Spacing between Venturi tees and other advice.

ReD_BaRoN

I have a radiator on the 2nd floor of my house, and it's never worked in the 8 years I've been at the house. We'll, it's time to try to make it work.



The radiator is feed via 1/2 copper pipe which is coming off a 3/4 copper loop. There were two scoop tees which were 4 inches apart. The radiator is 17 inches wide. From what I understood, the tees needed to be separated by 17 inches or greater, and I was also told that I didn't need the 2nd scoop tee on the return side. So I replaced the return side tee with a normal tee, and placed it 20 inches from the scoop tee on the supply side.



Things still don't work, hot water is not going up the brach off the main loop (main loop is indeed heating up) so what I'd like to do is replace the supply scoop tee and the return normal tee with B&G red ring venturis. The question I have is how far apart are they supposed to be placed? Is it just the width of the radiator, or do I have to take into account all the 1/2 copper to get up and back from the 2nd floor?



Any other things I should be checking on why this doesn't work? Will increasing the pressure in the system help to get that water up there?



Thanks!

Alan (California Radiant) Forbes

Mono-flow System

Bell & Gossett coined the term "Monoflow" when they manufactured their Venturi tees for hydronic systems.  It was a step up from a single series circuit, but there were rules.  You had to create enough pressure drop through the main to force water to want to flow through the branch to the radiator.  This was done by spacing the tees a minimum of the length of the radiator apart.  If the radiator was above the main, one Monoflow tee on the return was enough because the buoyancy of the hot water helped the heated water move up to the radiator .  If the radiator was below the main, one Monoflow tee on the supply and one on the return was required.



Monoflow system are notorious for being difficult to purge air to allow flow.  Your system, as you described should work fine with one Venturi tee on the return, even better with one on the supply and one on the return.  The buoyant hot water should want to ascend to the radiator.  I'd say that air in the 1/2" piping is your problem and you've got to find some way to remove it.

ReD_BaRoN

Bleeder on the radiator

Thanks Alan,



This is certainly stumping me, because there is a bleeder valve on the radiator in question, and I open it until water starts shooting out. I'm presuming that gets out all the air in that bypass loop.



Thanks,

Brian

STEVE PAUL_3

Overkill can be your friend

A few years back we had a very similar situation. We decided to go on an all out attack and use every play in the book.

1-  Installed a venturi tee on the supply as well as the return to "FORCE" the  flow.

2- Installed the tees far apart in the main, 15-20' to increase the main resistance.

3- Installed full port ball valves on both branches at the tees so the return and supply could be purged separately. 

4- Ensure that the radiator supply valve was fully wide open.

I can't tell you what actually did the job, but that radiator was beaten into submission and compliance when we were done.

ReD_BaRoN

You're likely right...

I think you're right, it might take some brute force. Couple of questions:



Just confirming you're talking 15-20 feet, not inches, correct? Typically does the space between tees have to cover the entire run of the bypass loop, or just the width of the radiator?



Do you think Venturi tees (e.g., B&G red ring) are better suited to this application than scoop (look like they have a ramp inside, not a cone) Tee's?



Thanks!

Thorp Thomas

You're over thinking the problem...

Water takes the path of least resistance. Leave it as you have it, but put a purge valve setup in the radiator return. Force the water to make a complete circuit. The radiator may be vented, but are both supply and return? Another approach is to install a ball valve between the tees and force the water to complete the circuit, then reopen for heating operation.



One other thing, make sure the water either feeds into the top and out the bottom or in on the bottom and out the other side of the radiator. Returning from the top is always problematic.

Alan_13

ball valve s and bleed

providing the monoflows are correctly installed (check direction),   I'd cut  a ball valve on feed and return branch, then back out the 1/8th vent and temp install a nipple and elbow and flush that rad really well into a 5 gal pail, one side at a time. Replace air vent.    

Charlie from wmass

Is this a split loop it is on?

Was this section always 3/4"? What size of pump are you using? I ask pump size because I had issues in a home with a kick space heater not warming before the rest of the zone heated up. It was a bad marriage between cast iron baseboard and a kick space heater. what mad it worse was it was a split loop of a 1" main and return split into two 3/4" loops. Oh the kicker was the circulator was a 005. Yes a 005 not 007. It works great with the cast iron baseboard. Not so much with mono flow tees and large diameter supplies and returns. I ended up making the bathroom its own zone. I ran home run pipe back to the boiler room for it as I wanted to test out the "new" product Fosta pex and see how it held up.

joe_94

Fun big word

AS  Dan has explained it in the past, the key element is that the monoflo T is on the RETURN pipe from the radiator.  The  water in the main line "looks ahead"  and 'feels' the back-up pressure from the restriction of the monoflo T up ahead, and chooses to go up to your radiator at the first opportunity.. If that isn't  anthropomorphism nothing is. If you are trying to persuade water to go down to a basement radiator you add a second monoflo T at the pipe feeding down, as well. [What is down "riser" called?]

Anyhow, I have them, and where the piping was difficult the 1940 builder put them fairly close together, less than the rad width, and they work anyhow.

Mark Eatherton

The word for riser going down....

is drop or down comer.



As for minimum centers, I built my own 3/4" X 1/2" Venturi tees using Nibco insert drop in venturi's for all of the radiators/radiant floor circuits in my home, and most of them are running 2" on centers, same as the Buderus panel radiators that are connected to the tees. They are a  diverter as well as a venturi (use both for high pressure drop circuits) and I have not had any issues at all. The addition of even 20' of piping is NOT going to make that big a difference in the grand scheme of things.I am moving 3 GPM through my main (visual flow meter) and it works great.



I believe that when Gil Carlson and others recommended the minimum of a radiators width for distance between tees, they were assuming that the flow through the tees was best in a laminar flow versus erratic, violent turbulent flow, and that the radiators distance would give the water a chance to calm down before going through another violent session, but in reality, I don't think it really matters. Venturi tees functions are based on increased velocity to create a low pressure condition to induce flow through the side branch of the tee (or increased main resistance in the case of a diverter). Too small of a pump, and your velocity through the tee's run drops, and consequently the flow through the branches also decreases significantly.

More than likely, it is an air problem. You can address air problems by turning the temperature and pressure of the system (temporarily) REAL high, then revert to normal temperature and pressures once the bubble has been dislodged and normal flow has returned.



When bleeding, make certain that all circulators are OFF, otherwise, you are just chasing your tail.



Worse case scenario, you could add liquid dish detergent to help the bubble(s) move along... (Dawn works well for me, about 1 once worth.)



Done right, one pipe venturi systems can be very reliable. Done wrong, like anything in life, they can be a royal PITA....



Good luck with yours. Let us know how you make out. If it worked before, it will work again.



ME

Greg Maxwell

monoflo vs venturi

In my 26 years of experience, people get the terms "monoflo tee" and "venturi Tee" mixed all the time. On most situations, people use to use monoflo tees, or scoop tees on the supply and return, but when the venturi tees came out, that all but eliminated the use of scoop tees. The key is pressure differential. Hi pressure always goes to low pressure, even if it is slight. The venturi tee installed on the return side of the rad will ceate enough of a low pressure zone at the tee to create flow. Using two venturi tees means that one of them would have to be installed in the wrong direction, and can screw things up, and reduce the flow in the loop.