The LO unloader senses and maintains pressure at the most remote bearing at what setpoint?

• A. 15 PSIG
• B. 14.5 PSIG
• C. 12 PSIG
• D. 20 PSIG

Answer: (B)

This item tests how a lube-oil (LO) unloader keeps the minimum lubrication pressure at the farthest bearing. The pressure at the most remote bearing is the critical point because it experiences the largest drop from the pump to the bearing due to line losses and flow restrictions. By sensing and holding the pressure at that location, the system guarantees all bearings stay adequately lubricated under varying conditions.

Holding the remote bearing at 14.5 PSIG provides enough oil film to protect bearing surfaces during normal operation and transients, while avoiding unnecessarily high pressure that would waste energy and stress components. If the remote point fell much lower (around 12 PSIG), lubrication could become insufficient during changes in load or temperature. If it were much higher (like 20 PSIG), it would push more oil than needed through the system and could lead to excess heat and seal wear.

So, the setpoint of 14.5 PSIG is chosen to ensure reliable lubrication at the most distant bearing under all operating conditions.