View Full Version : Give me the scoop on air-flow meters...

08/15/2006, 04:04 PM
Dual Oceanrunne 3700s on a 8"x8" cube skimmer. What should I be looking at for an air-flow meter? Dwyer makes sooo many models alone. I also remember reading a conversation (I think it was with Barr) about how some meters are not good because they restrict too much of the flow (since our air intakes are somewhat passive unless we are using air pumps) and so they give improper readings.

What do I want to use? Something in the 5-50 range I hear...but what model will be the most accurate?


Roland Jacques
08/15/2006, 04:45 PM

i like have the RMB series better than what most hobbiest have, the RMA's 2"scale. The 10"RMC series are the most accurate. also i would recomend LPH over SCFH(more common in our hobby) and the conversion is questionalbe , i dont no why. try to pick a size that will hit most of your test subjects right in the middle of the scale or higher. i use 2 , One 0-20 scfh and one 5-50 scfh that way i stay the accurate reading range.

08/29/2006, 09:28 PM
Well, I got my hands on a RMC 10-100 SCFH model (the RMC-122-SSV). Too large for most of my needs unless I hook up both OR3700s at once to it.

One thing to note is that the RMC series doesnt have the smaller ranges like the RMA and RMB. I think I will pick up a RMB-51 (2-20) as well for my smaller mixing pumps.


08/29/2006, 09:35 PM
Roland not sure what you mean by questionable conversion from SCFH to LPH?

A liter and a cubic foot are very finite volumes, and an hour is a very finite amount of time. The conversion is direct (simple multiplication).


08/29/2006, 10:20 PM
Thats what I was thinking too, but perhaps the 'S' part which suggests the 'standard' part (as in the PV=nRT) is a qualification that could modify the comparative values. Im going with what you said Bean, and, FWIW, it seems like alot of people are starting to just use SCFH anyways, but I was going to look into what the 'standard' designation might mean as far as a fair conversion. FWIW, Im sure the small restriction of the meter itself plays a larger role though.

08/29/2006, 11:07 PM
The "standard" refers to Standard Conditions... or standard pressure standard temperature. The same as any time you talk about pressure. The S is used to designate this as opposed to possibly being ambiguous with regards to reading gauges and the like. It is not used with LITERS... as it is infered with the metric system that such measurements are corolated to standard temperature and standard pressure (1 bar, 273.15 Kelvin)

A scientist could give you a much better explanation... something that we really don't need to have, as we are converting between two standard readings at the same pressure and same temperature.


08/29/2006, 11:09 PM
If yuor dying to learn more...

There is a good history of STP parameters and how they were derived and have evolved. You know you wanted to revisit Avagadro and his number....

08/29/2006, 11:25 PM
Yeah, its been a long time since I have had to look at Ideal Gas Laws... what... frosh chem 105 or something? Lol. I am familiar with STP, but it doesnt say how it might explain an problem with LPH to SCFH... I suppose as long as we assume LPH to be STP as well... I suppose the idea that a flow meter itself creates/relies somewhat on pressure to get a reading on flow might have something to do with it. I think that was the concern of others that I remember reading earlier in other threads... some meters themselves having too much restriction to get an accurate reading.

Im sure it doesnt matter in the end... I see more people just comparing SCFH anyways on comparable Dwyer meters... so as long as everyone is using the same means of measure... its all the same in the end regardless.