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Compressed air piping question

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Forum topic by Robert posted 10-20-2019 11:33 AM 391 views 0 times favorited 13 replies Add to Favorites Watch
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Robert

3555 posts in 2016 days


10-20-2019 11:33 AM

Getting ready to redo my system with RapidAir kit.

What, if any advantage is a loop layout?

-- Everything is a prototype thats why its one of a kind!!


13 replies so far

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Madmark2

538 posts in 1124 days


#1 posted 10-20-2019 03:52 PM

Gives more airflow than linear systems.

Also do NOT use PVC for airlines.

M

View TungOil's profile

TungOil

1343 posts in 1030 days


#2 posted 10-22-2019 02:39 AM

PVC is a definite no-no for CA piping, too brittle, and I would not trust PEX. Black iron is traditionally the best choice although copper works well also. You should slope the lines slightly towards drip legs as well and drain the condensate occasionally. All taps off the header should come off the top of the pipe, not the side or bottom to prevent condensate from entering.

Looped systems are better, but if this is a typical size hobby shop a straight header will work fine if properly sized.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

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Robert

3555 posts in 2016 days


#3 posted 10-22-2019 11:54 AM

Thank, guys.

Who said anything about PVC? Are you guys clairvoyant or something?

@Tung oil I hear you now I’ll confess what I’m replacing is …..... PVC [gasp] Yes, I know it’s not recommended, I did it as a “temporary” set up that was 15 years ago. I’ve never had an issue the pipe is well protected from damage. No, it has not become brittle, either.

I believe RapidAir is a type of PEX.

I certainly feel better about everything being switched over. And for anyone thinking about using PVC, my advice is it’s your shop, but you should do it right, not the way I did it.

-- Everything is a prototype thats why its one of a kind!!

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TungOil

1343 posts in 1030 days


#4 posted 10-22-2019 01:55 PM

This topic has been discussed many times here. Everyone wants to use PVC- it’s cheap and easy to work with. But it is not safe for compressed gas use because it is a rigid plastic and it can shatter violently and unexpectedly. A few years ago I posted the relevant section on this from the Piping Handbook, a quick search will probably uncover it. PEX and similar ‘soft’ plastics might be OK, but personally I would avoid them due to potential for leaks. PEX fittings are designed for water use. Industrial machinery with pneumatics typically use a special fitting that has a barb and ferrule so the tubing is gripped both inside and outside. These will work but are likely more expensive than black iron. Rapid-air is a similar system but they use an o-ring style seal in their fittings if I recall correctly and should work fine in a home workshop (not sure about the pricing of it, probably expensive).

I ran copper in my first shop and it worked beautifully. Copper also has the advantage of turning your header into a heat exchanger to cool off the air after compressing. A little expensive to use these days. I didn’t bother running a header in my last three shops, I just pull a hose from the compressor.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

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pottz

6639 posts in 1520 days


#5 posted 10-22-2019 02:30 PM

ive always used copper and it’s worked quite well for 30 years.pvc,the thought puts a shiver up my spine,youve been lucky.

-- sawdust the bigger the pile the bigger my smile-larry,so cal.

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rustfever

778 posts in 3846 days


#6 posted 10-22-2019 05:30 PM

I keep hearing the pros and cons of PVC for air. I’d like to point out several factors and one experience.
1. MAXIMINE working pressure for 1” schedule 40 PVC is 450 lbs PSI [3/4” IS GREATER]
2. normal wood shop tools run best on 85 to 95 lbs PSI
3. 450# vs 90# is a 500% safety factor. OR 5 t0 1 safety factor.
4. OSHA standards are for business and industry that have employees.
5. Some employees tend not to be careful or considerate of employer’s facilities, equipment, thus the significantly high OSHA standards
I personally have used PVC piping in my personal wood shop since 1985, with NO explosions, failures or other problems. 34 years!
The only thing I have found….........You need to used PVC male threaded nipples when coupling into hard metal pipes/nipples/quick disconnect fittings. [Never metal male into PVC female as the female will fail]
Of course, you would want to place the PVC piping in a location that protects from being subjected to being hit, damaged, or otherwise abused.

BTW, 1” Type ‘L’ copper tubing maximum working pressure is 420 PSI for annealed pipe, or 825 PSI for drawn pipe.
Bursting pressure of Type L coppers is about 5 or 6 times the working pressure.

-- Rustfever, Central California

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TungOil

1343 posts in 1030 days


#7 posted 10-22-2019 06:16 PM

Rustfever- do what you like, but you are doing the readers of this forum a disservice if you are saying PVC piping is suitable for compressed air systems, that simply is not so. It has nothing to do with OSHA or working pressures of the pipe, it’s about the brittle nature of the material and what happens in the event of a failure. Suppose I could supply you with glass tubing rated for 450 psi- would you plumb your shop CA system with it?

As a Mechanical Engineer I have designed and installed several industrial compressed air systems over the last 3 decades. Every one was black iron pipe. They are all still in service.

I can assure you that PVC is really bad choice for CA applications.

Still don’t believe me? Do a Google search of ‘risk of pvc for compressed air’.

Just to be clear I’m only calling this out because I have experience in this area and the suggestion to use PVC pipe has come up numerous times over the years. Other readers now and in the future should be aware of the risks involved.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

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pottz

6639 posts in 1520 days


#8 posted 10-22-2019 06:24 PM



Rustfever- do what you like, but you are doing the readers of this forum a disservice if you are saying PVC piping is suitable for compressed air systems, that simply is not so. It has nothing to do with OSHA or working pressures of the pipe, it’s about the brittle nature of the material and what happens in the event of a failure. Suppose I could supply you with glass tubing rated for 450 psi- would you plumb your shop CA system with it?

As a Mechanical Engineer I have designed and installed several industrial compressed air systems over the last 3 decades. Every one was black iron pipe. They are all still in service.

I can assure you that PVC is really bad choice for CA applications.

Still don’t believe me? Do a Google search of ‘risk of pvc for compressed air’.

Just to be clear I’m only calling this out because I have experience in this area and the suggestion to use PVC pipe has come up numerous times over the years. Other readers now and in the future should be aware of the risks involved.

- TungOil


+1 a lot people do a lot of things they shoudn’t and get lucky,im not betting on luck with my well being,not worth it for the money saved.a trip to the er will quickly wipe that out.

-- sawdust the bigger the pile the bigger my smile-larry,so cal.

View TungOil's profile

TungOil

1343 posts in 1030 days


#9 posted 10-22-2019 06:26 PM

Back to the OP’s original question- the advantage of a loop system is that you are feeding all points of use from two ends. It has significant advantages in an industrial setting where multiple points of use might be drawing from the system at the same time, since it helps maintain a more consistent pressure across the header.

If this is a hobby shop or a small commercial shop (say, under 10 points of use) using a loop system is of questionable value in my opinion. More important is to follow good design practices by sizing the pipe appropriately for the use, adding drip legs (with drain valves), sloping your lines to the drains and tapping off the top of the pipe for your points of use. A filter/regulator and water separator between the compressor and header are a big help as well.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

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pottz

6639 posts in 1520 days


#10 posted 10-22-2019 07:07 PM

just took a look around the internet on the use of pvc for compressed air,found a lot of harsh warnings against it not one that recommend it.spend more and do it right guys.

-- sawdust the bigger the pile the bigger my smile-larry,so cal.

View MrRon's profile

MrRon

5767 posts in 3779 days


#11 posted 10-22-2019 08:39 PM

I am well aware of the dangers of using PVC pipe and I don’t use it, but if you can assemble a long line of PVC and hide it away from the public, like above a false ceiling, I would accept that. The drops although would have to be copper, black pipe, or even a rubber hose. If the PVC would ever explode, it would be away from the public and not pose any danger. In general, PVC is not a good idea, but if cost (long runs) is a factor, I would consider it. Shock is the biggest problem when using PVC. If you open a valve quickly and shut it quickly, the shock could cause PVC to rupture.

View controlfreak's profile

controlfreak

279 posts in 137 days


#12 posted 10-22-2019 09:16 PM

As someone who has done lots of work above drop ceilings I would hate to be face to face with a rabid PVC air line.

View Ocelot's profile

Ocelot

2365 posts in 3173 days


#13 posted 10-22-2019 09:59 PM

The only problem I’ve seen with PVC air lines is at my workplace when we left the compressor on all the time. A pvc line cracked on the weekend, and the compressor ran until it seized and then burned up the motor.

I just drag a 100’ hose around at home, and keep the compressor off except when I’m using air.

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