Compressed Air Long Distance Supply

It's just like electricity.

Same rules, different medium.

Use a floating lid for accumulator tank overwhich keep a weight which will give you approximately constant pressure as consumption increases.

What ID pipe are you using now?

How many joints, hosetail fittings, end stop fittings etc. are there in the line?

All of these, whilst not affecting static pressure, will affect flow rate and working pressure.

My quick calculation indicates that a standard 1/4" ID flex pipe in good condition (no internal ply separation etc.) 600' long with 125 psi input pressure and 4.5 cfm draw would drop a tad under 50 psi over its length. Increasing that pipe to 3/8" ID would reduce that to around 6 psi drop, and 1/2" ID would be about 1.5 psi drop.

Every fitting in the line will add pressure drop which is normally expressed as extra pipe length. Straight through hosetails will add about 2 feet for every fitting, end stop couplings can add around 15 feet each.

You may be able to use an accumulator, but it would have to be large enough to allow a reasonable use time before you would then have to wait for it to recharge.

A better option may be to lug in a portable generator and a smaller compressor that can handle the cfm rate, Most smaller belt drive units can manage that volume.

An even better option may be to hire a petrol post driver.

We have 6x100' of PVC hose in 3/8" which feeds a 50' x3/8" length of rubber hose. By your numbers(thanks!) we should have better pressure. But we have the nine connections and the hoses are of skeptical origin and quality. I have enough 1" sch 40 PVC pipe to make the run. Is it horribly dangerous or just stupid to use PVC pipe for a temporary service like this?

After posting that reply, I began to doubt your cfm figure, are you sure you haven't inserted an erroneous decimal point there? Most post drivers (I'm guessing at a star post driver) would use far more air than you have stated, 45cfm being more likely than 4.5cfm.

Although PVC-M is sometimes used for the purpose, and whilst it may survive the pressure, the available fittings generally won't. For this reason plus the fact that it is banned for use for this purpose in many jurisdictions, I would not use PVC.

Polyethylene (HDPE) pipes and fittings are available, and often used for compressed air delivery, but unless you have specific reasons not to do so, a petrol post driver could be a far cheaper option.

They normally weigh less than 20kg which is likely comparable to your pneumatic unit, and if you can't hire one you could probably purchase one cheaper than the cost and time of laying, moving and then repacking your new air pipe especially if the figure is closer to 45cfm where the pipe ID would need to be minimum 3/4".

I would think that you could purchase a reasonable petrol driver for around $400.

Agreed, by my calc 4.5scfm at 90psi gives something like 0.3kW at the driver, which doesn't sound enough. That's assuming it is scfm. If it's 4.5cfm at the pressure, it would be different, but the wrong way to specify an air flow.

I think Spades is right, your consumption is more than 4.5 scfm. You could use an accumulator if your post driver use is intermittant. (Think of it as a filter capacitor.) Or run another hose in parallel.

Regarding the PVC pipe, YES and YES.

PVC can be degraded by oil, and is relatively brittle, so if it bursts it becomes shrapnel. HDPE works, though.

As Spades notes, 3/8" is too small for the flow and distance.

That said, if you can keep people far enough away from the proposed PVC solution (say 550 feet of PVC with 50 feet of proper hose near the work), you might get by on a short-term basis. I'm not exactly recommending that, but I don't know your other constraints.

I would assume his 6x100' of PVC hose in 3/8" is flexible PVC (as implied by "hose"), maybe reinforced, which could be OK. uPVC pipe is a no-no for compressed air, for reason you gave.

Thanks to the comments by forum members, and our good friends at the orange box store, we are proud owners of a new wheelbarrow style gasoline engine air compressor.

We are also checking on a gasoline-driven post driver. After just two days, I am convinced we will be looking at a hydraulic driven skid steer option in the very near future!

Thanks again... in less than 12 hours I have learned four or five very valuable bits of information. CR4 is just too cool.

Tx

PVC pipe can be used safely, IF BURIED, with rubber at both ends above ground. Otherwise, don't use it.

You need bigger pipe, accumulator or both.

add wheels to the compressor, not a longer hose.

The compressor already has wheels, it's mounted on his truck, so likely too large to be portable. I assume that is why he has sought alternatives.

With your hose you will not be able to do a decent spray job.

A tank will help and make the pressure the same, only when the demand and pressure

on the demand outlet are within the feed limits.

You will save gas with a bigger diameter hose.

We don't know what you are doing there with the air, so my answer is not personalized to your application.

Sorry did not read "pneumatic post driver". A tank will probably help for a few more seconds, to minutes, depending on the volume of the tank.

let me just tell U what we did.

from our main compressor air-receiver we set up a line running the whole factory up to an adjacent unit, probably some 500'0 in total. WE used the most improbable pipe for this job (noone believed it would work but it's been over 10 years and it's still going, no leaks no nothing). The pipe used is Poly-ethylene pressure type water pipe of size 25mm, or 1" if U want. the inner diameter is about 3/4" or a bit less but larger than 5/8th of an inch.

Where the air is critical for opening a series of valves which have a precise sequence we put a 30 litre tank (as used on lorries fro their brakes).

That's it.

S

I had the same sort of problem. I solved it by putting large pneumatic wheels on the compressor so i could move it through the dirt. Also a crane on the truck to lift it on and off. I see that you have now done something similar.
We get these threads a long time after others do and so i often don't post as the solution is already given. Just thought i would put in my 2c worth.
Jim

1st yes increasing the hose size would allow higher flow at a higher pressure. PVC pipe a bad idea. It fractures and fragments causing shards to be expelled when it goes. That why it not allowed to be used.

2nd Yes a auxiliary tank would help. size would be depended upon how long the tools driven and how much air consumed.

3rd Since you didn't explain why you are unable to get no closer then 600 ft(1/8 mile) from the worksite. With the need to use truck supplied utilities. Find away to get it closer. Even if it's a terrain problem acqiure something that can transverse the terrain. Pull the compressor off the truck and put it on that.

'DO NOT USE SCHEDULE 40 PVC PIPE FOR COMPRESSED AIR.
If you are considering transporting/dragging an accumulator closer to the point of use...what about dragging a tag along 100 CFM compressor instead?

I didn't read all the postings but I haven't seen where you specified the following:

1. What size posts you are trying to drive.
2. Type of soil - rocky - sandy - loam?
3. Model and manufacturer of the pneumatic driver?

These things matter. Most post drivers must be powered with a HIGH CFM compressor.

Not sure if this has already been mentioned, but have you considered hiring/buying a smaller compressor with either it's own or separate power and carrying/transporting it to the work site? 1 x Google search revealed a 5 cfm compressor weighing ~75kg/166lb, so it looks doable.

Good luck

We drove 185 posts the first day with this -

http://www.tractorsupply.com/en/store/deluxe-post-driver

Holy Crap! You da MAN!!! Biceps of an OX!

It looks like the suggestions worked.

Good Luck.

P.S. If you fabricate the Fence Post Lawn Dart Launcher, I want to play. Oh, and Please post video!

Thanks for reporting back. I think you have a good solution. I'm still not sure about the pressure drop - maybe you had a kinked hose! 2 SCFM through a 3/8" hose should not have given that much drop. Maybe you had some leaks? It doesn't take much of a leak to be several CFM. That's a lot of fence - I've driven a few metal posts with the manual version, and that's still way better than a post hole digger and wood posts!

Happy fencing!

You said "We could not drive the truck, with its bed-mounted compressor, to the pastures to be fenced, because there is no bridge across the creek."

If you have pastures do you have a tractor? My farmer uncle used his tractor to push the posts into the ground using the tractors' weight and hydraulics. If you could get across the creek yourself i'm sure a tractor could also. He made a short tube/pipe receiver with arms coming down to attach to the TPL. If your TPL doesn't drive down you could use hydraulics and a ram. If you have a bucket you could temporarily bolt the tube/pipe under the bucket and push down with that.

JIm

txmedic3338
Thank you for the result report. I appreciate the feedback and I know many of the other contributors do also.
Good Luck and be careful.