In article , IMM abuse-
writes

"fred" wrote in message ...
In article , Andy Hall
writes
On Tue, 20 Apr 2004 23:56:40 +0000 (UTC), "Bink"
wrote:

I've decided that one of these auto bypass valves would be a good thing
on
my all-TRV system, up til now I've had the TRV head left off the hall
radiator as an uncontrolled bypass rad. So I ordered the Pegler valve
from
Screwfix. Before I fit it, is there any trick to calibrate these things
without the use of a pressure gauge? I was expecting some kind of
indicator
on the valve to show when it was fully open (I seem to remember seeing
some
other model that had this?) and thought that this would provide a good
way
of calibrating the thing, but alas, the Pegler valve just has an
adjuster
and a confusing calibration chart in the instructions. Well, confusing
to
an amatuer plumber without a pressure gauge that is.

Should I send this one back and try and source one with an "open"
indicator?
Should I buy expensive pressure measuing kit?

You don't need to do either of these.

Should I just set the control
half way and hope for the best?

To some extent it is a trial and error thing, but a simple way is to
close all the TRVs and then adjust the bypass valve so that it opens.
You may want to adjust slightly more so that it opens just before the
TRVs are completely closed to make sure that it does.

I approached it from the other direction:

Closed the automatic bypass, opened all TRVs fully and balanced the
system as per the faq.

Then eased the setting on the automatic bypass until it just opened
(indicated by its return pipe getting hotter), then backed it off a tad.

Then set TRVs to the desired temps.

Bypass now comes on as TRVs close down.

The "general" idea of the by-pass is to open up when all TRvs are closed
down. It appears that yours is opening up when some, or all, are only
partially closed.

Yes, that's true. As the TRVs close it is when they are reaching design
temperature so I wanted to indicate to the boiler that it was time to back off
a bit (it's a modulator). The action of the automatic bypass allows some
flow water to pass, raising the return temp and causing the boiler to
modulate its output. In the event that this caused any of the rooms to be
not to reach design temp I would back off the bypass another bit.

If I did not have a modulating pump you could consider that I was trying to
create a relatively constant flow of water at all times, irrespective of the rad
load. The other way leaves you with flow through the boiler dropping as rad
demand decreases until the bypass starts to operate which could make for
'untidy' operation on a non modulating boiler. Imagine the case of the guy
with a K130 we discussed recently, I would prefer to have a constant flow
through that beast at all times.
--
fred