Can I have your thoughts on this please - particularly for the last item.
Most regulators used for shielding gas in GMAW and GTAW welding are one of:
Typical uncompensated fixed orifice, variable pressure flowgauge-regulator
Typical compensated variable orifice, fixed pressure flowmeter-regulator
In either case, the single stage regulator might be replaced by a dual stage regulator to minimise the supply pressure effect.
Another type, which is becoming increasingly common, is a hybrid called an uncompensated flowmeter-regulator.
Harris Model 351 An economical zero compensated Flowmeter Regulator
This uncompensated flowmeter-regulator uses the variable pressure, fixed orifice of the flowgauge-regulator and the Thorpe Tube flow meter of the flowmeter-regulator. Unlike the usual flowmeter-regulator, this flowmeter operated at atmospheric pressure.
Recently, I have come across a variation of the uncompensated flowmeter-regulator that uses a dual stage regulator to compensate for the supply pressure effect, but it has a calibration pressure printed of the Thorpe Tube housing.
Bossweld hybrid flowmeter-regulator
Thorpe Tube calibrated at 1.5 kg/cm2 (about 20 psi or 150 kPa)
This implies that the Thorpe Tube is under pressure so it must be placed between the high pressure and the low-pressure regulators. This remains an uncompensated flowmeter-regulator but it is not sensitive to supply pressure effect and generates little surge because of the low output pressure of the second regulator. The advantage gained by pressurising the flowmeter seems minimal - it will remove inaccuracies caused by backpressure but these would be quite small with typical backpressures of about 4 psig.
I am yet to did-assemble and test one of these to verify my conclusion.
Flow Control for Shielding Gases
Most regulators used for shielding gas in GMAW and GTAW welding are one of:
Flowgauge-regulator
A single stage regulator followed by a flowgauge (Bourdon gauge) which is a standard pressure gauge with a small orifice and calibrated in units of flow. This is the typical fixed orifice, variable pressure, uncompensated type flow meter.Typical uncompensated fixed orifice, variable pressure flowgauge-regulator
Flowmeter-regulator
A single stage regulator followed by a flowmeter (Thorpe Tube flow meter). This is the typical variable orifice, fixed pressure, compensated type flow meter.Typical compensated variable orifice, fixed pressure flowmeter-regulator
In either case, the single stage regulator might be replaced by a dual stage regulator to minimise the supply pressure effect.
Another type, which is becoming increasingly common, is a hybrid called an uncompensated flowmeter-regulator.
Harris Model 351 An economical zero compensated Flowmeter Regulator
This uncompensated flowmeter-regulator uses the variable pressure, fixed orifice of the flowgauge-regulator and the Thorpe Tube flow meter of the flowmeter-regulator. Unlike the usual flowmeter-regulator, this flowmeter operated at atmospheric pressure.
Recently, I have come across a variation of the uncompensated flowmeter-regulator that uses a dual stage regulator to compensate for the supply pressure effect, but it has a calibration pressure printed of the Thorpe Tube housing.
Bossweld hybrid flowmeter-regulator
Thorpe Tube calibrated at 1.5 kg/cm2 (about 20 psi or 150 kPa)
This implies that the Thorpe Tube is under pressure so it must be placed between the high pressure and the low-pressure regulators. This remains an uncompensated flowmeter-regulator but it is not sensitive to supply pressure effect and generates little surge because of the low output pressure of the second regulator. The advantage gained by pressurising the flowmeter seems minimal - it will remove inaccuracies caused by backpressure but these would be quite small with typical backpressures of about 4 psig.
I am yet to did-assemble and test one of these to verify my conclusion.