Search and rescue robots often use tethers to provide power and communication, but tethers get caught on debris and small robots have difficulty with the added drag of the tether. This work investigates a self-actuating tether capable of remaining free while traversing obstacles. We present a physical model of the pressure transients actuated tether. The model relates forward motion of the tether (independent of a dragging force) to the relevant design parameters of hose stiffness, flow diameter, tether length, applied pressure, and valve selection. We present an experiment to test and validate our model. The experimental results correspond within 15% to the expected values from our analysis and also validate the functional dependence of our model on the design parameters