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- [Instructor] Let's have a look now
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at a valve, and its construction,
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and some of the main components.
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As you can see in front of us,
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we've got a valve.
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This is actually a globe valve.
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We'll just give it a little spin.
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What we're gonna do is work through
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the exterior of the valve first,
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and I'll explain to you the
main components of the valve.
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Then we'll take a cross
section of the valve,
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and I'll show you some of
the internal components.
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Let's start at top.
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At the top of the valve,
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we have what's called a actuator.
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Now, an actuator, it may
be pneumatic or hydraulic,
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or it may be manually operated,
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or perhaps even electrically operated,
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such as with a motor.
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The actuator is essentially
opening or closing the valve,
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or moving it to a position
between opening or closing,
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which is known as throttling.
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As we can see here, this
is a hand-operated valve.
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This is the hand wheel.
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We zoom in, we can see some labeling.
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On the right, we have close,
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and on the left, we have open.
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This means that, if we turn the valve
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to the right, we will put
it into the closed position,
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and stop the medium
flowing through the valve.
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This may be a liquid, or
a fluid, or perhaps a gas.
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Or we can turn it to the left,
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which is to open the valve, and again,
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we will then have a medium
that flows through the valve.
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The setup for valves is always the same.
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It's always righty tighty, lefty Lucy.
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Try and remember that.
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Otherwise, you're gonna put the valve
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into the wrong position.
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Let's zoom out.
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We can see the actuator.
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It's being turned to the left.
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The valve is now open, and the stem,
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which is this spindle or long screw shape,
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has now come out the top.
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This is known as a rising valve
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because we can see that the stem
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has risen out of the valve.
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If we go back the other way,
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the valve is now being
closed, it's being turned
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to the right, the hand wheel,
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and the stem has gone back into the valve.
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This is a rising type valve.
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Zoom out.
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Can see that the stem comes down,
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and can see it here, continuing down
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into the main valve body.
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At this point here, we actually enter
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the sealing arrangement, or
part of the sealing arrangement,
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for the valve, so there's always gonna be
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some sort of a sealing arrangement
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to stop the fluid or the gas
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passing between the valve and the stem,
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and leaking outwards.
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That is this sealing arrangement
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that we're looking at now.
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We're gonna take a cross
section of that later.
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Let's just zoom out a bit more.
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Can see another area of interest here.
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This is referred to as the bonnet.
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The bonnet is held on
by these array of nuts
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going around the entire top of the valve.
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The bonnet is designed so that
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we can open the valve
and access the internals.
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The internal components are
actually referred to as trim,
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so we're gonna access the trim.
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Almost all valves will
have some form of bonnet
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because it is essential to be able
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to get in there and maintain the valve.
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However, there are exceptions to this.
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Some valves are not
maintained in this manner,
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especially some of the smaller valves
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that have a lower monetary value.
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In other words, it doesn't make sense
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to repair them or maintain them.
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It's a lot easier and
quicker just to replace them.
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Let's go down a bit further.
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You can see we've got a
connection on the end.
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This connection, with all the holes,
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these holes are actually
for passing bolts through.
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Then we'll use a bolt and nut arrangement
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to tighten the flange, that is,
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if we look from the side
here, this whole section,
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that's referred to as a flange,
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and each end has a flange.
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We can see another flange here.
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The flange enables us
to connect to the piping
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and support the valve between the piping.
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Typically, we're gonna use nuts and bolts,
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although it is possible, also,
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to weld the flanges to the pipe work.
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Obviously, once you've welded the valve
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to the pipe work, it's a
lot more difficult to remove
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than if you've used a
nut and bolt arrangement.
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You'll generally only use
this welding type arrangement
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when the medium flowing through the valve
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is particularly hazardous.
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Now, each of the flanges also has
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a sealing arrangement.
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This allows us to seal the
valve to the pipe work.
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If we can see here,
this sealing arrangement
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is the black highlighted
area we're looking at now.
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It has a ridged profile.
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This helps it to seal, and typically,
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we use a paper gasket or maybe
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a nitro rubber gasket,
and that will help us
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to seal the valve to the pipe work
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when we clamp the nuts and bolts together.
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The main reason for the
gasket is simply that,
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if we try to clamp two
metal surfaces together,
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there would be some sort of leakage.
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This is because, when you press
two metal surfaces together,
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they're both quite hard, so
when you press them together,
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they don't seal very well.
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There's always some sort
of a gap between them
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unless you use a very soft metal.
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What we'll do, we use some sort of rubber
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or paper gasket, and we'll squeeze that
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between the two metal surfaces,
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and this will then form our seal.
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We can see the inlet and discharge holes.
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Not sure which is which.
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I have to have a look around the valve.
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Can see here on the side
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that there is actually a flow indicator.
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That is this arrow here.
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The flow is coming from the
left and going to the right.
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That means, on the left hand side,
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we have the suction, or the inlet,
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and on the right hand side,
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we have the discharge, or the outlet.
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Between the two flanges
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is actually the body of the valve,
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that is, the entire area
between the two flanges.
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Sometimes, people will
also include the flanges
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as part of the body.
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The body houses internals of the valve,
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referred to as trim.
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Let's now take a cross section
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so we can look at the internal components.
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Okay, there we are.
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Now we can see some of
the internal components,
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and as you can see, we've
also added some labels.
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Let's do the same again,
let's start at the top.
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You can see a hand wheel,
as it's labeled there,
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or handle wheel, as it's been labeled.
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We've got a yoke sleeve.
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That allows us to lower
and raise the stem.
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That is effectively a anchor point,
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and without it, we would
just be spinning the valve
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right or left, and we would not have
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any vertical movement, so
the yoke sleeve allows us
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to draw the stem up or lower it down.
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That is essentially its main function.
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If we look off to the right now,
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we can see a label for the stem.
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We can see something else,
which refers to as a gland bush.
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The gland bush is used to press down
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onto what we refer to as a gland packing.
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The gland bush will press
down onto the packing,
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and that will give us a seal.
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Now, gland packing has come a long way
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in the past 100 years.
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Traditionally, they
would've used something
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like horse hair, and they
would've wound it together,
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and then they would've inserted that
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in the area we're looking at now,
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where this gland packing is.
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That's the black three
stripes area we're seeing.
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This sort of wound horse hair
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would've been stuffed in there,
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and we would've used the gland bush
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to press down onto this horse hair,
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and squeeze it between the valve bonnet
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and the valve stem.
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That, essentially, then forms a seal,
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and prevents any liquid, or gas,
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or whatever the flow medium is,
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from leaking out of the valve.
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Obviously, we've come a long
way since using horse hair.
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We now often use plastics or Teflon,
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and it is a lot more
durable than horse hair.
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I should also mention that the horse hair
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would usually have been soaked
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in some sort of fat or oil
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to make it a little bit more durable,
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and to allow the stem to turn more easily.
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The way that this sealing
arrangement actually works is,
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if we go up to the top here,
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we can see, on the left
hand side of the screen now,
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we have a nut and stud arrangement.
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A stud is essentially a
bolt, but without a head.
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We can see that the stud has gone
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though the entire piece here,
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and it has two nuts on the end.
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Zoom in.
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There is one nut, and
there is the other nut.
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We're not using a nut
and bolt arrangement.
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We're using what's called a stud,
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and stud and nut arrangement.
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We're gonna clamp these two nuts down,
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and we're gonna do the
same on the other side.
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Just switch back so you can see it.
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When we tighten these down,
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we're essentially going to push
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this metal plate, the
top metal plate, down,
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and that is then gonna push
the gland bushing down,
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this section I'm wiggling about here.
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As the gland bushing gets pushed down,
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it's gonna compress the packing,
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and as it compresses the packing,
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it is going to seal the space
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between the stem and the valve bonnet,
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and that is how we get our seal.
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Important to realize that
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we don't want to over-tighten
the top nuts and studs
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because, if we do over-tighten
those nuts at the top,
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and we push the gland bush
too far down onto the packing,
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what we're actually gonna do is
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squeeze the packing tight onto the stem,
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and also the valve bonnet.
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This is gonna create a lot of friction
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when we try and open or close the valve.
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In fact, it can be incredibly difficult
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to open or close the valve
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when someone has
over-tightened the packing.
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Let's go down now.
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We're going past the bonnet.
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We can see that the
bonnet has been, again,
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sealed onto the body.
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There's another seal, that
is this black piece here.
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We've sealed the body, the lower piece,
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to the bonnet, the upper piece,
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and we've sealed the stem to the bonnet,
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and that's gonna be the
pressure boundary area,
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so we're gonna be
staying inside this space
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where I'm going around with my mouse now.
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That's very important.
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We want to ensure that we have
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as few seals as possible,
and where we do have seals,
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we want to ensure that they are adequate
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and sufficient to prevent leakage.
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As we can see now, we've
gone down, down, down.
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This is the stem coming down,
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and we're gonna finally reach
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what we refer to as a disc.
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A disc is also sometimes
referred to as the lid.
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This is the lid or the disc,
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and the disc is going to sit onto a seat.
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Let me just push play so that
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we can get some distance
between our seat and disc.
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We can see there that
the disc has moved up.
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The valve is now in the open position.
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Let's have a look at the seat.
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The seat is this area, just zoom in, here.
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Where I am with my mouse
now, this is the seat,
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and including the side piece.
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We want the disc to come
down and land on the seat,
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and form, ideally, a perfect seal.
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Then we will prevent any
flow through the valve.
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That is when the valve is
in the closed position.
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When we want it in the open position,
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the lid will rise, or will move away
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from the main seating area,
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and then we will allow the medium
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to flow through the valve.
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It is very important
that the disc and seat
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contact surface areas are clean.
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We want them to be as clean as possible
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because any debris or foreign bodies
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that get stuck between
the disc and the seat
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are essentially gonna stop
it from sealing correctly.
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Then we're gonna have a valve that allows
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the medium to pass
through when it shouldn't.
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Imagine, for a moment, that we had,
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just for example, a big piece of metal
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that got stuck across the valve seat here,
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and as the disc came down,
it tried to crush the metal,
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but unfortunately, it
wouldn't be able to do that,
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and what we'd actually have is a gap
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between the seat and the disc.
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Just zoom up.
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Imagine a gap here, and
the fluid, or liquid,
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or gas, or whatever's
moving through the valve
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is gonna pass through here.
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Then we've got a leaking valve,
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or what we refer to as
passing, a passing valve.
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That is not good.
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We don't want that.
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The idea of the valve is
that it can open or close.
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We can start or stop fluids flowing,
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and we can't do that if
the disc and the seat
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are not perfectly sealing together.
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We actually refer to this as seating.
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The valve should seat perfectly,
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and if it's not seating perfectly,
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then we are not gonna have a seal.
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Valves are almost always named
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after the type of disc they use.
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The type of valve we're looking at now
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is a globe valve.
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However, if you look at a plug valve,
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a butterfly valve, a
ball valve, a gate valve,
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they're all named after the type
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of disc that they are using.
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The valves may appear differently,
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but essentially, they're built
always for the same function,
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which is to start and stop a flow,
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control a flow, control the pressure,
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relieve pressure, they're
all gonna be working
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to obtain some of all of those objectives.
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When you're looking at a valve,
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ask yourself, what is it doing?
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Then, how is it doing it?
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Then apply the knowledge that you've got
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from this video, and you'll be able
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to figure out the rest.
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(soft electronic music)
