What causes the power stering fluid to shoot out the reservoir?

What is your question?

I have a 1999 ford taurus and the power stearing got hard so I checked the fluid and it was low so I added to the rigth level when I started the car it was oj but when I shut it off it started shotting power stearing fluid out the rereservoir left it at that level and its real hard to stear I already replaced the power stearing pump please need a hint or some info thanks?