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HFM-E-200/HFC-E-202
Page 18 of 30
Where:
Formula 1: Formula 2:
u
P
Q
D
σ
0028.0
=
σ
d
Q
D
Ρ•ΔΡ
=
0014.0
D = Diameter in inches
Q = Flow rate in standard liters per minute
P = Pu - Pd in PSI
Pu = Upstream pressure in PSIA
Pd = Downstream pressure in PSIA
σ = Specific gravity of gas
Choose the orifice form Section 5.0 that has the closes larger diameter to the calculated diameter.
4.7.1. HFC-E-202 Orifice
To change the orifice in the HFC-E-202 series, turn the instrument upside-down and turn the orifice
counterclockwise with a 9/64” Allen wrench until it stops coming out. Then grasp the exposed orifice
end and pull it straight out. See Figure 4.2.
Prior to reinstallation of the orifice, inspect the two O-rings mounted on it for damage. Replace if cut or
gouged.
Lubricate the O-rings slightly with a silicone based grease, and the threads with anti-galling compound.
Push the orifice into its hole and screw it in until it is flush with the instrument base. Apply pressure to
the inlet side of the instrument.
Turn the Valve Override switch to CLOSE or unplug the instrument. Screw the orifice in a few more turns
until the flow through the instrument stops, then turn it an additional 1/8 turn clockwise.
PARKER O-RING
#2-008 VITON
ORIFICE
(see P/L per P/#
Fig 4.2