Thread: Measuring static pressure

Originally Posted by mwells

Today I found a video with pressure measurements on a Felder AF22:
Dust Extraction in your Workshop - YouTube
He has a gauge installed that measures Pascals. I'm used to seeing gauges that measure airflow using a pitot tube and inches of water. Usually with airflow, more is better. I am pretty sure pascals and inches of water are different units for the same type of measurement.

Yes they are, 1000Pa = 0.145 inches of water.
All countries of the world except Burma, Liberia and the US would normally measure pressure in Pa.

He says in the video that the filters work "better" after a year based on his gauge. That makes no sense to me. It seems like a clean filter would have maximum airflow and that's desirable. Am I misunderstanding something?

They certainly do work better after some use - by "better" he probably means they are more effective at filtering fine particles as they partially self block without significantly compromising air flow. This is called "conditioning" filters. I'm not convinced a year is required for them to reach useful efficiency. My testing has shown that about 2 hours of continuous use with a bucket of sawdust in the collection bag will be enough to condition filters for as far as they will be conditioned. The swirling action of the sawdust self minces into finder and finer dust that is carried up and deposited into the filters.

Originally Posted by BobL

...1000Pa = 0.145 inches of water.

More like 1000Pa = 4" w.g.

I thought 1000pa = 4.01865 in H2O?

dmorse beat me to it😳

BobL is spot on re filters that are lightly soiled filtering better than new filters. On excavators the service manuals often state, re air cleaners, “do not service too often” for that very reason. They also use filter restriction gauges.

Yes, Bob, you guess it. I don't live in Burma or Liberia.

So I have seen a kit to monitor filter efficiency that is positioned after the cyclone and measures positive pressure: Realtime Filter Efficiency Static Pressure Gauge Kit | Oneida Air Systems
Here's my understanding: You measure the pressure with a clean filter and all the blast gates open. Then later on, if the pressure rises it means the filter needs to be cleaned. If the pressure has dropped with all the blast gates open, it means there is an obstruction in a duct.

His gauge was installed before the blower, so the pressure is negative. So if the filter gets dirty, then the pressure rises (less negative pressure). If the ducts are clogged, then the pressure drops as the fan tries to evacuate the ducts.

Am I thinking about this correctly? I had only seen those static pressure gauges used as a way to measure filter efficiency. Until I wrote this out, I had never thought of them as a way to also detect clogs.

Mark

Originally Posted by dmorse

More like 1000Pa = 4" w.g.

Yep sorry about that - I have a chart of various pressures conversions above my head in my study and I read the wrong line.

1kPa is 0.145 PSI

Originally Posted by mwells

Yes, Bob, you guess it. I don't live in Burma or Liberia.

So I have seen a kit to monitor filter efficiency that is positioned after the cyclone and measures positive pressure: Realtime Filter Efficiency Static Pressure Gauge Kit | Oneida Air Systems
Here's my understanding: You measure the pressure with a clean filter and all the blast gates open. Then later on, if the pressure rises it means the filter needs to be cleaned. If the pressure has dropped with all the blast gates open, it means there is an obstruction in a duct.

His gauge was installed before the blower, so the pressure is negative. So if the filter gets dirty, then the pressure rises (less negative pressure). If the ducts are clogged, then the pressure drops as the fan tries to evacuate the ducts.

Am I thinking about this correctly? I had only seen those static pressure gauges used as a way to measure filter efficiency. Until I wrote this out, I had never thought of them as a way to also detect clogs.

Mark

Thats basically it.
I made one myself a couple of years ago , see
DC temperature/pressure meter

It uses a high sensitivity pressure sensor as used to measure the shallow water depths in washing machines.
It can measure the difference in pressure between the air pressure at floor level and the very slightly lower pressure about 3ft above the floor and then if I have closed the door to my external DC enclosure or not.
There are multiple pressure sensing points on my DC system and a 6 way manifold to enable many pressure differentials.
I had plans to use it for filter bag blockages but I don't make a lot of wood dust so I've never really used for that purpose.