Hello,

I have a hydraulic valve that causes a problem
in a system because it is not rated for pressure
on one side of the valve.  The hydraulic pump
has some inertia and this cause a problem
with the hydraulics.

Anyhow, if the valve is kept open for a short
time after the pump is de-energized, it works
much better.  The control to the pump and to
the valve solenoid use the same source.

The signal to the solenoid is in the general
neighborhood of 24 VDC with some AC riding
on it.  By adding a diode in series with the
feed to the solenoid and a capacitor across
the solenoid enough delay is produced to
make it work.

I have a mental block or something because
I just don't understand how this works.  The
solenoid has a low resistance (around 45 ohms)
and it's inductance is not known (by me).

I know more total energy is stored in the
circuit (1/2 LI^2  +  1/2CV^2) and intuitively
know the coil will continue to hold in the
valve until much of this energy is converted
to heat by the coil resistance.

Can anyone offer a mathematical explanation
of how this works or otherwise help me to
understand this circuit?  RC = about 100 mS.
L/R is not known.

Thanks.

John Ely, W0GN

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