maintaining a siphon loop with circulator

[hodad]

I use large non-pressurized tanks to store solar heated water, which is later drawn off to heat via radiant tubing (pex).

Here's the problem: The tanks hold water in the temp range 100-180 deg F. Construction of tank includes an outer frame lined with semi solid insulation, and a high temperature rubber bladder on the inside. I don't want to poke a hole through the bladder, and so I pull the water out thru a siphon loop utilizing a closed-loop style hydronic circulator (Taco 009 usually). Each sunny day I send the water vertically about 16' to the solar panels. When the sun stops shining, the water "drains back" into the tank thru the siphon loop.

The system works well, unless air builds up in the siphon loop over time until the water column is interrupted and the siphon action stops. THis can happen if there are any microscopic air leaks in the siphon loop, but may also happen due to air coming out of solution. Then the circulator then spins until it burns up. I can "flush out" the air bubbles, but am not always there to monitor the siphon loop.

This doesn't happen very often, but does occasionally. I would like to include an active (and inexpensive) way to ensure that the siphon is maintained (i.e., any air bubbles are continuously removed from the siphon loop). Note that hHe "drainback rush" when the pump turns off is impeded somewhat by flow control valves and the circulator, and so doesn't have the force necessary to "push back" the bubbles to the siphon intake at bottom of the tank. An air bleed valve (top hat or Spirovent won't work because of the vacuum inside the loop.

Diagram (hopefully not garbled):


_______________
/ /
/______________/
|
|
|
|
|
_____ |
| | |
____|____ | |
| | | | |
|^^|^^^| | |
| | | | /\ circulator
| | | | |
| | | |___|
|___^____|


Any suggestions would be appreciated.

Thanks!

 

[BigInch]

An air release valve might work. Check into it.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[Castlemoor]

An air valve won't work on a partial vacuum.

At the siphon apex, you could try adding a vertical leg or a secondary loop that extends above the elevation of the active siphon. You will need a valving arrangement, a fill cock on top, or some other arrangment to fill the leg/loop. When filled, it will act as a reservoir in which the water will gradually be displaced by air coming out of solution, while the siphon below continues to function. This approach, while not fully automatic, will reduce the frequency of having to recharge the siphon. And if you construct the leg/loop of suitable translucent tubing, you'll be able to monotor the level and refill before the siphon is broken.

 

[BigInch]

I thought it work enough when the pump's on. I thought that might be enough to clear the air, but don't know how long it might stay clear, in which case the pump could be run a bit.

But, your solution is better.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[rmw]

Castlemoor has given you a good solution. I once saw a large power plant replace a condenser manufacturer's rube goldberg vacuum pump w/associated controls arrangement for air evacuation from the circ water siphon loop's air off take with a simple loop like the one that C'moor described. They used PVC and ran the loop all the way up to the turbine deck (about 100 feet above the siphon loop). It was amazingly simple but brutally reliable. It solved a lot of problems.

Your problem is that as your water heats up the oxygen solubility of the water decreases and it gives off some of the air in it. That air has to be removed, or it will build up and break you siphon. That is what is happening in your case.

So it is a vacuum pump or an upper leg. Your choice.

rmw