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Air Flow Meter Medical: Oxygen and Nitrous Oxide Thorpe Tube Systems
Quick Answer
Silver Automation Instruments supplies Thorpe tube flow meters for medical oxygen and nitrous oxide lines. These meters cover low gas flow ranges from 0.1 to 15 liters per minute at working pressures up to 4 bar. Send us your gas type, flow range, inlet pressure, and connection size for a quote.
What Is a Thorpe Tube Flow Meter?
A Thorpe tube flow meter is a variable area meter built for low pressure medical gas delivery. It uses a tapered glass or acrylic tube and a small ball or bobbin float. Gas enters at the bottom and lifts the float. The operator reads flow from the float position against a scale. In practice, this design works well for oxygen therapy, anesthesia gas supply, and dental nitrous oxide panels.
Why Oxygen and Nitrous Oxide Systems Use Thorpe Tubes
Medical oxygen and nitrous oxide lines run at low flow. A patient may need 1 liter per minute for a nasal cannula or 10 liters per minute for a mask. Thorpe tubes give a direct mechanical reading without power. That matters in a clinic when the power fails. We have seen this on customer sites many times in Southeast Asia and the Middle East.
Nitrous oxide is more sensitive to pressure drop than oxygen. The float must stay stable even when the cylinder pressure falls from 50 bar to 4 bar at the regulator. Silver Automation Instruments selects float materials and tube tapers for each gas. Do not use an oxygen tube for nitrous oxide unless the calibration matches.
Common Flow Ranges and Accuracy
Most medical oxygen Thorpe tubes cover 0 to 15 liters per minute. Pediatric units often use 0 to 3 liters per minute. Dental nitrous oxide mixers may need 0 to 10 liters per minute for oxygen and 0 to 10 liters per minute for nitrous oxide. For a standard adult oxygen line, specify Silver Instruments model SI-MT-15. For pediatric oxygen, specify SI-MT-03. For dental nitrous oxide, specify SI-MT-10-N2O. Accuracy in the field is normally plus or minus 5 percent of full scale. For a 15 liters per minute tube, that is about 0.75 liters per minute error. That is enough for patient use.
Last year a customer in Vietnam asked for a nitrous oxide Thorpe tube with a 0 to 10 liters per minute scale. The gas panel pressure was 3.5 bar. The connection was 1/8 inch NPT female. We supplied a 150 mm acrylic tube with a black glass float. The unit read within 4 percent full scale after a 15 minute warm up at ambient temperature.
Materials and Gas Compatibility
Wetted parts matter. Oxygen service requires clean materials. No oil, no grease, no hydrocarbon residue. Silver Automation Instruments cleans each oxygen Thorpe tube before packing. The tube body can be acrylic or polycarbonate. The float can be stainless steel, glass, or PTFE depending on gas. Seals are usually EPDM or Viton. For nitrous oxide, avoid materials that degrade under slightly acidic moisture.
Inlet pressure after the regulator should stay between 2 and 4 bar. Flow calibration is done at a reference pressure, often 3 bar. If your site runs at 2.5 bar, tell us before ordering. The scale can be adjusted during production.
Installation and Calibration Notes
Mount the tube vertically. A tilted tube changes the float position and adds reading error. Connect the inlet and outlet according to the arrow on the body. The flow scale faces the operator. Most engineers skip this part, but a backward connection can damage the float and give false readings.
Before first use, purge the line for 10 seconds with the gas. Then set the regulator to the working pressure. Adjust the needle valve slowly. Do not snap the flow open. A fast pressure surge can push the float into the top stop and crack the tube. After installation, compare the reading against a calibrated reference meter once a year or after any tube replacement.
Ordering Information and Contact Details
Send us these details for a quote: gas type, flow range in liters per minute, inlet pressure in bar, connection size and thread type, tube length, and quantity. If you need a panel mounted version, state the cutout size. We ship to customers in Australia, Southeast Asia, Latin America, Africa, and the Middle East. For pricing, contact Silver Automation Instruments at Tel: +86-135-1213-1526, Whatsapp: 86-135-12131526, WeChat: +86 13512131526.
FAQ
Can a Thorpe tube measure both oxygen and nitrous oxide?
Yes, but the tube must be calibrated for each gas. A float calibrated for oxygen will not read correctly on nitrous oxide because gas density and viscosity differ. We supply separate scales for oxygen, nitrous oxide, air, and carbon dioxide.
What flow range should I select for a dental or hospital gas outlet?
For adult oxygen therapy, choose 0 to 15 liters per minute. For pediatric oxygen, choose 0 to 3 liters per minute. For dental nitrous oxide sedation, select 0 to 10 liters per minute for each gas.
Do the tubes come with DISS or NIST fittings?
We supply common connection threads including 1/8 inch NPT, 1/4 inch BSP, and G 1/8. DISS and NIST fittings can be supplied as adapters. Tell us the exact outlet standard used in your country.
What is the typical working pressure for medical Thorpe tubes?
Most of our medical Thorpe tubes are rated for 2 to 4 bar working pressure. The calibration reference is usually 3 bar. If your regulated pressure is different, we can recalibrate the scale during production.
How do I order from Silver Automation Instruments?
Send your gas type, flow range, pressure, connection size, and quantity by phone or WhatsApp. Our contact details are Tel: +86-135-1213-1526, Whatsapp: 86-135-12131526, WeChat: +86 13512131526. We reply with a price and lead time within 24 hours on working days.