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welcome to this Swagelok video
today's topic is considerations in design for minimizing droop
In a pressure reducing regulator
the purpose of a pressure reducing regulator is to reduce the pressure in
the system
while minimizing flow rate changes
droop is defined as a decrease in outlet pressure as downstream flow increases
this flow curve illustrates droop
the vertical axis represents outlet pressure
with the horizontal axis representing downstream flow rate
notice how the curve slopes downward as the flow increases
this is droop
every regulator will exhibit some droop
but you can take steps to minimize it
you can achieve a flatter flow curve
by choosing the right regulator configuration for your system
this leads to more consistent pressure downstream
the most common type of regulator is a spring-loaded regulator
in this design a spring applies force on a sensing element either a diaphragm or
a piston
which moves the poppet closer to or away from the orifice
controlling the downstream pressure
in this configuration the inlet pressure is a constant 30 bar or
435 psig
the regulator is set to 8 bar or 116 psig
there is no flow at this time as the downstream valve is shut off
as the downstream valve is slowly opened you'll be able to hear the increase in
flow
the outlet pressure starts at 8 bar
or a 116 psig
but drops to about
5.5 bar or
80 psig
this gradual drop in pressure is droop
the pressure drop looks like this when represented on a flow curve
now we will improve droop by using a different type of regulator
this is a dome loaded regulator
the load force in this type of regulator
is controlled not by a spring but by pressurized gas in the dome chamber
the gas flexes a diaphragm which moves the poppet away from the orifice
controlling the downstream pressure
a pilot regulator is used to control the supply of gas to the dome chamber of the
dome loaded regular
And an outlet loop
relieves the gas from the dome chamber
when the downstream pressure is too high
this keeps the pressure constant in a dome loaded regulator
let's see how it works
as before the inlet pressure is a constant 30 bar or
435 psig
the regulator is set to 8 bar
or 116 psig
there's no flow at this time as a downstream valve is shut off
as the downstream valve is slowly opened
you'll be able to hear the increase in flow
the outlet pressure starts at
8 bar or 116 psig
but drops to about 6.5 bar
or 95
psig
or a lower drop than the system using the spring loaded regulator
the pressure drop looks like this when represented on a flow curve
while there was still droop
the flow curve is flatter than it was for the spring loaded regulator system
let's look at one more possible configuration
this time we will add external feedback to the pilot regulator
we will accomplish that by connecting a tube from the downstream process line back
to the pilot regulator
this will allow pressure changes to be detected
thus adjusting the gas supplied to the dome of the main pressure regulator
once again
the inlet is constant at 30 bar or 435 psig
the regulator is set at 8 bar or 116 psig
there is no flow at this time as a downstream valve is shut off
as the downstream valve is slowly opened
you'll be able to hear the increase in flow
however
This time as the flow increases the outlet pressure drops only slightly to about
7.5 bar
or 109 psig
the pressure drop looks like this when represented on a flow curve
while the regulator still exhibited droop
the flow curve is flatter than it was for the spring loaded regulator
and the first configuration using a dome loaded regulator
all regulators will exhibit some droop
depending on your system
droop may be acceptable
but when it is critical to keep the pressure constant as flow changes
The right regulator configuration can help
refer to Swagelok dot com and the product literature for additional
information
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