『King Instrument Company Flow Meter Manual: Maintenance Procedures for High-Temperature Liquid Indicators』Related information(clamp on meter|electromagnetic meter|venturi meterrotameter|orifice meter|ultrasonic flow meter|mass flow meter|coriolis mass flow meter|coriolis flow meter|magnetic flow meter|magmeter flow meter|magflow flow meter|mag meter flow meter|electromagnetic flow meter|vortex flow meter|turbine flow meter|thermal mass flow meter|thermal flow meter|rotameter flow meter)
High-Temperature Liquid Indicator Maintenance: King Instrument Manual Field Notes
Quick Answer: You can extend the life of a King Instrument high-temperature liquid indicator by checking the sight tube, seals, and torque values every 30 days. Replace any PTFE or Viton O-ring that feels hard after 12 months. For hot lines above 150 °C that need an electronic signal, Silver Automation Instruments offers flow meters and pressure transmitters that fit the same pipe run.
Why High-Temperature Liquid Indicators Fail in the Field
High-temperature liquid indicators from King Instrument Company are common on heat transfer oil skids, boiler feedwater lines, and chemical dosing panels. We have seen units running at 170 °C to 200 °C in Vietnam and Indonesia. Most failures start with a small leak at the seal or a hairline crack in the glass tube. Thermal cycling does the damage. The metal body expands at one rate. The glass tube expands at another rate. Over time the O-rings lose elasticity and the glass can shift. For DN15 and DN25 sizes, PTFE seals are rated up to 200 °C. Viton seals are rated up to 180 °C. Silicone seals are not suitable for hot oil service.
Maintenance Procedure from the King Instrument Manual
First, isolate the indicator. Close the inlet and outlet isolation valves. Let the line cool to below 40 °C. Do not touch the body with bare hands. Use an infrared thermometer to confirm the temperature. The manual for King Instrument high-temperature liquid indicators gives these field checks as a minimum.
Second, inspect the borosilicate glass tube. Look for clouding, scratches, or internal etching. Replace the tube if you see any crack longer than 3 mm. Do not reuse a scratched tube on hot oil service. A small scratch can turn into a rupture after a few thermal cycles.
Third, remove the end fittings and check the O-rings. PTFE O-rings work up to 200 °C. Viton O-rings work up to 180 °C. A hardened O-ring feels like plastic. Replace it. Here is the thing most maintenance workers miss: an O-ring can look fine but still leak at 10 bar. If the surface has a flat spot, replace it.
Fourth, clean the metal end blocks with a soft cloth and isopropyl alcohol. Do not use a wire brush on the sealing face. A single deep scratch can cause a leak at 10 bar hot water. Wipe the sealing faces in one direction only.
Fifth, reassemble and torque the nuts in a cross pattern. The King manual suggests 6 to 8 N·m for DN15 and 10 to 12 N·m for DN25. Check the values for your model. Over-torque cracks the glass. Under-torque leaks at the seal.
When to Replace Instead of Repair
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Some maintenance teams replace the same glass tube three times a year. A paint manufacturer in Southeast Asia spent more on labor and downtime than a new meter would cost. For process lines above 150 °C or 10 bar, a glass tube indicator is a wear item. Silver Automation Instruments supplies alternatives with electronic output. A vortex flow meter with a 4-20 mA HART output works well on thermal oil from DN15 to DN200. A Coriolis mass flow meter handles hot chemicals up to 200 °C and gives mass flow, density, and temperature in one device. If you need to keep the visual indicator but add a record, use a Silver Instruments pressure transmitter on the same line plus a paperless recorder to log temperature and pressure.
Recommended Silver Instruments for High-Temperature Liquid Lines
We recommend a few models based on field conditions. For heat transfer oil up to 180 °C, choose the Silver Instruments vortex flow meter with DN25 to DN100 wafer body and a 4-20 mA HART output. For high viscosity hot liquids above 100 cP, choose the oval gear flow meter with PTFE gears rated to 150 °C. For chemical dosing at low flow rates from 0.5 to 50 kg/h, the Coriolis mass flow meter is a better fit. If you only need to replace the transmitter or display, our pressure transmitters and paperless recorders work with existing process signals.
Need a quote? Send us your pressure in bar, temperature in °C, pipe size DN, and flow range. Tel: +86-25-68650347. Whatsapp: +86-25-52155837. WeChat: +86 15365082610.
Frequently Asked Questions
How often should I service a King high-temperature liquid indicator?
Service the seals and inspect the glass tube every 30 days for continuous hot oil service. Replace O-rings every 12 months or whenever they feel hard.
What seal material works above 180 °C?
PTFE seals can handle 200 °C. For service above 200 °C, switch to a metal-sealed flow meter such as a Coriolis mass flow meter from Silver Instruments.
Can I replace only the glass tube?
Yes. You can replace the borosilicate glass tube if the metal body is still flat and clean. Use a new O-ring set and torque to the value in the King manual.
What is the safe torque for a DN25 indicator?
The typical torque range is 10 to 12 N·m for DN25. Always use a calibrated torque wrench and tighten in a cross pattern.
Where can I get an electronic flow meter for a high-temperature line?
Contact Silver Automation Instruments. Send us your pressure in bar, temperature in °C, pipe size DN, and flow range. Tel: +86-25-68650347. Whatsapp: +86-25-52155837. WeChat: +86 15365082610.
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