Direct Acting refers only to solenoid valves. They use a spring to help actuate the valve, and thus do not need a minimum pressure to activate. This can be very important, depending on the system. For instance, if clearing out water lines, it may be pumped in short bursts, so there will not be constant pressure. Most of our solenoid valves are of the direct acting variety, because of the convenience that it affords. Take a look at our wide range of direct acting solenoid valves below.