We operate an LM2500 and are experiencing a trip due to sensor fault on the synthetic supply pressure transmitter, the transmitter goes over rang. Sometime shortly after reaching idle speed the lube supply pressure is observed to increase over a two minute period from our normal operating pressure of 4.5Bar to greater than 10.5Bar (transmitter over range). This appears to coincide with cold (Ambient) oil returning to the tank via the thermostatic control valve on the scavenge return, the oil cooler is some distance from the unit. We only experience this on cold days (below 5DegC), otherwise conditions remain steady. I’d like to understand why the internal relief on the lube pump does not maintain the pressure around 6.9bar setting and therefore how we can see pressures on the discharge of 10bar. Are there any other system pressures that could cause this increase in pressure other than a change in viscosity of cold oil, could this cold oil cause a change like this? Thanks for any replies.

 

You may need lube oil preheat when its cold.