WHY  REGULATOR/FLOWMETER SYSTEMS

ARE DESIGNED WITH HIGH GAS PRESSURES

(or Higher Output Pressure Designs are a "Good Thing!”)

Gas Delivery Pressures Were Designed to be Above 25 psi Since the Invention of TIG and MIG Welding--For Good Reason!

Understanding why flow control systems are designed to operate at  higher pressures requires an knowledge of how these systems work:

HOW CONVENTIONAL REGULATOR/ FLOWMETERS WORK  

Regulator/flowmeters or regulator/flowgauges work on essentially the same principle.  Gas passing through a very small orifice will reach a limiting velocity based on the orifice size and the pressure upstream of the orifice.  This is called a critical orifice.  The pressure downstream of the orifice will not influence the flow rate as long as it is less than about ½ of the upstream pressure (all measurements in absolute pressure, or the pressure you read on the gauge plus 14.7 psi).  We won't bore you with the 20 term equation which defines critical flow for the proof of that statement! 

The following two figures show the types of flow regulating devices used in welding.  One operates with a fixed pressure and varies the orifice size (a needle valve), the other fixes the orifice size and varies the pressure.  A fixed orifice in a gas pipeline delivery operates in a similar manner. Systems employing flow tubes operate at the fixed pressure and read accurately regardless of the downstream pressure or restrictions in the system. 

Note: Regulator/Flowgauges used on cylinders (those with an output pressure gauge calibrated in CFH) usually operate over a range of from 30 to 70 psi depending on flow setting and also provide "Automatic Flow Compensation."

AUTOMATIC COMPENSATION FOR HOSE AND TORCH RESTRICTIONS

Shielding gas flow rate will not change if the pressure downstream of the flow controlling orifice is less than 1/2 the upstream regulator or pipeline pressure (all measured in absolute pressure; i.e. gauge reading + 14.7 psi).  This is very important since as the welder moves, his shielding gas delivery hose may become twisted, contain numerous bends, or even be partially crushed, creating a pressure drop.    The torch gas hose may also become bent and its gas passages may partially clog with spatter, increasing pressure drop.  However, as long as the restriction (plus the pressure drop to flow gas though the delivery hose feeder and torch) does not exceed ½ the regulator pressure, no flow change will occur.  The restrictions need not be noticed by the welder.  They are compensated for automatically since the regulator or pipeline pressure is sufficiently high.  If the pressures were significantly lower, any changes in restriction would result in a reduced the flow rate.  If this occurred on a flowgauge regulator system the welder would not even know it.  The gauge would still read the same and not the reduced flow rate! 

Low pressure devices, including those that control flow at the feeder, do not have the ability to compensate for torch restrictions which occur due to spatter buildup in the nozzle or with twisted torch cables etc. The gas diffuser  at the nozzle end of the torch can partially clog with spatter causing extra back pressure.  In addition the gas passage at the diffuser end of many MIG torches is also the wire passage.  It can clog with debris such as drawing lubricate, copper flakes etc.  Our test results show very significant flow reductions can occur with low pressure systems.  With adequate pressure the flow will not change, it will be automatically compensated.  See Flow Tests Below.

Still Have Questions About How With No Moving Parts Automatic Flow Control Is Accomplished?  CLICK HERE

“… there are applications in which a compensated unit (referring to higher pressure flow compensating regulator/flowmeters) may be required. When long lines from the flowmeter to the gun cause back-pressure or when wind causes the shielding gas to blow off, the compensated system may be the solution to these problems.”

In addition to the problems with low pressure devices mentioned in the article; some of these devices mounted at the feeder do not provide sufficient extra gas at the start to purge air from the weld start zone, gas nozzle etc.  This air causes internal if not visible porosity.  When humidity is high the introduction of hydrogen makes matters worse!  See information on "Compensating for Air Diffusion..."  that Stauffer knew and patented in 1982!

When inevitable flow restrictions occur in production, some low pressure systems reduce flow rates significantly below what is preset. They also read incorrect flows if a pressure calibrated flow gauge is employed. Flow restrictions occur in production as the gas hose or torch cable becomes coiled, kinked and twisted.   Restrictions also occur when the torch nozzle and gas ports accumulate spatter or when the combination torch gas passage/wire conduit fills with debris from the welding wire.  We have found over 30% flow reductions occurring with such systems with no indication on the pressure calibrated flow gauge!

FLOW TEST RESULTS: The following table provides test results with a conventional flow control device (Photo Left) and a commercial low pressure system (Photo Right) subjected to varying restrictions. Both were initially set to flow 31 CFH as noted in Blue.  The controls were left at the initial settings as if they were padlocked.  Torch restrictions were then added and removed (as if the gas ports were alternately clogged and cleaned) to vary the amount of restrictions.  The resulting flow rates are shown in the table below.  Flow rates were validated with calculations:

COMPENSATING FOR AIR DIFFUSION IN THE WELDING TORCH

Another reason to have higher delivery hose pressure is to quickly supply a small amount of extra gas flow at the weld start to displace the air  and associated moisture that diffuses into the torch and conduit  when welding is stopped. With the GSS the extra flow rate is controlled with a restriction orifice installed at the feeder end of the hose so  the proper (not excessive) amount of extra gas flow is rapidly applied, displacing the air in the torch hose. This controlled amount of extra gas at the weld start also quickly fills the gas nozzle and floods the weld start area with shielding gas.  Maintaining the designed higher pressure and incorporating a restriction orifice in the hose fitting  at the solenoid end rapidly provides the extra shielding gas at the weld start  but limits the flow rate to an acceptable level.

Some devices designed to reduce gas waste do not supply any or insufficient extra gas to counteract the air entering the torch nozzle, body and cable when welding is stopped.  Some of these devices control flow at the wire feeder.    Stauffer in a patent published in 1982 discusses this issue.  He clearly understood the problem and designed around it; he states in the patent teaching, "... air leaks back into the torch and lines when welding is stopped.  The air must be quickly purged and replaced with inert gas to produce high quality welds. Also, it is critical to displace the air at the weld zone of the work piece upon initiating the weld. " 

We have validated the Stauffer findings.  See Production Example showing problems when no extra gas is available at the weld start.

Another fabricator found they had weld start porosity when no extra gas was supplied at the weld start.

 A welding engineer at a major automotive supplier reports that after purchasing and using 32 low pressure gas saving devices (Photo Right) that mounted at their wire feeders he had to discard all of them!  He reported two problems:

1) Lack of sufficient extra gas at the start made inferior starts and

2) Large flow variations from preset levels were evident when he would check flow at the torch.  In fact as he stated; "Even if the flow was blocked, the flow calibrated pressure gauge supplied with these devices had the same preset reading!"

Schematic from Stauffer Patent

ALLOW WELDERS TO HAVE SOME CONTROL OVER GAS FLOW RATE

In many cases the welder should control the shielding gas flow rate to compensate for drafts, the type of weld joint, his torch to work distance, etc.  These factors may change from job to job or day to day.  If there is a concern that they will set excessive flows, we have a solution.  Our Flow Rate Limiter^TM allows the maximum flow rate to be defined and locked into the flowmeter.  The welder can lower the flow from that level by 10 to 20 CFH depending on the specific flowmeter being used.  In some cases it can be locked at a specific flow if desired.  Check it out

BENEFITS OF THE WA TECHNOLOGY GSS

The WA Technology GSS saves shielding gas waste by reducing the volume of gas stored in the gas delivery hose and utilizing a flow restrictor at the wire feeder end of the hose.  It does not alter the pressure and therefore the flow compensating feature of the regulator/flow device being used. Hose restrictions, even those caused by unintentional crimping or kinking, are compensated for without the welder having to interact with the system. (Note that the GSS hose OD/ID ratio of 2.7 is much less susceptible to crushing than the conventional hose which has an OD/ID ratio of typically 1.8 or less)

The GSS surge flow restrictor size is selected to allow full control over the gas flow rate within usable limits.  By maintaining the original delivery pressure, a controlled amount of extra gas flow is quickly available at the weld start to displace any air which diffuses into the torch nozzle and hose when welding is stopped.  It also quickly provides extra gas to purge air from the weld start zone at a flow rate that is not excessive causing air to be aspirated into the gas shield.

At typical shielding gas flow rates and for most gas delivery hose lengths the small pressure drop in the GSS hose is easily handled.  With most gas delivery pipeline pressures and regulator/ flowgauges the GSS can be used with hose lengths up to 75 to 100  feet.  However for lengths above 50 feet we recommend you contact us and define the pipeline pressure you are using or if on cylinder supply the regulator model being employed.

"Lean Welding Manufacturing"   Learning Program

Want a greater explanation of this self compensating flow phenomena? Want to know what minimum delivery pressure is needed to assure good performance?  It's all in our:  "Optimizing Shielding Gas Use and Eliminating Waste" includes details of this information in a Do-It-Yourself 11 Module Program 

It quantifies waste due to surge flow, leaks, ways to monitor leaks and the gas flow settings where air is pulled into the shielding stream.  Unfortunately many are using far too much gas flow, wrongly employing the philosophy, "If Some is Good More Must be Better" !

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