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Kelly Pneumatics Digital Mass Flow Meter Manual: Proving Proportional Valve Micro-Gas Capillary Controls
Quick Answer: The Kelly Pneumatics digital mass flow meter manual explains how to prove proportional valve micro-gas capillary controls on low flow gas lines. The goal is to verify that the valve position signal and the mass flow signal agree within the stated accuracy band. Silver Instruments supplies thermal mass flow meters and 4-20 mA HART pressure transmitters for parallel verification on air, nitrogen, carbon dioxide, and natural gas lines.
What the Manual Section Actually Covers
The proving section focuses on small bore gas lines where a proportional valve feeds a micro-gas capillary sensor. These loops often appear in gas chromatography, bioreactor sparge lines, food packaging, and pilot plant reactors. The manual treats the valve and capillary as one control loop, not as two separate parts. Most engineers skip this part until the flow reading drifts or the valve hunts around setpoint. In practice, a proving run takes less than 20 minutes and saves a full recalibration.
You prove the loop by stepping the command signal while watching the measured flow. The command is normally 0-5 VDC or 4-20 mA. The meter then converts the command into valve lift. The capillary sensor reads actual mass flow. If the valve opens 20 percent but flow changes only 6 percent, you likely have a clogged capillary or a supply pressure drop.
Field Proving Sequence We Use
Start with dry gas. Set the supply pressure to the value printed on the meter label. Wait 30 minutes for the sensor temperature to stabilize. Zero the meter with flow blocked. Then send a 0 percent setpoint and confirm the flow signal sits below 0.2 percent of full scale. Step the setpoint to 25, 50, 75, and 100 percent. Hold each step for 60 seconds and record the flow in slpm or kg/h.
Check the return path next. Step the setpoint back to 75, 50, 25, and 0 percent. If the upscale and downscale values differ by more than 2 percent, look for hysteresis in the valve or moisture in the capillary. On one gas blending skid in Malaysia, a 6 percent offset on a 0-10 slpm air line disappeared after the capillary was purged with dry nitrogen for 10 minutes. We have seen the same offset pattern on customer sites many times.
Key Parameters to Record During a Proving Run
Record the gas type, inlet pressure in bar, outlet pressure in bar, temperature in °C, setpoint signal, flow signal, and valve drive current. Also note the tube size. A DN4 or DN6 tube behaves differently from a 1/8 inch capillary line. The manual often lists the nominal pressure drop for the micro-gas capillary. If your measured pressure drop is higher than the manual value, the capillary may have particle buildup.
For most small gas loops, the proving test is not a substitute for a factory calibration. The proving test is a field check. The distinction matters for audits and maintenance records.
Cross-Checking the Capillary Control with a Thermal Mass Flow Meter
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For micro-gas flow below 10 slpm, choose a low flow thermal mass flow meter. For higher flow gas batching, our Coriolis mass flow meters handle flow ranges from 0 to 600 kg/h on DN10 to DN80 lines. The key is matching the meter size to the expected flow, not to the pipe size alone.
Sizing Data to Send for a Quote
Do not just send a model number. Send us the gas type, flow range in slpm or kg/h, inlet pressure in bar, outlet pressure in bar, process temperature in °C, tube size in DN, power supply, and required signal output. The data allows us to quote a thermal mass flow meter or pressure transmitter within 24 hours. A common request is a 0-50 slpm air flow meter with 4-20 mA HART output for a gas analyzer rack. For natural gas or biogas service in ATEX Zone 1 areas, tell us the hazardous area classification.
Contact Silver Automation Instruments by phone at +86-25-68650347 or WhatsApp at +86-25-52155837. WeChat is +86 15365082610. You can also visit flow-meter.com.au for product pages on thermal mass flow meters, Coriolis mass flow meters, electromagnetic flow meters, ultrasonic flow meters, and pressure transmitters.
FAQ
Can I use the Kelly manual proving sequence for another brand of capillary control?
Yes. The step test and return path check are generic. You must match the signal scaling and wiring to the valve you use. The manual values for pressure drop and accuracy apply only to the Kelly Pneumatics device.
What is the first fault to check when the micro-gas capillary control will not hold setpoint?
Check the supply pressure stability first. Then purge the capillary with dry nitrogen. Many offset issues come from moisture or oil in the gas line, not from the electronics.
Which Silver Instruments meter works for low flow gas verification?
A thermal mass flow meter with 0-5 VDC or 4-20 mA output works well for air, nitrogen, carbon dioxide, and biogas below 50 slpm. For corrosive gases, tell us the full composition before quoting.
Do I need HART to prove a capillary control loop?
Not for a basic loop check. A 4-20 mA signal is enough. HART helps with remote zero trim, diagnostics, and audit records. We recommend HART if the meter is installed in an analyzer shelter with limited access.
How quickly can Silver Instruments quote a reference meter or replacement pressure transmitter?
Within 24 hours if you send the fluid, flow range, pressure in bar, temperature in °C, pipe size in DN, and signal type. For urgent shutdown work, contact us by phone or WhatsApp.
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