SUBJECT: Troubleshooting and Repair of Vacuum Leaks.

PROBLEM: Problems have been reported by UPS commissioning technicians. UPS units in storage for six months or greater have had problems achieving a proper vacuum on the flywheel. Technicians report that the black polymer elbow (suction side) of the vacuum pump (Cat p/n 180-6246) is causing the leak. Replacement of the elbow has achieved acceptable results. However, Failure Analysis Reports do not concur with these results. Failure Analysis Reports do not show any structural defects in the elbow which would cause the vacuum leak.

WARNING: Personal injury or death can result from high voltage.

When the flywheel is spinning, the following components are energized: the bus, the armature leads, and the flywheel armature fuses.

High voltage and current are present when the Uninterruptible Power Supply (UPS) equipment is in operation.

Improper test equipment can cause a high voltage shock hazard to the user.

Make sure that testing equipment is designed for and correctly operated during high voltage and high current testing.

SOLUTION: After review of the Failure Analysis Reports, the o-ring seal of the polymer elbow (suction side of the vacuum pump) is the suspected vacuum leak. The o-ring seal is concluded to have dried out due to the extended storage period of the UPS. Re-lubricate the o-ring seal on both sides of the elbow using the approved High Vacuum Grease (Cat p/n 6V-2055).

As a precaution, when removing foam shipping materials surrounding the vacuum pump assembly, do not exert any undue force on vacuum hoses. Hoses could be entangled within the shipping material. This could result in loss of a proper seal at the o-ring.

In order to provide further assistance in troubleshooting a vacuum leak, the following information is provided.

When the system is first energized, a vacuum reading of 9999T could be displayed. This is normal. This value indicates the interior flywheel atmosphere equals the exterior atmosphere. This value will change as the vacuum inside the flywheel changes. The next probable value displayed is 2400T. This indicates that the flywheel is achieving a vacuum draw, but the vacuum is out of the range of the sensing device.

A vacuum reading on the flywheel of 30mTorr or less is proper. A flywheel, which has been commissioned and operated for a week can have a vacuum reading of 18 to 23mTorr.

When performing the "flywheel preheating process", an initial vacuum reading of 50mTorr or greater is expected. The display an alarm (yellow light) when the vacuum reaches 60mTorr. The alarm status will change to normal when the vacuum drops to 57.3mTorr. The UPS vacuum reading will cycle up and down during the preheating. This is normal. (Note: the Preheat processing time cycle is 42 minutes and must be complete the entire period. Refer to TIBU3818-00). If the vacuum reading is above 30mTorr after completion of the Preheat cycle time, check the armature temperature. If the armature temperature is 55 to 60 deg C, the flywheel is attempting to achieve a proper vacuum level. Allow the vacuum pump to continue working. The high vacuum reading is caused by the elevated armature temperature. The elevated armature temperature evaporates moisture out of the flywheel chamber, which directly affects the atmosphere inside the flywheel chamber. Extend the operation time of the vacuum pump prior to proceeding with the calibration procedures. If armature temperature is below 50 deg C, the flywheel has a "vacuum leak". Troubleshoot to find the leak.

Confirm the vacuum pump control switch positions. Set the gas ballast control switch to zero. Turn the mode selector switch to the full clockwise position.

To identify a vacuum leak, check the vacuum pump oil level sight glass. Determine if any "air bubbles" are floating in the oil. The presence of air bubbles indicates that either exterior air has been drawn in or excessive moisture is present inside the flywheel chamber.

To confirm the vacuum leak location, use a spray bottle of Isopropyl Alcohol and spray the target area. After spraying the target area, monitor the vacuum mTorr reading. If the vacuum reading fluctuates, the vacuum leak has been located. If the confirmed target area is a seal, examine the seal closely for deformation and then re-lubricate the seal sufficiently with High Vacuum Grease (Cat p/n 6V-2055). Apply just enough lubricant to cover the entire surface area of the seal. Do not over lubricate the seal.

Do not handle components with o-rings (such as RPS Sensor, Bearings, SAE Plugs, etc.) with bare hands. Wear rubber latex gloves. Oil residue from the skin can result in an inadequate seal between the o-ring and the component.

Areas for potential vacuum leaks are:

Vacuum Pump Assembly. This includes attached hoses, fittings, couplings and the vacuum oil itself.

The SAE plugs in the flywheel housing.

The RPS Sensor Seal.

Top and bottom flywheel bearing Seals.

The Static Ground device Seal.

The Vacuum Sensor Seal.

These components and associated part numbers may be useful in the troubleshooting and repair procedure. See Table 1.

Table 1.