Put two back pressure regulators in parallel in a fluid application. They are using one as a primary and one as a back up in case the first one fails. They were not meant to run concurrently. So after a year of service with no problems they have decided to turn both BPR's on at that same time. The setpoint pressure on one is 45psi on the other is 55psi. When one is on you get 45 psi, when the other is on you get 55psi when they are both on you get 25psi. I have no idea why this is the case. I would think that it would take the path of least resistance and still be 45psi. Generally the set pressure with a BPR is the cracking pressure. 
Pressure experienced in the system should not much exceed 45 psi. They should act with proportional only control but the proportional band should start at 45 psi.  Typically the proportional band is about 10% of the range, so if these are adjustable to 60, the PB would be about 6, so cracking at 45, full open by 51 on the first one. 
In a first-ever event:  These are not like parallel resistors,if you want an electrical analogy, but more like parallel zener diodes.  The breakdown voltage is analogous to the setpressure, and there should be no flow until the pressure reaches the magic number.  UNLESS THE BUTTERFLY VALVES ARE STUCK OPEN.
This is weird, and I think you will find that they are using a remote sensing line on the high-pressure side of a partially-closed balancing valve or some such strange piping effect.  Verify that the sensing point is actually at the point of interest.

MORE NEWS