TRV on single pipe system

[Andrew Gabriel]

Just fitted a TRV (Drayton TRV4) to a radiator on a single pipe system, partly as an experiment (if it works, there are about another 6 to do).

However, it seems not to work. The flow restriction through it when fully open is too much resistance to get enough flow through the radiator, resulting in a hot area along the radiator top only. I might try moving the inlet to the top so the hydrostatic pressure difference between the hot and cooling water helps the flow, but I'm not hopeful this will make enough differemce to notice.

Just wondering if anyone has come across any suitable product for a single pipe system?

[Tinkerer]

Never used one so I am not familiar with their operation, but is it possible to fit it on the outlet side of the rad?

[YAPH]

Fitted Danfoss RAS-C2s on the rads on my mum's single-pipe system (actually two parallel single-pipe systems) and they work OK. Maybe just a matter of getting more oomph from the pump?

[Tabby]

Why not just restrict the flow in the shorting pipe more? With an adjustable valve.

NT

[Tabby]

te:

how on earth would adding a little more restriction do that?

NT

[MJA]

The Americans use Monoflow tees for single pipe systems, see:

I have never seen Monoflow tees for sale in the UK, but have come across proposals to fabricate a venturi tee out of a tee and reducer, such as:

Anyone tried this to soup up an older UK single pipe system?

MJA

[Andrew Gabriel]

Ah, that was a good clue. They're called full flow TRVs, and it looks like Danfoss still make them (single pipe systems are still common in large commercial installations). Danfoss RA-G.