Spray gun air pressure query

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PostPosted: Tue Feb 01, 2022 8:04 am
It's not an issue of the carbon filter clogging up but that the activated carbon loses its ability to filter out the isocyanates (which are not the same as VOCs). This is why your face mask has a particulate filter in the front and a carbon filter behind, and why you should store in a sealed container when not in use. They have a limited use time, too. Depending on how thick the concentrations are in your booth, average is about 8 hours.
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PostPosted: Thu Feb 17, 2022 10:04 pm
If I decided to build a copper air dryer / moisture trap that is installed between the tank and the end hose (as opposed to how NFT5 did it before the tank) using say 3/4" pipe do I still need to be concerned about pipe lengths and pressure loss like with the smaller air hose?

Just seeing that a lot of these copper air dryer / moisture trap setups use a fair bit of copper length to achieve their goal. Would hate to build one and be back to square one with too much piping between the compressor and the spray gun killing psi.



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PostPosted: Fri Feb 18, 2022 5:11 pm
LittleJerry wrote:If I decided to build a copper air dryer / moisture trap that is installed between the tank and the end hose (as opposed to how NFT5 did it before the tank) using say 3/4" pipe do I still need to be concerned about pipe lengths and pressure loss like with the smaller air hose?

Just seeing that a lot of these copper air dryer / moisture trap setups use a fair bit of copper length to achieve their goal. Would hate to build one and be back to square one with too much piping between the compressor and the spray gun killing psi.


Its not the length of pipe that kills air flow, Its a drop in Pipe inner diameter or fitting size that will cause a drop in air flow.
In example your running 3/4 pipe and fittings through whole system BUT Your Air filter inlet is only a 1/4 inch inner diameter, Your not loosing PSI The drop in size causes a RESTRICTION limiting your CFM air FLOW. The air pressure on both sides of the restriction will be the same but your available cubic feet per min air flow will be dramatically reduced through the restriction.

Rule of thumb for water trap 20 feet of pipe after Air compressor tank to get an air temp drop so water can drop out and condense that where you place water trap / Moisture trap then plumb shop from the trap.
Dennis B.
A&P Mechanic, FCC General radio Telephone Operator
Line Maintenance A&P Mechanic and MOC Tech specialist.



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PostPosted: Mon May 09, 2022 2:21 am
Doright wrote:Its not the length of pipe that kills air flow, Its a drop in Pipe inner diameter or fitting size that will cause a drop in air flow.


This is actually incorrect. Length of pipe does matter. That is the reason why I'm rebuilding my shop's entire pneumatic system. Length with Diameter is the restrictor of air flow. CFM drops with length, because length is friction.

3/8 hose at 50 feet has CFM of 14 and at 100 feet CFM of 10, all at 90 PSI. So length does matter. Hence we up the pipe diameter to make up for the added length. That is exactly what I'm doing right now, because I noticed 2 things at 50 feet:

1. My sand blaster simply has no blasting power do to limited CFM with my 3/8 hose at 50 feet.
2. My gun while at wide open can not sustain 25 PSI at 75 feet or 50 feet hose. It starves.

So having an awesome compressor means nothing if you can't deliver the air. The compressor is actually working much harder, much longer. I will build my new entire system from 1 inch pipe all the way to the sand blaster, and from there onwards I will use 3/4 inch pipe for my painting and air tools. This will give me the sweet spot of dry air without losing my compressor's CFM.

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