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Refrigerant Flow Meter High Pressure Rating: Bursting Disc and Shell Safety Rules
Quick Answer: Any flow meter used on the liquid or discharge side of a refrigerant circuit must handle pressures well above the critical point of the gas. Silver Instruments supplies high pressure Coriolis mass flow meters with optional certified bursting disc assemblies and reinforced shell constructions rated to 350 bar (5076 psi). This covers R-744 (CO2), R-290 (propane), R-32, and ammonia blends in production charging skids, heat pump test stands, and chiller OEM lines.
Why Refrigerant Systems Demand High Pressure Rated Flow Meters
Standard flow meters with 16 or 40 bar ratings fail quickly when you push them into transcritical CO2 or propane service. R-744 heat pump high sides routinely reach 120 bar to 140 bar. Even subcritical R-32 can settle at 45 bar on a hot day with the compressor off. A burst sensor housing on a charging skid does more than leak gas. It sprays liquid refrigerant and oil across the factory floor. That is why plant engineers in Malaysia and Saudi Arabia now specify a documented bursting disc path and a shell that holds 3x the maximum allowable working pressure.
In practice, the shell safety design gets more attention than the sensor itself. For Ammonia and hydrocarbons like R-290, you also need ATEX Zone 2 or Zone 1 compliance. We have seen this many times on customer sites: a meter body cast from standard 316L can pass a hydrotest but still crack after 200 thermal cycles between +60 °C and -40 °C. The right shell material and minimum wall thickness calculation per ASME B31.3 or PED 2014/68/EU Module B make the difference between a 3-year and a 10-year asset.
Bursting Disc Function in Refrigerant Flow Meters
A bursting disc is a one time use, calibrated rupture element. It sits inside a dedicated vent port on the meter housing. If internal pressure exceeds a preset value (say 130 bar for a 100 bar MAWP shell), the disc ruptures and directs the refrigerant flow to a safe vent pipe. There is no re-seating, no spring, just a clean burst. This is safer than a relief valve for applications with quick pressure spikes because the disc reacts in under 5 milliseconds. Most engineers skip the disc on sub-40 bar circuits but it becomes mandatory when you charge flammable refrigerants at mass flows above 20 kg/h inside an enclosed skid.
The burst disc rating is typically 1.1x to 1.2x the maximum operating pressure. For a Coriolis meter on an R-744 heat pump test bench running 120 bar, we set the disc at 132 bar to 138 bar. The disc holder uses a sanitary clamp or flanged connection so you can replace it in 10 minutes without removing the meter body. Silver Instruments sources discs that meet ISO 4126-2 and are batch tested at the factory. Each disc ships with a 3.1 material certificate and burst pressure test report.
Shell Safety Design and Pressure Rating
The shell of a refrigerant flow meter must survive both static pressure and vibration flexing from compressor discharge pulses. Thin wall chambers with straight circular cross sections are common in water meters but they fatigue fast at 140 bar. We machine our high pressure Coriolis meters from duplex stainless steel (1.4462) or Hastelloy C-22 bar stock, not welded tube. The minimum wall thickness follows PED Annex I, clause 7.4, and we hydrotest every production unit at 1.5x the nominal pressure rating. A DN15 meter body rated for 350 bar gets tested at 525 bar for 20 minutes. You get the hydrotest plot with the shipment.
Flange connections on the shell use type-approved UNI EN 1092-1 flanges. Threaded process connections are available in NPT or G-thread with bonded seals. We strongly recommend a vent hole tapped into the secon
Materials and ATEX Compliance for Flammable Refrigerants
R-290 and R-1270 are hydrocarbons. They sit in the A3 flammability group. The flow meter shell and wetted parts must not be a source of sparks. Silver Instruments delivers the MFC series Coriolis sensor with an intrinsically safe excitation circuit and a fully welded case without O-ring seals. The electronics remote mount with IS barriers, certified to ATEX II 2G Ex ib IIC T4 Gb. For ammonia, avoid copper alloys completely. Even brass cable glands will crack from stress corrosion. We use stainless steel cable glands and AISI 316L wetted parts throughout.
Because a high-pressure shell also deals with thermal expansion, we allow for a minimum 20 K temperature margin above and below the fluid temperature range. If your chiller runs at -35 °C, the meter shell needs to hold pressure at -40 °C without a drop in CVN impact toughness. This is why we refuse carbon steel shells for low temperature refrigerant. The savings do not justify the risk.
Silver Instruments High Pressure Coriolis Meters for Refrigerant Charging
Our RCM series Coriolis meter handles 0 to 250 bar and measures mass flow, density, and temperature from one sensor. We have shipped these to chiller factories in Thailand, refrigeration rack builders in Qatar, and a CO2 transcritical test lab in Australia. Pipe sizes go from DN3 to DN25 with mass flow accuracy of ±0.1 % of rate. Density accuracy of ±0.0005 g/cm³ lets you catch the difference between liquid and vapour feed, a common trouble during sub-zero charging.
Every meter comes with direct support from our engineers. Send us your refrigerant type, high side pressure in bar, pipe size (DN), and the flow range in kg/h. We will return a 3D dimensional drawing, a pressure-temperature rating table, and a quoted price in less than 24 hours. Email [email protected], call +86-25-68650347, or message us on WhatsApp at +86-25-52155837. You can also reach us via WeChat: +86 15365082610. Visit https://flow-meter.com.au for more details on the full product range.
FAQ
Does a Coriolis flow meter need a bursting disc for R-32?
Not always. At pressures up to 45 bar a standard 100 bar rated shell without a disc is acceptable. Add a bursting disc if the system MAWP exceeds 80 bar or the skid is fully enclosed.
What shell test pressure do you recommend for transcritical CO2?
We recommend a shell rated for 250 bar and hydrotested at 375 bar. The bursting disc should set at 150 bar to 165 bar depending on the maximum operating pressure of the particular test stand.
Can I use a flow meter with a welded shell in a Zone 1 ATEX area?
Yes, provided the electronics are certified Ex ib or Ex d and the sensor circuit is intrinsically safe. Our MFC series is certified for Zone 1 with propane and butane blends.
How often do I replace the bursting disc?
Replace it every 12 months if the meter is in continuous service. Also replace it after any known overpressure event even if it did not rupture. Fatigue cycles on the disc reduce the burst accuracy over time.
Which material is safe for ammonia refrigerant at high pressure?
Only stainless steel (AISI 316/316L) or carbon steel with a verified stress corrosion resistance rating. Do not use brass, copper, or any copper alloy. Our ammonia meters ship with full material traceability per EN 10204 3.1.