Chapter 7 - System Description
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MNL000301.doc
Revision 2
01/04/2019
SourceSystem TE11
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7.9.2 Valve And Transducer Numbers And Nomenclature
V10
= HPLT supply valve (pneumatic).
V11
= low pressure purge inlet valve (pneumatic). This is also a high pressure valve, and is installed
opposite to the purge flow direction allowing HPLT gas pressure to seat against the inlet side of the
valve body.
PT1
= cylinder pressure transducer.
PT8
= purge back pressure transducer. Not required on all systems. Senses process gas back flow and
contamination of purge line/cylinder. PT8 is supplied for certain hazardous gases where the cylinder
pressure is high enough to back contaminate the purge gas. PT8 is typically a 250 PSI transducer,
however 1000 PSI transducers are supplied on HPLT systems where PT8 is needed (so a higher leak
test pressure can be used without damaging the transducer).
7.9.3 Description of Operation
HPLT is supplied in order to more effectively verify the leak integrity of the pigtail-to-cylinder CGA
connection after a cylinder is changed. It is an improvement on the standard leak testing. Leak testing
done at a higher pressure will indicate leaks faster and of a lesser magnitude than leak testing done at a
lower pressure.
The maximum value of the leak test pressure is dependent upon several factors;
the service pressure of the fittings and valves that will be exposed to it.
the pressure rating of PT1
the pressure rating of PT8
the pressure available from the leak test gas supply.
If PT1 is a 1000 psi transducer, the recommended HPLT supply pressure is 950 psig, but shall not
exceed 970 psig. If PT1 is a 250 psi transducer, the recommended HPLT supply pressure is 220 psig,
but shall not exceed 230 psig.
HPLT is automatically initiated as part of the cylinder change sequence following cylinder change out.
Upon initiation of the cylinder change sequence, a prompt will appear to close MV4 on the opposite
side. Upon completion of the cylinder change out portion of the cylinder change sequence, the HPLT
will open V10 and V4 allowing the system to pressurize with leak test gas between V10 and V2. When
the HPLT is initiated
,
the high purge back pressure alarm associated with PT8 is disabled. A period of
3 minutes is allowed for the system to stabilize, after which time V10 and V4 are closed. After
stabilization, the pressure is monitored by PT1 for 10 minutes. During the test, the message “HP
LEAK L (or R)” is displayed, and the 10 minute period is counted down on the screen.