Confused about water traps and oil/water filters

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PostPosted: Tue May 28, 2019 2:06 pm
Hi All
A few questions about compressor set up:
1 Is the water trap a different thing than the oil/water filters?
Can anybody supply pictures of both, of maybe a weekend warrior variety?
2 Why in the set up graphs do I see an air regulator in line?
If all the guns have an air guage with regulator connected to them then why is another regulater needed along the line?
3 I have seen a few graphs having ball valves before the water filter. Why?
Is the reason for shutting off access evaporation in the line to the filter when the compressor is not in use?

Thanks for all replies.

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PostPosted: Wed May 29, 2019 8:54 am
You want at least 20' of copper line before your water separator. This will give the warm compressed air time to cool and the water to condense.
The first stage is the water trap which allows the condensed water to be collected and usually has a clear sight glass and drain at the bottom.
The oil/particle filter is designed to remove any contaminants other than water from the compressed air before sending it down the air hose.

Wall regulators are used for a couple of reasons. Sometimes the tool you are using requires more or less air than a spray gun. Some guys use the wall regulator to set their spray guns up instead of a regulator at the gun. They install a temporary gauge at the gun and once the gun is set up they remove it.

Combo set ups like the following are fairly popular:
Water Trap Combo.jpg


I have a another filter type just prior to my refrigerated air drier. It is a Coalescing style:
Pre-filter  Wilkerson M30-06-S05.jpg
Pre-filter Wilkerson M30-06-S05.jpg (13.75 KiB) Viewed 3375 times


A ball valve in the line allows you to shut the air supply off at the booth, while leaving it on for other areas. Also, if you have a leaking connector or a tool that bleeds off air, your compressor won't be cycling needlessly.
1968 Coronet R/T


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PostPosted: Sat Jun 01, 2019 4:06 pm
Maplehead wrote:Hi All
A few questions about compressor set up:
1 Is the water trap a different thing than the oil/water filters?
Can anybody supply pictures of both, of maybe a weekend warrior variety?
2 Why in the set up graphs do I see an air regulator in line?
If all the guns have an air guage with regulator connected to them then why is another regulater needed along the line?
3 I have seen a few graphs having ball valves before the water filter. Why?
Is the reason for shutting off access evaporation in the line to the filter when the compressor is not in use?

Thanks for all replies.


1. Yes a water trap is different from an Oil/water filter. A water trap will have at least 20 feet plus of line to cool the air before entering a Moisture trap/water trap.
2. I don't run a regulator after my compressor I run strait full pressure to all my regular air tools. I should run one though set it at 90psi at the compressor then a water trap then around shop.

You need a Regulator at your painting area/Paint booth after your filters
(and a desiccant drier if your gonna use one).



I run a Ball vale before my desiccant drier just to keep it isolated from the rest of the system when not being used.
I also have a Ball valve at my compressor so I can shut air off to my system and keep air in the Tank.
Dennis B.
A&P Mechanic, FCC General radio Telephone Operator
Line Maintenance A&P Mechanic and MOC Tech specialist.

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