🚀 go-pugleaf

In article <28@bartal.CRLABS.COM> phillip@bartal.CRLABS.COM (Phillip M. Vogel) writes:
>In article <2011@randvax.UUCP> lacasse@blaise.UUCP (Mark LaCasse) writes:
>>I'm not sure if washing machine, sprinkler, or other binary
>>solinoid valves would suffice the original poster, but
>>what I would like and can't find are PROPORTIONAL valves
>>of some sort.  Something like a gate value with a stepper
>>motor attached.  Something that can take water at 80 PSI.
>>(Which leaves out $100 each heating system zone valves.)
>>
>The plan is this: Get a number of on/off valves, and add flow restrictors 
>to them.  The flow restrictors should be set such that the flow through 
>each valve is twice the flow through the previous valve ie. 1gpm, 2gpm, 
>4gpm, 8gpm, 16gpm, 32gpm, 64gpm etc. What you have then is a digital to 
>analog converter which puts out water instead of electricity. We all 
>learned that electrical current through a conductor is analagous to water 
>flow through a pipe, so I guess this is a natural extension of that 
>theory.

Some potential problems with this setup: 1) It will be large and
require quite a bit of plumbing.  2) It will be noisy.  Both the
electrically-operated valves and the flow restrictors will add their
share of noise (it will tend to sound like the fill cycle on a washing
machine.  3) The current draw at full-flow will be quite high,
compared to a single-valve setup, since all 'n' valves will be on.

Depending upon the application, you may not care about any of the
above; on the other hand, this setup would not be acceptible inside
the wall of your typical domestic bathroom for example (especially
times two; one for cold and one for hot!).

>Another advantage to this is that once the flow restrictors are set up, 
>you will have precise and PREDICTABLE flows. Wit a proportional valve 
>connected to a stepper motor, you will have to do a lot of experimentation 
>to determine the proper settings for desired flow rates.

The flow will be predictable only if the input pressure is relatively
constant, which may or may not be true depending upon application.

The stepper-motor approach is *much* better if you use feedback.
There's a company called Omega which publishes thick, glossy catalogs
of flow-control sensors.  Put a flow meter downstream of your
stepper-controlled proportional valve, and read the amount of flow
you're getting.  Then adjust the valve up or down accordingly.  A
little care in avoiding oscillation, and you will get precise,
variable control from a single valve.  You will still need two for
hot/cold mixing applications.  A thermocouple downstream of the mixing
point can also give you temperature feedback, which you can combine
with your flow-rate data for accurate temperature and flow control.



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