Annual Calibration and Service Visit Proves the Importance of Regular Maintenance to Avoid Costly Machine Repairs - UK Missile and Defence Sector

Minor Faults 

During our site visit, it was apparent that there was a fast-flowing leak from the servo valve on one of the actuators, and the top two bolts were loose from general wear and tear.

We tightened the bolts, and the issue was resolved.  If the bolts had remained loose, there is a possibility that debris or contaminants could get into the servo valve, causing more damage to the actuator and hydraulic system of machine.

Hydraulic Power Pack and Actuator Issues 

When starting the calibrations, one of the actuators was not able to reach its maximum applied force of 50kN, instead reaching only around 10KN. The engineers found that both HPU’s had been connected to the manifold, which resulted in the oil being pumped from the smaller tank into the larger tank.

To resolve this, new hydraulic oil was pumped into the smaller pump and the larger HPU was disconnected from the manifold.

The calibration was attempted again, but this time only 20kN of applied force could be reached. The engineers checked the pressure, but it was not able to perform the required pressures, reaching only 50-60bar.

We believed there could be two possible reasons:

1. There could be an issue causing the pump to dump the oil, therefore reverting the pressure back to the tank instead of the actuator.
2. An issue may have arisen in the pump due to it running dry when both HPUs were connected to the manifold.

In addition to this, it was found that there was a slow leak within the actuator from the connection points between some of the hoses and the actuator. The hoses had noticeable damage on the outer layer from constant use over time.

Load cell issues

During this year’s calibration visit, a considerable amount of drift was noted within the 250kn load cell compared to last year’s readings. Although the results were satisfactory for the work being carried out, the amount of drift was concerning and could be an indication that the load cell had reached the end of its life span.

Following the calibration, the Phoenix engineers made several recommendations, including:

1. Further investigation is needed to examine the smaller HPU to find out why the pressure reading is so low when the pump is engaged
2. New hoses are required on the small HPU to avoid any further leaking or damage
3. Over the next six months, the load cell needs to be observed carefully to ensure that it continues to operate as expected. The Phoenix service and calibration engineers will return in six months to conduct a calibration check to see if any further drifting has occurred and replace if required.

It is important to carry out preventative maintenance checks during calibration visits, so that we can identify any issues related to machine performance and help to rectify them before a machine stops functioning completely and results in machine down time and costly repairs. 

Ryan Hart
Service and Calibration Engineer
Phoenix Materials Testing