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How Much Gas Waste Can Be Stored in a 1/4 Inch Hose?
The volume of shielding
gas wasted every time the torch trigger is pulled can
be 6 times the physical shielding gas delivery hose volume from source
to feeder/welder.
HOW?
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 THE EFFECT OF
PRESSURE ON GAS VOLUME
Consider an
Argon gas cylinder. One holding 310 Cubic Feet (CF) of Argon (measured
at Standard Temperature and Pressure (STP); that's what you pay for) has only
1.8 CF of physical internal volume. How does it hold all that gas?
Because of the increased pressure over atmospheric.
The volume of gas in the cylinder
at STP is directly proportional to the
absolute pressure. At 2500 psi = 2515 psia (psia = absolute pressure.
That is the gauge reading +14.7 psi at sea level.) Therefore the volume will be 2515/14.7 or
171 x 1.8 (physical) CF = 310 CF of gas at STP.
Interesting fact -
At full cylinder pressure Argon is still a gas but it's actually pretty heavy!
(310 CF weights about 31 pounds.) When the gas is contained in the 1.8
CF cylinder it's about 30% the density of water!
Therefore when the shielding gas delivery hose is pressurized it holds
much more gas than
the actual internal physical volume of the hose. How much more depends on the pressure.
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WHAT
IS OCCURRING IN THE GAS DELIVERY HOSE FROM THE FLOW CONTROL AT THE GAS SUPPLY
TO THE FLOW CONTROL SOLENOID?
This schematic presents the volume of extra gas in the
gas delivery hose. The "bar graph" is shown as Red and Blue bars above
the Green gas delivery hose. Area in Blue
 represents the extra volume of gas in
the hose over the physical volume due to the
~ 5 psi need to flow the required amount of gas when welding. The flow
control (needle valve or orifice) creates the lower pressure when
welding. The Area
in Red  shows the amount that can be
excess due to the pressure in the gas delivery hose over the ~ 5 psi when
welding stops. This higher pressure is set by the regulator/flowmeter;
regulator/flowgauge or pipeline pressure. The Blue and Red areas are
sized relative to the hose area shown in Green to provide proper
perspective. |
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How Does
The Pressure Get That High?
A restriction orifice or a
needle valve is used to control shielding gas flow. With Regulator/Flowmeters
(Photo Below Left) outlet pressures range from 25 to 80 psi. For CO2 shielding 80 psi is used
to help prevent ice formation.
Flowmeters
used on pipelines allow pipeline pressure to exit the flow control valve
when welding stops. A typical pipeline pressures 50 psi.
Flowgauge/Regulators (Photo Right)
operate by setting a pressure above a critical orifice (a very small hole). For most MIG
shielding gas flow rates the pressure exiting the control orifice when welding
stops will range from 40 to 70 psi.
However the pressure needed at the feeder to flow the
shielding gas though the solenoid, fittings and torch
can range 3 to 8 psi depending on torch length and restrictions. When
welding is stopped, gas continues to flow through the needle valve or critical
orifice and increases in the gas delivery hose to that of the
regulator output or pipeline. Therefore the pressure in the gas
delivery hose will be about 25/3 = 8
to 80/3 =
26 times the pressure needed to flow
the desired amount of gas! For Flowgauge/Regulators
13 to 23
times what may be needed!
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HOSE EXPANSION
 We have been
asked about the effect of hose expansion on the extra volume of stored gas
when welding stops. Making measurements of a relatively heavy wall
(0.093 inch wall, 1/4 inch ID) commercial gas delivery hose we obtained the
following data:
When welding
stopped, using a CO2 80 psi regulator/ flowmeter,
the hose expanded 13% in volume. Therefore in this case 87% of the
excess gas in the hose is due to the increased pressure and the additional
13% due to the hose expanding. In total the excess gas waste (most of
which is wasted with each torch pull) = about 6 times the physical hose
volume!
Note: with the
Gas Saver System the excess is reduced by about 80% and there is very slight
hose expansion since that hose has a very heavy wall to diameter ratio and
is fiber reinforced. |
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Want more details on pressure versus gas waste
and much more?
Purchase
"Lean Welding Manufacturing"
Learning Program For Welders
"Setting Shielding Gas
Flow and Eliminating Waste"
a
Train-Yourself 8 Module Program
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| BOTTOM LINE
The amount of gas in a hose depends on the pressure. For some
regulator/flowmeters and many regulator flowgauges (those that have a
pressure gauge reading cubic feet per hour, CFH) can cause a pressure of 80
psi in the hose when welding stops. Therefore the volume of gas in the hose
is (80+15)/15 = 6.3
times the hose volume. Accounting for
the hose expansion that can be an extra 13% or 6.3 x 1.13 =
7.1 times the hose volume. Therefore the gas
waste created every time the torch trigger is pulled is much more than the
hose volume would indicate. Our patented Gas Saver System
reduces the amount of excess by 80%!
CAUTION! The high pressure in the
gas delivery system is designed to provide automatic flow compensation (along with
other benefits) - lowering the
pressure defeats this very important feature. Higher pressure is needed to maintain the automatic control of gas flow when
restrictions in the gas hose, torch cable and torch nozzle occur in
production.
See this link
for an explanation.
That's why system pressures were designed that way since the invention of
TIG and MIG welding!!
See high pressures are a "Good
Thing."
Why is most MIG gas delivery hose 1/4 inch ID?
Hint; it's not for the very low pressure drop at the low flow rates used!
CLICK to SEE WHY.
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What Are Gas Costs as a Percent
of Total Weld Cost?
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