I am looking at an application where we are using fixed speed gear pumps (Viking) to pump fuel additives to tanker loading bays. The existing system seems completely over-engineered and I would like to design something simple and effective, in terms of pump protection. There is no internal relief valve on the pump. There is an external relief valve mounted directly on the discharge with its outlet piped to the suction side.

The pump is connected to the additive storage tank.
The application will start the pump when there is demand for the additive at the additive injector units. When the demand stops, the pump continues to run for a few minutes (existing procedure, I believe there is a minimum run-time to limit the amount of stop-starts) and the end of the line is dead-headed, there will need to be some sort of pump protection, as I do not believe the relief valve should be used as an operational flow device, but only a safety device.

My first question is: Is a re-circulation line back to the tank the best way of provding the pump protection?

My second question is: How do I correctly size the line? If it is too large, it will be pumping too much liquid back to the tank, instead of to the additive injectors. If it is too small, when the line is dead-headed, it will not allow enough flow back to the tank, and probably lift the relief valve anyway.

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