I have 4 expansion vessels on my system ... each has a different 'charge'
pressure. (all set to the design documents)

Just interested as to 'in general' what the pressure should be .... should
it be set to match the operating pressure of the pipe it is attached to, is
it set higher, lower ?

On 28/11/2011 11:56, Rick Hughes wrote:
I have 4 expansion vessels on my system ... each has a different
'charge' pressure. (all set to the design documents)

Just interested as to 'in general' what the pressure should be ....
should it be set to match the operating pressure of the pipe it is
attached to, is it set higher, lower ?


It needs to be lower than the static (cold) pressure in the water system
so that the air gets compressed a bit when you fill the system.
Otherwise, you'd never be able to bleed a radiator.

Setting the air pressure to 0.7 Bar (10 psi) and the static water
pressure to 1 bar works for most systems.

Not sure why you've got *four*! Are they all in the same system, or are
any for a mains pressure hot water system? Assuming they're all in the
same system, you could pre-charge them to different pressures so that
they get used progressively as the system pressure rises.
--
Cheers,
Roger
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Please reply to Newsgroup. Whilst email address is valid, it is seldom
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On Nov 28, 11:56*am, "Rick Hughes"
wrote:
I have 4 expansion vessels on my system ... each has a different 'charge'
pressure. (all set to the design documents)

Just interested as to 'in general' what the pressure should be .... should
it be set to match the operating pressure of the pipe it is attached to, is
it set higher, lower ?

on a related question...

It is never clear to me how you are supposed to 'top up' the air in an
expansion vessel without draining the water pressure. Maybe you
can't do this. Isthere some trick to it?

If you drain the water you can then pump air in until the pump reads 1
Bar (or whatever the official precharge value is), but can it be done
without draining the water?

Robert

On 28/11/2011 12:50, RobertL wrote:


on a related question...

It is never clear to me how you are supposed to 'top up' the air in an
expansion vessel without draining the water pressure. Maybe you
can't do this. Isthere some trick to it?

If you drain the water you can then pump air in until the pump reads 1
Bar (or whatever the official precharge value is), but can it be done
without draining the water?

Robert

It can't be done while the air in the expansion vessel is partially
compressed by water, because that would give a false air pressure
reading. So you simply need to *de-pressurise* the water system - not
drain it completely. Better still, if the expansion vessel is connected
via an isolation valve and drain cock, you can easily isolate and drain
the water in contact with it without affecting the rest of the system.
[This won't actually have much effect on the *volume* of water you have
to remove - unless you've got lots of radiators full of compressed air!]
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On Nov 28, 1:51*pm, Roger Mills wrote:
On 28/11/2011 12:50, RobertL wrote:



on a related question...

It is never clear to me how you are supposed to 'top up' the air in an
expansion vessel without draining the water pressure. * Maybe you
can't do this. *Isthere some trick to it?

If you drain the water you can then pump air in until the pump reads 1
Bar (or whatever the official precharge value is), but can it be done
without draining the water?

Robert

It can't be done while the air in the expansion vessel is partially
compressed by water, because that would give a false air pressure
reading. So you simply need to *de-pressurise* the water system - not
drain it completely. Better still, if the expansion vessel is connected
via an isolation valve and drain cock, you can easily isolate and drain
the water in contact with it without affecting the rest of the system.
[This won't actually have much effect on the *volume* of water you have
to remove - unless you've got lots of radiators full of compressed air!]


Aha, thanks. I wish people would routinely fit such isolators and
cocks.

Robert

On Mon, 28 Nov 2011 07:30:44 -0800 (PST), RobertL wrote:

I wish people would routinely fit such isolators and cocks.

The one on the new solar circuit apparently simply unscrews from it's
mount which contains an automatic valve that closes when the
expansion vessel is removed.

--
Cheers
Dave.

On 28/11/2011 15:30, RobertL wrote:
On Nov 28, 1:51 pm, Roger wrote:
On 28/11/2011 12:50, RobertL wrote:



on a related question...
It is never clear to me how you are supposed to 'top up' the air in an
expansion vessel without draining the water pressure. Maybe you
can't do this. Isthere some trick to it?
If you drain the water you can then pump air in until the pump reads 1
Bar (or whatever the official precharge value is), but can it be done
without draining the water?
Robert
It can't be done while the air in the expansion vessel is partially
compressed by water, because that would give a false air pressure
reading. So you simply need to *de-pressurise* the water system - not
drain it completely. Better still, if the expansion vessel is connected
via an isolation valve and drain cock, you can easily isolate and drain
the water in contact with it without affecting the rest of the system.
[This won't actually have much effect on the *volume* of water you have
to remove - unless you've got lots of radiators full of compressed air!]

Aha, thanks. I wish people would routinely fit such isolators and
cocks.

Robert

On a combi or system boiler where the EV is usually built in, the
quickest way I found was to use the drain off and isolators* on the flow
& return to the boiler, leave the drain valve open while pumping up the
EV and then close them and re-pressurise when your done

One thing though, on some boilers the isolators and drain valves LEAK
and never seal properly again

* I don't always use the isolators either, unless the boiler is on the
ground floor but even then you could make sure there is no air in the
system, close radiator valves and screw done the AAV so no air can enter
the system.

--
David

"Roger Mills" wrote in message
...
On 28/11/2011 11:56, Rick Hughes wrote:

It needs to be lower than the static (cold) pressure in the water system
so that the air gets compressed a bit when you fill the system. Otherwise,
you'd never be able to bleed a radiator.


Don't have any radiators :-)


Setting the air pressure to 0.7 Bar (10 psi) and the static water pressure
to 1 bar works for most systems.

Not sure why you've got *four*!

One on boiler primary loop, (whole of thermal store volume cycles around
boiler)
One on DHW circuit - pumped loop
One on Domestic heating circuit
One on incoming mains

In article , Rick Hughes
wrote:

"Roger Mills" wrote in message
...
On 28/11/2011 11:56, Rick Hughes wrote:

It needs to be lower than the static (cold) pressure in the water
system so that the air gets compressed a bit when you fill the system.
Otherwise, you'd never be able to bleed a radiator.


Don't have any radiators :-)


Setting the air pressure to 0.7 Bar (10 psi) and the static water
pressure to 1 bar works for most systems.

Not sure why you've got *four*!

One on boiler primary loop, (whole of thermal store volume cycles around
boiler)
One on DHW circuit - pumped loop
One on Domestic heating circuit

without radiators? Tell us more.

One on incoming mains

--
From KT24

Using a RISC OS computer running v5.16

On Tue, 29 Nov 2011 09:09:58 +0000 (GMT), charles wrote:

Don't have any radiators :-)

Not sure why you've got *four*!

One on boiler primary loop, (whole of thermal store volume cycles

around boiler)
One on DHW circuit - pumped loop
One on Domestic heating circuit

without radiators? Tell us more.

At a guess all underfloor heating. Best way to heat with a thermal
store in the system. The temp of the store doesn't half drop quick
when a radiator based CH system kicks in an lots of water at 20C gets
shoved into it. Radiators heat up quick mind...

One on incoming mains

Not quite sure why the mains needs an expansion vessel though.

--
Cheers
Dave.

"charles" wrote in message
...
In article , Rick Hughes
wrote:

"Roger Mills" wrote in message
...
On 28/11/2011 11:56, Rick Hughes wrote:

It needs to be lower than the static (cold) pressure in the water
system so that the air gets compressed a bit when you fill the system.
Otherwise, you'd never be able to bleed a radiator.


Don't have any radiators :-)


Setting the air pressure to 0.7 Bar (10 psi) and the static water
pressure to 1 bar works for most systems.

Not sure why you've got *four*!

One on boiler primary loop, (whole of thermal store volume cycles around
boiler)
One on DHW circuit - pumped loop
One on Domestic heating circuit

without radiators? Tell us more.




17 zone underfloor heating system .. each with own thermostatic control ....
all fed from Thermal store.
Having lived with this for a few years now ..it is far superior to rads.
Especially on ground floor where it is pipe-in screed, so they whole floor
becomes a massive thermal store for the heat.
Obvioulsy I built with insulation in place to suit this.

Even heat, no convection currents, no hot spots, can place furniture
wherever.

The pressurized Thermal store is like a DHW tank in reverse .. boiler
primaries circulate full volume of store around boiler .... which means long
efficient burns .. not continually cycling.
There are 2 heat exchangers in the store .. the upper feeds a domestic HW
loop ,, mains in .. DHW out... i.e. 22mm pipe out with take offs at all
taps, bath, showers etc., then at last point a 15mm pipe runs back to store.
On this is a very low speed (timed) circulator ... this means when you open
any tap you get instant mains pressure hot water. No delay, no waste of
water running it to get hot.
It's on timed (about 20 time segments) so it only works this way at set time
... remainder its normal system.

This means due to the large volume of heat in the store you can fill a bath
with water really fast (22mm pipes on mains pressure) ... we never ever run
out of HW.
3 showers in house also benefit of having fully balanced mains pressure hot
& cold water ...... tons of flow & pressure.

The lower part of store has heat exchanger for heating cct ... this is set
at low temp (compared to rads) and is a closed pressurized loop feeding
manifolds on each floor via 28mm pipes. These manifolds have zone actuators
that take a feed off to each zone.

Great system .... and a diy install.

In article o.uk, Dave Liquorice wrote:
On Tue, 29 Nov 2011 09:09:58 +0000 (GMT), charles wrote:

Don't have any radiators :-)

Not sure why you've got *four*!

One on boiler primary loop, (whole of thermal store volume cycles

around boiler)
One on DHW circuit - pumped loop
One on Domestic heating circuit

without radiators? Tell us more.

At a guess all underfloor heating. Best way to heat with a thermal
store in the system. The temp of the store doesn't half drop quick
when a radiator based CH system kicks in an lots of water at 20C gets
shoved into it. Radiators heat up quick mind...

One on incoming mains

Not quite sure why the mains needs an expansion vessel though.

Presumably stopping hammer when a valve closes sharply somewhere rather
than to allow for expansion. I'm not sure why there's one on the mains
_and_ one on the mains pressure hot water loop though.

(The overall system design sounds very similar to my house, but better
implemented, and without the radiators replacing the upstairs underfloor
heating pipes that rotted (Nu-Heat Contraflo). But I've only got the
one expansion tank (well, actually two because new boiler has one inside
too, but it's on the same circuit).)

"Alan Braggins" wrote in message
...

One on incoming mains

Not quite sure why the mains needs an expansion vessel though.

Presumably stopping hammer when a valve closes sharply somewhere rather
than to allow for expansion.

Correct.

I'm not sure why there's one on the mains
_and_ one on the mains pressure hot water loop though.

The hot water loop will have a check valve to prevent expansion down the
mains pipe, so an expansion vessel to prevent hammer when a hot tap is
turned off.

"Dave Liquorice" wrote in message
ll.co.uk...
On Tue, 29 Nov 2011 09:09:58 +0000 (GMT), charles wrote:

Don't have any radiators :-)

Not sure why you've got *four*!

One on boiler primary loop, (whole of thermal store volume cycles

around boiler)
One on DHW circuit - pumped loop
One on Domestic heating circuit

without radiators? Tell us more.

At a guess all underfloor heating. Best way to heat with a thermal
store in the system. The temp of the store doesn't half drop quick
when a radiator based CH system kicks in an lots of water at 20C gets
shoved into it. Radiators heat up quick mind...

A condensing boiler re-heating the store operates at high efficiencies when
this occurs.

"Alan Braggins" wrote in message
...

(The overall system design sounds very similar to my house, but better
implemented, and without the radiators replacing the upstairs underfloor
heating pipes that rotted (Nu-Heat Contraflo). But I've only got the
one expansion tank (well, actually two because new boiler has one inside
too, but it's on the same circuit).)

I think you mean expansion "vessel" not "tank".

"Dave Liquorice" wrote in message
ll.co.uk...

The temp of the store doesn't half drop quick
when a radiator based CH system kicks in an lots of water at 20C gets
shoved into it. Radiators heat up quick mind...

If there is no central room stat and all rads have TRVs and CH is off the
store via a Smart pump, this would only occur on morning switch on. In
normal operation the TRVs would close up somewhat, or even all of them
closed right off, and only trickle heat out of the store.

Recovery rate should be quick as all the boiler heat is dumped into the
store.