Chromatographic Troubleshooting

Pressure check

Pressure check

The pressure•checkmethod will indicate, but sometimes not isolate, a leak in the flow path. Since this method does not necessarily isolate the leak, one of the leak•checkmethods 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.

1.Disconnect the detector from the valve system.

2.Cap the valve system at its outlet and pressurize to 689 kPa (100 psi). Allow 2 to 5 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 13.78 kPa (1 to 2 psi) drop during a 10•minuteperiod.

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 soap•bubble technique. Do not assume the leak must exist only at a valve. Often plumbing connections such as unions or bulkhead fittings are at fault.

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.

217