High pressure air enters the unit from the top
and the chamber on the left is maintained at the current cylinder
pressure.High pressure air enters the unit from the top
and the chamber on the left is maintained at the current cylinder
pressure.
The
chamber on the right is open to the enviroment and is consequently
always at the ambient water pressure.
The
chamber at the bottom is maintained at the intermediate pressure of
9-10 Bar above ambient
The
Second Stage draws air directly from this
bottom chamber at the above ambient pressure
As air is
drawn from the second stage the pressure on the left hand side of the
diaphram (blue) falls.
Falling
pressure in the chamber deflects the diaphram and operates the
actuator (red) and opens the valve, thus maintaining the interstage
pressure.
As the
diver descends the ambient pressure on the diaphram increases and
tends to open the valve, this keeps the interstage pressure at 9-10
Bar above ambient.
Courtesy of Apeks - Shown below is a
schematic diagram of a Balanced Apeks
first stage.
As can be
seen this is very similar to the schematic diagram of the unbalanced
regulator shown above.
High
pressure air enters from the top, intermediate pressure air leaves to
the second stage via the bottom.
As this is
a sealed first stage the water pressure is transmitted to the
diaphram assembly, by means of the load transmitter (Black "T;"
shape on the right)
This is a
balanced first stage. This means that low pressure air is allowed to
both sides of the valve.
This
balancing allows the valve to be opened with very little force
regardless of tank pressure.
Balancing
a regulator in this way reduces the effects of the changing tank
pressure throughout the course of your dive.
For a more
detailed explanation of balancing here is some appropriate text from
John Foley's 1990 diving manual.
To achieve a balanced condition it is essential that both ends of the valve head be exposed to identical pressure. The valve head seals against an orifice and that portion of the the valve head actually over the orifice is exposed to the interstage pressure. To counteract this, the stem of the valve head is led back into a small chamber which is also open to the interstage pressure. The diameter of the stem is exactly equal to the orifice diameter so the valve head is held in balance by the interstage pressure acting simultaneosly on both ends. The effect of cylinder pressure on the valve head has been neutralised: any tendency for the cylinder pressure to push the valve forward (into the orifice) is opposed by an equal tendency to push the stem backward, into the balance chamber.