Service Technician Course

Service Technician Notes

These notes will help you to revise for your SERVICE TECHNICIAN course and exams.

OXYGEN HAZARDS
Oxygen does not burn
Oxygen is an oxidizer
All common metals burn in oxygen
Many materials that will not burn in air will burn in the presence of oxygen!
Therefore: Oxygen is considered a hazardous substance!

FIRE TRIANGLE
O2 can’t be removed
O2is It’s own ignition energy
Fuel is always in system
O2“fans” the fire
Lowers auto-ignition temperatures

HYDROCARBONS
Hydrocarbons = Hydrogen & Carbon
O2reacts violently in the presence of hydrocarbons
Hydrocarbons can promote “flashing” which can introduce toxic gasses (including CO)

ADIABATIC COMPRESSION
Gasses heat up when compressed suddenly
Can occur wherever there is a block or restriction

Theoretical Temperatures:
Final Pressure

100 psi / 7 bar will be 453°F / 234°C
1000 psi / 70 bar will be 1303°F / 706°C
2000 psi / 140 bar will be 1688°F / 920°C

OTHER CAUSES
Localized Frictional Heating
Particle Impingement

FIRE PREVENTION
Proper system design
Proper system use
.RULE #1 is: Slow Slow & Slower!

S.D. -METALS
CGA Recommends SS up to 1000 psi
In areas of impingement use:
Copper or Nickel Alloys
Never Use:
Aluminium or Carbon Steel

SYSTEM DESIGN -TUBING (1)
Consider maximum pressure during selection
Free of sharp curves, large radius turns
Piping mustbe thoroughly de-burred
Materials for:
Monel Alloy 400 is A632 SS
Type 316 SS is B165 CA

S.D. -TUBING (2)
Must be softer than the fitting material
High pressure tubing must be  seamless and fully annealed
Wall thickness must be carefully checked
Surface finish is very important to proper sealing
Oval tubing should never be forced into a fitting.

S.D. -CONNECTORS
Usually nickel or copper alloys
Stainless steel possible substitute

S.D. -NON-METALS
Most non-metals will:
Burn violently, producing system fire
Flash, producing toxic gasses

S.D. -GAUGES
Analog:
Large face, small graduations
Less accurate than digital

Digital:
Readings seem to “jump around” (temperature fluctuations, small leaks, etc.)
More accurate than Analog

S.D. – VALVE SETUP
NEVER USE 1/4 TURN VALVES!!!!
Select needle or metering valves with:
fine pitch thread
low Cv factor
Tapered or Metering stem

APPROPRIATE Cv VALUES
1.For use in oxygen filling, select a slow opening valve that has a maximum Cv Factor less than 0.05.
2.For use in EAN blending(adding air), select a slow opening valve that has a maximum Cv factor less than 0.2.

CHECK VALVES
Added Safety
Valve allows for one way passage of gas only
Prevents back flow into cylinders
Suggested reseal pressure 5 psi (.33 bar)

FILTERS
Generally: 0.1 mg/m3is acceptable for hydrocarbon contamination
Much less is desirable

O-RINGS
Materials include: Viton & EPDM
Selection criteria include:
Durometers, Sizes, Shapes