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Flow Rate Changes With Pipeline Pressure

Both Flowmeters and  Flow Control Orifices alter flow rate as pipeline pressure varies.  Depending on the pipe size and configuration, pipeline pressure changes occur as additional welding machines are placed in use.  Just how much does the flow change?  We conducted the following Laboratory tests to demonstrate these flow changes.

Want a Detailed Report on the Following Test Data?   

It includes a table with correction factors to  calculate actual from measured flow when pipeline pressure varies.

CLICK HERE to Download FREE PDF Copy:

Alert !!

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(See Details in Video)

Time to "Lock" Your Flowmeters with Our Flow Rate Limiter.

The Flow Rate Limiter (FRL) is our latest gas saving patent.  It's simple and does not alter the flowmeter.  Just set the maximum flow desired and slip the billet aluminum FRL over the control knob so its stainless pin prevents further increases.  Then tighten the setscrew with included Allen wrench.  An optional brass lock prevents setscrew access.

CLICK Here or Picture for Details

Our FRL is a Perfect Compliment to Our Gas Saver System (GSS.)  With Both You'll Save Over 50 to 60% of Shielding Gas Use!


A pipeline flowmeter was connected to a test pipeline that had its inlet pressure controlled by an inert gas regulator connected to an Argon/CO2 shielding gas cylinder.  The cylinder regulator allowed pipeline pressure to be varied from 20 to 75 psi. To assure pressure reading accuracy a calibrated 2 inch diameter gauge was installed in the regulator outlet gauge port.

The flowmeter selected for the test was a commonly used Victor* FM372 (photo right.)  As noted in the Victor literature, all their flowmeters are calibrated at 25 psi (accept one for CO2 which is calibrated at 80 psi to avoid ice particles in the needle valve.)  They note that the pressure is used to provide what we refer to as "Automatic Flow Compensation" that requires a pressure of 25 psi or greater.  Therefore the flow reading scale will only be accurate at a pipeline pressure of 25 psi.  Increased pressure will produce a higher flow than what is read on the flow tube.  These Laboratory tests demonstrate just how much more flow variation occurs with pipeline pressure changes with a fixed flow control knob setting.


To measure the actual flow we used a portable flowmeter, our part number WAT- PFM.  This uses the same flow measuring principle defined by Bernoulli in the 1700's.  It is accurate and very repeatable.  It was used in a way recommended in our Lean Welding Manufacturing Self Study Training Programs which is to measure flow with the wire feeder gas hose  fitting placed in the gauge (photo left.)  Therefore there is no possibility of leaks between the Victor FM372 and the portable flowmeter. Instructions shipped with the WAT-PFM define how this measurement approach in combination with measuring at the MIG torch nozzle quantifies leaks in wire feeder plumbing, torch to feeder connections, backflow through wire outlet guide etc and what differences are excessive.

As we do with each batch of flowmeters, we checked the one used for these tests with calibrated regulator/flowmeters placed on the cylinder.  The WAT-PFM was accurate and correlated with the regulator/flowmeters within our measurement precision from 20 to 40 CFH.

The following are the results of the tests:

Pipeline Pressure Reading on FM372 Flowmeter Flow Tube Published Correction Factor  Flow Using Correction Factor Actual Flow Measured on Portable Flowmeter
25 psi 20 CFH 1.00 20 CFH 20 CFH
30 psi 23 CFH 1.05 24 CFH 23 CFH
35 psi 24 CFH 1.12 27 CFH 28 CFH
40 psi 26 CFH 1.18 31 CFH 32 CFH
45 psi 27 CFH 1.23 33 CFH 34 CFH
50 psi 31 CFH 1.28 40 CFH 40 CFH


Looking at the first row of data.  The pipeline pressure was set at 25 psi which is the calibration pressure for the FM372 flowmeter.  The 2nd column shows the reading on the FM372 flowmeter which was 20 CFH since the flow knob was adjusted to that flow setting.  The next column is the published factor used to correct for pressure differences between the actual pipeline pressure and the calibration pressure. Since 25 psi is the calibration pressure the factor is one.  Therefore applying the factor shows 20 CFH in the third column.  The last column is the flow measured on the WAT-PFM which, as expected, is also 20 CFH.  This also validates the calibration of the FM372 and the WAT-PFM flowmeter are the same.

Examining the third row of data; the pipeline pressure was raised to 35 psi with NO CHANGE IN THE INITIAL FLOW KNOB SETTING.  The FM372 flow now read 24  CFH.  The published correction factor for the increase in gas density is 1.12.  Applying this correction factor shows an actual flow for an observed 24 CFH reading to be 28 CFH.  Therefore although the gauge on the Victor FM372 was reading 24 CFH the actual flow was theoretically 28 CFH.  The extra flow is because the density difference in the gas from the 25 psi calibration pressure and the 35 psi in the pipeline.  The actual flow as measured on the WAT-PFM was 27 CFH which is within our measurement precision of the theoretical 28 CFH.

Looking at the last row of data.  Pipeline pressure was raised to 50 psi and the FM372 flowmeter now read 31 CFH.  The correction factor for 50 psi is 1.28 yielding a theoretical flow of 40 CFH (31 X 1.28) for a 31 CFH FM372 flowmeter reading.  The calculated flow is the same as the  actual flow measured on the WAT-PFM that was also 40 CFH.   That is 29% more actual flow then measured on the FM372 flowmeter [(40-31)/31=29%. ]

Therefore if this flowmeter (or any calibrated at 25 psi, as are many) is operated at a pipeline pressure of 50 psi and gas flow set at a reading of 31 CFH using the  flowmeter scale, the actual flow would be 40 CFH!  That is 29% more flow than read on the pipeline flowmeter scale.  Not only is this wasting gas but it could exceed the allowable range defined in a Welding Procedure Specification (WPS.)


Similar tests were conducted using variations in pipeline pressures with our Standard Flow Control Orifice, OGSS-45.  We compared the theoretical flow rate based on orifice size and pressure with that read on the WAT-PFM.  Here are the results:

Pipeline Pressure

Theoretical Flow Based on Orifice Size and Pipeline Pressure

Actual Flow Measured on Portable Flowmeter WAT-PFM
25 psi 25 CFH 25 CFH
30 psi 30 CFH 30 CFH
35 psi 33 CFH 33 CFH
40 psi 35CFH 36 CFH
45 psi 40 CFH 41 CFH
50 psi 45CFH 44 CFH

As seen from the data, the flow measured on the WAT-PFM through a OGSS-45 Flow Control Orifice is very predictable and within the measuring precision of the theoretical flow based on orifice size, pressure and flow calculations.


If employing pipeline supplied shielding gas and using an Orifice to Control Flow, a Portable Flowmeter is the way to verify the actual flow.  The flow through the Orifice changed about 8 CFH with a 10 psi pipeline pressure change.  This is as predicted by "critical flow" flow equations. 

When using a Flowmeter to control shielding gas flow from a pipeline, when pressure changed 10 psi the actual flow changed a similar 8 CFH.

Therefore pipeline pressure changes produced essentially the same flow variations in both Flowmeters and with Orifices used to set flow.

Note: When using Regulator/Flowmeters on cylinder shielding gas supply, these flow reading variations DO NOT exist as the regulator maintains the proper calibration pressure of 25, 50 or 80 psi.

Why Not Use a Cylinder Regulator/Flowmeter on a Pipeline Supply to maintain a fixed pressure?

Answer: Because it will not maintain a constant pressure with only a 40 to 100 psi input!  These devices are designed to operate over a wide range of inlet pressure, from 2500 psi  though about 200 psi and the accuracy of control even decreases at the lower inlet pressures!  Valve size, diaphragm size and spring pressure are all designed to this wide pressure range, especially the very high pressure.  If you want to use a regulator, you must select the proper type. See below, and email:

Check Pipeline Pressure with our WAT PTD

The WAT PTD consists of a 0 to 100 psi industrial pressure gauge with a CGA 032 "B" female fitting on one side and male CGA 032 "B" fitting on the other.  Just unscrew the gas delivery hose from the gas supply or feeder end and insert the WAT PTD.  The pipeline pressure can be tested since the gas pressure in the gas delivery hose rapidly increases to the pipeline pressure when welding stops.  The device can be used to quickly test pipeline pressure at the wire feeder gas inlet in several areas of the shop.

Full details are provided with the Instructions that accompany the product.

Download this PDF for more details:

WAT PTD Purchase Details:

Click to See Video Overview

Click to See Full Video Details

Does Your Pipeline Pressure Vary a Lot?

There are several things you can and should do:

You can add a regulator designed to control pressure from pipeline pressures to a stable 50 psi or 25 psi before flowmeters or fixed orifices.  We have seen cylinder regulator/flowmeters used in attempt to provide this function.  This DOES NOT work!  Being designed to control from 2500 psi they are not accurate with low inlet pressures! 

The proper regulator to use must be designed with proper size valve seats, correct diaphragm and spring.  There are regulators designed for that purpose usually called station regulators.  Some of these are expensive high flow models, however there are other lower cost models which can be used for one or two flowmeters.  The one shown on the left is designed to accept up to 200 psi inlet pressure and will hold a constant output at the preset pressure. .  A flowmeter (or a fixed orifice) can be easily added to the output fitting.

This regulator has the capacity to handle several flowmeters.  On the right is an inexpensive adapter that makes it easy to add two flowmeters.  This system works great with our GSS.  The GSS. will quickly save enough shielding gas to pay for the regulator within a few weeks! 


Email for details and part number information:

Using Small ID Shielding Gas Pipelines and High Pressure to Offset Pressure Drops?

We Have Two Patents that Accomplish Pressure Control and Gas Savings While Keeping Pressure Above 25 psi to Maintain "Automatic Flow Compensation" 

These systems work with any length gas delivery hose.  One simple system is available that works with any length existing gas delivery hose, even one 200 feet or longer!

Email for details.



Email with the following information:

1) Location: City and State

2) Pipeline pressure range

3) Type of existing flow control (flowmeter, orifice)

4) Range of gas delivery hose lengths (pipeline drops to feeders)


Want a detailed report on the above test data?    It includes a table with correction factors to  calculate actual from measured flow when pipeline pressure varies over a range from 20 to 70 psi.

CLICK HERE to Download FREE PDF Copy:

Measure Pipeline Leak Rate:

Having problems with leaking pipeline and hoses?  There is a simple way to measure the leak rate.  Use a leak down Pressure Test.  The equations needed to develop a  Spreadsheet are provided with our "Lean Welding Manufacturing-Shielding Gas" (part # LWM-SG) Program that makes it easy to calculate.  It is available for purchase on this web page.



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