We are using lot of external gear pumps in our industry for pumping oil. normally one pump will be running and one will be standby. if we stop the pump for a week, then while start up it is not developing pressure. but if we do priming then it will start developing pressure.

Most of the times when we open the discharge line of the pump, the line will be full of oil, and also the pump if full of oil.

due to this issue, standby pumps are not serving their purpose of working during emergency.

we are facing this issue regularly, is there any way to solve this problem,

As it is a gear pump it is capable of self priming, but it is not doing so,

kindly tell me what to do, and why is this happening again and again.