I was having major problems with them as well trying to create a closed loop system with the LHE. They seem to work fine when they're near or at full capacity. And so the solution in my case was just to keep adding more coolant fluid as a buffer. Once everything is up to a consistent full speed and efficiency, the pipes are wonderful, however with processes involving large amount of flowrate variation I find them to be so unreliable. Literally had 100,000+ coolant sifting around in the pipes slowing making their way over to where they have to be.
Just curious, how exactly were the pipes limiting your system?
My setup was as simple as it gets... I calculated the amount of steam required for 85% efficiency LV Steam Turbines to run at full blast, which is 2 steam per EU divided by 0.85 times 32 EU/t, or approx. 75 mb/t of steam required per turbine, which converts to 1500 L/s of steam. I run 6 of these turbines, so I need 6*1500 steam, or a GT Fluid Conduit capable of 9000 L/sec flow rate. The Large Steel Fluid Pipes can carry 9600 L/s, so I ran that as my "trunk line" directly connected to a Railcraft Tank Valve, on the bottom side of the tank so I don't even need a pump.
Off that main trunk, I put a shutter set to "output only" mode, then I place six Small Steel Fluid Pipes (capable of 1600 L/sec flow each) off the main trunk line connecting to each of my six LV Steam Turbine. I also placed a shutter along every segment of the main trunk, set to "output only" to prevent backflows and "sloshing" inside (as per the Chloe tutorial video for GT Fluid pipes).
So the math on my flow rates works out perfectly, I have 600 extra steam per second in the system (so in other words, the system is "full" without any room in it). And yet... at the end of the main trunk, those LV Turbines do not get enough steam. Even tho the math shows an excess capacity, and even tho I have a shutter everywhere I can. GT Fluid pipes simply do not work in the manner I need them to work. It is possible, I suppose, that the problem lies with me and my methodology... but in the end, GT Fluid Pipes are not worth the headaches. Not when there is a headache-free solution available (Ender IO conduit).