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Positive Displacement Gas Flow Meter: High-Accuracy Low-Flow Diaphragm Senses
Quick Answer: A positive displacement gas flow meter with diaphragm sensing delivers high accuracy at low flow rates. The SIL-PD-G series from Silver Instruments covers gas flow from 0.02 Nm3/h to 10 Nm3/h with pulse or 4-20 mA HART output. This meter type suits natural gas, nitrogen, biogas, and CO2 applications.
What Is a Positive Displacement Gas Flow Meter?
A positive displacement gas flow meter traps a fixed volume of gas inside a chamber. The chamber fills and empties many times per minute. A mechanical counter or electronic transmitter counts each cycle. This principle works well for low flow because the meter does not need high velocity to create a signal.
In practice, most engineers skip this part. They know positive displacement meters are common for viscous liquids. The gas version uses a diaphragm and a sealed measuring chamber. That design gives stable readings even when pressure varies.
How the Diaphragm Senses Low Flow
The diaphragm inside the meter flexes as gas moves through the measuring chamber. Each flex equals a known volume. The movement operates a gear train or a Hall effect sensor. Silver Instruments supplies models with pulse output and with 4-20 mA HART output.
Low flow performance is the main reason customers choose this meter type. At 0.1 Nm3/h a thermal mass meter can drift. A diaphragm PD meter still produces a clean pulse train. This characteristic supports pilot plant gas feeds and burner fuel gas lines.
Here is the thing. The diaphragm also gives a mechanical memory effect. The meter records volume even if the electronic transmitter loses power for a short time. This feature supports custody transfer and internal energy audits.
Typical Applications and Installations
We have seen these meters on customer sites many times. A paint manufacturer in Southeast Asia uses one to measure nitrogen blanketing flow on solvent tanks. The gas flow is only 2 Nm3/h. The meter sends a pulse signal to a batch controller.
Another common use is natural gas consumption monitoring for industrial boilers. DN15 and DN20 sizes cover most burner pilots and small burners. Biogas from digesters also works if the gas is clean and dry. CO2 injection in food and beverage lines is another fit.
Because the meter has moving parts, install a 50 micron filter upstream. Keep the gas dry to avoid diaphragm damage. A pressure regulator before the meter improves repeatability.
Key Specifications to Check
Do not compare these meters only on price. Check the following parameters before you send a request.
Accuracy of plus or minus 0.5% of reading is common for DN15 and DN20. R
Output options include pulse, 4-20 mA, and 4-20 mA HART. Power is 24 V DC. Hazardous area approvals include ATEX Zone 1 and IECEx. Process connections are usually DN15, DN20, DN25, G1/2, or NPT. Materials for the body are aluminum or stainless steel. The diaphragm is PTFE or a fluoropolymer blend.
Silver Instruments Supply Scope
Silver Automation Instruments supplies positive displacement gas flow meters for OEM skids and end user upgrades. We keep standard DN15 and DN20 models in stock for fast delivery. For larger sizes up to DN50, lead time is normally 2 to 3 weeks.
For pilot gas lines, the DN15 model SIL-PD-G15 is the standard selection. It handles flow from 0.02 Nm3/h to 1 Nm3/h depending on gas density and inlet pressure.
We also supply accessories. Filters, pressure regulators, PT100 temperature sensors, and flow computers are available in one shipment. This helps customers in Vietnam, Indonesia, Mexico, and the Middle East reduce freight costs.
How to Get a Quote
Send us your gas type, pressure in bar, temperature in °C, pipe size in DN, and minimum flow rate. We will reply with a model number, price, and delivery time. You can reach us by phone or message.
Tel: +86-25-68650347
Whatsapp: +86-25-52155837
WeChat: +86 15365082610
FAQ
What gases can a positive displacement diaphragm flow meter measure?
Natural gas, nitrogen, CO2, air, biogas, and clean process gases. Avoid dirty or wet gas unless you install a filter and dryer upstream.
What is the lowest flow rate this meter can measure?
Typical low flow starts at 0.02 Nm3/h for DN15 meter size. The exact value depends on gas density and pressure. Provide your minimum flow to our engineers for a correct selection.
Does the meter require a straight run of pipe?
No. Positive displacement gas flow meters do not need long straight pipe runs. Install the meter with a filter upstream and a short isolation valve. This saves space on small skids.
Can this meter be used in hazardous areas?
Yes. Silver Instruments offers ATEX Zone 1 and IECEx certified versions. Specify the hazardous area classification when you ask for a quote.
What output signal should I choose for a PLC or flow computer?
A pulse output is common for totalizing gas use. A 4-20 mA HART output is common for continuous flow rate and diagnostics. We can configure one or both outputs depending on the electronics.