Thread: Anyone used RapidAir Compressed air piping kit?

I haven't used it but the need to paint or cover the tubing to protect from UV light would give me pause.

I'll be running it in wall, UV isn't an issue. It's probably only an issue if used externally, thermoplastics need carbon black pigment added for UV protection.

I wouldn't worry about the need to paint it to protect from UV, if it's inside a shed, UV exposure from the sun will be low - pipe located within a few metres of any welding will need painting but you are better of covering it completely with some sheet metal to protect it from welding spatter and any grinding sparks - easier still would be doing that section in metal piping.

It depends on the size of your shed (length of the pipe), the compressor - hence the max air flow generated, and what pressure drop you are prepared to accept.

For example,
- for a 3/8 ID pipe, over 10m, at 8 bar and 10 CFM will lose about 1.2 bar,
- in my sled I have 15mm ID pipe and 7m is my longest run which loses 0.1bar
- at the mens shed, we used 20mm ID pipe and it has a longest run of 25m, it loses 0.26 bar

AT the mens shed we used a combo of stiff and flexible Bue Line Poly pressure pipe, and PhilMac compression style Poly fittings.

We ran a complete loop of stiff pipe around the main Woodwork area (14 x 7m) on slopes (see picture) so that any water drains to 4 drain points (taps) on each wall.
Because we had to span 3m distances between the RSJs we laid the pipe in some tin hat otherwise even the stiff pipe droops and water will pool in the droop.
To further decrease the amount of water that can come through the lines we used upwards take offs - you can use 2 elbows to achieve this but because we had the height we bent the flexible pipe thru 180º the minimum radius of turn of the flexible poly depends on the diameter.

The stiff poly is expensive ($6/m) but the flexy is $1/n for a 50m roll, the fittings are expensive if you need to do a lot but are not so bad if you have only a few.
eg a 20 mm elbow costs $8, and a T costs $12 (we of course used 25mm)
If I was to do it again I would do it all in the flexible Poly because we had to support the stiff pipe anyway. If you use the flexy pipe you will need a support clip every metre or so so it does not droop.

In the picture below you can see where the compressed air comes into the shed at the back corner of the shed and goes up to the start of the loop.
The 54CFM compressor is located in an enclosure outside the shed.
There are downwards pointing drains, and upwards take off points, on each wall, with poke thru's to the metal workshop and the wood turning are both in separate rooms.

The system was designed by yours truly and installed by one of our 80 year old members, - this bloke is pure gold and can do just about anything, although he can only work about half a day at a time before he gets too tired but he has no problem climbing ladders and at times he seems fitter than most other members.


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It is a great concept with many advantages but you need at least 3/4" ID not 1/2'' OD. Surely you can buy bigger than 1/2" OD.

3/4 ID is overkill for what I need. It will allow 100cfm at 90psi over a 30m run from 100psig at the regulator if memory serves. What BobL has said is right, cross sectional area determines pressure drop. Half inch ID will have 20 times less pressure drop than quarter inch over the same length. I'm tossing up if I need to use 1/2 rather than 3/8 ID, but anything over that is unnecessary expense. I'm not using anything with big air requirements, finish nailer mostly.

Originally Posted by richmond68

3/4 ID is overkill for what I need. It will allow 100cfm at 90psi over a 30m run from 100psig at the regulator if memory serves. What BobL has said is right, cross sectional area determines pressure drop. Half inch ID will have 20 times less pressure drop than quarter inch over the same length. I'm tossing up if I need to use 1/2 rather than 3/8 ID, but anything over that is unnecessary expense. I'm not using anything with big air requirements, finish nailer mostly.

It has nothing to do with pressure drop off it has to do with air speed. Any given volume through a smaller diameter pipe will cause a rise in air speed and higher air speeds cause more moisture to stay suspended in the air stream. Ask anyone who installs compressed air systems, they will tell you exactly that.

Originally Posted by richmond68

3/4 ID is overkill for what I need. It will allow 100cfm at 90psi over a 30m run from 100psig at the regulator if memory serves. What BobL has said is right, cross sectional area determines pressure drop. Half inch ID will have 20 times less pressure drop than quarter inch over the same length. I'm tossing up if I need to use 1/2 rather than 3/8 ID, but anything over that is unnecessary expense. I'm not using anything with big air requirements, finish nailer mostly.

There's a bit more to it than area especially when the pipes are small, flow is turbulent and wall effects become very significant.
For small pipes flow rates Poiseuilles law applies and flow approaches 1/r^4
To work it out have a look at this Pressure Drop: Calculation of pressure drops in pipes

Air tools manufacturers are also notorious for understating the CFM and pressure required.
The die grinder I bought with a 4.6 CFM rating needs more like 7 CFM to run properly.

Likewise compressors. 3HP compressors cannot generate more than ~11 CFM otherwise they violate the law of conservation of energy.
In practice the are less, sometimes way less than this.

Finish nailers do indeed need relatively little CFM and pressure but there is nothing worse than installing something and then finding it cannot do the job.

The other advantage of a bigger pipe ID is it increases your tank volume although you have to go a long way to make a real difference.

Originally Posted by BobL

The other advantage of a bigger pipe ID is it increases your tank volume although you have to go a long way to make a real difference.

Reminds me of the story of Smokey Yunick, the legendary NASCAR mechanic who noticed that while the rule book specified the fuel tank size, it didn't stipulate the size of the fuel line. So he put in a 2 inch line that held 5 US gallons. So I can see where it might be useful

Thanks for the links, I do have copies of training materials from Binks so Ill be going through them and doing my calcs before making a final decision. But I'm also trying not to overthink it, my needs are modest and I'm aware it's just as easy to overspend as it is to underspend. To be honest the highest consumption comes from an air duster at about 2cfm, the nailer is about 0.5. I have to be conscious that others recommend based on their own use not mine.

Originally Posted by richmond68

the nailer is about 0.5. I have to be conscious that others recommend based on their own use not mine.

That figure is 0.5 cubic feet. Divide that by the actual time that it draws the air (fractions of a second) and you will get the CFM.

In use you will need to run the gun at a higher pressure to get it to seat the nails properly and that will shorten the life expectancy of your gun.

Originally Posted by richmond68

Reminds me of the story of Smokey Yunick, the legendary NASCAR mechanic who noticed that while the rule book specified the fuel tank size, it didn't stipulate the size of the fuel line. So he put in a 2 inch line that held 5 US gallons. So I can see where it might be useful .

One of my Bils was a tanker truckie for a fairly high profile Margaret River wine company and used to drive a full wine tanker 250 km to their bottling plant in the Swan Valley. When he arrived at the bottling plant he would pump the wine into large SS tanks until the tanker was empty but there was always a flagon or so left in the hose. To speed up the transfer he recommended using a bigger diameter hose which left more wine in the hose. Back at his place he had his own bottling setup and he did quite nicely out of that little exercise until they discovered was he was doing.

Originally Posted by Bohdan

That figure is 0.5 cubic feet. Divide that by the actual time that it draws the air (fractions of a second) and you will get the CFM.

In use you will need to run the gun at a higher pressure to get it to seat the nails properly and that will shorten the life expectancy of your gun.

It's a very rough guesstimate. Air consumption is quoted at 1.5 litres per shot, which is 0.05 cubic feet. I allowed a firing rate of 10 per minute. I've done an entire project with it before realising I hadn't switched the compressor on, so whatever the air use is, it's not a lot. Bostitch have a 7 year warranty, so I'm not too worried about longevity. It'll have paid for itself well before then.

Just a quick follow up, I decided against using the RapidAir kit despite the attractive price on Amazon. The reason was the use of NPT threads on the ports and manifold, which would mean using NPT to BSP adapters to connect readily available fittings.