Current position > News detail
『Dual Flow Meter: Two-Sided Argon Gas Regulators for Back-Purge Welding』Related information(flow rotameter|digital flow meter|balo meter|hydraulic flow meter|volumetric meter|positive displacement meter|pitot tube flow meter|displacement meter|cfm meter|variable area flow meter|inline flow meter|differential pressure flow meter|calibrated flow meter|velocity meter|paddle wheel flow meter|oval gear flow meter|anemometer hvac|multiphase flow meter|doppler flow meter|thorpe tube flowmeter|heat flow meter)
Dual Flow Meter: Two-Sided Argon Gas Regulators for Back-Purge Welding
Quick Answer: A dual flow meter argon regulator splits gas supply into two independently controlled streams. One side feeds the TIG torch. The other side feeds the pipe internal back-purge. This setup stops weld root oxidation on stainless steel and alloy pipe. Silver Automation Instruments supplies direct mass flow meters and inline flow sensors that integrate with two-sided argon systems to give digital readout, 4-20 mA output, and purge data logging for weld traceability.
Why Back-Purge Gas Flow Control Matters
On a stainless steel pipe butt weld the root pass gets exposed to oxygen if no inert gas shields it from the inside. Welders call the result sugar or black scale. That oxide layer can cause pinhole leaks, fail X-ray inspection, and cost a full cut-out and re-weld on site. In a chemical plant in Malaysia an EPC contractor tracked rework on 6-inch Schedule 40 pipe at 22 percent of joints before they switched to metered dual purge. After the change the reject rate dropped below 3 percent. Three things control the result. The oxygen level inside the pipe must stay under 50 ppm. The purge flow must be high enough to displace air during the initial purge. Then it must drop to a low hold flow for the actual weld. Too much flow and the arc can blow; too little and oxidation comes back.
How a Two-Sided Argon Regulator Works
A two-sided regulator starts with one argon cylinder connection and one high-pressure reduction stage. The low-pressure output then splits into two branches. Each branch has its own metering valve and a small variable-area flow meter tube with a steel or glass ball. The operator can set 8 L/min to the torch and 4 L/min to the back-purge line independently. Most basic dual flow meter units have low accuracy once the argon pressure fluctuates, because the float tube reads well only at the calibrated inlet pressure. In practice a welder in a Thailand fabrication shop told us he adjusts the purge flow by feel, checking how fast a piece of masking tape flutters at the open end of the pipe. That method gets the job done most days. But when a third-party inspector asks for a purge flow record, there is nothing to show.
Common Problems With Manual Purge Flow Settings
Float-style purge meters have some limits. The scale on the tube is valid only for a specific gas and a specific back pressure. A long purged pipe with an exit dam builds up some internal pressure. That pushes back on the flow meter and makes the ball read higher than the actual flow. Temperature drift also shifts the reading when a cylinder sits under the sun on an open deck in Papua New Guinea. We measured the difference once. A flow meter showing 10 L/min on a 35 °C afternoon delivered only 8.3 L/min of actual argon flow at a pipe pre-heat of 80 °C. That gap is enough to let oxygen seep back into the root pass. If you weld duplex or super-austenitic pipe for a desalination plant in Oman, a root oxidation trace can trigger a full pipe replacement mandate from the asset owner.
Silver Instruments Flow Meter Solution for Argon Back-Purge
Silver Automation Instruments builds inline thermal mass flow meters that read argon mass flow directly without pressure or temperature correction. The sensor element sits in the gas stream and measures the cooling effect of moving gas molecules. Our SRK-D series for argon takes flow ranges from 0-15 L/min up to 0-100 L/min, with process connection 1/4 inch NPT or G1/4. The meter outputs 4-20 mA with HART, so a weld
Real Application: Stainless Steel Pipe Spool in an Indonesian Fabricator
Last year a spool shop in Batam Island asked us to improve their back-purge consistency on 4-inch 316L pipe. They used a standard dual float regulator and still got occasional root oxidation on the 6G position because the welder could not see or record the actual flow at the far end of a 9-meter pipe. We supplied two SRK-D-20L meters mounted in a portable enclosure with quick-connect fittings. The operators purged with the first meter monitoring the high initial flow at 20 L/min. After the oxygen meter at the exit showed below 100 ppm, they switched to the second meter set at 4 L/min hold flow. The data recorder printed a purge report for every spool. Over 460 spools the radiography reject rate went from one in eight to zero.
FAQ
Q1: What argon flow rate do I set for back-purging a DN100 stainless steel pipe?
A DN100 (4-inch) Schedule 10 pipe typically needs an initial flush flow of 15-20 L/min until the oxygen level drops, then a hold flow of 3-5 L/min during welding. The exact number depends on the dam type and the pre-purge time. Our thermal mass flow meters let you dial in both stages and log the values for the weld pack.
Q2: Can I use a single flow meter with a Y-splitter instead of a dual regulator?
You can, but the torch flow and purge flow will not be independent. If the torch flow changes during welding, the purge flow also shifts. A two-sided regulator or separate meters keep the purge steady. With two independent SRK-D meters you get stable purge and a clear audit trail.
Q3: Do I need an ATEX-rated flow meter for argon purge applications?
Argon itself is inert and non-flammable. In most pipe shops and open construction sites no hazardous area classification applies. If your purging station is inside a Zone 1 or Zone 2 area due to other flammable gases, we can supply the SRK-D with ATEX Ex ec certification. Send us the zone classification and gas group when you request a quote.
Q4: Does Silver Instruments offer a complete two-sided argon purge panel?
We supply the flow meters and the recording instruments. Many customers mount two SRK-D meters on a sheet metal panel with inlet and outlet fittings themselves. We can provide a wiring diagram and a bracket drawing to make the build straightforward. For turnkey purging carts we partner with two local panel builders in Southeast Asia. Ask us for a reference.
Q5: How do I get a price for a thermal mass flow meter for argon?
Send us your required argon flow range (L/min), pipe connection size, operating pressure and temperature, and whether you need 4-20 mA loop power or 24 V DC with local display. We will return a fixed price quotation within one working day. Contact us at Tel: +86-25-68650347, Whatsapp: +86-25-52155837, WeChat: +86 15365082610. Typical delivery for the SRK-D series is two weeks from order.