TRV's and one pipe system

[stem]

I keep seeing references on this site that normal thermostatic radiator valves cannot be fitted to a one pipe system and that special ones that cost big bucks are needed.

Why is this? I have Terriers by Pegler fitted to all of my rads on a one pipe system (except the hall where the thermostat is) and they work great. It also sort of auto balances, as the ones at the downstairs end of the loop get full heat when the upstairs ones reach temp and shut down. Also as the pump effectively only circulates water around a simple loop with a few bends, the pump runs on the lowest speed so that it's silent. When I bought the property I had intended to upgrade it, but it works so well I've left it well alone. Apart from flushing it out and converting it to "S" plan. we have small bills and are toasty all winter.

So why the special valves?

 

[Gasguru]

Although the single pipe system is pumped the radiators heat up by gravity, therefore the valves for 1 pipe systems have a larger body ie they have far less resistance to flow. For example the Danfoss 1 pipe valves have twice the Kv (flow factor) of a standard valve body.

 

[doitall]

It also makes a big difference when the flow is connected to the top of the radiator TBOE.

Peglar valve for one pipe systems is the Belmont VBG

http://www.pegler.co.uk/literature/pdfs/newPDFs/Terrier-controls-Brochure.pdf