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Ball Flow Meter: Thorpe Tube Oxygen and Shielding Gas Visual Scales
Quick Answer: A ball flow meter with a Thorpe tube gives a direct visual measurement of oxygen, argon, helium and other shielding gases. No power supply is needed. Silver Automation Instruments offers these meters with borosilicate glass tubes, engraved dual scales and optional flow control valves for welding, laboratory and medical gas delivery.
How a Thorpe Tube Ball Flow Meter Works
Inside a tapered borosilicate glass tube sits a small spherical float. Gas enters at the bottom and lifts the ball. The ball rises until the annular gap around it balances the float weight against the gas drag force. The top edge of the ball indicates the flow rate on an engraved scale. This is the simplest variable area flow principle. The Thorpe tube design orients the tube straight and places the scale beside it, often with a mirrored background to reduce parallax error. Visual scales are usually marked in L/min and SCFH for shielding gases.
Common Applications for Oxygen and Shielding Gas
Welding workshops and fabrication shops use these meters to set argon or helium flow for TIG and MIG torches. A stable gas shield prevents weld oxidation. Laboratories meter oxygen into gas analyzers and bioreactors. Medical oxygen concentrators and respiratory setups use small Thorpe tube flowmeters with brass or stainless steel bodies. Food packaging lines inject nitrogen or CO2 via a visual ball meter. Aquaculture systems meter pure oxygen into fish tanks. A welding distributor in Vietnam recently ordered 30 pieces of argon flow meters with 0 to 25 L/min scale for TIG cart integration.
Materials and Wetted Parts for Gas Compatibility
Body and end fittings can be brass, stainless steel 304 or 316L. For oxygen service, all parts must be cleaned for oxygen use, free of oil and grease. Silver Automation Instruments delivers oxygen-flow-meter assemblies with degreased brass or 316L stainless steel fittings. The glass tube is high-strength borosilicate glass. The ball float is commonly 316L stainless steel or glass, some models use PTFE or black glass for better contrast. Seals are Viton or PTFE. For shielding gas like argon, a standard brass body with a glass ball works well and keeps cost low.
Key Specifications You Should Know
Pipe connection sizes are typically DN4, DN6, or NPT 1/8 inch and 1/4 inch. Some models have barb fittings for flexible tubing. Flow ranges span from 0.1 L/min up to 100 L/min for air equivalent. Common oxygen scales are 0 to 15 L/min or 0 to 5 L/min. Accuracy is plus minus 4 percent of full scale under stated conditions. Maximum working pressure is often 6 bar or 10 bar, temperature up to 60 degree C. The visual scale length is around 150 mm. Most engineers skip the conversion charts when the scale is printed for the target gas. Always specify the gas type and working pressure when ordering.
Installation Tips and Oxygen Safety
Mount the flow meter vertically, inlet at the bottom. If the tube is tilted, the ball will rub and reading shifts. Clearance around the glass tube is necessary to avoid breakage. In practice, a small panel mount bracket saves time. For oxygen lines, do not use any thread sealant that contains oil. Silver Automation Instruments pre-cleans the wetted parts an
How to Read the Visual Scale Correctly
Read the gas flow at the center of the ball, not the top or bottom. A mirrored scale strip helps align your eye. Because the ball spins and bounces at very low flows, wait for the float to stabilize before recording. Most TIG welders set shielding gas flow between 8 and 15 L/min for argon. A small flow meter with 0 to 25 L/min range covers this easily. To check repeatability, try lowering then raising the flow, and see if the ball settles at the same mark. Here is the thing, if the tube gets dirty inside, the ball may stick. Periodic cleaning with a soft brush and isopropyl alcohol restores accuracy.
Why Purchase From Silver Automation Instruments
Silver Automation Instruments keeps stock of oxygen-ready ball flow meters and argon shielding gas visual scale meters in our warehouse. We ship to Southeast Asia, Oceania, Latin America, Africa, and the Middle East. A paint manufacturer in Thailand contacted us for nitrogen blanketing flow meters and received the shipment in 6 days. Small and medium businesses from these regions buy from us because we provide fast technical support and do not require large minimum orders. Contact details are below.
Contact Silver Automation Instruments
Email: [email protected]
Tel: +86-135-1213-1526
Whatsapp: 86-135-12131526
WeChat: +86 13512131526
For a quote, send us your gas type, pressure in bar, flow range, and pipe connection size like DN4 or DN6. We will recommend the right Thorpe tube ball flow meter with visual scale for your process.
FAQ
Q: Can this ball flow meter work for pure oxygen?
A: Yes. We supply oxygen-cleaned ball flow meters with degreased brass or 316L fittings. Do not use standard meters that are not cleaned for oxygen service.
Q: What gases can a visual scale Thorpe tube meter measure?
A: Oxygen, argon, helium, nitrogen, CO2 and air are common. The scale is calibrated for a specific gas at a specific pressure because density affects the float rise. We can print custom dual scales for L/min argon and flow equivalent.
Q: How do I replace the glass tube if it breaks?
A: The tube and float are replaceable. Unscrew the top and bottom nuts, remove the broken tube, fit a new borosilicate glass tube and reassemble. We keep spare glass tubes and float kits in stock.
Q: What is the difference between a Thorpe tube and a standard rotameter with a direct reading tube?
A: The Thorpe tube places the scale beside the glass tube on a solid back plate. A standard direct reading rotameter has the scale on the tube itself. Thorpe tubes reduce parallax error and are easier to read in low light.
Q: Do these flow meters come with an adjusting valve?
A: Many models include an integrated needle valve at the inlet or outlet. If you prefer a separate valve, order the meter without an internal valve and add a precision metering valve upstream.
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