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Medical Air Flow Meter: Thorpe Tube Regulators for Hospital Therapy Outlets
Quick Answer: A Thorpe tube medical air flow meter measures and controls oxygen or medical air flow at hospital therapy outlets. Silver Automation Instruments supplies common models with ranges from 0 to 15 LPM, 0 to 30 LPM, and 0 to 75 LPM. The units work with DISS, NIST, Chemetron, Ohmeda, and 1/8 NPT wall outlet connections.
What Is a Thorpe Tube Medical Air Flow Meter
A Thorpe tube flow meter uses a tapered glass or acrylic tube and a ball float. Gas enters the bottom and pushes the ball up. The ball stops where the gas flow force balances the float weight. The tech reads the flow against a scale printed on the tube. Most hospital therapy air and oxygen models are calibrated at 50 psi inlet pressure.
Thorpe tube regulators include an inlet connection, filter, needle valve or dial flow control, tube, float, cover, and outlet barb. Some units are non-compensated. Others are compensated for back pressure changes. In practice, hospitals use compensated units because humidifiers change downstream resistance.
Where These Flow Meters Are Used
These meters fit medical air, oxygen, nitrogen, and nitrous oxide wall outlets in emergency rooms, ICUs, general wards, and operating suites. A hospital in Vietnam may use a 0 to 15 LPM air flow meter for nebulizer treatment. A clinic in Saudi Arabia may install a 0 to 15 LPM oxygen flow meter with a humidifier bottle. In Nigeria and Indonesia, 0 to 75 LPM models support high flow oxygen therapy.
Silver Instruments supplies hospital equipment distributors and biomedical engineering contractors. The body is often chrome plated brass or all brass. The tube is polycarbonate or acrylic with a stainless steel ball. We avoid aluminum parts in oxygen wetted surfaces.
Key Specifications for Medical Air and Oxygen Flow Meters
When you send an inquiry, specify gas type, inlet pressure, flow range, inlet connection, outlet connection, and whether the unit needs a DISS hand tighten nut or a Chemetron probe. A typical order looks like this: oxygen, 0 to 15 LPM, 50 psi inlet, DISS 1240 female inlet, 1/8 NPT male outlet. Another common order: medical air, 0 to 30 LPM, 50 psi, NIST 9/16-18 inlet, hose barb outlet.
Accuracy is normally plus or minus 5 percent of full scale. The scale marking is screen printed on the tube. The valve should hold its setting and not creep. We have seen cheap units with nylon washers crack after one month of ward use. Silver Instruments uses metal to metal control valves where possible.
Materials, Cleaning, and Oxygen Service
Flow meters for oxygen service need oil free and grease free cleaning. Internal parts must be free of hydrocarbon residue. Silver Instruments can supply oxygen clean assembly with sealed packaging. The clear tube lets staff read the ball position quickly. A polycarbonate shield protects the tube from trolley impacts in busy wards.
Installation and Calibration Notes
Most Thorpe tube regulators mount directly on a wall outlet or cylinder regulator. The flow meter must stay vertical. The ball float reads incorrectly if the unit is tilted. The inlet connection must match the hospital gas outlet standard. Common inlet standards include DISS, NIST, BS, DIN, Chemetron, Ohmeda, Schrader, and Japanese JIS. We have supplied adapters for cus
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Calibration is done with a reference flow meter at 50 psi or at the pressure marked on the label. Some customers ask for 4 bar calibration. In that case we calibrate with the specified gas at 4 bar inlet pressure. The tube scale is gas specific. Do not use an oxygen flow meter on medical air and expect accurate readings. Gas density changes the float position.
Common Problems Seen on Hospital Therapy Outlets
Ball float sticking is the most common issue. Dust, oil, or humidified oxygen residue can make the ball stick. A cracked tube is the second common problem. Third is leakage at the DISS or NIST inlet when the O ring is missing or worn. We include spare O rings in every shipment. Most engineers skip this part during installation and call us later for leaks. We recommend checking the O ring before mounting.
Another problem is low flow adjustment. In pediatric therapy, flow settings below 1 LPM need a finer needle valve. Standard valves can be hard to adjust at low flows. Some flow meters have an arrow on the body. Mounting the unit upside down can damage the stop pin.
Recommended Silver Instruments Models
Silver Instruments offers the SAI-MAF100 for oxygen and medical air with ranges of 0 to 3, 0 to 5, 0 to 15, and 0 to 30 LPM. The SAI-MAF200 is for higher flows up to 75 LPM. Both models have a chrome plated brass body, polycarbonate tube, stainless steel float, and adjustable valve. The inlet connection can be DISS, NIST, Chemetron, Ohmeda, or 1/8 NPT. The outlet can be a hose barb or 9/16-18 threaded outlet.
We also supply replacement tubes, floats, O rings, and repair kits. For hospitals with old Chemetron outlets, we supply a Chemetron to DISS adapter or a Chemetron inlet flow meter. For clinics in Latin America that use Schrader outlets, we can match the Schrader probe style.
How to Request a Quote
Send us your gas type, flow range in LPM, inlet pressure, inlet connection standard, outlet connection, and quantity. Tell us the hospital gas standard in your country if you are not sure. We reply within 24 hours on weekdays. Contact Silver Instruments at Tel: +86-135-1213-1526, Whatsapp: 86-135-12131526, or WeChat: +86 13512131526.
We ship to Southeast Asia, the Middle East, Africa, Latin America, and Oceania. Most orders under 50 units ship by DHL, FedEx, or TNT within 5 working days after payment. For distributor pricing, send your company profile and target country. More product details are at flow-meter.com.au.
FAQ
Can I use the same flow meter for oxygen and medical air? No. The tube scale is gas specific. Order one model calibrated for oxygen and another for medical air.
What inlet pressure should I specify? Most hospital wall outlets use 50 psi. Specify 4 bar if your country uses metric pressure. We calibrate to your pressure.
Do you offer Chemetron style inlets? Yes. We supply Chemetron probe inlets and adapters. Send a photo of your outlet if you are not sure.
What is the accuracy of a Thorpe tube flow meter? Expect plus or minus 5 percent of full scale at the marked calibration pressure and vertical mounting position.
Can you supply replacement tubes and O rings? Yes. We keep spare tubes, floats, O rings, and repair kits for our SAI-MAF100 and SAI-MAF200 models.
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