RE: Re: Zoned Heating Control

["Neil Ball" <neilball@xxxxxxxxxxxxxxx>]

Depends on which type of valve you are talking about. The TRV valve
body and
UFH manifold valves are rising stem valves (more commonly known as plug
&
seat) and generally opens by lifting the valve up away from the valve seat.
There is no need for rotation of the valve stem although most use round
stems, plugs and valve seats so some rotation is not a major problem. The
actuators are matched to the valve type both in stroke (movement from fully
open to fully closed) and torque to avoid damaging the plug and seat by
using too much force to close. Internally within the actuator there are
rotating gears to move the actuator stem and drive the valve, but this does
not impart rotation to the valve itself. This type of actuator can also
position these valves at some intermediate point to allow a degree of
modulation from the valve.



There is also another class of valves such as butterfly, rotary shoe etc
where the open/close mechanism is rotational and with these the actuator
mechanisms do indeed rotate.



HTH



Neil B.

_____

From: ukha_d@xxxxxxx [mailto:ukha_d@xxxxxxx] On Behalf Of
Mal Lansell
Sent: 16 April 2007 17:28
To: ukha_d@xxxxxxx
Subject: [ukha_d] Re: Zoned Heating Control



--- In ukha_d@yahoogroups. <mailto:ukha_d%40yahoogroups.com>
com, "Neil
Ball" <neilball@...> wrote:
>
> The actuators do not rotate, they simply move the valve stem up &
down hence
> why it is not a problem :-)
>
>
>
> Neil B.
>
>

I thought these were add-on controls, though - i.e. ones that are
supposed to fit on existing valves (which would normally be of the
rotating type)

Mal



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