Thread: Air compressor fittings

The first picture tells me nothing.

The second one I'm guessing is the compressor outlet (only because the picture title is "compressor) and the third one looks like a 3/4" pipe.

Compressors like the GMC are likely to be NPT thread so you will need to adapt the compressor NPT to the 3/4" pipe which is usually BSP.
You may not find this in a single NPT to BSP adapter and may have to do it in two or three steps.

At the end of the pipes you will need adapters that adapt from BSP to the quick change air fitting your tools will use.
Rather than making each "end of pipe" fit a specific tool it's better to settle on one type of quick change fitting for your whole shed and change all your tools to that style of fitting.

I found it easiest to take off the compressor fitting and go into Bunnings or a plumbers and do a mix and match on the spot.

Thanks Bob, the first picture which was taken at night is the air compressor outlet. The 2nd picture has an attachment t the gal pipe that I had lying around that I thought I could attach to some air hose. The 3rd picture is a gal pipe elbow that I need to attach the air compressor to.

Tiger, The tank on the compresser should have a plug in at least one of the domed ends. It is common to remove this and tap directly into the tank bypassing the regulator/water trap, and fitting larger commercial sized units down stream. The most restrictive element is generally the mini reg built into the comp, but with a small GMC and small tank, the unit will still be limited in its supply rate.

If you want to go this way, I have pipe threading and cutting gear available that you can use. It is normal to make the bridge from comp to delivery line with a flexible line to avoid coupling vibration into the line and through the building. 10mm air hose would probably be adequate for the delivery capacity of the comp. If you have to buy pipe etc, 3/4 is probably an overkill, 15HP industrial setups for multiple high volume machines only use 25mm ID for factory wide reticulation. On the other hand, if you have clean pipe available and only need a few fittings go for it.

General air fittings are available from autoshops/toolshops/industrial supplies/ebay etc fairly cheaply.

If you go this way, you need to be regular in bleeding down the tank and draining it, as if you end up with the tank about 45% full of water/oil mix it flows into the delivery lines as liquid instead of vapour and causes havoc.

Mal

When I reticulated the air in my shed I used 1/2" galv pipe because I already had heaps of 1/2" fittings and some 1/2" pipe. Although I had more 3/4" pipe than 1/2" pipe, I had far fewer 3/4" fittings.

When I eventually went to buy the rest of the 1/2" pipe I needed I found the price of 1/2" was almost identical to to the 3/4".

3/4" pipe has twice the volume per unit length of the 1/2" pipe so if you install a lot of pipe the effective reservoir created by using 3/4" is twice that of the 1/2"
In my case I only used 12 m so that only adds 2 L to the air reservior.

To vent the tank which is outside the shed I installed a garden retic solenoid on the tank vent valve and I drive this via a 24V A power pack inside the shed. This saves me having to go outside the shed to vent the tank.

Pressure drop is strongly proportional to the diameter of the pipe.

Air flow is strongly dependent on radius to the fourth power so I plugged the data for 10 mm versus 15 mm ID pipe into the online pressure drop calculator and the results are quite interesting.
At 150 psi inlet the loss of pressure for a 15 mm is 0.06 psi/m so a 10 m long pipe will drop 0.6 psi.
For a 10 mm diam pipe the pressure loss is 10 time worse so if you are worried about losing any PSI then 1/2" will make little difference.
For a 20 mm diam pipe the pressure loss is 0.015 psi/m

Thanks Mal and Bob again, I used the gal pipe because that's what I had lying around.

Mal, will standard 10 mm air hose do as a connector from the compressor to the pipework or does it need it to be more flexible? Had hoped to go straight from the current compressor outlet to the pipe but will consider your suggestion of going from the tank, I had not noticed any plug at the ends of the compressor. I don't use the compressor much anyway but 2 of the factors hindering me at the moment are the noise and lugging the hose through tools and around cars etc.

Re reusing 3/4 pipe, you would need to make sure that it is scrupulously? clean inside, i.e, no dried sludge, scale, rust etc inside the pipe, as the airflow will slowly strip the muck out and transfer it to your airtool cylinders causing premature wear, or if intercepted before the tools clogging the passages in regulators etc that trap it. Once it gets into things you can't get it out.

Re feeding through 10mm air hose, should not be an issue provided that you have access to a plug at one end. For comparison, the original inbuilt reg would probably have internal flow passages of around 1.5-2mm diameter max which restrict flow. Assuming a 5:1 ratio between feed hose and reg passage diameters, this corresponds to a 25:1 ratio for cross section area and potential flow. Obviously there would be some restriction at the far end as you probably need a reg at the end of the piping, but a full sized reg there will also flow much better than the minireg built in to the compressor, and would be much closer to the tools.

Water suspension is a big consideration when choosing the pipe size. The larger the pipe the slower the air speed and less water stays in suspension. Gal pipe will eventually corrode no matter what you do and debris gets carried in the air stream.

Originally Posted by Chris Parks

Water suspension is a big consideration when choosing the pipe size. The larger the pipe the slower the air speed and less water stays in suspension. Gal pipe will eventually corrode no matter what you do and debris gets carried in the air stream.

The water is initially not in suspension like a dust but as a vapor or a gas. The reason it will condense to form a liquid is more to do with temperature changes than air speed. The air coming from a compressor is hot and can hold a lot of water vapour - as the air moves along the pipe it cools and condenses. If the pipe is cold the water will condense sooner, if hot later. If the air is moving fast the water vapour may not have as much time to time to condense and some may then make it to the end of the line although my experience with a small compressor is it all condenses in the first 2-3 m of pipe following the compressor which is a good place to locate a low point in a pipe network and also locate a drain tap.

Just a small input from me.

Where you terminate the gal pipe throughout the shed most times it is run vertically. So if feed air comes from top down install a tee piece and 300mm of pipe pointing down. Install a ball valve on the bottom and your quick fitting off the tee. This will create a low point drain at each connection point. Water will trickle down the walls of the pipes during night time temperatures and collect in the pipe not the back of a quick fitting etc.

Other than that I would personally use poly pipe.

Originally Posted by BobL

The water is initially not in suspension like a dust but as a vapor or a gas. The reason it will condense to form a liquid is more to do with temperature changes than air speed. The air coming from a compressor is hot and can hold a lot of water vapour - as the air moves along the pipe it cools and condenses. If the pipe is cold the water will condense sooner, if hot later. If the air is moving fast the water vapour may not have as much time to time to condense and some may then make it to the end of the line although my experience with a small compressor is it all condenses in the first 2-3 m of pipe following the compressor which is a good place to locate a low point in a pipe network and also locate a drain tap.

Using a high volume tool such as a grinder on 3/4" system which has auto drainers on the compressor I have seen it happen to such an extent that in the water separator prior to the tool it looked like someone had turned a tap on. This was on a high humidity day, 18 cfm compressor (mine) working flat out. I am guessing but there has to be 10 metres of pipe before the separator and a lot of that is a vertical. This issue was one I was warned about and the guy who told me from Pulford Compressors said that 3?4" is marginal if high volumes are used. On a normal day to day basis it is no issue. I wish I had taken a video of it happening, I was absolutely amazed.

Make sure that you use good quality fittings of a reputable brand that will continue to be available in the future. Then change the fittings on all of your air tools to the same brand