In 1977 band replaced their Binson Echorec 2 units with rackmount digital devices by MXR. MXR Digital Delays were usualy shipped with one 320 ms delay chip while the expansion model - containing four chips - produced up to 1.28 seconds of delay. I don't know about Waters but Gilmour's rig, for instance, included two MXR Digital Delay units and two upgraded MXR Digital Delay System II units working simultaneously, each with the different tap.more
I have several of these units since buying one working unit is as much as buying four bad units. This one is the System I, which came out in 1976, until it was superseded by System II. Watch out as these units can run hot, affecting your delay time!