Need expansion tank help please

[chubby]

Om

 

Thanks again nicknorman

 

in the end i called speedfit for technical assistance . They advised me that the item i needed was the tap connector i referred to on one of my recent posts above .

I went to screwfix got the part and fitted it . I now ( fingers crossed ) appear to have a watertight system which is always a bonus !

I have followed your instructions from yesterday .

when i ran the pump according to the second bit of this process the gauge went to 33 psi before cutting out .

I have then followed part 3 of your advice and inflated the expansion tank to 31 psi .

 

SO - does this start to sound like the beginning of the end for this problem ???

I will now turn on the pump again and then switch on the immersion . IF the PRV still leaks then does this mean either

1) i need to make a few tweaks on the expansion vessel - maybe a psi down for instance - retest it - maybe lower it one more psi etc OR

does it mean that the PRV is faulty and should be replaced ?

 

Hopefully this saga is drawing to a close and my last question is for now theoretical until the water has heated enough to increase the pressure inside the calorifier to test the system

 

watch this space ...

 

cheers again - i really cannot express my very sincere gratitude enough to all who have assisted me thru this problem

[Alastair]

changes to the expansion vessel will not alter the pressure in your pipes. That is governed by the pump.

 

You set your expansion vessel to slightly lower than the pump pressure so that the pump 'pressurizes' the vessel. When a tap opens, initially the water will flow due to the expansion vessel expelling some water then the pump will cut in.

[nicknorman]

Alastair. No no no, you are confusing the function of an accumulator with that of an expansion vessel. Please don't confuse the OP as well! An expansion vessel should remain empty or thereabouts after the pump cuts out. It only fills if the immersion heater etc is then turned on causing water trapped by an NRV, to heat up and expand. Thus its setting does determine the pressure in the system under these circumstances. Too low and its capacity is effectively reduced, so there will be more pressure rise for a given increase in temperature. Too high and it won't fill at all resulting in much more pressure rise for a given temperature. The correct setting will result in the minimum increase in pressure for a given rise in temperature. The correct setting is the pump cut-out pressure, but its better to err on being slightly too low than slightly too high, hence the advice to set it a couple of psi lower.

Om

Thanks again nicknorman

in the end i called speedfit for technical assistance . They advised me that the item i needed was the tap connector i referred to on one of my recent posts above .

I went to screwfix got the part and fitted it . I now ( fingers crossed ) appear to have a watertight system which is always a bonus !

I have followed your instructions from yesterday .

when i ran the pump according to the second bit of this process the gauge went to 33 psi before cutting out .

I have then followed part 3 of your advice and inflated the expansion tank to 31 psi .

SO - does this start to sound like the beginning of the end for this problem ???

I will now turn on the pump again and then switch on the immersion . IF the PRV still leaks then does this mean either

1) i need to make a few tweaks on the expansion vessel - maybe a psi down for instance - retest it - maybe lower it one more psi etc OR

does it mean that the PRV is faulty and should be replaced ?

Hopefully this saga is drawing to a close and my last question is for now theoretical until the water has heated enough to increase the pressure inside the calorifier to test the system

watch this space ...

cheers again - i really cannot express my very sincere gratitude enough to all who have assisted me thru this problem

Good one. Sorry if I confused the issue by assuming the thread on the expansion vessel was female - I guess it must be male?

 

Anyway, yes if it still dribbles after the immersion heater is on I think it must be the PRV. Did you ever determine at what pressure the PRV is supposed to release at?

[Alastair]

I think we are all getting confused.

 

Which circuit is this being added to? The heating circuit from the engine, or the hot water feed from the hot water cylinder to the rest of the boat?

 

From the OP's description, I think they are adding it to the latter. If it is the former, then it should be lightly pressurised. The heating circuit from the engine should have a PRV of its own but won't be pressurised by the main water pump.

 

If they are adding the vessel to the hot water circuit (pressurised and supplied by the water pump) then the expansion vessel is functioning as both an accumulator and an expansion vessel (since when starting with a cylinder full of cold water this will be at pump cutout pressure and pressure will rise when heated). In this case the expansion vessel should be pre-pressurised to below the pump-cutout (but not much below). This is easily achieved; pump it up hard, then let air out until you hear the pump cut in. Let a smidge more air out. Done.

 

An accumulator/expansion vessel is needed after the hot water cylinder as there should be a non-return valve on the cold water feed into the cylinder. Without an expansion vessel, this is essentially a sealed vessel and can get over-pressurised when heated.

[chubby]

Thanks again folks

 

Just to clarify . The expansion tank is on the hot side from the calorifier ( about 3 ft away ) and before the first tap .

When going thru the installation procedure as advised by the legend nicknorman the pump cut out at 33 psi . I have therefore set my expansion tank at 31 psi . I have turned water & pump back on and so far all is watertight . I have switched on the immersion and now wait to see if the PRV still trips once there is pressure build up inside the calorifier . All being well this will not happen as the excess pressure ought to be taken up by the expansion tank . I expect to wait several hours for the water to heat up and hopefully by say 9 pm i should have a better idea as to whether this has worked .

Many people will from time to time say " if i can do it then anyone can " . Others reading this post should really understand that i am a complete & utter novice at this kind of thing and this statement is 100% true . i found it a very daunting prospect tackling plumbing like this , not to mention the electrical problems that occured half way thru so IF it turns out all is well later on this evening then i very much hope that others who have to tackle this issue can make use of this thread .

 

Again - my truly heartfelt thanks to everyone for thier assistance . Im overwhelmed by your generosity . This may be childsplay to many but for me it has been a big job .

 

PS - later this evening once the hot water can be drawn off , if its all worked i shall post here to say . If it hasnt worked ....... i shall post here to say so

[chubby]

hello all

 

 

Ive checked the system and nothing has vented thru the PRV on my calorifier so it seems the excess pressure is going into the expansion tank as hoped so thankyou again for your help

 

cheers

[Tobymonster]

Right then, to the next problem. Did it actually take 5 hours for your hot water to heat up? :0/

[smileypete]

To go from 3/4" BSP male to 15mm push fit this should do:

 

http://www.screwfix.com/p/wras-speedfit-hose-x-13mm/32762

http://www.screwfix.com/p/wras-push-fit-tap-connector-0-75-x-500-x-13mm/51443

 

The second one doesn't state the push fit size but looks to be 15mm, best buy in person and check.

 

With the pipe inserts see which brand the pipe is then buy matching ones, worth having a few for future jobs.

 

cheers, Pete.

~smpt~

Edited October 24, 2013 by smileypete