Also, many applications simply don’t need ultrahigh
performance and sensitivity, so a regulator made
for extreme performance may be overkill (and often
significantly more expensive).
Seat orifice size also is very important. A bigger
orifice flows more, but bigger isn’t necessarily better, as it can lead to more pressure drop and more
“rise” (see Rise Explained sidebar). Seat material
choice is critical to a regulator design, and many different materials are used in their construction. Soft
seat materials, such as urethane, provide excellent
performance at low pressures and are very forgiving
of contaminants and surface finish imperfections.
However, soft seats move under pressure, so performance can sometimes seem sluggish, especially at
low temperatures. Hard seat materials, such as PCT-FE or nylon, offer more precise response, can handle
high inlet pressures, and work well in cold temperatures. However, these can be very susceptible to surface imperfections and contaminants, so they often
need to be encapsulated for cleanliness and require
more critical machining and surface finishes.
A regulator is considered to have good performance
when it consistently delivers the pressure required
for the application, as set by the operator. It must
continue to deliver the set pressure no matter what
application demands are placed on it and for as
much of the cylinder contents as possible. Using a
size 3 acetylene cutting tip as an example, a stan-
dard tip chart shows that this application requires
40 to 45 PSIG (210 to 240 SCFH) of cutting oxygen
and 5 to 10 PSIG of preheat oxygen. If the operator
sets the regulator to deliver 40 PSIG, the operator
should expect 40 PSIG when the cutting oxygen le-
ver is depressed. If the pressure drops to 35 PSIG,
that’s poor performance.
A good regulator delivers the set flow rates from
extremely heavy flows (such as a large cutting tip or
multiflame heating attachment) to extremely small
flows (such as a size 0 welding tip, which requires
just 3 to 5 PSIG of oxygen). To evaluate regulator
performance, look at a flow data graph. A good-
performing regulator has a nearly flat line, mean-
ing that it delivers close to the set pressure across
its entire flow range. In contrast, delivery pressure
from a poor-performing regulator may start out flat
at very low flows but then arc rapidly down as flow
demand increases. This delivery pressure drop can
have serious negative consequences to application
A premium regulator can provide decades of
trouble-free performance, but even the best regulator wears eventually. Performance issues generally
fall into one of five areas: seat failure (from contami-
The characteristic of rise occurs when outlet pressure increases as inlet pressure decreases (typically as
a result of cylinder contents emptying). Fuel gases such as acetylene and propane have very low cylinder
pressures, and their cylinders largely permit consistent pressure and flow performance until the cylinder
is just about empty. High-pressure gases, such as oxygen, nitrogen, and air, are a different story.
Here’s how rise works:
1. Inlet pressure applies a force on the regulator seat, essentially forcing it closed.
2. When the regulator is adjusted, the adjusting spring has to counter this force in addition to the force
it needs to achieve the required output pressure. If the inlet pressure is generating 15 pounds of force
pushing the seat closed and the delivery pressure requires 40 lbs. of force to be obtained, then the
adjusting spring is loaded to 15 lbs. plus the 40 lbs. required for delivery pressure, for a total net force
of 55 lbs.
3. As inlet pressure decreases, inlet force also decreases. This means the adjusting spring has less force
than it needs to overcome to obtain delivery pressure. So if the original 15 lbs. of force pushing the
seat closed decreases to 10 lbs., then the force remaining for the delivery pressure now equals 45 lbs.
( 55 lbs. – 10 lbs.) instead of the original 40 lbs.
4. As a result, delivery pressure increases slightly, and in a cutting application, the cutting flame becomes slightly oxidizing. The operator will need to stop cutting and readjust the regulator back to
the original delivery pressure to achieve a neutral flame.
Internal components of a single-stage gas regulator are shown. This next-generation regulator also includes a
particle trap and diffuser, both of which increase safety.
Adjusting the regulator knob opens gas flow to downstream equipment. When cutting commences, high-pressure gas refills the regulator’s low-pressure chamber, and a full cycle begins anew as long as demand is
Cycle testing has demonstrated that new stainless steel
diaphragm designs can withstand 50,000 cycles, which
is five times more than UL requires for stainless steel
and twice as high as what UL requires for elastomers.
If a gas cylinder should fall on the regulator, the adjusting knob’s crumple zone spreads the force of the impact over several areas, not focusing the force in the
center of the gas connection.