Saturday, 25 January 2014

My Compressed Air Dryer

Since buying a cabinet sand blaster early in 2012 I have been very unhappy with its performance; the silicone suction tube, (that lifts the grit from the bed to the blast gun), regularly sucked shut and the nozzle blocked up, it seemed every five minutes. I replaced the silicone tube with a reinforced plastic type, but the nozzle still blocked with damp grit. After some investigation on the Interweb I found it is a common problem especially in humid climates, and as the average year round humidity in Brisbane is approximately 80%, it was going to be an ongoing problem – so a solution had to be found. There are many and various commercial compressed air dryers available – at a cost, (the decent ones around the $300 - $400). My compressor did come with a combined oil/water & pressure regulator bolted to the frame, but as I was to lean from my Interweb investigation apart from regulating the pressure it did nothing else. As many of us are aware air increases in temperature when it’s compressed, so the humidity in the air remains as a vapour because as it’s above ‘Dew point”  So a way to cool the air down, cheaply, had to be found!
I found two on the net, one I have made and installed, see pic below, the other uses a condenser coil from an obsolete wall air conditioner, with the refrigerant flushed out with paint thinners, methylated spirits & water then blown out with air. Fitted with a fan or placed in the refrigerator to cool the air. The fridge method would be good if you are going to use the air for spray painting. It’s piped up between the compressor head/s outlet before the air receiver, an oil/water trap fitted, (I would use an automatic one for this task myself in case I forgot to drain it), then piped back into the air receiver. This type of air cooler/dryer will also reduce moisture accumulating in the receiver.
The one I chose to use is made up of 2 x 3 m (10’) lengths of 32 mm (11/4”) galvanized pipe, threaded both ends. These are assembled in a skinny upside down shape using 2 x elbows and 1 x nipple at the top, then a ‘Tee’ fitting screwed to each pipe end at the bottom. Reducers are then screwed into the ‘Tee’s’ outlets –1/14” to ½’ in each bottom outlet. On the side outlets a 11/4” to 3/8” or ¼”epending on the size of the fittings you use for the inlet and outlet. (I used 10 mm (3/8”) Nitto fittings). From the now reduced 11/4” to ½” pipe threads on the bottom outlet I screwed in a 15mm (½’) galvanized pipe stub 150mm (6”) long, with the 15mm (1/2’) ball valves screwed on each – these will be used to drain the water out of each pipe column. Or use whatever valves you have on hand.
In the outlet side of the ‘Tee’s’ I reduced to ½” and added another ‘Tee’ so I could screw in a pressure gauge. (I had one on the outlet of the compressor but it was small and hard to read, and I had a spare larger one). I reduced the outlet of the ½” Tee down to 3/8” and fitted a female Nitto fitting which self-seals when disconnected from a compressor hose. I made up a couple of clamps from 3/8” threaded bar which went through 25mm x 25mm box section (1”x1”) and tightened with nuts. I chose 3/8” threaded bar at it would have to be pulled pretty tight to hold up about 10 kg (22lbs) of pipe. The box section was left with enough length to weld to one of the shed posts.
On testing the sand blaster worked better than before, with zero moisture. Another thing I picked up from the articles on the net was to occasionally block the blaster gun nozzle with your gloved hand and slowly pull trigger, this will force the compressed air back down the grit pick up line and dislodge any obstructions. I do it when I feel the gun is not picking up enough grit – it works! I’d been blasting for about 30 minutes and slowly opened the drain valve on the inlet pipe column it had indeed condensed some of the water which was blown out. I bought all the pipe and fittings for this ‘condenser’ because I couldn’t find any scrap or old fittings and it cost me about A$150 all up, but I’m sure an enterprising person could do it cheaper. Now the obligatory Safety Warning – Anything under pressure can be dangerous, don’t use dodgy pipe of fittings that may rupture under pressure. When you first test your master piece DO IT SLOWLY, and only pressurize in stages. – from a distance if possible.