120vdc controls

Hi, I registered here to see if anyone could help me with a problem I am Having. I purchased a dc welder (lincoln sa 200) that has 120vdc output for operating ac/dc power tools. The welder uses a solenoid to speed up the engine for welding. I have connected another solenoid valve to bring the engine to operating speed but I need the valve to open only when a power tool is turned on. I thought maybe a current sensing switch would do the trick but cant find much info on them. The welder's voltage range is 90 to 130 and the valve is 120v 7w. Hoping to buy the parts and hook it up. Thanks for your help.