🚀 go-pugleaf

In article <2011@randvax.UUCP>, lacasse@blaise.rand.org (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.)

Someone already mentioned the "hydraulic DAC" approach, so I'll
offer another whimsical translation of electronics technique to
the water world:  the hydraulic switchmode buck converter!

Find a large tank somewhere.  A possibility would be a defunct hot
water heater whose element is shot, but doesn't leak at the stipulated
pressure.  Plug up its normal (hot) outlet.  Connect its cold inlet
through one of those binary solEnoid valves, to the water supply.
If significant lengths of plumbing are involved, you'll need a
healthy standpipe on one or both sides of the valve.

Take your output either from the "inspection drain", or tee it from
the the inlet, hopefully through a lengthy pipe.

Drive the solEnoid valve with either a fixed frequency, variable duty
cycle ON/OFF control train, or a fixed pulsewidth, variable frequency one.
The ON and OFF pulsewidths should be longer, by at least an order of
magnitude, than the operating speed of the valve.

You can read in Circuit Cellar Ink all about how such a system can be
driven by a relatively straightforward controller running a multitasking
operating system, using as little as 32K of RAM.  Or, if you're willing
to work with your windowshades down, you might use a dual op-amp instead.


Brian Rhodefer