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King Instrument Flow Meter: Variable Area Rotameters and Glass Measuring Tubes
Quick Answer: King Instrument variable area flow meters, commonly called rotameters, use a tapered glass measuring tube and a float to give a direct visual flow reading without external power. Silver Automation Instruments supplies direct replacement glass tube rotameters that match King Instrument dimensions, connection sizes, and flow ranges. You get equivalent accuracy and reliability, often at 30–40 percent lower cost, with short delivery to Southeast Asia, Africa, the Middle East, and Latin America.
How a Variable Area Rotameter Works in Practice
A rotameter is one of the simplest flow measurement tools. It has a vertical borosilicate glass tube with a slightly larger inner diameter at the top. A float sits inside. When fluid pushes up from the bottom, the float rises until the annular gap around it balances the float weight. The top edge of the float points to the flow rate on a scale printed directly on the glass tube. No electronics. No external power supply. Just a direct reading at the process line. Most engineers use these for purge flows, cooling water circuits, gas analyzers, and chemical dosing skids. Typical pipe sizes are DN15, DN20, and DN25. Flow ranges cover 0.1 L/h for low liquid doses up to 100 m³/h for air at standard conditions.
King Instrument Rotameter Features and Where You See Them
King Instrument rotameters are known for a wide product line. They offer scale lengths of 65 mm, 150 mm, and 250 mm. Tube materials are borosilicate glass as standard, with wetted parts in 316L stainless steel, PTFE, or PVDF. The floats are often stainless steel, glass, or carboloy. Accuracy is typically ±2% to ±5% of full scale depending on the tube size and float design. Standard models handle up to 100 °C and 10 bar. In practice, we see these meters on nitrogen blanketing lines, boiler feed additives, laboratory test racks, and wastewater sampling panels across Southeast Asia and the Middle East. Because the brand is strong in oil and gas and specialty chemicals, many plants keep them in operation for decades. When the glass tube becomes dirty or cracked, the maintenance team wants a direct physical replacement that fits the same mounting holes. That is exactly what we help you find.
Glass Measuring Tubes vs. Metal Tube Rotameters
Glass tube rotameters give you an immediate visual indication. You simply look at the float position. This works well for transparent, clean fluids. If your fluid is dark, sticky, or operates above 10 bar, a metal tube rotameter with magnetic follower and 4-20 mA HART output is the safer choice. Silver Automation Instruments supplies both types. For King Instrument glass tube replacements, we match the tube O.D., length, and connection style. Typical connections are 1/4 inch NPT, 3/8 inch NPT, or DN15 flange. We also provide indicators with PTFE liners for dilute acids and caustic solutions.
How to Specify a Replacement for King Instrument Rotameters
Here is the thing. A model number alone is often not enough. Floating positions shift with fluid density and viscosity. What we really need from your side: the fluid name, operating temperature in °C, upstream pressure in bar, and the exact flow range w
A Real Case from a Paint Manufacturer in Vietnam
Last year a mid-sized paint factory near Ho Chi Minh City contacted us. They were running ten King Instrument 7400 series rotameters on solvent dosing lines. The flow medium was a mixture of toluene and ethyl acetate at 25 °C, with flow ranges between 0.5 L/h and 3 L/h. The original glass tubes had become opaque after three years. We supplied identical DN15 borosilicate glass tubes with 316L stainless steel floats, engraved scales in L/h, and Viton O-rings. The replacement cost was 42 percent less than the local distributor quote, and delivery took 9 days to Vietnam via DHL. The plant engineer later asked us to keep backup tubes in stock for their regular maintenance cycle.
FAQ
Can Silver Instruments supply a King Instrument rotameter with an alarm or transmitter function?
Yes. We offer glass tube rotameters with optional limit switches or a 4-20 mA transmitter via a magnetic follower. You can set a high or low flow alarm to send a signal to your PLC or DCS. Mention this when you send your fluid data.
What if my fluid is not water or air? Can you calibrate the scale for other media?
We calibrate scales for the actual process fluid when you provide density and viscosity. For example, we regularly produce scales for caustic soda (20% concentration), diesel fuel, liquid CO2, and natural gas. The scale is printed on the glass tube for direct reading.
How long does delivery take for a glass tube rotameter replacement?
Standard models with air or water scales ship within 5 to 7 working days from our Nanjing warehouse. Custom scales or exotic wetted materials (Hastelloy C, Monel) add about 2 weeks. We dispatch by DHL, FedEx, or sea freight based on your preference.
Do you provide ATEX or IECEx certification for glass tube rotameters?
Our basic glass tube rotameters are for non-hazardous areas. For Zone 1 or Zone 2 applications, we supply metal tube rotameters with ATEX-certified transmitters and enclosures. Tell us the zone classification and gas group when you inquire.
Can you match odd thread types used on older King Instrument installations?
We have machined adapters from NPT to BSPT, JIS, and SAE threads many times. Include a photo and a thread gauge measurement in your email. Our workshop can replicate the end fittings so the new tube drops right in.
Send your fluid details, pressure (bar), temperature (°C), pipe size (DN), and flow range today. Contact Silver Automation Instruments at [email protected] or call +86-25-68650347. For instant messaging, use Whatsapp: +86-25-52155837 or WeChat: +86 15365082610. Our technical team will help you find the exact replacement for your King Instrument glass tube rotameter.
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