Hey there guys, Paul here
In this video we're going to look at how vacuum pumps work,
the main parts, and why we use them.
Vacuum pumps are used extensively by air conditioning
and refrigeration engineers to remove air
and non-condensables, such as water, from a system.
We need to remove these with a vacuum pump
because they cause the refrigeration system
to operate inefficiently and they can also corrode
the internal parts.
This procedure is carried out before a new system
is charged with refrigerant or when an existing system
has undergone some repairs,
or the refrigerant has already been recovered.
In either case, there's a chance that air or moisture
have contaminated the inside of the system.
On a typical air conditioning system,
you'll see the vacuum pump is connected
via manifold across the high and low pressure side
of the system.
A better way to do this is to remove the manifold completely
and connect the vacuum pump to the suction line
with a pressure gauge connected to the liquid line.
We connect the pressure gauge here
because it's the furthest point in the system
so you get a true reading.
Now I've teamed up with my friend Brian
over at HVAC school for this video and he's going to
run you through how to actually connect a vacuum pump
to a real world system.
He's also got lots of great technical tips to help
build your knowledge and skills.
So do check that video out, link is down below.
If we take a standard vacuum pump,
which looks something like this,
then we have the electrical motor on the back
and the compressor on the front.
On the top we have a handle and on the bottom
we have a support base.
We then have an inlet, which connects to the system
to remove the air.
And then above the compressor section,
we have the exhaust or the outlet.
On the front of the compressor section we find
an oil sight level glass and we can tell how much oil
is in the chamber as well as it's condition.
As we take the unit apart we can see we have a fan
in protective casing mounted at the back of the motor.
Then inside the motor we have the stator, which holds
the copper coils but we're going to look at this part
in detail just shortly.
Concentric to this, we have the rotor and the shaft
which drives the compressor.
At the front we have the compression chamber.
These are the two stage compression version,
which allows us to pull a deeper vacuum.
So we, therefore, have two compression chambers.
Inside the chambers are the compressor rotors
and the vanes which move the air out of the system.
On top of the compression chamber is a reed valve
which vents the exhausts.
When we remove the fan's protective casing,
we see that the fan is connected to the shaft,
which runs it through the pump.
The fan is used to cool down the electrical motor
and it will blow ambient air over the casing
to dissipate this.
The fins on the casing increase the surface area
of the casing which allows us to remove more unwanted heat.
Inside the motor, we have the stator, which is wound
with copper coils.
When an electrical current flows through the copper coils,
it will generate a magnetic field.
The rotor is affected by this magnetic field
and this forces it to rotate.
The rotor is connected to the shaft
and the shaft runs along the length of the pump
from the fan all the way up to the compressor.
This way, when the rotor rotates, so will the compressor.
And that's what we're going to use to create
the vacuum effect and evacuate the air from the system.
Just to note, that when we think of a vacuum,
we usually think of a sucking force.
That's not actually the case and we're going to see why
If we look inside the compressor, we can see we have
the inlet, which is connected to the system we're evacuating
Then we have the outlet and the reed valve,
which vents the air and moisture out which is being
evacuated from the system.
In the centre, we have the compression rotor
and the compression chamber.
Notice the rotor is eccentrically mounted
inside the chamber.
This means it isn't perfectly central.
That's a key feature which we'll see in detail shortly.
The shaft connects to the rotor and will cause it to rotate.
Mounted inside the rotor are two spring loaded vanes.
The springs always trying to push the vanes outwards
but they're held in place by the compression chamber walls.
Therefore, the tips of the vanes are always in contact
with the wall and there's a thin layer of oil
which helps to form a seal between the two.
When the rotor rotates, the springs continue to push
the vanes outwards so the vanes will follow the contour
of the compression chamber.
When the pump starts the rotor is going to move across
the inlet and expose an error inside the compression chamber
This error will be at a lower pressure compared to the
pressure inside the system.
So the air and moisture inside the refrigeration system
is going to rush in to try to fill this empty region.
So then why does it do this?
Well pressure always flows from high to low.
So if we connected, for example, two balloons
of different pressures then the gases will move
from the high pressure side into the low pressure side
until both are of equal pressure.
In this example, the low pressure side was a vacuum
but it didn't suck the gases in.
The high pressure side pushed it's way in.
That's the vacuum effect.
Gases want to equalize and will flow from a high pressure
to a low pressure.
Therefore, we use a vacuum pump to create a region
of lower pressure so that the unwanted gases
inside a refrigeration system will rush out of the system
to try to fill this lower pressure region.
So in our scenario the connection hose
and the new low pressure error
within the compression chamber have become an extension
to the refrigeration system.
So the gases in the system are going to rush in
to try to fill this and try and make that the same pressure
between the two.
But it's actually a trap.
Because as the rotor continues to rotate,
the second vane sweeps in and traps that volume of gas
in the chamber between the two vanes.
The other vane then passes across the inlet
and creates another low pressure region.
So more gas rushes in from the system
to try and fill this void.
As the compressor rotates, the volume of the chamber
is going to start to decrease.
That's why the rotor isn't perfectly centered
so that we can vary the volume of the trapped gases.
This decrease in volume is going to compress the gases
into a tighter space.
That would increase the pressure and the temperature.
It continues to rotate into a smaller volume
until the pressure becomes high enough that it forces
the reed valve of the exhaust to open
and the gases are then discharged.
The compressor continues to rotate,
and as it does so, the next batch of gases
is poured into the system and the cycle continues.
Most vacuum pumps will be two stage,
which means there are two compression chambers
linked in series.
The exhaust from the first compressor links directly
into the inlet of the second chamber.
This design allows the pump to achieve a deeper vacuum.
When we have a single compressor, the outlet is
pushing against atmospheric pressure.
But with the two stage design, the outlet is
pushing against a much lower pressure because it's simply
the inlet of a second rotating compressor
and the low pressure region it's created during that rotation.
As the vacuum pump continues to run, it will eventually
pull the gases out of the closed system,
which will reduce the pressure down below the pressure
of the atmosphere, which is surrounding the outside
of the system.
As the pressure reduces, any moisture in the system
will become easier to boil and evaporate.
We can add a little heat with a heat lamp or heat gun
to help it vaporize and that way we can extract it
from the system.
Okay that's it for this video but to continue your learning
then check out one of the videos on screen now
and I'll catch you there for the next lesson.
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