🚀 go-pugleaf

In article <2925@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes:
>	Since the above are all solenoid valves, a position encoder is
>not required...

Unless, of course, you want to be sure that the valve has really
operated when you ask it to, which is usually considered necessary
in critical control systems.  (If you don't think controlling a
shower justifies this degree of reliability, consider the consequences
of turning off cold but not hot in a place with an enthusiastic water
heater -- non-trivial injury might result.)

I think the original poster wanted proportional control rather than just
on/off, which is why he specified that solenoid valves weren't of interest.
Short of the (plausible) suggestion of building a 4-bit hydraulic DAC with
four valves, it looks to me like he's going to need something like a
motor-controlled needle valve, not normally a consumer item, except perhaps
in some fancy washing machine.  He'll also need a separate shutoff valve,
since needle valves aren't usually designed to reduce flow to zero.
-- 
"God willing, we will return." |     Henry Spencer at U of Toronto Zoology
-Eugene Cernan, the Moon, 1972 | uunet!attcan!utzoo!henry henry@zoo.toronto.edu