The Net Work Done by  equation calculates the change in work done by a fluid per a given time, given the first tube's pressure and the second tube's pressure and the volume of fluid passing through a cross-sectional area of the tube per given time.

Reference

Young, Hugh and Freeman, Roger.  University Physics With Modern Physics.  Addison-Wesley, 2008. 12th Edition, (ISBN-13: 978-0321500625 ISBN-10: 0321500628 ) Pg 468, eq 14.13