Drain back theory ,Pump priming

[jarrod9155]

  Well im ready to finish my setup and run it this weekend for the first time but my one thing im not sure about is the drain back u pipe that keeps the pump primed for the next run after the pump shuts off . The guy I bought the panels from had a problem when the pump shut off the water rushing down would over come the u pipe and create a vacum of some sort and suck the u pipe dry . His tank was only 150 gallons and that could maybe been his problem not providing enough back pressure . Before I fill the tank I might do a through hole and not worry at all instead of going over the wall of the tank . Has any one else had a problem like this . I will be draining back with a hight of 25 feet and 70 feet of 3/4 type M pipe total on the discharge side .  The u pipe drope down 2.5 feet below the water level .

Thanks Jarrod

[Photon]

I would not recommend using a standard pump for this application.

Use either a `self priming pump` or `submersible pump` in tank.

The two way auto valve on collector can be adjusted if its draining too quickly at present.

Hope this helps

[Ungrounded Lightning Rod]

  Well im ready to finish my setup and run it this weekend for the first time but my one thing im not sure about is the drain back u pipe that keeps the pump primed for the next run after the pump shuts off . The guy I bought the panels from had a problem when the pump shut off the water rushing down would over come the u pipe and create a vacum of some sort and suck the u pipe dry . His tank was only 150 gallons and that could maybe been his problem not providing enough back pressure . Before I fill the tank I might do a through hole and not worry at all instead of going over the wall of the tank . Has any one else had a problem like this . I will be draining back with a hight of 25 feet and 70 feet of 3/4 type M pipe total on the discharge side .  The u pipe drope down 2.5 feet below the water level .

Sounds like a siphon.

[jarrod9155]

Im using a taco pump , the guy i bought the panels off used a check valve with a small hole drilled in it to slow down the drain back .

[wpowokal]

I know I have a language difficulty but exactly what are you doing, what is the source of the water and is it higher or lower than your pump, and you are pumping it into a storage tank presumably to supply a dwelling. By Google I see that taco pumps are circulating pumps.

allan

[jarrod9155]

Basically there is a tank in the basement 370 gallons and it pumps up 25 feet to the roof and back down . The pump is on the side of the tank 2.5 feet below the water line . The reasson is so I dont have to use a thru hole fitting on the tank , so I go up and over the wall of the tank and down 2.5 feet .

[Ungrounded Lightning Rod]

Basically there is a tank in the basement 370 gallons and it pumps up 25 feet to the roof and back down . The pump is on the side of the tank 2.5 feet below the water line . The reasson is so I dont have to use a thru hole fitting on the tank , so I go up and over the wall of the tank and down 2.5 feet .

Bingo!  You've built yourself a siphon and it sucks the prime out of the pump.

My suggestion:
 - Get a couple reducing Ts and hook a narrow bypass, with a valve, between the intake and outlet of the pump, at a location some inches above the pump.
 - Set the valve so it is ALMOST closed.

When the pump is running it will represent a tiny leak and reduction in efficiency.

During drainback, when the air gets down to the bypass level it will suck through and break the siphon, leaving a bunch of water in the pump and plumbing below the bypass.

But the other suggestion of a leaky check valve to slow the drainback should also work (without lowering the efficiency of the pump).  Slowing the drainback means that once air passes the pump it has a chance to bubble up the U pipe and leave some water (that was in the pump leg of the U pipe) in the pump, rather than having all the water sucked into the tank in one quick shot.

[jarrod9155]

I dont like the check valve becauce it will slow down the flow in the winter i need to empty up to seven panels asap.

[wpowokal]

Put the return pipe underwater and if there are no leaks there will be no siphon.

allan

[jarrod9155]

That was what I thought also, the pump pipe that goes over the wall drops down almost 3 feet 5 inches lower than the pump is on the other side of the wall .

[jarrod9155]

[jarrod9155]

Couple pics of the tank

[wpowokal]

What I meant was the return pipe from what I assume (bad word that) is a hot return from solar collectors on your roof, if the pump suction and the return pipe are below water then there should be no siphon.

I am not quite sure what the aversion to a "through" pipe is, one can only assume "if" it leaked there would be some water in the basement, and if chicken little was correct then the sky did fall in. I can only suggest getting a hold of yourself, plumb the pump into the bottom of the tank do a good job, sit back and take a drink, if it ever leaks then accept that sh** happens, live with it and get over it.

Not meant as a personal affront but I fail to understand why people complicate life.

allan

[jarrod9155]

It is not about coplicating things it is about learning diffrent methods and more efficent ways of doing it . Second im a bodyman buy trade not a f....n plumber this drainback setup was a copy of a sytem I had studied . The point of the thread was not to harp on it and cry but provide future diy people a method that works . Thru hole fitting or bulk head fitting is fitting that would go thru the tank trust me im not scared to put a hole in the tank just finding the fitting at a local plumbing store hasnt been easy order only . And the sytem was already done this siphone
Problem was brought to my attention a little late in the game.
I fail to undstand Why people must be rude , maybe you should sit back and have a drink and just read . I hope this post hasnt become to complicated.

[Tom Sullivan]

Jarod,

   I've studied a lot of drainback systems, and always had a bit of concern about the pump suction line going over the top of the tank lip, which requires never getting any air into the line or you could lose your prime.  You obviously cannot place your return under water line, as you would lose drain back function.  I've penetrated my tank in 5 places (wooden tank with pool liner), and never had a leak.  You can look at the penetrations of my tank on my web site, about half way down the page this link takes you to.
http://www.aluminum-solar-absorbers.com/building-home-solar-collector.html 

   I always use a small piece of aluminum inside the tank, and have yet to use a bulkhead fitting (I'm familiar with them, use them at my dealership all the time).  I measure the distance through the tank wall, including the Stryo, etc. and then use two unions and a nipple of the appropriate length so when the combination is tightened, it's also tight on the tank.  I flatten the coupler on the water side for a nice fit, and seal that to the tank with silicone during the installation.  I install a good healthy bead of silicone on the back side of the aluminum plate, completely around the penetration hole, and a real good pipe sealer on the threads of the nipple and unions.
   Pump prime should never be a problem with this system.  Well, almost never.  I'm dealing with a current issue on my system deriving (I think) from pump "reactivation" too quickly after shutdown (sunny, but partly cloudy, days).  The pump was turning back on while drain back was still in progress, with a bit of air in the line "air locking" the pump.  I think I've remedied this with a delay timer I installed last night, creating an 8 minute minimum delay everytime the pump shuts off to ensure drain back is completed before the pump turns on again.

Tom

[wpowokal]

Jarrod, I seem t have missed the intent of your post, or maybe as one who does not live in a freezing environment I did not understand your need for drain back, apologies for that, it was not clear in your original post, not all members of this board live in the US of A and not all live in extreme environments.

However I did take your advice and sat back with drink in hand this afternoon (morning for you), this is a clear case of not setting out the scenario in your initial post, some understood I id not.

allan

[TomW]

It is not about coplicating things it is about learning diffrent methods and more efficent ways of doing it . Second im a bodyman buy trade not a f....n plumber this drainback setup was a copy of a sytem I had studied . The point of the thread was not to harp on it and cry but provide future diy people a method that works . Thru hole fitting or bulk head fitting is fitting that would go thru the tank trust me im not scared to put a hole in the tank just finding the fitting at a local plumbing store hasnt been easy order only . And the sytem was already done this siphone
Problem was brought to my attention a little late in the game.
I fail to undstand Why people must be rude , maybe you should sit back and have a drink and just read . I hope this post hasnt become to complicated.

Jarrod;


Be nice. He is trying to help. Folks from different cultures see comments differently.

None of us can read your mind.

Allan has been a contributor here for many years and has the respect of many here.

Say thanks for the advice and move on.

One mans "rude" is another mans "direct" I see no rudeness in his post but do in yours. Just for perspective on how things can appear differently. Remember you came to us for help!

Rude would be telling you to learn to use your spell checker but I will not go there because it would be off topic and rude to some.

Tom

[jarrod9155]

My response was to his post word for word i gave no more abuse than he gave me chicken little , have a drink , dont complicate and so on Tom sulivan gave good advice .wpowokal just said stop crying . Im big boy it really no big deal i had frogoten all about it and he posted back with his opinion of things Im cool . But you Tom w you seem make it worse i see he has alot of posts but that doesnt give him the right to  talk to some one that way language or not he had sarcasm down just fine . Tom w your hippocrit and ya my spell checks broken plus i cant spell for crap Sorry

[wpowokal]

Tom I suspect you and I have been crossed off Jarrod's Christmas list.

[TomW]

Tom I suspect you and I have been crossed off Jarrod's Christmas list.

Allan;

I don't know about you but I am truly devastated.

I will get over it and hope you do.

Sorry for the thread diversion

Tom

[tomtank]

We have done several hundred drainback systems here in Maine over the years.
Some were done with tank penetrations through the sidewall but most were done with syphon pipes over the side
of the tank. I don't like making holes in my tanks. We can do it, but unfortunately cannot rely on customers/installers
to get it right. It just is not worth the risk for us.

Syphon tubes work well if you do it right. I think you can see some reasonable plans on builditsolar.

We build a tank that is 4' deep, so the syphon goes about 3' into the tank.
The pump hangs on the outside of the tank down as low as we can do it (usually 3'). There are then two 90 degree elbows
to get the direction pointing up. We then install a boiler drain and a ball valve before running to the collectors.
This allows us to prime the pump. Air does not usually break the syphon.

The return line from the collectors has to have a vent installed in it, near the tank. We usually just cut in a tee with a vertical
pipe about a foot long for a vent. It gurgles, but we know that the system is functional when this happens. This allows for proper drainback.

It is important to use a properly sized, non-ferrous pump. You have to make sure that the pump has some reserve head
capacity beyond the system requirements.

A submersible pump is a much better solution, but there are none currently that can handle the high temperatures.
As far as I know, a self priming pump will not allow proper drainback. The system has to drain in about 2-3 minutes,

My 2 cents worth from 30 years of doing drainbacks.

[GaryGary]

Hi Jarod,

Lots of people use the U tube and most have no trouble with it.
I've got one drainback system that uses the through the tank wall and another that uses the U tube -- both work fine.
I think I would lean a bit toward the U tube just to avoid lining penetration, but the through wall is fine if you do it carefully.

TomTank and Tom S both offer some good advice.

I have heard from a couple people that did have trouble with the U tube emptying too much when the system drains back, and the pump losing prime, but this is not common.
I'd just go ahead and try the U tube -- the odds are it will work fine -- you can work the problem it it does occur.

I don't use the vent in the return line that TomTank mentions, but I think it might reduce the chance of the U tube emptying during drain back.

Its handy to add a garden hose style valve on a T off the U tube.  This allows you to prime the U tube by just hooking a garden hose to the valve, opening the valve, and turning on the garden hose to fill the U tube and get rid of all the air for the initial prime.  You should only have to do this once.

Question for TomTank:
You mention the need for non-iron pumps.
I've about convinced myself that in most cases (maybe depending on the water and pH) you can use an iron pump on this kind of drain back system:
http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm

The reasons I'm thinking iron might OK:
- The system storage tank gets filled with water once, and then no new water is introduced -- unlike many open systems where new water is introduced regularly.
- While the system is vented to atmosphere, the vent can be quite small, and (I think) little new air is introduced into the system.

I have had an iron case pump (a Grundfos) in service for 10 years that came with the house when we bought it that circulates water to the far bathroom.
It ran 24/7 for 8 years with new water being introduced all the time.  The pump has very little rust and still works fine.
I've also heard from other people who have had good luck with iron case pumps.

I'm sure Grundfos and Taco would rather sell a $300 bronze of stainless pump than a $80 cast iron pump, but I'm really wondering if its necessary in these kinds of systems with very limited introduction of new oxygen?

Have you actually seen iron pumps fail by rust in drain back applications?

Some of the internet references seem to indicate that keeping the water pH high also provides some rust protection for iron.

Gary

[tomtank]

Hi Gary,
Many people do use ferrous pumps. They are cheaper and do work for a while.
I feel that they will eventually fail well before a bronze, stainless or plastic pump will.
The iron pump will tend to stick if it sits for a short period without operating.

The other option is to use a corrosion inhibitor, which helps keep the investment cheap.

I don't like to make life more complicated. They way I keep costs down is to look on Ebay. If you are a little patient,
you can find some great deals on Grundfos and
Taco bronze pumps, which I use.
You do need to be patient, though.

The water is always going to be oxygenated by the air that is introduced during the drainback process and the fact that this is an open tank.
Tom
American Solartechnics

[jarrod9155]

Well thanks on the feed back I didnt have the greatest luck sunday with the taco pump and U pipe for some reason it just couldnt get it done , pumping all the way up 28 feet I reprimed it many times but would just start pumping really good and slowly fall off . I tested this by putting my hand in the tank near the suction pipe could just be the pump was bad it was a used unit . I was able to get a rigid 1/2 horse sump pump and it pumped it just fine actually yesterday was the first day of operation and the tank at 370 gallons 54 degrees  was at 118 deg F by ends day  . Im thinking I will try a taco 009 next becauce the sump pump sucks down 450 watts and hour and that just a little high for me . And the spliced epdm liner didnt work leaked the pressure was just to much for the seams had to add a full liner with no splices .

[Volvo farmer]

You sure that Taco pump you got is rated for 28' of head? A 009 is only rated for 34 foot of head, and only will push about 4GPM at your 28' head.  Looks like a 010, 012 and 014 aren't even rated for your amount of head.

http://s3.pexsupply.com/manuals/1249544537780/101-032.pdf

[jarrod9155]

Your right I think its only rated to 25 feet that might be the problem with the taco . Ill have to wait for a good ebay deal on a taco 009 my funds are running short .
          Also has any one measured there drain back time from when the pump shuts off I'm at 7 minutes to complete drain that's through 134 feet of 3/4 copper pipe type m cold weather on its way and I'm a little worried

[DanG]

Good luck on that, waiting for a Taco deal - there are enough resellers sniping auctions it hardly ever happens, I watched until I found another way to do it...

[tomtank]

The big factor with drainback is the pump rating.
You need a 009 or a Grundfos 26-96.

The only deals on either are on Ebay and then you need to have some time to wait for a deal. They do come up.
I can usually find them for 50% less than trade price.

I guess I am getting old since the prices on pumps really seem high.

The company that comes up with a great drainback pump will make money, from me, at least.

Another alternative is a Procon gear pump. It can pump really high heads at modest flows, but will not drain back.

There is a Dutch drainback module that uses a pump that does not allow drainback , but uses some sort of valve to open a drainback path once the controller shuts down the system.

We have been playing with gear pumps and they are interesting. Thermo-Dynamics in Nova Scotia sells them in their Solar Boiler, which uses antifreeze.
Head height and pressure drop become a non-issue with this type pump in most DHW systems.

But they ain't cheap either.

God, I must be getting really old...

[jarrod9155]

I talked with a local plumber today and said I should try putting two taco 011 or two taco 009 to get my head pressure and flow rate . Also has any put a vent on the top discharge pipe outside on the solar array like a check  valve that would open during drain back to allow air to enter and speed up drain back .  I think this weekend I will try to find a taco 011 and tie two to gather . Thanks Tom  for the gear driven idea I will look in to it .

[GaryGary]

I talked with a local plumber today and said I should try putting two taco 011 or two taco 009 to get my head pressure and flow rate . Also has any put a vent on the top discharge pipe outside on the solar array like a check  valve that would open during drain back to allow air to enter and speed up drain back .  I think this weekend I will try to find a taco 011 and tie two to gather . Thanks Tom  for the gear driven idea I will look in to it .

Hi Jarrod,
The Taco 009 does 34 ft of startup head -- I think that will be enough to get the flow started -- it meets the ground rule of having 20% more pump startup head than the 28 ft you have from tank water level to top of collector. 
It is important to carefully measure the 28 ft and make sure its not more than that.
http://www.builditsolar.com/References/Pumps/PumpCurves.htm

Once flow is established, the system behaves like a close system, and the 28 ft of startup head requirement goes away -- you only have pipe friction left.   My guess would be that the 009 will easily do the 4 gpm (and more) unless you have an awful lot of pipe in the system or the pipe diameters are quite small.

You can go through my pump sizing procedure here to be sure:
http://www.builditsolar.com/Projects/SpaceHeating/PipeSizing/PipeSizing.htm

The 009 has nearly 25 ft of head capability at 4 gpm -- this is enough to cover quite a bit of pipe friction.

If you have to add a 2nd pump to make the startup happen, then the 2nd pump should be on a time delay relay so that it turns off once flow is established.  This system by Alan uses two 009's in series with the 2nd one on a time delay relay -- think that his tank is about 50 ft below the collectors:
http://www.builditsolar.com/Projects/WaterHeating/LargeDB/LargeDrainBack.htm


If the single 009 is able to get flow going "over the top", but the flow does not appear to be filling the return pipe completely and establishing full flow, then it might be beneficial to add a little resistance (like a part open valve) in the return pipe near the tank end of the return line.

I don't get the stuff about the 0011 -- it does not have as much startup head as the 009, and is really made for system that require more flow than you need -- seems to me it will just use  more power for no gain -- and it may well not even start the flow at all.

Tom -- do you agree with all this?

Gary

[tomtank]

You need to be careful when installing two pumps in series. There has to be some spacing in between the two pumps, otherwise, cavitation can occur.
The pumps need to be below the water level of the tank or they will have issues also.
I don't like to pump through an impeller that is not operating. There is a fair amount of restriction there.
I can't say that two pumps in series has ever worked well for very long for me. If I cannot get a stock Taco or Grundfos pump to do it, then I make the system an antifreeze system.
I would suggest not using an air vent on the roof. It allows cold air in the winter into the system when it is draining back and is also like a little radiator up there on the roof. It WILL stick open and piss water eventually.
It is far more practical to have a positive vent on the return line in the heated space by the tank. I think I described cutting in a tee and a vertical vent pipe about 12-18" long out of PEX or copper right by the tank to allow air into the system when it shuts down. It does work well, although it gurgles. I happen to like the sound, you might not.
I am reluctant to ever restrict the return line. If there is a flow issue, then change out the pump. If a 009 can get the system filled, I am usually happy.
I like to see 1/2 to 1 gpm per 4x8 collector.  Less is not the end of the world, as long as there is balanced flow through an array. This usually happens with reverse return plumbing of the array.
Tom

[jarrod9155]

Well the taco 009 got it done , just finished the install worked  great  . A little difficult to bleed plus I muted it vertical this time like taco suggested my meter showed it drawing 167 watts  better than 460 that what the sump pump used. Also added 1 inch copper on the u pipe  so far so good the next thing to do is measure flow rate . Just wondering what I should be seeing for tank temps in the winter on good sunny days on average . Thanks again for all the help out there   
                                                      Jarrod

[MattM]

You'll probably be getting something like 700 BTU per square foot on the 5 hours of peak average during the winter months.