Extraneous Peaks; Locating Leaks; Pressure Check - HP 5890 SERIES II Service Manual

gas purity or flow rate in the detector. Poor carrier gas or improperly conditioned filters and traps should be
suspected whenever offsets occur.

EXTRANEOUS PEAKS

Air peaks are sometimes seen in a chromatogram when leakage occurs because the valve rotor does not
seal properly. These leaks may not be detectable by using the soap bubble method. The Leak Test proce-
dure is described in Section 3 of this manual. If a leak is suspected but cannot be located with soap
bubbles, a pressure check will determine definitely if a leak exists. Extraneous peaks can occur sometimes
due to improper conditioning of the valve or contamination. If leaks are not apparent, clean or condition the
valve. Obviously other causes, totally unrelated to the valve, may exhibit similar symptoms. Impure (i.e.,
containing water) carrier gas can cause extraneous peaks.

LOCATING LEAKS

Leak checking the plumbing involved in a valve configured system must be done carefully and methodically.
Several methods may be used, and the best choice will depend upon expediency, accessibility, and the
magnitude of the leak. Refer to Initial Supply Pressures and Leak Testing in Section 3 for details.

PRESSURE CHECK

The pressure check method will indicate, but sometimes not isolate, a leak in the flow path. Since this meth-
od does not necessarily isolate the leak, one of the leak check methods may be needed to locate the leak
specifically. Note that each valve in a system has two flow paths, ON and OFF. A leak sometimes occurs in
only one of these two positions. Check both. To do so perform the following:
1. Disconnect the detector from the valve system.
2. Cap the valve system at its outlet and pressurize to 689
minutes for pressure to equilibrate. (If a flow sensor exists, it should read zero flow.)
3. Turn the knob on the regulator counterclockwise until it turns freely. The regulator is now
turned off and the gauge is indicating pressure within the valve system.
4. Commonly, the pressure will drop quickly for approximately 30- 60 seconds; then stabilize.
After this initial drop, the gauge should not show more than a 6.89 to
during a 10 minute period.
5. If no leak is indicated, actuate all valves and repeat steps 2 through 4.
6. If a leak does show up, try to pinpoint the source with a
not assume the leak must exist only at a valve. Often plumbing connections such as unions or
bulkhead fittings are at fault. See Valve Box Top Assembly Removal in this section if exposing the
valve system is necessary.
7. If the leak cannot be found easily, divide the system in half and repeat the pressure check.
Continue dividing by halves, and pressure check until the leak is isolated.
Artisan Scientific - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisan-scientific.com
SVC 7- 8
kPa (100 psi). Allow 2 to 5
13.78 kPa (1 to 2 psi) drop
soap bubble technique. Do