3.INSTALLATION B-70315EN/02
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3.3.2 External Laser Gas Piping Leakage Check (Clamp Test)
When you have installed or modified laser gas piping, conduct a
clamp test that checks for any leakage by sealing laser gas inside the
piping and observing the pressure change after a specified period of
time.
(1) Measurement
Measure and record the gas pressure as described below.
For recording measured data, use the external leakage record
table presented in Appendix H.
(a) Stop the oscillator. At least five minutes after purging is
completed, turn the secondary pressure adjustment handle
of the regulator in the pressure-reducing direction to
completely close the adjustment nozzle, then close the main
plug of the gas cylinder.
(b) Record the primary pressure (P
1S
), secondary pressure (P
2S
),
and start time (t
S
) of the regulator connected to the cylinder.
(c) When about eight hours have passed, record the primary
pressure (P
1E
), secondary pressure (P
2E
), and end time (t
E
) of
the regulator.
(d) Open the main plug of the gas cylinder
(Note)
, and measure
and record the primary pressure (P
1ST
) of the regulator. (The
temperature-corrected primary pressure is measured.)
NOTE
When opening the main plug of the gas cylinder,
you should stand at an oblique position to the
regulator. Never stand just in front of the pressure
gauge. If significant leakage is present, opening the
main plug causes an abrupt pressure to be applied
to the regulator, which can damage the regulator.
(2) Determination
Calculate the change ratio from measured values by using the
equation below to determine the leakage state.
(a) Primary pressure change ratio
(P
1ST
- P
1E
) 8 hours × 100
Primary pressure change ratio=
P
1ST
×
(t
E
- t
S
) hours
If the primary pressure change ratio is 5% or less, no
leakage is assumed on the primary side.
(b) Secondary pressure change ratio
(P
2S
- P
2E
) 8 hours × 100
Secondary pressure change ratio=
P
2S
×
(t
E
- t
S
) hours
If the secondary pressure change ratio is not greater than the
following value, no leakage is assumed on the secondary
side:
• 10% when a polyfro (polyethylene) tube is used for piping
• 6% when a metallic pipe such as a stainless pipe is used
for piping