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This document is believed to be accurate and up-to-date. However, Agilent Technologies, Inc. cannot assume responsibility for the use of this material.

The information contained herein is intended for use by informed individuals who can and must determine its fitness for their purpose.

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Error message, Foreline pressure has exceeded 300 mtorr

Applies to 5971, 5972 and 5973A/N MSD

Foreline Pressure

Only diffusion pump equipped MSDs have foreline pressure gauges, and therefore theability to read foreline pressure. Foreline pressure can be displayed from several

locations: the tune report, and from vacuum status. The foreline pressure is displayedin mtorr or milli torr units.

Foreline Pressure is determined by several factors: condition of the foreline pump,efficient operation of the Diffusion pump, column flow rate, column length anddiameter. Even oven temperature can cause changes in foreline pressure, althoughelectronic pressure control minimizes this.

So, knowing those factors it can be determined that a higher flow rate, shorter columnlength, wider column internal diameter, lower oven temperature, or any factorseffecting pumping efficiency of the vacuum system could have the effect of raising the

foreline pressure.Foreline pressure is measured by a foreline pressure gauge that is a cylindrical objectwith a cable attached, physically located between the diffusion pump and the HighVacuum hose that runs to the foreline pump.

Even though foreline pressure in most cases will mirror manifold vacuum, it is not to beconfused with the absolute vacuum measured in the Vacuum manifold, which can onlybe read by a gauge tube or triode gauge tube, depending on what model of MSD youare operating.

During proper operation, the foreline pump will lower the foreline pressure, (pressure atthe exit of the diffusion pump), down below 300 mtorr, before the MSD electronicsallows power to be applied to the diffusion pump to reach ultimate vacuum. If, duringnormal operation, the foreline pressure goes back above 400 mtorr, the error, Foreline

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pressure greater than 300 mtorr, will be generated and the MSD vacuum system andelectronics will be shut down.

The following Suggestions can aid in correcting or isolating foreline pressure problems.

Things to check for foreline pressure problems

Check for foreline pump operation

Verify that the foreline pump is plugged into the foreline power receptacle at the rearof the mass spec or into a suitable wall power receptacle.

If the pump is plugged into the rear of the MSD it should start running as soon asthe power button is depressed; if not, check MSD fuses. If the pump is plugged intoa wall outlet the pump should start running immediately; if not, verify that this

particular pump does not have its own on/off switch and that power is available atthe wall outlet; verify the circuit breaker for the wall outlet.

Check the foreline gauge connector

If it has been verified that the foreline pump is running, verify that the foreline gaugeconnector is firmly connected to the foreline gauge tube. If this connector is notconnected, the data system will interpret the bad connection as a failed forelinepump.

Note: On 5971 and 5972 MSDs the foreline gauge tube and cable is located at the

rear of the Mass Spec. On 5973 MSDs this cable is located at the rear of theMass Spec and is labeled High Vacuum control, while the actual gaugetube is located on the side of the diffusion pump.

Check column connections

Verify column connections/installation making sure that column is not broken. Dontover look possible break in the windings on the column basket.

A broken column closest to the Mass Spec will most likely cause a foreline pressureproblem because the column will act somewhat as a restrictor, however columns ofshort length or wide bore columns can cause a problem no matter where the break

may be.

Check the hose between diffusion pump and foreline pump

Make sure that the foreline hose is not damaged or torn in any way; also pay closeattention to the inside of the hose (the hose is clear) to verify that the hose has notcollapsed on itself. If the hose is damaged, replace or call for onsite service.

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Check for a large air leak(foreline pump exhaust flow greater than 2 to 3ml/minute for 5971/5972 MSDs orgreater than 5ml/minute for 5973MSDs may indicate a leak)

1. If the MSD will still operate check for an air leak.

2. If the MSD will not operate, or if you were unable to locate a leak, shut down andvent the MSD.

3. Inspect the foreline hose, foreline trap, GC interface nut, KF fittings, and manifold O-ring. Look for a broken or split hose, loose fittings and loose nuts, bad gauge tubeseal or broken gauge tube.

Replace the absorbent pellets in the foreline trap

CAUTION: Vent the MSD before opening the foreline trap. Otherwise, diffusion pumpoil will back stream into the vacuum manifold. This will contaminate thevacuum manifold.

Note: If you are not familiar with changing foreline pump trap pellets, refer to theappropriate hardware manual or search case database for replacing foreline trappellets.

Check foreline pump

(The foreline pump may be operating but not providing any vacuum)1. Shut down the MSD.

(follow the vent procedure but do not remove the column from the GC interface)

2. Disconnect the foreline gauge fitting from the diffusion pump. Do not disconnectthe foreline gauge cable.

3. Plug the fitting with a rubber stopper.

4. Turn on the MSD, the foreline gauge will still work.(This allows you to check the vacuum capability of the foreline pump)

5. Monitor the foreline pressure. If the vacuum fails to fall below 300 mtorr (0.3 torr),then the foreline pump or the foreline gauge tube is defective. Replace pump andor gauge tube or call for onsite service.

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