Filter Pressure


New member
Hi, I've attempted to measure my filter pressure; drilled a tiny hole (3/64) in the side of the transition to the filters and connected a tube from there to the high side of a digital manometer. I get really weird numbers though; ranges from -0.9"WC to +0.9"WC within a minute. Doesn't really make sense, would expect + pressure. Any thoughts on why the fluctuation?
Is the tube in the air flow by any chance? The designs for DIY fluid-filled tube manometers that I've seen (not digital meters) have the tube entering a small PVC chamber via a barb and with the tiny hole into the transition entering that PVC chamber from the opposite side - sometimes with cotton balls stuffed in the PVC chamber to reduce any turbulence.

Here's a link to the Wynn Environmental instructions for building the DIY version in which they talk about using a PVC pipe cap for form the chamber:
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Stumpy Nubs has a video on building your own Manometer: Video 59
His first version had the connection at the transition. He was disappointed with the results. He moved the connection to the dust box after the filters. His experience was more satisfactory. I built mine using his ideas: Clear vinyl tubing, rubber stopper, Mystery Oil and a simple analog graduated board. I like his version because it is simple and tells me when it is time to clean the filters.