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Nitrogen Gas Flow Meter and CO2 Flow Meters for Modified Atmosphere Packaging

Quick Answer: Thermal mass flow meters fit most nitrogen and CO2 lines in MAP machines. They measure mass flow directly in SLPM or kg/h and work from DN4 to DN25 at 1 to 10 bar. One meter can handle both gases if you select a model with multi-gas calibration. Send us your gas mix, pressure, pipe size, and flow range for a model and price.

What MAP Gas Lines Look Like in a Real Plant

Modified atmosphere packaging lines run small gas flows. A single tray sealer often uses 20 to 60 SLPM of nitrogen per cycle. Vertical form fill seal machines may use 10 to 30 SLPM of CO2. Gas supply pressure at the flow meter usually sits between 1 and 3 bar. Some central supply lines run at 6 to 10 bar. Tube sizes are small. Most MAP machines use 6 mm, 8 mm, or 12 mm OD tube. Some use 1/4 inch or 3/8 inch NPT.

Which Meter Types Actually Work

Thermal mass flow meters are the standard choice for this duty. They measure gas mass flow directly without separate temperature and pressure transmitters. A DN15 inline thermal meter handles 0 to 100 SLPM nitrogen easily. Accuracy of ±1.0 percent of reading plus 0.5 percent of full scale is common. Response time below 0.5 seconds works well for cyclic filling. Coriolis mass flow meters are more accurate, around ±0.2 percent of reading, but cost more and weigh more. Most customers buy Coriolis for gas blending panels or for checking other meters, not for every packing line.

We do not recommend rotameters for MAP control because they have no 4-20 mA output. A rotameter cannot send flow data to the PLC that controls gas flushing.

Nitrogen vs CO2 Calibration

Here is the thing. Thermal mass flow meters are gas dependent. A meter calibrated for air will not read CO2 correctly. The thermal conductivity and heat capacity of CO2 are different from nitrogen. We calibrate each meter for the target gas or a fixed gas blend. For a 70 percent nitrogen and 30 percent CO2 mix, we set the calibration curve to that composition. In practice, if your gas mix ratio is fixed, one calibration works well. If you change the mix often, select a multi-gas model that stores up to 10 gas curves.

A Real Customer Example from a MAP Line

We have seen this on customer sites many times. A frozen seafood packer in Vietnam used a needle valve on a tray sealer nitrogen line. The operator adjusted flow by feel and the waste rate was high. We supplied a DN15 inline thermal mass flow meter with 4-20 mA HART and a local display. The customer measured 30 SLPM per cycle and cut nitrogen use by 18 percent in the first month. Another customer in Saudi Arabia runs a bakery MAP line with CO2 and wanted a meter for 0 to 50 SLPM. We supplied a 1/4 inch NPT thermal mass flow meter with Modbus RTU output.

Key Specifications for MAP Flow Meters

Our MAP flow meters cover 0 to 10 SLPM up to 0 to 500 SLPM full scale. Process connections include G1/4, G1/2, 1/4 NPT, 6 mm compression, 8 mm compression, and Tri-Clamp. Wetted parts are 316L stainless steel with FKM seals as standard. EPDM seals are available for food-grade dry gas. Outputs include 4-20 mA HART, RS485 Modbus RTU, and two alarm outputs. Power is 24 VDC. Standard pressure rating is 10 bar and optional high pressure is 25 bar. Display shows instantaneous flow, total flow, and gas type.

Installation Tips for Nitrogen and CO2 Lines

Install the meter downstream of the pressure regulator and a 5 micron filter. Keep 10 pipe diameters straight upstream and 5 downstream. Do not mount the meter directly after a solenoid valve. High frequency pulses disturb the sensor. Zero the meter after installation with no flow. For CO2 lines, avoid condensation by keeping the gas dry. Use a dew point below minus 20 degrees Celsius.

FAQ

Which flow meter is best for nitrogen ga