What do I need to understand about PSI for a small air compressor?

I know that PSI means pounds per square inch but that doesn’t really translate to anything meaningful to my real life.

I’m interested in acquiring a compact air compressor for two primary reasons:

  1. Inflate my bike and bike trailer tires, maybe a few air-filled pieces of exercise equipment.

  2. getting a cheap blowgun like this or this to use instead of a can of air to blow dust out of corners and delicate bits.

I bought one last week that was $9 - and then I learned that it had a cigarette-lighter power connection only. Well, I don’t own a car anymore. After researching adapters, I learned that no easily available cheap adapter has enough “amperage” (?) to run even a small compressor, they are designed for cell phones and the like.

So I returned the tiny cheap compressor and went searching for one that has a normal house-current plug on it. (110 volt? 120 volt?) Found some. Found one that seems just fine. Even though it seems unnecessarily rude to only make super-chea in cig-lighter versions, but whatever…

Anyway, in reading the comments, I see things like this:

Not able to “handle” the 70 PSI required for bike tires??? But it should do fine with normal tire pressures up to 38 PSI? What does this mean? That it could turn out to be unable to inflate bike tires because…?

Can someone clarify this for me, very simply?

This is specifically designed as a tire inflator.
Its not going to work for an air gun. You need a compressor that has a tank for that (or add a tank to this one).

You compress air by pushing it into a fixed volume. The more you push in, the higher the pressure. The higher the pressure, the harder to push more air in. I think a lot of the smaller compressors use a vibrator driving a piston. They only have so much power and deliver less and less compressed air each stroke . You will have a curve of flow rate against psi with the flow going down as the pressure goes up. So a compressor will deliver more air at 38 psi than at about twice that.

Part of it depends on the type of motor and compressing mechanism. Some just draw more power as the pressure goes up. Factories often have large synchronous drive electric piston compressors. Such a compressor pulls in a fixed volume of atmospheric air every stroke and shoves it into the compressed air system drawing whatever current it needs. Other systems take in less air as the going gets tougher.

Car tires take a larger volume of air, but less pressure than many bike tires. Atmospheric air is about 15 psi. To reach the 30 psi gauge many tires take requires a 3 to 1 compression. You have to push twice the volume of atmospheric air in addition to the the air in the tire to reach 30 psi.

I have a cheapo tire inflator that seems to “struggle” pumping up a car tire, but that is because, as you say, car tires hold a lot of air. I had a slow leak for a while and in the time it took to put 5 psi in I could go have a sandwich. For my daughter’s little training wheeled bike I can go from 20 to 40 psi in about 30 seconds. I think you will be fine Stoid

Note also that the pressure for bike tires varies tremendously with the type of bike. A mountain bike might only take 30 or 40, but a road bike can go as high as 120. And any given pump will have some maximum pressure that it simply can’t go above.

I know this isn’t the answer you are looking for but really, a good hand bike pump does the job so well and so efficiently, I’d struggle to see why you’d bother with an electric pump.

The manufacturer’s website says it goes up to 150 psi, although it is troubling if it really doesn’t mention that on the box or in the manual. Who knows where the sales guy that wrote that got the info from? He could have just based it on the gauge.

You don’t want to use air from an air compressor to blow out things as you suggested unless you add a filter and dryer to the mix. Compressed air has a lot of moisture in it and can also pickup oils and such from the compressor. This all would be bad news if sprayed inside some delicate electronic components.

You are looking at the wrong specification… You should be looking at the SCFM (US) “Standard Cubic Feet Per Minute” rating of the compressors. Inflaters have an extremely low SCFM delivery, and won’t develop any pressure when used with a blowgun. Well, not without a tank and a LOT of recovery time.

Look for a small “Pancake” compressor, or something similar in the catalogs. About $150 to $350 or so. You won’t need a full blown dryer, but you should have an air-water seperator and filter on it

So far this has not proved true. I can’t even get the things to stay on and I’ve tried two. Maddening.

That’s gotta be piss poor pumps or a lack of understanding how the locking lever works. I’ve got several friends who use bike pumps with no problem. This Blackburn model is well regarded; I have one and it stays on like a champ.

I can’t help but feel you’ll be disappointed with the type of compressor you’ve mentioned. It’s shown with a car tire, motorcycle tire, and basketball, but very conspicuously has NO reference to bicycles or their tires. I suspect the company knows it’s not really suited for bike tires, and I can assure you it’s not suited for blowguns. At about half the price, a good bicycle floor pump is likely to be a much better purchase.

The methods of attachment of a hand pump are in principle no different to those for motor driven pumps. You don’t have a pump problem you have a connection problem. If buying a motor driven pump happens to solve your problem, that will be more luck in happening on a connector that suits you than anything inherent in motor driven pumps.

So what’s the secret to the blowgun?

Curare and inhaling before you put up to your mouth!

CMC fnord!
Stand-up comic Jesus kills a kitten whenever a straight-line is left without a response. Comedians 2:14

Already answered:

As a rough explanation: What air compressors do is compress air – squeeze it down like you might squeeze a spring. Just like there’s a limit to how far you can squeeze a spring with your bare hands, there’s a limit to how much any air compressor can squeeze the air. That limit is the psi rating of the compressor.

In addition, though, air compressors come in different sizes (or run at different speeds), meaning different compressors will compress larger or smaller amounts of air every minute (they have different flowrates). This should be intuitively easy to grasp: an air compressor the size of your bedroom will be able to suck in more air (ie, the flowrate will be larger) than one the size of your toothbrush.

For every application, you’ll require some different combination of pressure and flowrate. Inflating a road bike tire might require a relatively high pressure, but very low flowrate (because the bike tires are low volume). A blowgun require little pressure, but a substantial flowrate, because you want to move air quickly.

Other applications, say inflating a truck tire, might require *both *higher pressures and higher flowrates. A problem here is that producing both pressure and flow requires a lot of power, and that means the air compressor will be large and expensive.

For you, it sounds like you don’t need high pressure *and *high flowrate, it sounds like you need high pressure *or *high flowrate. I suspect that you’ll get better performance for less money by looking for two dfferent systems: one for your bike tire and one for your blowgun.

Large enough volume capacity of air. Think of how much air you can blow through your lips, and for how long, after taking a deep breath. Now compare the volume of your lungs to the volume of the pump cylinder inside this device – it’s probably smaller than your fist. On top of which this style pump doesn’t have a reservoir or tank to store any compressed air. The pumps that do are quite a bit bigger and quite a bit more expensive.

I’m only talking about the kind of blow you get from cans of air. The air being “blown” out of a small pump isn’t that forceful? Seems like it would be…maybe it would peter out quickly, but so do air cans, actually. A few good blasts and they lose force, you have to wait a while.

I LOVE the way air cans work, but I can’t stand the incredible waste and cost of them- it seems strange that the same action can’t be created in a handy little compressor…

I think there are rechargible air cans. As mentioned many posts back, you need to be careful of moisture and oil in conpressors. Mostly smaller ones, but some air compressors are oilless. Inherent in compressing and cooling air is raising its relative humidity. That can lead to condensation and blowing water out. There are filters and traps to remove oil and water.

One way of converting a little high pressure air into a larger volume of lower pressure is to have holes in the nozzle allowing the venturi principle to suck in more air. OSHA forbids solid blow gun nozzles.

This type of pump compresses air in very small volumes (that’s the low flow rate mentioned above). The specs say it will fill a car tire to 28 psi in 2½ minutes. My shop compressor (60 gallon tank, 120 psi) can do that in 15 seconds, and can also operate one of those blow guns at full open all day long, and that’s at 100+ psi. It’s somewhat like the difference between a faucet opened to just a small stream vs. one opened all the way. Using a garden hose with a faucet fully open you can really flush away some dirt; with the faucet just open to a small stream there’s just not the power to do much.

There’s also the logistical matter of actually connecting one of those guns to the air source. The pocket one has an integral fitting for standard shop air (you’d have to get the fitting separately for the other one). That little compressor’s air hose connects to its own proprietary fittings, which are maybe ¼ that size.

I haven’t tried to use one of those tire-filling compressors to run a blow gun. If you could get it hooked up, maybe it would work well enough for your purposes. Frankly, though, I’d be quite surprised if it provided a useful stream of air.

The ones I have seen definitely will not. They produce a small flow of air, but can do so at relatively high pressure. They will be useless for blowing things clean. You’d do better with your lungs.

The cost and bulk of a compressor that will produce the volume and cleanliness of air to blow things clean will be totally out of proportion to what Stoid needs for occasional home use. It is going to take a compressor with a tank to provide the requisite burst of air, and I don’t think you can get that outside of small shop compressors, which would be waaaay disproportionate to the task.