Re: [APD] how do solenoids work?

["S. Hieber" <shieber at yahoo_com>]

Ignoring lots of details:

Solenoids, such as those we use on our CO2 systems are very
simple devices. The is a small chamber inside the main body
between the inlet and outlet ports. The chamber has a very
small opening over which a plunger is placed. A spring on
the lunger shaft holds it tightly against the opening
thereby sealing the opening and preventing anything from
passing from the inlet port to the outlet port -- sort of
like holding you thumb on the end of an opened sodapop
bottle to keek the gas from leaving the bottle. Around the
shaft of the plunger is a coil of wire which, when
electirfied, creates a magnetic field that attracts the
shaft of the plunger and pulls it up further into the the
center of the coil and thus off of the opening. When the
current to the coil is stopped, the spring pushes the
plunger back onto the opening.

A small bit of debris can keep the plunger from seating
properly and prevent it from sealing. I pulled a small
strand of brass 1/4" long and about 1/3 the tickness of a
human hair from a solenoid yesterday that wasn't sealing.
The brass strand was created when I threaded a fitting into
the body of the solenoid.

The solenoid typically is mounted on the low-pressure side
of the regulator. The pressure will not get higher than
whatever the low-side pressure is set at on the regulator.
Diff solenoids are rated to withstand diff pressures, diff
amounts of current -- some are designed to withstand
intermittent duty, some for continuous duty (running
constantly).  The ones we use on CO2 systems need to be
rated for continuous duty since they might run for hours at
a time. They do not need to withstand much pressure since
the low side pressure on a CO2 system is usually less than
50 psi. They do not need to withstand extreme temps since
the CO2 passing through the solenoid won't be at an extreme
temp. solenoids that handle liquid nitrogen or high heat
gas or fluid systems need to be designed to handle the very
low or high temps.

You should be able to put a solenoid on a low-pressure side
of a regulator, have the solenoid turned off for an
indeterminate length of time without any damage to the
regulator or the solenoid.

The high-pressure side of the regulator should be able to
withstand the pressure from the CO2 tank for an
indeterminate time provided that the regulator is one rated
for service at the pressure of the tank. For CO2 systems on
compressed-gas tanks, the tank pressure is usually about
750-1,000 psi depending on room temperature.

A rise in pH of 0.3 units shouldn't be harmful to any fish,
unless, perhaps, you already had high levels of ammonia. As
the pH rises, the ratio of ammonia to ammonium increases.
But this is not an issue in most planted tanks since the
ammonia/ammonium levels are very low.

With a good metering valve on the CO2 line, the rate of CO2
flow should be limited even if the regulator "wants" to
dump the CO2 tank.

I think dumps are rare and when they occur its when the
bottle is nearly empty. The way regulators work, when the
pressure starts to decline in the CO2 tank (when all of the
liquid is gone and only gas remains in the bottle) the
low-side pressure will start to increase. The high-side
presure holds the regulator's internal valve closed, while
that pressure agaisnt the valve is balanced by an opposite
push in the other direction of a spring and the low-side
pressure. The spring tension is adjusted with a knob or
screw so you can control how much high-side gas pressure is
required to open the valve. In effect, you adjust the
balance point and the the regulator holds the low side
presure at a steady state. As long as there is enough CO2
in the tank, there will be liquid CO2 in the tank and the
pressure will be constant (if the temp is constant). As gas
is removed from the tank, more of the liquid converts to
gas. Once the liquid is gone and only gas remains, then the
high-side pressure starts to decline -- the effect on
regulator operation is *as if* you turned up the tension on
the spring to raise the low-side pressure. This is why it's
best to go ahead and get a refill once the high-side
pressure starts to decline. Some regulators might dump at
100 psi, some might dump at 500 psi.

A 2-stage regulator (not to be confused with a 2-gauge
regulator) is two regulator valve assemblies in series
built into one unit. The first stage reduces the high side
pressure down to something in the neightborhood of 10-100
psi (depending on the specs of the regulator) and the
second stage is then is adjustable and allows a further
reduction in pressure. 2-stage regulators tend to keep
maintaining low-side (output) pressure even when a CO2 tank
is out of fluid. 2-stage regulators tend to be very
expensive and their value for a planted tank setup is hard
to justify.

If a regulator dumps otherwise, then the regulator is
probably defective.

Hope that helps,
Scott H.
 
--- Amy <amyh at comcast_net> wrote:
> 
> 
> Forgive the silly question, but does anyone know exactly
> how solenoids 
> "turn off" the flow of CO2? As the valve on the bottle
> remains open, 
> would there be a danger of the pressure damaging the
> regulator? I'd like 
> to turn off the CO2 at night. Would the resulting rise in
> pH (from about 
> 6.8 to 7.1) hurt the fish?
> 
> rant: My expensive Harris regulator dumped last weekend,
> nearly killing 
> the fish. This CO2 thing is very frustrating and somewhat
> scary, but the 
> results are so wonderful, I want to continue using it.
> I'm hoping a 
> solenoid will help make for a safer setup. Oh well. $$$$$


=====
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