Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!gatech!ncar!noao!asuvax!enuxha!kluksdah
From: kluksdah@enuxha.eas.asu.edu (Norman C. Kluksdahl)
Newsgroups: sci.electronics
Subject: Re: electrically operated valves
Summary: another idea
Message-ID: <137@enuxha.eas.asu.edu>
Date: 17 May 89 21:11:19 GMT
References: <23526@shemp.CS.UCLA.EDU> <11170007@hpfcdj.HP.COM> <631@corpane.UUCP>
Organization: Arizona State Univ, Tempe
Lines: 43

In article <631@corpane.UUCP>, sparks@corpane.UUCP (John Sparks) writes:
> 
> I don't know, but we've (Corpane) have been looking for such an animal for a
> while now. We have water cooled machines and would like our on-board
> microprocessor to control how much water is let into the system. So a stepper
> motor controlled proportional water valve is exactly what we need.

This brings to mind a problem encountered by my father-in-law when he was
working on biomedical instrumentation for the Air Force (actually, for NASA).
One experiment which flew on Skylab required digital control of a vacuum
chamber.  I think the idea may have some possibilities with your application.

It works like this-- take 3 or 4 (or more) electrical ON-OFF valves, and
connect them in parallel to a LARGE inlet manifold.  The key is to have 
very little pressure drop from the first valve to the n'th valve, and to have
lots of capability for flow.  Follow each valve with a manual valve, which
you then adjust for a given flow.  The first manual valve is adjusted for
 n gallons per minute, the second for 2n, the third for 4n, etc.
By selecting which valves are on, you can control the total flow.  The output
of the manual valves is then fed to an output manifold, again large.
ASCII graphics of this:
                    ------| e valve 1 |---|m valve 1|---------
                    |                       n gpm            |
                    |                                        |  
                    |-----| e-valve 2 |---|m valve 2|--------|
                    |                       2n gpm           |
                    |                                        | 
          ----------------| e valve 3 |---|m valve 3|----------------------
          ----------|                       4n gpm           |--------------
     inlet manifold |                                        |  outlet manifold
                                     etc.


This may provide at least some measure of digital control.
Hope it helps.


**********************************************************************
Norman Kluksdahl              Arizona State University
            ..ncar!noao!asuvax!enuxha!kluksdah
alternate:   kluksdah@enuxc1.eas.asu.edu

standard disclaimer implied