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Case Study: Five-Gas Thermal Mass Flow Meter Application — Hydrogen, Propane, Oxygen, Nitrogen, and Chlorine Application: Laboratory / Process Gas Control | Product: Silver SRK-DL Micro Thermal Mass Flow Meter | Tags: MFC-140101 to MFC-140105
Silver Automation Instruments supplied five SRK-DL micro thermal mass flow meters for a multi-gas laboratory application covering hydrogen, propane, oxygen, nitrogen, and chlorine. All five tags share a common 1/4" 3000# threaded connection, 24V DC / 4-20 mA / RS485 interface, and a 3 MPa pressure-rated body — selected as a cost-effective alternative to Western-brand MFC instruments with equivalent measurement performance.
A customer sent us an instrument data sheet covering five mass flow controllers on a single P&ID — B01-100-PR-DWG-14-002. Each tag runs a different gas: hydrogen, propane, oxygen, nitrogen, and chlorine. Flow rates are small, all in the range of 0.02 to 0.2 kg/h at normal conditions. Design pressure is 6 barg. Connection is 1/4" 3000# threaded throughout.
The original specification called for globe-type control valves with positioners (4-20 mA signal, M20x1.5 cable entry, equi-percentage characteristic). The customer was looking for a capable, budget-friendly supply source to cover the measurement portion of that scope. We proposed the SRK-DL series thermal mass flow meter — one platform, five gases, same wiring, same signal.
| Tag | Fluid | MW | Normal Flow | Max Flow | Pressure | Notes |
| MFC-140101 | Hydrogen (H2) | 2.02 | 0.1 kg/h | 0.2 kg/h | 2 bara / 6 barg | 002L range, Fluororubber |
| MFC-140102 | Propane (C3H₈) | 44.1 | 0.1 kg/h | 0.2 kg/h | 2 bara / 6 barg | 500C range, Fluororubber |
| MFC-140103 | Oxygen (O2) | 32 | 0.1 kg/h | 0.2 kg/h | 2 bara / 6 barg | 200C range, O₂-clean |
| MFC-140104 | Nitrogen (N2) | 28 | 0.15 kg/h | 0.25 kg/h | 2 bara / 6 barg | 200C range, Fluororubber |
| MFC-140105 | Chlorine (Cl2) | 70.9 | 0.1 kg/h | 0.2 kg/h | 2 bara / 6 barg | 200C range, confirm wetted mat. |
MFC-140101 — Hydrogen Gas
Hydrogen is the lightest gas on the list, with a molecular weight of 2.02. That low density means the SLM-equivalent flow range is relatively large for a small mass flow. We specified the 2 SLM range (002L), which gives comfortable span coverage at the stated maximum of 0.2 kg/h. Fluororubber seals handle the application without issue at the 2 bara normal inlet pressure.
One thing to flag: the datasheet shows cryogenic design temperatures down to -253°C (near liquid hydrogen territory). The SRK-DL is rated 0 to 50°C at the meter body. We confirmed with the customer that the meter itself sits at ambient temperature — the extreme low temperature is a line design condition, not an operating condition at the instrument location.
MFC-140102 — Propane Gas (C3H8)
Propane has a molecular weight of 44.1, roughly 22 times heavier than hydrogen. The 500 SCCM range (500C) converts to approximately 75 SCCM equivalent for C3H8, keeping the normal flow well within the linear range. Fluororubber seals are compatible with dry propane gas service.
Propane is flammable. The customer's line class (S82A) and the 3000# threaded connection are appropriate for the 6 barg design pressure. If the installation zone requires ATEX or IECEx certification, the standard SRK-DL does not carry explosion-proof ratings — that would require a discussion on alternative enclosures.
MFC-140103 — Oxygen Gas (O2)
Oxygen service requires special attention. Organic contamination inside an oxygen line can ignite under pressure. We specified the 200 SCCM range for O2 (MW 32), which covers the 0.2 kg/h maximum. Fluororubber seals are generally compatible with gaseous O₂ at moderate pressures.
The key requirement here is O2-clean degreasing of all wetted parts before dispatch. This is a factory-confirmed process step. We flagged this explicitly in the quotation notes, and the customer must confirm it before placing the order. Skipping this step on an oxygen line is not acceptable practice.
MFC-140104 — Nitrogen Gas (N2)
Nitrogen is the most straightforward of the five gases — inert, dry, non-corrosive. MW is 28, and the 200 SCCM range comfortably covers the 0.25 kg/h maximum. Standard Fluororubber seals apply. No special treatment or confirmation required. This tag is a textbook thermal MFM application.
MFC-140105 — Chlorine Gas (Cl2)
Chlorine is the most aggressive fluid in this set. MW is 70.9, the heaviest gas here, and it is highly corrosive — especially in the presence of any moisture. The 200 SCCM range covers the 0.2 kg/h maximum at normal flow.
We raised a material compatibility question on this tag. SS316 wetted parts may be adequate for dry Cl2gas at low concentrations; we also use perfluoroelastomer (FFKM) as the sealing material to improve the corrosion resistance for chlorine measurement. The customer needs to confirm the Cl2 concentration and moisture content before we finalise the material selection.
SRK-DL thermal mass flow meter
The customer's original instruments were specified from a European brand. Lead times for that brand in this region run 10 to 16 weeks. The SRK-DL ships in 7 to 10 working days from China. For a project commissioning schedule, that difference matters.
Beyond lead time, there are several technical reasons the SRK-DL was a good fit here:
• One model platform covers all five gases. Same body, same wiring, same signal (4-20 mA + RS485). The instrument technician deals with one product, not five.
• 1/4" 3000# threaded connection matches the customer's line class exactly. No adapters.
• 3 MPa pressure rating — well above the 6 barg design pressure.
• RS485 output allows integration with a site SCADA or DCS without additional signal converters.
• Operating range 0 to 50°C covers the ambient conditions at the instrument location.
Western-brand thermal MFMs for this kind of multi-gas laboratory service typically run at a significant cost premium, often two to four times the per-unit cost of the SRK-DL. For five instruments of similar specification, the budget difference is material. The SRK-DL is not a stripped-down product — it offers the same 4-20 mA / RS485 dual output, integral display, and SS316 wetted construction that the European alternatives provide.
| Parameter | Value |
| Measurement principle | Thermal mass flow (bypass capillary type) |
| Gas flow range | 2 SCCM to 30 SLM (model-dependent) |
| Accuracy | ±1.5% F.S. (typical) |
| Repeatability | ±0.5% F.S. |
| Pressure rating | 3 MPa (30 bar) |
| Operating temp. | 0 to 50°C |
| Output signal | 4-20 mA + RS485 (Modbus RTU) |
| Power supply | 24V DC |
| Display | Integral LCD, instant + totalised flow |
| Seal material | Fluororubber (standard); O₂-clean on request |
| Process connection | 1/4" compression / G-thread (standard) |
| Body material | SS316 |
| Protection | IP65 |
Three items need customer confirmation before this order can be placed:
• 1. MFC-140103 (O2): Confirm O2-clean degreasing requirement with factory. This is non-negotiable for oxygen service.
• 2. MFC-140105 (Cl2): Confirm Cl2 concentration and moisture content. If wet chlorine or high concentration, Hastelloy C-276 wetted parts are required instead of SS316.
• 3. Process connection: The SRK-DL ships with a 1/4" G-thread compression fitting as standard. If the customer's piping uses NPT threads or socket weld ends, confirm whether a thread adapter is acceptable or a special end connection is needed.
If you have a similar multi-gas flow measurement or control application, send us the following and we will size and quote within 24 hours:
Contact Silver Automation Instruments: inquiry@silverinstruments.com | WhatsApp +86-18936759191 | SRK-DL product page
