Injector Tee distance from bend

deezell

I've upgraded my central heating and part of the installation is an injector tee to allow the gravity flow to the cylinder from the back boiler to continue when the pump is on . The pump in the hot press pulls the cold return from the rads into the tee straight through facing down to the floor and turns sharp right to the boiler. The cold return from the cylinder coil enters the tee horizontally. Gravity circuit is fine, but when the pump is on the cold return from the rads seem to be pushing back up the cylinder cold return instead of drawing it down by the vortex effect of the tee. Its as if the return path underfloor back to the boiler (about 3 metre) is causing enough restriction that that the pump output is putting positive pressure on the injector tee branch to the cylinder coil. The tee is correctly located after the pump but only 10-15 cm above the underfloor elbow which sends the return flow to the back boiler, and i'm wondering if this is too close, causing back pressure on the jet from the downward facing injector from the pump. I can raise it to the level of the bottom connector on the cylinder return, but before I do I'm wondering is there a minimum distance after the tee to preserve the vortex effect.

Dtp1979

deezell wrote: »

I've upgraded my central heating and part of the installation is an injector tee to allow the gravity flow to the cylinder from the back boiler to continue when the pump is on . The pump in the hot press pulls the cold return from the rads into the tee straight through facing down to the floor and turns sharp right to the boiler. The cold return from the cylinder coil enters the tee horizontally. Gravity circuit is fine, but when the pump is on the cold return from the rads seem to be pushing back up the cylinder cold return instead of drawing it down by the vortex effect of the tee. Its as if the return path underfloor back to the boiler (about 3 metre) is causing enough restriction that that the pump output is putting positive pressure on the injector tee branch to the cylinder coil. The tee is correctly located after the pump but only 10-15 cm above the underfloor elbow which sends the return flow to the back boiler, and i'm wondering if this is too close, causing back pressure on the jet from the downward facing injector from the pump. I can raise it to the level of the bottom connector on the cylinder return, but before I do I'm wondering is there a minimum distance after the tee to preserve the vortex effect.

A picture would be good if you can manage that.
As for distances, honestly I don't know. But as you state above, that is why I don't use elbows after injector tees. I'd 99% of the time use a pulled bend on the cooper after the tee

roy rodgers

Dtp1979 wrote: »

A picture would be good if you can manage that.
As for distances, honestly I don't know. But as you state above, that is why I don't use elbows after injector tees. I'd 99% of the time use a pulled bend on the cooper after the tee

Bit off topic but have you used or seen the injector tee system link are doing now??
Looks the job..

deezell

Picture of tee just above 1/2" head tank feed, stove pump is directly above. Underfloor elbow is part of the legacy system from the 80s, I don't fancy digging up to put in a curve, I can raise the tee by about 50cm, this might reduce the turbulence caused by the sharp left turn under the concrete. Tee is a DIY injector made from a standard 3/4x1x1 with a 3/4 —1/2 solder reducer fitted internally facing down as copied from a number of DIY tee sites. Image 2 is the new layout except an oil boiler instead of a heat pump.

deezell

Probably a more accurate diagram.

Dtp1979

roy rodgers wrote: »

Bit off topic but have you used or seen the injector tee system link are doing now??
Looks the job..

Only saw this now sorry. Is that the one that can be cut to use for different purposes ?

deezell

Dtp1979 wrote: »

Only saw this now sorry. Is that the one that can be cut to use for different purposes ?

Meant to ask about this too. I've not seen a tee on the systemlink site. Perhaps a link to it?

deezell

I've spoke to Harry in NRGsystems whose manifold I'm using to combine Oil boiler and solid fuel properly, a real expert and a gentleman. He maintains I'm on the right track with the elbow too close to the outlet of the injector jet. Simple physics, the jet is shooting the pumped water past the branch of the tee, and hitting the wall of the bend thus creating pressure and back flow. it needs a good run to set up the flow, so raise the pump and tee first, I can get about a half metre, after that, dig floor and replace bend with a smooth curve of 1". It would be handy to be able to buy such a curve, I struggle to get 90° with a spring and an improvised jig without creasing the pipe. Harry also gave me other tips too numerous to relate, his videos and schematics on the NRGAwareness.ie site are really full of answers to combining systems of all types.

Dtp1979

Bring a metre of 1" pipe to any plumber. I'm sure they'd bend it for you

deezell

I raised the pump and tee about .6m higher above the floor bend. Still not working right. There could be a lot of gunk in that horizontal floor pipe to the stove, it's there 30 years. I'm thinking it could also be the hot flow pipe down from the attic. It's a vertical 1" pipe which goes straight into a tee just above the manifold. This tee branches left and to the manifold, right and to the cylinder gravity in. When the stove pump kicks in it is pulling via a straight horizontal path through that tee and probably from the cylinder gravity hot in. If I eliminate this path by dropping separate hot flow from the ceiling horizontal pipe, down to the manifold and pump, leaving the other vertical drop to the cylinder gravity hot, perhaps the pump won't act on the gravity circuit as it currently does, overcoming the venturi pull of the injector tee. I don't think now there's a 90° soldered elbow under the floor, I dug around another vertical pipe, the hot to the rads, ( to see if it branched there in order to implement pumped zoning), and the pipe was quite deep, under 50mm screed, 50mm dry fill and 25mm of polystyrene insulation, curving with a soft bend towards the hall and presumably branching there. I'll have to assume the cold return to the stove was installed in a similar fashion and would have a similar curve.