Technical Engineering types, I have a question about air cfm

I am looking at buying a bigger blast cabinet. I have the whole shop plumbed in 1/2" steel pipe.
The manual for this particular unit says the minimum should be 3/4" preferably 1". I am trying to figure out how to plumb this into the existing system without having to replumb it all.

The good thing is the compressor is close to where the blast cabinet is going to be located. I was wondering if I get close enough to the compressor and had a T that went to 3/4 or 1", would that little bottleneck be enough to affect the volume/pressure required? The T will be about 12" from the compressor and then change to the larger pipe. Probably be about 15' of total length.

Make sense?

 

How about trying the existing line first and see how it works? You might be surprised.

 

Can the compressor handle a 3/4" pipe? If so, then it would be best to add a 3/4" to 3/4" to 1/2" T coming off the compressor. Then as long as there was no draw on the 1/2" side in the rest of the shop you would have the full compliment of the compressor going to the blast cabinet.

 

I Have a 3/4" braided flexible coupling coming off the compressor. Kinda like this one.


I'll try and take a pic of it tonight. I can't remember how I reduced it down. Does the rest of the line act as an accumulator, if nothing else is running? It's a big 7hp, (2 stage 80 gal) Champion industrial compressor.

 

Instruction do not know if one has a short run or a looooonnnnnnggggggg run.

 

Exactly. The rest of the line will initially fill with air but then after that the air will travel the path of least resistance. Very similar to how lake pipes work with and without the caps.

 

I assume you have multiple quick connectors in your pipe run remove the one closet to where the blaster will be so that is 1/2 pipe and start your compressor to see if it will build presser. If it does not going to a bigger pipe probably won't help much.

 

What size is your compressor? Not gallons but hp and cfm.

 

Bigger pipe means more capacity to store air not expel. Not to be confused with flow.

 

A good point to note. Most quick connects ALREADY throttle down your ID of the pipe quite a bit! I think it was @Tuck ? that mentioned years ago about fittings that flowed better air that standard ones.

 

So you have 3/4" coming off the compressor, that gets necked down to 1/2, then you're considering teeing into the 1/2" to supply a 3/4" line to the blast cabinet, right?

The 1/2" section will act as an orrifice, it will provide some restriction to airflow to the cabinet but not as much as sticking with 1/2" all the way; it really depends on how long the 1/2" section is between the outlet and the tee. The longer that section is, the more restriction there will be and the less the benefit will be to tee off and go back to 3/4". The bigger issue I see is potentially increased condensation in the line to the cabinet as the air will expand as it leaves the 1/2" section into the 3/4" section. I think I would try using 1/2" to the cabinet instead of 3/4" and see if that will provide what you need. Otherwise I'd replumb with 3/4" between the tee and the outlet.

 

It's a 7.5 hp. The cfms are around 23 at 175 psi.

 

A friend of mine builds vehicles for a living, has a two-stage compressor at each end of the shop because when using air tools or a blast cabinet you need not only pressure but also volume. Another option is to add an air reservoir as in another compressor air tank.

 

Here is a little help thinking like an engineer.

1. Pumps and compressors do not create pressure, they create flow.
2. Resistance in the line / system down stream of the pump creates the pressure.

Therefore, your 1/2" T is essentially a nozzle or orifice as Blues4U described, creating a pressure drop as air flows across the T. On the back side will be 175 psi air (or what ever the compressors shut off point is). The down stream pressure will be dependent on the flow rate and restrictions within the system after the T. Larger air flow requirements will create a larger pressure drop across the T. Bigger pressure drops correlate to larger temperature drops and could result in condensation or even freezing problems.

 

Your compressor will do in the 24 to 27 cfm range @ 90psi. I think your current pipe setup will be okay so long as you don't have any significant choke points in the line such as quick couplings or undersize valves.

Assuming you're looking at a siphon feed blast cabinet, there should be some spec from the manufacturer on the air jet size and nozzle size. These sizes determine how much air air the blast gun will use. Both these parts are usually interchangeable for size so that the gun can be tailored to the available air supply.

 

When I read this question, I remember Bruce Lee. You must become the water. Something like that.

But if you think of the air like water flowing from a tap, you'll get it. And you'll never have enough if your squeeze the trigger, push the pedal and don't let up. You'll think you need a bigger compressor like he said they were going to need a bigger boat.

 

Check out the nozzle i.d. Chances are it's about 1/4", which is .049 sq. inchs. 1/2" is .196 sq. in. or 4 times the nozzle area. If you are close to the compressor, you won't have any problems as long as you don't restrict it much more. My blast cabinet is close to the compressor, 1/2 pipe plumbing and I put a 3/8" size quick coupler on it and have no problems. Of course, there are two air filters in line before it. If the element begins to clog up, you will notice a drop off in performance and it will be time to change elements. I really suggest an air dryer, too. I have had the HF refrigerated dryer on mine and never had any moisture problems.

 

Root,
What you want to do is T in before you neck down to 1/2. What you get when you neck down is an increase in pressure but a loss of volume. Your blast cabinet needs volume to move the blasting media not pressure.

Make sense? I can try and explain it a different way if you want but that would require thinking on my part.

 

Plumb 1" from compressor to blast cabinet, hook in the 1/2 off of that for the rest of the system.

Consider a cooling / chilling loop in 1" and water trap. Ability to cool the air and line and remove water after chilling really helps blasting. May only have to use it in hot weather but it's there.

 

Not quite - it depends on the machine.

An early Rootes blower does not create pressure as it has no ability to compress internally. It compresses the air in the inlet manifold. It makes flow.

A vane supercharger has internal compression. It produces compressed air that flows into the manifold. It makes both flow and pressure.

Most air compressors deliver pressure by smooshing the air in the cylinder against the compressor poppet exhaust valves. They then store that pressure in the compressor tank. They do not store flow.

Tmans suggestion is a good one. Run the piping ya got, and if it is not to your liking for the things you do then upgrade the diameter.

Cheers,
Harv

 

I just relocated my cabinet a few weeks ago was a little shocked to see the size of the restriction in the hose (5/32”) been using it for 30 years with a regulator and similar air compressor as yours with no problems
With your air compressor being close I don’t think you will have any problems

 

https://www.tptools.com/Skat-Blast-USA-985-WIDE-LOAD-Abrasive-Blasting-Cabinet,7907.html?b=d*45143

 

Here’s a pic.

 

Biggest problem I have is, where is the water trap. And that’s probably the biggest problem with blasters is moisture. When that compressor is running hard it takes 20-40 ft of pipe to cool the air enough to condensate. So you can trap the water. I really think the 1/2” will flow enough. You also have to realize air and water flow similar. As in the friction loss. 1/2” line to your house vs a 1” or 2” line

I never liked trapping water right before the source. It should be done before the main line

 

I have 6’ of climb and then a water trap, then another 10’ of pipe then a second water trap.

 

You can build this water trap for less than a 100 and

Ok. Just wanted to make sure. A lot of people think you can trap it right out of exit hole. I have 30’ of copper and the boy of mine will blast for an hour straight sometimes. Never any water problems. I did wish I would have done 40’ copper though.

 

Nozzle size will dictate air flow. I doubt the nozzle is 1/2 inch....
I'd try it as is, should be fine. I run my pressure blaster off a 50' 1/2 inch hose...seems to work fine.
Edit, as said, moisture will be your bigger problem being that close to the compressor.

 

One thing I found, back yrs ago I did some blasting with 1/2" plumbing at home, later I used another blaster at my brother's and his worked alot better. We had almost matching specs on the air compressors and the only difference? He had 3/4" lines.

I thought mine was just fine until I used his then I seen and felt the difference. His did the job better and faster so I'm of the camp that there's no substitute for volume which is exactly what the bigger pipe gave.

I redid my entire shop compressor plumbing this last yr and it's all 3/4".

.

 

I have a blast cabinet now running on the same system...never had any issues with moisture. With that said, I had pondered adding a drier.