The valve between the 3-way motorized valve and main return pipe is only for isolation purpose (isolation valve) for disconnecting the coil assembly from the main lines for maintenance issue. The isolation valve can be either gate valve or globe valve, but globe valve is fast closing valve versus the gate valve and it takes much less time for opening or closing because the distance between the seat and stem (disc) is about 50% shorter than the gate valve for full closing. This is a reason that globe valves are preferred to use for isolation valve, but gate valves are cheaper in price.
