Valve Motors

[Walden]

In air conditioning systems there are small motors opening and closing water valves, dampers etc.. These motors often have a permanent 24 volt AC supply and a variable 0 - 10 volt DC supply. By altering the DC supply the motor opens or closes the valve. At 0 volts the valve is closed and at 10 volts the valve is fully open. How do these motors work?

 

[kevinf]

Dear Tmpirrie,

They are typically DC brushless motors with multi-step gear trains. Some have AC synchronous sub-motors with magnetic clutches.

I suggest taking a look at the Electric Control Fundamentals chapter of Honeywell's Engineering Manual of Automatic Controls (the bible for HVAC Controls).

http://hbctechlit.honeywell.com./techlit/PDF/77-0000s/77-1100.pdf