0:30
that we have two valves. Valve A and
0:33
valve B. Now here the valve A has a
0:36
capacity of 10 GPM while valve B has a
0:38
capacity of 5 gpm. Now which valve has a
0:42
higher flow capacity? If the answer to
0:44
it is that valve A has a higher flow
0:47
capacity, then the answer is not
0:49
correct. Why? In order to understand
0:52
this concept, we must have a very
0:54
thorough understanding of what is CV in
0:56
a control valve. This concept is
0:59
extremely important while dealing with
1:01
control valves. In this video, in a very
1:04
logical way, we'll learn so that you can
1:06
remember whether it's an interview or
1:08
when you're preparing data sheet of what
1:11
is CV and control valve. So without
1:13
further delay, let's get into it. The
1:16
first thing is that whether you have a
1:17
temperature control valve, pressure
1:19
level or flow control valve. Actually
1:22
they're nothing but a simple control
1:24
valve which has only one basic function
1:28
which is to control the flow within the
1:32
valve. Now how does CV help in that is
1:36
in the most simple terms we can say that
1:39
CV is nothing but a tool so that you can
1:43
compare flow capacity from any valve
1:46
throughout the world. But let us dig
1:49
into this concept in such a way that
1:51
we'll remember this concept forever. As
1:53
we had initially discussed imagine that
1:56
for valve A and for valve B we have a
2:00
different flow rate. Valve A has a flow
2:02
rate of 10 gpm and valve B has a flow
2:04
rate of 5 gpm. Here as we had said we
2:08
cannot say that this means that valve A
2:10
has the higher flow capacity. Why?
2:12
Because there could be the case that
2:14
both the valves are made of the exact
2:16
same construction same size but the
2:19
pressure drop across the first valve is
2:21
15 psi while the pressure drop across
2:24
the second valve is just 1 PSI. So we
2:27
know that as you increase the pressure
2:29
drop across the valve the flow through
2:32
the valve increases. So this flow
2:35
increases just because of pressure drop
2:37
and not because of the valve size. So
2:40
here if we want to compare two valves
2:43
flow capacity we have to keep them under
2:46
the same pressure. So let us take a
2:48
standard of 1 PSI as pressure between
2:50
the two valves. again. Now what I do is
2:54
I'll measure the flow between the two
2:56
valves. But here I see the flow between
2:59
the first valve was 10 gpm and the flow
3:02
with the second valve was 4 GPM. Why?
3:05
There could be the case that for the
3:07
first valve the fluid was water and for
3:10
the other valve the fluid was honey. Now
3:13
we all know in such cases that honey is
3:15
very dense. So it will have a lower flow
3:18
rate as compared to water. So even
3:20
though the valves are made of same
3:21
construction, we have to also ensure
3:24
that the liquid between them is the same
3:26
if you want to compare the flow capacity
3:29
between two walls. So let us select
3:31
water because water is one of the most
3:33
available substance and very easy to be
3:36
found at any site or at any vendor
3:39
location. Now let's keep water for both
3:41
the valves. I've kept the same pressure
3:44
drop. I have kept the same liquid.
3:46
Ideally I should get the flow rate to be
3:48
same but for this valve I get 10 gpm as
3:51
the flow rate and for this valve which
3:53
is valve P I'm getting 12 gpm. Now what
3:56
is the issue here? There's another
3:58
parameter which comes into play which is
4:00
the temperature. So both water being the
4:04
same fluid might have different
4:06
temperatures. So first may be at 60°
4:09
Fahrenheit and the other one might be at
4:11
150° F. So we know as the temperature
4:14
increases there's again a difference in
4:16
flow rate. So we will have to maintain a
4:18
constant temperature as well. So we'll
4:22
select 60° F. A lot of people ask that
4:25
in CV definition why 60° Fahrenheit is
4:28
specially taken. The answer is because
4:30
the specific gravity of water is 1 at
4:33
60° Fahrenheit. So this will help
4:35
greatly when we are doing CV
4:37
calculations. So we'll have three
4:39
standard parameters which is the psi
4:41
drop is 1 psi, the water is the fluid
4:44
which is taken and the temperature 60°
4:47
Fahrenheit. That being the case, we can
4:49
say the definition of CV is as follows.
4:52
CV is the number of US gallons of water
4:56
that can flow through a valve with one
4:59
psi pressure drop at 60° Fahrenheit for
5:04
1 minute. So this is the definition of
5:06
CV. Also, I want to share one more thing
5:09
that I produce a new video every
5:11
Saturday. So, if you want to learn
5:13
something new every Saturday, please
5:15
click on the bell icon and subscribe so
5:17
that you can learn a new video.
