restrictions.
 

Last edited by GregH; 08-13-02 at 09:13 PM.
  #14  
Old 08-13-02, 08:39 PM
SNAKEMANN233
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PUSH OR PULL

I THINK THE PUSH AND PULL IS ONE IS ON A HOT WATER BOILER THE OTHER IS IF YOU HAVE A STEAM BOILER AND WANT TO PUT A BASEMENT ZONE
 
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Old 08-14-02, 08:02 AM
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Responce from Taco

In a low head residential system, circulator location is not critical. If you were to purchase a packaged boiler most will have the pump on the return side. It would be very rare to have any issues caused by pump location on a low head system. The correct location (and our recommendation) is on the supply side of the system, pumping away from the expansion tank. This should eliminate any possible issues. If you have any questions please feel free to contact us anytime.

Regards,
Rick Brindamour
Technical Services
401-942-8000 Ext. 275
 
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Old 08-14-02, 06:33 PM
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Good info. I usually replace Taco pumps with Bell & Gossett , but I would be interested in what Old Red at B&G has to say about this.

Interesting point also on their response was about the expansion tank. Have seen these everywhere on systems. Usually most convient location for plumber to place it. The assumption is made by them that it is on the heated water side.
 
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Old 08-14-02, 07:19 PM
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I do not have the email for "Old Red" but if he is monitoring the forum I would also be interested in his input.
 
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Old 10-01-02, 10:33 AM
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Well, after some searching I did find the B&G web site. (www.bellgossett.com). There I found quite a bit of good information. One of the most relevant was a "CounterPoint" newsletter article titled Five Good Reasons to Pump Away!, vol 8 Issue 1, published January 2001,

I would encourage all to go to that site and read this article.
 
 

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