Vacuum Pumps Explained – Basic working principle HVAC

Hey there guys, Paul here from 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 just shortly. 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.

pexels photo 2539462

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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