i wouldnt belt it in mate because you can damage the rubber. never use oil or anything which will soften or break down rubber. the way to test is fill the mixing pot with water as you would at the beginning of a spray. make sure the tester tap is open, push the green button so water comes out of the pump tester, then shut the test tap of and you will see the bar presure rise, after a couple of seconds push the red button to stop the machine. The presure dial will now start to drop a little and then stop, its needs to be above 7 bar and also hold it for a couple of min. if the presure drops and wont hold then the R&S needs changing. A new R&S will be around 30 bar. hope this helps