[galaxy-dev] Run a tool's workflow one by one ?

Hi ! I have a big workflow and sometime when I launched it, I got an error message for some of my tools : unable to finish job. I think it's maybe Galaxy ran multiple job so I get this error message. I'm looking to run my workflow "step by step". For example this workflow: http://hcsvlab.org.au/wp-content/uploads/2014/02/PsySoundTest1.png I'm looking to run Hilbert THEN FFT THEN SLM and no Hilbert, FFT and SLM at the same time. Is it possible to make a workflow which wait to finish a job before run an another job ? Thanks