Water System Back Pressure

We have discovered a low flow condition on a couple of our machines that appears to be back pressure from the return line. I get very good flow when the circuit is open looped(3 gpm), but when close looped it drops to .6 GPM. This is on a circuit that is not running through the mold only a line running from one manifold to the other.

Any thoughts on what to check? The machine next to it has +2 gpm under the same closed loop condition so it points me toward the temperature control unit more than the system, but I'm sort of running out of ideas.

Water will always flow the path of least resistance, This maybe a situation where you don't have enough pump to get the water to where it needs to go at a good pressure. However since your needing a solution I would look for water circuit, possible another machine that is as free flowing as a river. That water circuit and it could be more then one needs to be restricted limiting the amount of water it passes. As you evaluate your system, its important to open the valves that supply water to machine all the way open and only use the return line as a way to restrict flow. When you choke off or restrict flow on the supply side you restrict water pressure as well as flow.

Thanks Bryan, When I am testing the circuit all the other valves to the mold are turned off to provide max. flow to the test circuit. All valves to and from the temperature control unit (Machine A) are fully open. There is no restriction to the circuit when open looped. My thought is that either the entire system that feeds all 10 machines is creating a back pressure or that it is specific to this machine (Machine A) or brand of temperature control unit. I think it is the latter, because the machine next to it (Machine B) with a different temp. control unit has very good flow, but a machine on the opposite side of this one (Machine C) has the same temperature control unit brand and it also shows very low flow.

Based on what you are saying I agree it sounds like the temperature control unit. Is it possible to swap the unit with the one from machine B? It is interesting that two same brand unit have the identical issue. If not, then you may want to check the Vent valve on the control unit to see if it is clogged up. That's a fairly common failure but more often then not it will stick open and not heat properly. My next thought which is easy to confirm is to check the pump rotation and make sure it's going the right direction. Let us know what you find.

Is this machine in good working order?