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Engineering Toolbox/Closed-Vessel DP Range

Pressure, Level & Process

Closed-Vessel DP Range

Calculate transmitter LRV, URV and calibrated span for conventional closed-vessel level measurement using dry or wet impulse reference legs.

Installation inputs

DP sign convention: HP − LP.

Positive when the transmitter is below the lower tap; negative when above it.

Field use

Range a DP level transmitter from installation geometry.

Useful when checking zero elevation/suppression caused by transmitter position and a liquid-filled LP reference leg.

Assumptions & sign convention

The high-pressure side is connected to the lower tap and the low-pressure side to the upper vapor-space tap. Common vessel static/vapor pressure is present on both sides and cancels in the differential measurement.

Dry leg: LP vapor head ≈ 0
Wet leg: LP head = ρwet × g × wet-leg height
DP = PHP − PLP

Conventional impulse-piping model only. Condensation in a dry leg, evaporation in a wet leg, capillary/seal fill-fluid density changes and installation temperature effects can shift the measurement and require separate engineering treatment.

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