Air Compressor flow rates question

Submitted: Tuesday, Jan 01, 2019 at 14:46

ThreadID: 137629 Views:8080 Replies:8 FollowUps:2

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smwhiskey

Serious question.

For tire inflation, Whats the maximum air flow rate that a tire valve will handle without removing the valve core?

Just seems to me that if the valve will only handle X litres/minute then having a compressor that will produce significantly more than X litres/minute is probably overkill.

Or are we getting to the stage where we'll soon be removing the valve core to increase inflation rates just like we do with the rapid tire deflators.

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Reply By: Bob Y. - Qld - Tuesday, Jan 01, 2019 at 16:45

Tuesday, Jan 01, 2019 at 16:45

Not a pyshics scholar by any means, but I’d suggest it would be a relationship between supply pressure & FAD, free air delivery. No good having 120psi going out of your compressor, if you haven’t got the volume to back it up.

No doubt it all depends where you’re pumping up these tyres? If in the Simpson, putting another 10-20psi into them probably calls for a bit of smoko, but if you’re topping off 70 x 11R22.5 truck tyres on a triple fuel tanker, you’d like the flow to be almost instantaneous!

Bob

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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jan 01, 2019 at 17:45

Tuesday, Jan 01, 2019 at 17:45

.
Bob's right. The flow rate of air from the compressor into the tyre is a function of the differential pressure between the compressor output and the pressure within the tyre. This flow is further affected by the restriction of the tyre valve and other restrictions in the flow path. The valve does not limit the air flow to a particular value but it does reduce the flow much as a resistance in an electrical circuit.

As Bob says, you may have a compressor capable of attaining a high pressure but not capable of delivering a decent volume. By the same token, it is futile if a compressor is capable of high flow volume but not being able to maintain sufficient pressure to deliver air into the tyre.

The published pressure and flow figures from the compressor manufacturers/retailers can give false impressions of the capabilities of their products. They usually quote 'maximum output pressure' and 'free-air delivery rate' neither of which provide adequate information of their compressor's practical performance in inflating a tyre at the operating pressure of typically 30 to 50 psi. The real test is how long the compressor will take to inflate a tyre up to operating pressure. Some reviews have tested using that as the comparative criteria, which gives a realistic assessment of the performance.

I do often wonder just what gauges are used in these compressor tests. Pressure is pretty easy to measure but air flow does require somewhat more complex instruments to achieve a reasonably accurate determination. I suspect that they may simply compute the theoretical air flow by multiplying the piston displacement by the shaft revolutions, or even worse just pulling a suitable figure out of the air. (Tell 'em what they want to hear!)

But to address your actual question..... removing the valve core would always improve the air flow just as it does in deflation, but probably without as much benefit. In both deflation and inflation the flow rate will progressively decrease as the process proceeds. However, with a decent compressor, the differential pressure can be maintained at a higher value than when deflating so the flow is also better maintained and it may not be worth the trouble of valve core removal when inflating. Better to purchase a compressor which is capable in the first place.