Does the sight glass go before or after the dryer?

Should a Flow Indicator Go Before or After the Filter on a Mold?

You're battling inconsistent parts and hot spots on your mold. You suspect poor cooling, but your flow indicators say everything is fine. You're losing time and money chasing a phantom problem.

Always place the flow indicator after the filter. This simple rule ensures you are measuring the clean, actual flow entering the mold circuits, and it protects the indicator itself from debris that could give you a false reading.

I learned this lesson the hard way early in my career. We had a large, multi-cavity tool that kept producing parts with warpage on one side. The setup sheet was perfect, the process parameters were dialed in, and the flow indicators on the cooling manifold showed beautiful, steady flow to all circuits. We were stumped. For two days, we tweaked the process, blaming the material, the machine, everything but the mold. Finally, out of pure frustration, I disconnected a return line and barely a trickle of water came out. The flow indicator, a simple ball-in-tube type, was completely jammed with rust scale, holding the ball in the "good flow" position. The indicator had been installed before the filter. The filter was doing its job and was completely clogged, but the lying indicator on the supply side told us a different story. We moved the indicator to after the filter, and we never had that problem again.

Why Does Putting the Filter First Protect Your Entire Process?

You know filters and flow meters are important parts of a mold cooling system. But does the order really matter if they are both in the line somewhere?

Yes, the order is critical. Placing the filter before the flow indicator and the mold is not just about keeping things clean; it's about protecting expensive components and ensuring your data is trustworthy.

A filter's only job is to capture contaminants. Placing it first means it protects everything downstream: the delicate, easily-clogged cooling channels in your multi-thousand-dollar mold, and the sensitive, often plastic, flow indicator that you rely on for diagnostics.

Think of your cooling system as a supply chain for heat removal. Water from your plant, whether from a chiller or a tower, is never perfectly clean. It contains rust, scale, and sometimes even biological growth. If this debris enters the mold, it can clog the small cooling channels, creating hot spots that lead to warped parts and cosmetic defects. The flow indicator, especially a visual one with a spinning impeller or a floating ball, is also very sensitive to debris. A tiny piece of scale can jam it, giving you a completely false reading. By placing the filter first, you create a protected zone for your critical components. The filter acts as a security guard, stopping trouble before it can enter the most important parts of the system. This ensures the water reaching your mold is clean and the data you see on your flow indicator is real.

The Logic of Component Order

Can a Flow Indicator Also Tell You When to Change a Filter?

You don't have pressure gauges on your cooling lines, and you hate shutting down production just to check a filter. Can you use the flow indicator to monitor the filter's health?

Absolutely. A gradual decrease in flow over time is a classic sign of a filter slowly getting clogged. By monitoring your flow indicator, you can move from reactive to predictive maintenance.

A flow indicator placed after the filter is a perfect diagnostic tool. As the filter element collects debris, it becomes more restrictive. This restriction reduces the volume of water that can pass through, which you will see as a drop on your indicator.

The best way to use this is to establish a baseline. When you install a new, clean filter, make a note of the flow rate shown on the indicator for each circuit. You can even write it on a tag right on the manifold. Let's say your baseline is 4 gallons per minute (GPM). Over a few weeks of production, you notice the flow has dropped to 2.5 GPM, even though all the valves are set the same. This is a very strong signal that the filter is clogged and causing a significant pressure drop. You now have a data-driven reason to schedule a quick shutdown to change the filter element, rather than waiting for bad parts to appear. For an even more advanced setup, you can place one master flow indicator before the filter manifold and keep the individual ones after. A large difference between the "master" reading and the sum of the individual circuits points directly to a system-wide restriction, which is almost always the filter.

Diagnosing Problems with a Post-Filter Indicator

Conclusion

Always install your flow indicator after your filter. This protects your mold, ensures your diagnostic data is accurate, and allows you to predict maintenance needs before they cause production problems.