Pressure and Flow-rate issues

[adam.stone]

We have a system that is giving us some grief. The system has 4 evacuated tube collectors, a 119 gal dual coil tank, and uses a Wilo 30U pump, it was initially a Wilo 20U but we upgraded to try and solve our flow-rate issue. We want the flow rate to 6 GPM but we can't get it above 2 GPM. The piping is a corrugated stainless steel from pump station to collectors that was installed by others, with a head height of 20' not including the friction head pressure. We have a feeling that the piping was installed with a few sharp bends in it, which is causing our issue.

However, we did a test on the pressure throughout the system. We placed a pressure gauge at the top of the system, a pressure gauge at the bottom of the system, and the pump station(PS) has a pressure gauge built into it. When the system is idle with the pump off, the system pressure at the PS read 22 psi, the pressure at the bottom of system read 22 psi, but the pressure at the top of the system read 12 psi. When the system was active with the pump on, the pressure at the PS remained constant, the pressure at the bottom of the tank dropped to 16 psi, and the top of the system dropped to 6 psi. We can't figure out why we aren't getting a nice balance through the system, and why the pressure would fluctuate so much, particularly at the top of the system.

Any ideas?

[LucMan]

How old is the system, how old is the heat transfer fluid?
The most common problem with flow rates is Air in the system especially with corrugated tubing. Purge the system and see what happens.
Also check the specs as to what the static system pressure should be.
Check the accuracy of your gauges.