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Old 12-10-14, 07:35 PM   #33
Mikesolar
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Quote:
Originally Posted by solarhotairpanels View Post
Sunspot...


Oxygen entering copper pipes over time can damage internal pump parts without a doubt.. however we are talking years here for this type damage to occur as far as I've read.

It's very important to remember on a drainback system that a vacum lock does not occur inside the piping during drainback to the tank.

If when the pump shuts off the water is vacum locked, all of the water will not drain back to your storage tank.... thus the remaining water outside in the pipe or collector could FREEZE causing all kinds of issues.

So note.. my findings are that...
You have to allow some air to enter the pipe when the pump shuts down.

Many DIY drainback tank designs similar to yours has the collector return pipe enter the top of the tank but does not allow that pipe to touch the water when the tank is at it's most full level.

This way.. when pump shuts down and water begins to return, air is sucked into that pipe allowing the water to flow freely in BOTH directions. Down the return pipe and also back down the pipe thru the pump.

The other thing that can cause a problem is what I mentioned before to you is the check valve inside your collector pump.

If your pump is so equipped...That valve can stop water from returning back down the pipe THRU your circulator pump. The valve would have to be removed to allow free flow back thru the pump. Know what I mean?

Some pumps have the valve in there to keep the pumps primed with water for next startup...

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A couple of corrections here. There are very many well designed drainback systems (I am talking about 1000s of installs mainly in Europe) where there is no ability for external air to get into piping during drainback. They work very well, even better than those that allow air in.

When you have a sealed system, the water DOES drain back, but it does so a bit slower and this is not an issue if the piping is sized correctly. Also, the sealed air means that the O2 in the air adheres to the pipe wall and ferris components and you are left with mostly nitrogen in the piping which is preferable. Iron pump corrosion is almost non existent.

Pump check valves on normal circulators are not there for the reasons stated. They are there to prevent reverse flow in parallel circuits. Using a circulator in a non pressurized open system is a tiny part of the market.
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