New expansion vessel on water system - is pressure too high?

[Mick Canavan]

Hello all, I'm currently in Ireland and in a small cottage where the plumbing system has me scratching my head a bit. When the place was done up the builders decided that the tank in the loft was no longer needed and put a tank out back in a small extension where ALL (well, except for the cold water tap in the kitchen which comes directly from the mains supply) is driven into the house using a large water pump which sits inside the water tank. Recently this died and I had a new pump fitted and all is fine EXCEPT whenever we flush the toilet the pump kicks in and then tends to 'loop' or 'cycle' for 9 or 10 times before it stops. The toilet flush valve fills the cistern and towards the end of the fill it 'dribbles' or 'drips' which kicks the pump into action - because the pump responds to 'pressure' . Ok so far. Now, I noticed that there is a small expansion valve attached to the system and was told that this is to prevent cycling like i have just mentioned. It was very old and when I 'tested' it by tapping with a screwdriver and listening for the tell tale signs (i.e. one should be a 'ting' where the air is and the other should be a 'thump' where the water is) - the diaphragm had failed as it was simply full of water. I bought a new one (exactly the same model) and successfully swapped them over. I was sure that this new vessel would solve the problem...but it is exactly the same as before. I did a quick test with the screwdriver just to see if I could quickly tell if there was a problem but this time all i get is the higher pitched 'ting' both at top and bottom of vessel - as if it is full of air and no water is in it at all. Initially when I plumbed n the vessel there was a small leak and i took it off the system again to wrap some more plumbers tape around the thread and I thought it strange then that there was hardly any water in the vessel...i re-plumbed it and there was no resulting leak at the connection BUT I still suspect no water is actually getting into the vessel. Of course the pump (when it kicks in) causes the pressure in the system to rise for the duration it is on (I don't have the exact figures to hand) ...and the vessel I have put in was pre-charged to 3.5 bar. I am wondering whether I need to reduce the pressure in the expansion vessel? Any help or suggestions would be gratefully received and sorry for the long post! Many thanks in advance. Mick

 

[John.g]

Reduce the pre charge pressure to the pump cut in pressure minus 0.2 bar.

 

[Mick Canavan]

Reduce the pre charge pressure to the pump cut in pressure minus 0.2 bar.

Many thanks John, I will take a look at how to do that. Not sure at all tbh...I'll look for the pump paperwork...Thanks for the suggestion.

 

[John.g]

You might post a link to that pump package especially referenced to the cutin/cutout pressures etc.

 

[Mick Canavan]

You might post a link to that pump package especially referenced to the cutin/cutout pressures etc.

I'll look for the paperwork as I'm no longer sure of the name of the pump..it's submerged so I can't read the name from the pump itself...it is definitely a DAB Divertron and I 'think' (almost certain) it is the model 1000. But as I say I will look some paperwork before giving a link, just to be sure. Thanks again.

 

[John.g]

Hi Mick,
Had a quick look at the model 1000 pump curve, its max pressure at 0 flow is 3.8bar and will pump 30LPM at 3.0 bar , it says a inbuilt pressure switch stops/starts it, it may have a flow switch as well to stop it, just don't know. there will probably be 0.5bar between cutin/cutout pressures. I would suggest switching off the pump and disconnect the water side from the pressure vessel then set the air side pressure to say 2 bar initially, reconnect to the water side and see if this solves your problem.

What is the volume of the expansion vessel?.
Is there a pressure gauge anywhere on the system?.