Plumbers? Circulation pump location?

Mat the trasher

Hi, replacing a old boiler, its circulation pump is on the return to the boiler, but on all the diagrams I see it is normally shown after the boiler on the hot out, does it make any real differance? Also it has a non return valve fitted before and after the boiler should I keep these in place or ditch one or both?

cheers.

DoneDL

I cant see a logical reason for the non-return valves but pump position in down to manufacturers instructions. If its an oil boiler it has to be commissioned by an oftec engineer otherwise the warranty is void, if its gas you need an RGI to do the removal and install

heinbloed

Hi, replacing a old boiler, its circulation pump is on the return to the boiler, but on all the diagrams I see it is normally shown after the boiler on the hot out,

Would you have a link towards these diagrams? Who is publishing them?

See, usually the pump is placed at the cold part of the boiler for two reasons:

It should NEVER be exposed to steam, and with a malfunction of the boiler (for example a defect temperature sensor) this could happen if it was placed at the hot side (flow).
If the pressurised water is at 90 or 99 degrees Celsius (just to give a sample!) and the pressure is let's say 1.5 bar at the boiler then the pump in action will create a suction force on the boiler side. This means pressure drop and therefore steam creation. And this can lead to an explosion further up, banging and ratteling of the radiators and plumbing.

The second reason is the logevity of the pump and it's seals. The hotter it is exposed the less it lasts.

For an e-learning course on plumbing/pumps/valves/sensors Grundfos offers a pump installation course, for free. See

http://www.grundfos.com/web/Homeuk.nsf/Webopslag/C8AD126508F0A47B412568880038BAA1

Danfoss has a similar course for free as well, but only in German language.

Another reason to place the pump NOT at the hot side is to allow the air separator/-valve at the boiler to function properly.

The Danfoss e-learning link, just in case:

http://www.dancademy.de/

Mat the trasher

heinbloed wrote: »

Would you have a link towards these diagrams? Who is publishing them?

See, usually the pump is placed at the cold part of the boiler for two reasons:

It should NEVER be exposed to steam, and with a malfunction of the boiler (for example a defect temperature sensor) this could happen if it was placed at the hot side (flow).
If the pressurised water is at 90 or 99 degrees Celsius (just to give a sample!) and the pressure is let's say 1.5 bar at the boiler then the pump in action will create a suction force on the boiler side. This means pressure drop and therefore steam creation. And this can lead to an explosion further up, banging and ratteling of the radiators and plumbing.

The second reason is the logevity of the pump and it's seals. The hotter it is exposed the less it lasts.

For an e-learning course on plumbing/pumps/valves/sensors Grundfos offers a pump installation course, for free. See

http://www.grundfos.com/web/Homeuk.nsf/Webopslag/C8AD126508F0A47B412568880038BAA1

Danfoss has a similar course for free as well, but only in German language.

Another reason to place the pump NOT at the hot side is to allow the air separator/-valve at the boiler to function properly.

The Danfoss e-learning link, just in case:

http://www.dancademy.de/

Thanks for your reply
http://www.worcester-bosch.co.uk/installer/products/oil-boilers/greenstar-camray-external-2532/fully-pumped-sealed-primary-systems
http://www.worcester-bosch.co.uk/installer/products/oil-boilers/greenstar-camray-external-2532/open-vented-primary-systems

Installed a open vented circuit, but I would agree with all your points. As I'm not a plummer by trade, I said I'd ask incase there was some reason I may have over looked.

Sparkpea

It makes no difference whether the pump is on the flow or the return so long as its pumping in the correct direction. Return pumping towards the boiler and flow pipe away from the boiler. I personally install them on the return where possible however some boiler manufactures that supply pre-pumped boilers often have them installed on the flow.

The way I see it is the pump sucks the cold water back to the boiler to be reheated rather than the pump pushing the heat into the system.

As for the the non return valve well depending on the type of system and if its a link up etc. then thats when it comes into play.

If its a straight forward system then the non return valve probably isn't needed however if you're not sure and the system worked before with the non return valve then I would just leave it in place.

yoshytoshy

On open systems it's important to place the pump in the correct position.
The location of the cold feed will determine whether or not you'll get pitching.

I don't install open systems myself ,but I know there are negative and positive effects on the head of water ,due to the location of the pump and cold feed.

If you've an interest ,check out the term ,"inverted cold feed".

A negative open heating system is more likly to draw in air with small leaks and a positive open heating system is more likly to drip water with small leaks.

Micky Dolenz

Matt, had you or have you a back boiler fitted elsewhere in the house. It would explain the non return valve.

I would normally fit pumps on the cooler return. So times this is not practical as in the case of outside heatpac boilers, there is no space on return for pump so it ends on on the flow by default.

heinbloed

Thanks for the links (Worcester-Bosch), Mat the trasher.
At
http://www.worcester-bosch.co.uk/installer/products/oil-boilers/greenstar-camray-external-2532/fully-pumped-sealed-primary-systems

(showing a closed pressurised system) the drawing clearly shows the pump in the wrong positioning. If we listen to the pump manufacturer.

I quote from the Grundfos brochure

" Energy handbook, the hottest facts of energy efficient circulators ",
at page 20:
" These tips apply to the following products:Alpha2/Alpha2N,Magna,AlphaPro,Alpha+,UPE,UPS,UP Solar."...

"Positioning is important .....the pump inlet should be placed as close as possible to the expansion tank if installed...."

and further on page 21:

" Surrounding temperature is a factor....In closed expansion systems,if possible, place the pump at the return pipe due to the lower water temperature."

Now, this is only a thin brochure aimed at the hobby installers and DIYers, available for free at the counter of Heatmerchants and other suppliers, and these two pages in the brochure don't show any system drawings or any advice on open systems (those with a feeder/hopper tank in the attic).

But certainly the life time of the pump will suffer there as well if the pump is exposed to higher temperatures than necessary.

The air valve at the boiler won't function anyhow if the pressure is to low. Check the head of this little brass device, it will give a min.pressure at which it would work. Positioning a pump BEHIND the air valve ( between boiler and pump as shown in both links from Worcester-Bosch) will certainly reduce the pressure at the airvalve, maybe to low to operate at all. Making it obsolete.

One should contact Wocester-Bosch and tell them about the obvious errors shown at these drawings.
It influences the guarantee/profitability of the company after all, wrong installation manuals leading to demage/underperformance will give the client a life-long guarantee.

Thanks again for the links.

heinbloed

To make things even more confusing Grundfos publishes this manual:

http://net.grundfos.com/doc/webnet/poweredby/pdf/installer-guiden.pdf

At page 13 it shows (as far as I understand these wordless pictograms) that the pump should be installed at the hot side (flow) if the heating system has an automatic night time temperature reduction build-in. And it should be installed at the cold side (return) if there is no night time reduction build-in.
Very mysterious...