Megaflow / water hammer

[harry]

in the last few minutes of it's heat-up cycle (before the boiler cuts out) - water hammer occurs close to (or in) the Megaflo cylinder.

water is used or not used), nor does water hammer occur if CH set to radiat ors only.

t few-minutes of cylinder heat-up, if both cylinder heating and radiators a re on.

tlet pipes to the cylinder equally (and sometimes also the cold mains water inlet to the cylinder, but not the hot water outlet).

on heating to the radiators (and temporarily stopped by drawing off some h ot water).

essure up to 6 bar. Seems to be a standard megaflow configuration with genu ine Heatrae Sadia parts.

afety valve both manually operate, and discharge to tundish.

letting the boiler do a how-water warm-up cycle with the Megaflow depressu rised - to attempt to prove the problem is definitely CH side, and not main s-water side (incidentally the quarter-turn valve just before pressure-redu cing valve is frozen in the fully-on position, so have to use the under-sin k main cold-water stopcock to isolate the hot-water system).

it bypass valve not operating correctly? My impression (but not certainty) is the that the 2-port valve to the cylinder is still open when water hamme r occurs.

Seems to be a major issue with megaflow cylinders.

[John Rumm]

ok, that's fairly normal on larger cylinders...

Yup. (small cylinders sometimes actually deliberately back water into the supply pipe to handle the expansion)

That presumably means that the air pocket gets absorbed over time as it defuses into the water?

[tabbypurr]

is in the last few minutes of it's heat-up cycle (before the boiler cuts ou t) - water hammer occurs close to (or in) the Megaflo cylinder.

t water is used or not used), nor does water hammer occur if CH set to radi ators only.

ast few-minutes of cylinder heat-up, if both cylinder heating and radiators are on.

outlet pipes to the cylinder equally (and sometimes also the cold mains wat er inlet to the cylinder, but not the hot water outlet).

ng on heating to the radiators (and temporarily stopped by drawing off some hot water).

pressure up to 6 bar. Seems to be a standard megaflow configuration with ge nuine Heatrae Sadia parts.

safety valve both manually operate, and discharge to tundish.

nd letting the boiler do a how-water warm-up cycle with the Megaflow depres surised - to attempt to prove the problem is definitely CH side, and not ma ins-water side (incidentally the quarter-turn valve just before pressure-re ducing valve is frozen in the fully-on position, so have to use the under-s ink main cold-water stopcock to isolate the hot-water system).

cuit bypass valve not operating correctly? My impression (but not certainty ) is the that the 2-port valve to the cylinder is still open when water ham mer occurs.

e mains and depressurised. Nada, nothing, zilch. No water hammer.

-up cycle), this time with the cylinder pressurised - this time got water h ammer.

eem to be at the CH inlet to the cylinder, and slightly less at the CH outl et. Virtually none at the cold water inlet, and definitely none at the HW o utlet.

nder heat-up cycle, but *before* the the cylinder 2-port valve closes.

H side at all).

et side, and/or the >8-bar/>90c safety valve.

in the cylinder and a defective non-return valve?

sounding a sensible course of action.

Adding air pockets (capped up-pointing pipe) to where the noise is loudest has to be a much easier quicker cheaper approach.

One can also eliminate water hammer with a little added resistance, using a valve or if your feeling Mr Beanish just squashing the pipe slightly. Whet her a little flow reduction there is ok I couldn't say.

The 2 together are even better.

NT

[dom]

Exactly so.

[Michael]

replying to dom, Michael wrote: My megaflow system too having the same nature of bang! issue when the motorise valve in the primary flow get shut off. If any one can suggest a firm solution please advise.