Rotating spray balls require a flowrate AND pressure for optimal operation. One condition could be 10gpm/30psi, while another could be 12gpm/40psi.

Is there a way to control both flowrate and pressure with a positive displacement pump?

I'm not sure how to increase the system head and maintain it, especially when I assume that the spray ball is open to the atmosphere...

 

A positive displacement pump is essentially a constant-flow device, with discharge pressure building up to whatever is needed to push that flow through the external resistance. Flow is usually directly proportional to speed.

So you could vary the pump speed to give the required flow rate, and have a control valve in the pump discharge to set the pressure.

You will need a pressure relief valve in the discharge in the event of the pressure control valve failing closed.

 

Unless my command of physics has abandoned me, the sprayball will act like an orifice, in other words the pressure will dictate the flow. The only way to control both would be to have some way of changing the size of the individual spray nozzles. Or am I missing something?

Regards
cww