If you've read your operating manual for this vacuum pump, you'll see that it isn't intended to be switched on and off more than 3 time an hour. Unless your cycle time is more than 20 minutes, you'll be putting additional wear and tear on the pump. If you do a search for Mac valves, you'll see that they are essential a 2 way valve. In the case of your vacuum hold down system, when the valve is in one position, it is channelling vacuum to your hold down device from the pump to hold your part. When it is switched to the second position, it is isolating the vacuum from the pump and venting the vacuum fixture to atmospheric pressure (releases the work piece). The pump should be running all the time until you've processed all your parts. The valve is typically operated electrically and can be initiated by G code. The folks who set up the robot station should have the capability to do this for you.