So far no problems with the pumps. At this stage I wouldn't worry about the pressure.
One question for you.
I posted this (reply #2)
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1237599919
Is this H bridge fine for the motor?
http://www.sparkfun.com/commerce/product_info.php?products_id=8902