The Alnor Velometer Jnr

Posted on May 23rd, 2004 in Opinion by Julian Edgar

I have always liked gauges and instruments. My first car – an air–cooled Honda Z – gained an oil temperature gauge. It was a daring move for someone who knew nothing about cars. Subsequent cars were equipped with gauges including auto trans temp, intake air temp, boost pressure, oxygen sensor output and intake air restriction.

And my interest in instrumentation hasn’t been confined to those gauges normally found under the ‘automotive’ tag. Instruments from completely different fields also often have a place in car modification. The Dwyer Magnehelic gauges, for instance, are useful in assessing aerodynamics, radiator and intercooler flows, and pressure drops through intakes. (For more on using the Magnehelic gauge, do an AutoSpeed site search.) 

But the trouble with non-auto gauges is that in the past they have often been very expensive. Primarily because they’re made in small numbers, these specialist gauges from other industries have often retailed for more than they’re worth. More than they’re worth for automotive use, anyway.

But on-line auctions have changed all of that. On eBay, for example, you can find the most obscure instruments and gauges at bargain prices. They’re mostly being sold by people who don’t know what they are, what they do, or how they work. So that makes the starting price low. And if they’re really obscure, then bidding will be lukewarm too…

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Take this Alnor Velometer Jnr.

This what?

Yeah, I’d never seen them before either but when one popped up on US eBay and the bidding was stalled at about ten bucks, I just had to bid. Throw in airfreight from the US and for about AUD$45 I had sitting on my desk what looked to be a brand new instrument – complete with calibration certificate.

But what does it do? The Velometer is a very sensitive device that directly measures the speed of air movement. To give you some idea of how sensitive it is, the full scale on this particular one is just 200 feet per minute air speed. Yes, feet per minute, not feet per second.

I admired, it, blew in one port (instant full scale needle movement!), admired it some more, measured the intake and exhaust cooling flow speeds on my PC, admired it, placed it on top of one of my monitors and watched the faint breezes through the room move the needle, admired it….

After about a week I thought I might do a web search on the instrument. One of the first sites I found had a retail price – try US$345! Hell, I thought it was a pretty nice instrument….

The Alnor site itself – – says of the instrument: “The Velometer Jr. Anemometer is a palm-sized meter for fast, accurate air velocity measurements. The meter is compact, direct reading, and requires no attachments. You simply hold it in the air stream and read the displayed velocity measurement on the analog scale.”

Along with the big brother Velometer 6000AP, it is used by “contractors, balancing professionals, plant engineers, and industrial hygienists.”  The Velometers “are used for HVAC balancing, static pressure measurements, energy audits, and more. Since these instruments using a swinging vane measuring technique, they do not require a power source or batteries.”

So it’s a nice bit of gear. But what use is it with cars? At the full retail price I’d never recommend it for anything. But for the prices that they’re going for at web auctions, well….

I’ve already used mine twice.

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The underbonnet intercooler on my Maxima V6 turbo uses a fan to force air through it. We’ve covered in AutoSpeed the fitting under the ‘cooler of a very powerful centrifugal blower, but unfortunately that particular unit proved to have a short bearing life and had to be retired. (It originally came from the tip, so I can’t complain too much!) Its replacement was a smaller axial fan driven by a radiator fan motor. (The fan blade assembly also came from the tip.)

The fan is run at slow speed when the vehicle speed is low and at high speed when a temp sensor buried in the intercooler fins indicates that the ‘cooler is getting hot.

The previous centrifugal blower moved so much air that even with the car stopped and the blower running at low speed, it was obvious that air was being drawn in through the bonnet scoop. But with the less powerful fan – again being run at a slower speed when the car is stopped – it wasn’t nearly as clear whether there was a definite air movement in through the scoop.

Enter the Velometer.

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Placed in front of the scoop with the car stationary but the fan running, the outside air being drawn in through the intercooler core can be easily measured. As this pic shows, it is around 150 feet per minute. That’s not huge, but it at least shows that the heat chimney effect of the hot engine bay (which would tend to cause hot air to flow out through the intercooler and scoop) is being well and truly overcome by the fan. (But what about when the electric rad fans are running? Think about it….)

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And talking about chimneys, what was happening at the newly-installed bonnet vents placed above and slightly behind the radiator? Well, even without the radiator fans running, after the engine had warmed up air was flowing out through these vents – in fact, again something like 150 feet per minute of flow. (Note that the Velometer can be orientated any way up and still read accurately.)

The Velometer is useful anywhere you want to check for very subtle air movements. Sure, that might not be too often, but for under AUD$50 for an instrument that will literally last a lifetime, you can’t go wrong.

Now, I wonder how much hot air is flowing through the intercooler and out of the bonnet scoop of an Impreza WRX when it’s stopped….?

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