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USER MANUAL
P
b
= Minimum back pressure, pounds per square inch gauge (psig)
Δp = Pressure drop through the meter at the maximum operating flow rate for the
liquid being measured, pounds per square inch (psi).
P
e
= Equilibrium vapor pressure of the liquid at the operating temperature, pounds per
square inch absolute (psia), gauge pressure plus atmospheric pressure.
Figure 2-1
illustrates the effects of back pressure. Insufficient back pressure leads to
measurement inaccuracy. The resulting flashing and cavitation is extremely damaging to
the flow meter and pipe work.
Figure 2-1: Effects of back pressure
Back pressure calculation
Equation 2-2: Back pressure calculation
P
b
≥ 2Δp + 1.25p
e
P
b
= Minimum back pressure, pounds per square inch gauge (psig)
Δp = Pressure drop through the meter at the maximum operating flow rate for the
liquid being measured, pounds per square inch (psi).
P
e
= Equilibrium vapor pressure of the liquid at the operating temperature, pounds per
square inch absolute (psia), gauge pressure plus atmospheric pressure.
Additional devices for accurate measurement
Valves
The metering system should have a flow rate control valve located at a convenient
distance downstream of all measurement equipment. The function of the control valve is
to limit and maintain system pressure on the meter. This avoids cavitation.
Operating conditions and specifications
User manual
September 2020
P/N 3-9008-513
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Daniel Series 1200 Liquid Turbine Meter