Piping specs for compressed air and water 4

[foodprojengr]

My project involves providing my maintenance person specs to run piping from a 3hp air compressor and dryer to a propietary machine and from a water softener to a vacuum pump (for cooling water) to that same propietary machine. The air compressor can provide up to 10 cfm at max pressure (see

http://www.grainger.com/Grainger/items/4YW09

and

http://www.grainger.com/Grainger/items/2HUF8).

Based on this, I was planning on running a 1" ID PVC line for the compressed air and a 1/2" ID PVC line for the soft water from the water softener to the vacuum pump and from the pump to the drain, as well as from the water softener to the drain for when it regenerates.

The vacuum pump requires 1 L/min cooling water = 0.26 gal/min = 60 cuin/min). I assumed a max flow rate of 5 ft/sec and calculated a minimum diamter of 0.15 in. I sized it up to 1/2" ID for safety.

I know I need to also consider temperature and pressure. The water from the softener should be room temp and the plant water supplying the water softener is 60 psi.

For the compressed air, I also assumed 5 ft/sec maximum flow rate and using the max 10 cfm I calculated 1.2 in.

I'm not sure what to consider for pressure and temp for the compressed air.

I'm choosing PVC because of a tight budget and the fact that the client may be adding more machines in the future and so we'll have to resize the line anyway.

Does this make sense?

I'm obviously new at spec'ing piping so sorry for the dumb question.

 

[foodprojengr]

I just got feedback from a technical person from the air compressor supplier that it would probably be better to use black iron piping than PVC.

 

[TBP]

Many jurisdictions specifically prohibit PVC for compressed air lines above grade.

 

[LUDPEKA1]

The typical piping spec. for “Utility Air”(150# rating), that I’m use to using, at 1” dia. in size would call out for SCH-XS, ASTM A106 Gr.B , seamless pipe and 3000#, ASTM A105, screwed fittings.

 

[foodprojengr]

Does it make sense that I chose 5 ft/sec as a maximum compressed air velocity (that's how I came up with the 1" ID).

 

[simplemath2]

Try to determine velocity and pipe size of compressed air upon the pressure drop. That is :
1. Feed pressure P1
2. Consumer pressure needed: P2
3. Calculate pressure drop from pipe friction and local loss, dp
4. Make sure (P1-P2) > dp

That is normally how I do it.

 

[TBP]

facilities123 - Here's a table for sizing compressed air lines:

http://www.perfecting.com/dpl/dpl_page/2008/531.pdf

 

[jdarco]

Do NOT use PVC for compressed air! All the major pipe and fitting manufacturers advise against PVC for compressed air and you void all warranties. In a failure, PVC will become like schrapnel and the compressed air has a lot of energy. If you have a corrosive environment, look at some of the plastic pipe systems for air that are out there.

Otherwise, listen to your compressor supplier and use black iron!

 

[MJCronin]

Ummmmmm.... like everybody says above, PVC is a bad choice for compressed air service. Lawyers, of course, are much more expensive than upgraded piping...

Black iron pipe (Sched STD or better)with threaded fittings will be about the same price as the PVC.

Your "5 ft per second" is a good criteria for LIQUID pipe sizing, not air or gas pipe sizing.

-MJC

 

[cheute79]

You might also consider rigid copper for compressed air. The pipe/tube itself is more costly than black iron or PVC, but sweating it can be a lot less costly than threading iron. Another downside to PVC is it's mechanical strength - you need more pipe supports. rigid copper and black iron can sustain much longer runs without supports, making them less costly than any thermoplastic.

 

[TBP]

If you're going with copper for compressed air service, then consider using something other than soft solder - brass compression fittings (Swagelock, Parker, etc.) or silver solder. If soft solder is used, my concern is that if there's ever a fire in the building, the joints may fail.

 

[lowedogg]

don't know what your pressure is, but type L copper will do the trick for most CA applications. Black steel may be cheaper as raw material than copper, but will take more labor to put in. threading or welding always takes longer than brazing for the size pipe you are dealing with.

 

[Technome]

On-Line Compressible Flow Pressure Loss

http://www.freecalc.com/gasfram.htm

OSHA and insurance companies will make you pay for PVC. As MJC points, out lawyers have no issue with it.

 

[dcasto]

you can afford a propritory machine but not the connections.
I'd use 3/8" copper on the water. 1/2" copper or even 3/8" may work. What matters on the air is not what the compressor can do, what does your equipment need.