Magaflow - Description and Questions

[DavidM]

I need to change some basin taps in a house equiped with a megaflow HW "cylinder". I've not dealt with these beasts before and have a couple of questions:

Can anyone point me at a link to a description of a megaflow system/cylinder, so I can get an understanding of how it works? I've tried the DIY WIKI, and Ed Sirretts pages but can't find anything there. Also nothing on Google searching megaflow+description.

The taps don't have isolationg valves on them, so I'll need to isolate them somewhere else, or drain down the system. Can anyone describe how to do this, and get it back up a running afterwards. Are there any pitfalls to watch out for? The hot and cold taps seem to be at about the same pressure (thumb over tap test), so the cold tap might be connected into the cold side of the HW system, rather than fed direct from the mains, but maybe this is just my lack of knowledge of how megaflows work!.

Thanks for any advice. David

[Ed Sirett]

really it could not be easier, there will be (almost certainly) a valve on the inlet to the megaflow. Possible on the outlet. Closing this will shut off the hot. You may have to draw off a few gallons to relieve the pressure if you use the inlet one.

[DavidM]

There seem to be rather a lot of pipes attached to this beast, which is one reason I wanted to understand a bit more about them. Is the

22mm pipe coming out of the top likely to be the HW outlet, as in a conventional cylinder? The beast is bigger than me, so I'd rather not abuse it or blow it up! David.

[Ron Lowe]

The installation manual used to be available on the Heatrae Sadia website, and it had good diagrams of the installation. I couldn't see it when I looked there right now, so I've dumped it on my web-server for you to look at.

's all very simple.

The mains pressure cold comes in to the blue-coloured connection at the bottom, via 2 items:

1) a combined shutoff valve /pressure reducing valve; This limits the incoming pressure to 3 bar. 2) The expansion relief valve. This prevents the thermal expansion of the hot water going back into the mains. This valve has a discharge, which will go to the tundish.

The Hot Water is drawn off the top, via the Red connection.

The 2 grey connections at the bottom, on the same level as the cold inlet, are the Primary ( radiator circuit ) flow and return, which provide the heat. The flow will have a 2-port electric zone valve fitted.

The grey port on the side near the top is the Pressure and Temperature Relief Valve, and is marked as such. This is a safety device, and must be functional. It too has a discharge route into the tundish ( black open plastic funnel-type thing ). The tundish drains to outside.

There is an internal air volume to take up the thermal expansion of the water. This needs re-generating around once a year. Follow the instructions on the big lagel on the front.

To work on the hot water pipework, simply shut off the cold supply at the combination valve. Then open the lowest HW tap, and allow the flow to stop. This may take a fair old volume ( like enough to run a decent bath ! ). Then go ahead on do the work.

[DavidM]

Brilliant Ron, just what I needed. Thanks very much. David

[Mike Humphrey]

Thanks for that, its quite useful as I haven't got the manual for mine (even though it says "leave this for the user" in it!). My installation doesn't quite match their suggested way of installing - the pressure reducing valve and expansion valve are combined, so there is no balanced cold supply, but all the cold water goes through a separate pressure reducing valve. I'm not sure why they've done it this way rather than installing the two valves separately as suggested in the manual.

Mike