housing 176 the movement of piston 180 can be reversed by simply applying pressure into annular space 226 to push down piston 180 while displacing fluid from cavity 194 through ports 222 and then 196 followed by a return into the string 218 rather than relying on a pressure differential between the inside of string 218 and the annulus 226 around it as in fig1 19 an alternative using applied pressure is illustrated in fig2 22 the parts in the housing 176 u2032 are identical to the fig1 19 embodiment what is different is that work string 230 has an internal sleeve 232 with a series of radial ports 234 that emerge between seals 236 and 238 annular cavities 240 and 242 are formed respectively between seal pairs 238 and 244 for cavity 242 and seals 236 and 246 for cavity 240 passage 248 fluidly connects cavities 240 and 242 passage 250 exits from cavity 242 through the wall of string 230 and above external seal 254 passage 252 exits cavity 240 between external seals 256 and 258 ports 234 provide a radial exit from within string 230 through its wall and between external seals 254 and 256 assuming string 230.