Yes on the newer motors with a case drain line that line always has to go back to tank and basically zero pressure. Case pressure makes shaft seals wear out and break cases, and misc other not nice things.

However newer motors with case drains CAN be hooked in series as long as the maximum pressure ahead of the first motor is within motor design limits.

One would NOT want to do this on motors without a case drain. However almost all newer planters have a separate case drain line as far as I am aware.

IF the motors are hooked in series, all flow has to go thru both motors. The only difference in flow and therefore motor/fan speed would be due to internal leakage which should not be significant. Maybe 5% difference in fan speeds???

Has anyone done this series plumbing of the planter vacuum motors? Seems like a waste to be using two sophisticated SCV valves to run two vacuum fan motors. Besides, I need one of those in many applications!

Thanks again for any information on this series hookup.

Jim at Dawn