To avoid high pressure,I made a hole on the cap of the
reservoir,glued on with epoxy,a small plastic tube and curved the tube of
360 °,fixing the loop with a tie wrap.Till now it works fine

Alain,

 

Nice solution.  The pump reservoir needs to breathe.  If the reservoir is overfilled, the fluid will be pushed out the breathing hole - a very nice mess.  I tried a "standpipe" breather and  if there was too much fluid, it still came out.  Now, I have a small drilled hole in the filler port and I keep the fluid to the minimun necessary -- no mess.