automatic bypass valves - how to calibrate

[Bink]

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? Should I just set the control half way and hope for the best? Should I give up and fit a room stat? :-)

------ bink

[Andy Hall]

You don't need to do either of these.

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.

You shoulld have some for of room stat anyway and in a space where there is not a TRV on the radiator or that it is open fully. On a simple boiler, this is used to interlock it off when the house is up to temperature. You need to arrange things so that the rooms with TRVs are warm and valves are closing before the thermostat operates.

.andy

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[fred]

In article , Andy Hall writes

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.

[IMM]

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.

[fred]

In article , IMM writes

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.

[IMM]

You are living with it and tweaking as you go along until fine.

That boiler modulated, if I recall. Still I would rather have a constant flow through it, via a primary and secondary loop/pump arrangement. Keston recommend a 42mm vertical copper tube as part of the primary loop if two boilers are taken off. Works fine, but 42mm appears overkill. The intention is to create a neutral spot. I prefer the constant flow back to the boiler that a good primary and secondary loop system gives.

If the system say, heats a duct heater battery or Meson heaters, these require a high temperature operation. I would prefer a blending valve to ensure a constant flow back and that only 80C water reaches the coils.

[Christian McArdle]

Set it to around 0.3 bar. Mine had markings for this purpose. It will start opening even when not all the TRVs are closed, but this is a good thing that reduces noise through the radiators that are still open. The 0.3 bar left over should be easily enough to push enough water through those rads.

Christian.

[Bink]

Yes, but how do I know when it's opened? There's no indicator on the Pegler one.

I thought the boiler would just switch off when the flow/return temps were very close, but I guess this would stop it cycling every time the water in the pipes cooled a bit. I've got the cable in place for a room stat soI think I will fit one as well.

[Bink]

Ah, yes, of course! Thanks.

[FrancisJK]

My system has three zones plus dhw.

Only one zone has TRVs.

Do I just need the automatic bypass valve in this zone?

Or should it cover whole system?

FrancisJK

[Andy Hall]

Put it on the complete system, because if all zones close, (TRVs or not) because their thermostat is satisfied; there is otherwise no bypass.

.andy

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