Frequently pneumatic cylinders of international, ISO, origin have the bore and stroke listed in Millimeters, mm, instead of inches as had been the North American standard.

The majority of compressed air information in North America that relates to flow rates and usage is given in SCF (Standard Cubic Feet) or SCFM (Standard Cubic Feet per Minute). The compressed air pressure is most frequently listed in PSIG (Pounds per Square Inch, Gage)

This presents a challenge when designing, sizing or evaluating the amount of compressed air required or used. It is laborious to convert each metric dimension to the English inch, psig and scfm system.

From Norgren Helpful Engineering Information, NC-77, formula we crunched the constants.

You may enter the bore and stroke of a cylinder in inches (Formula 1) or in millimeters (Formula 2) and get results in SCFM.

Another pair of formulas will aid calculating the volume and how much compressed air a cylinder may hold.

In the event your cylinder is listed in inches just use the original formula as follows:

PEAK FLOW

1. INCH Qscfm =.001857 x D²" x L"x (PSIG + 14.7)/ tsec

2. METRIC Q scfm = D² mm x L mm x (PSIG + 14.7)/ (t sec. x 8823803.69)

VOLUME – SCF

1. INCH Qscf =.001857 x D²" x L"x (PSIG + 14.7)

2. METRIC Q scf = D² mm x L mm x (PSIG + 14.7)/ 8823803.69

VOLUME PER CYCLE (Ignoring rod diameter)

1. INCH Qscf = 2 x [.001857 x D²" x L"x (PSIG + 14.7)]

2. METRIC Q scf = 2 x [ D² mm x L mm x (PSIG + 14.7)/ 8823803.69

VOLUME PER CYCLE (Subtracting rod diameter)

1. INCH Qscf = .001857 x [(2 x D²") – d²] x L"x (PSIG + 14.7)]

2. METRIC Q scf = [(2 x D² mm) -d^2 mm] x L mm x (PSIG + 14.7)/ 8823803.69

Now estimate the total number of each type of cylinder. Multiply by the number of cycles estimated per minute times the Volume per Cycle and add them all together for the total SCFM of compressed air per minute for cylinders.

From the formula for Volume Per Cycle take any cylinder result for "Q scf" and multiply by a reduced pressure. "Q scf" x [ 1 – [ (New PSIG + 14.7) / (Original PSIG + 14.7)]]

Example: 20 scfm x [1 – (104.7psia/114.7psia)] = 1.74 scfm. Approximately 9% of the air can be saved by reducing the pressure from 100 psig to 90 psig.

A recent figure of $.07 per Kilowatt Hour. One kilowatt hour = 1.341 Horse Power hour.

With a rule of thumb of 4 SCF per horse power x 1.341 x .07 = 5.36 scfm for $.07 electrical

RECYCLE EXHAUST AIR Sept. 27, 2005

Does it seem illogical to compress, dehydrate, filter, regulate and add lubricant to prepare compressed air then expand it through a valve into a cylinder or air motor and dump it out? An exhaust manifold at 30 PSIG could be a ready source of clean, dry, "FREE" compressed air. Many systems currently have an exhaust manifold to contain the exhausted air and pipe it out of the immediate work area. The additional plumbing for most other applications and systems could easily be justified with the pay back of free air.

• By using special quick connect fittings blow guns normally regulated to 30 PSIG could be directly connected.
• By using the 30 PSIG as an air spring to return cylinders to the home position the saving is multiplied.*
• The exhausted air can be filtered, coalesced, further dehydrated if necessary and regulated down for Instrument air.
• Air for venturi vacuum generators, blow off, agitation, cooling, tension, mist bearing and chain lubrication is free.

Compressed air used as a spring has advantages over mechanical springs. The air has a flat rate that does not change with extension/compression as mechanical springs do. With 30 PSIG clean lubricated compressed air to return cylinders they would start faster. For example with a typical system using 80 PSIG for both the work stroke and return a slight delay occurs when the valve is shifted into the work stroke. The 80 PSIG return air must decay to provide a differential pressure adequate to break away and provide energy for thrust. After break away a cylinder is often moving at a rate of imbalance of only 20 PSID. The velocity and force are controlled by the rate of exhaust. By using an 'air spring' at 30 PSIG the differential would be approximately 50 PSID. The cylinder would start sooner, move faster with more thrust. The final force and return stroke speed would be slightly reduced. Air motors would have an ample supply of clean, lubricated air. A larger motor can be used to compensate for lower pressure.

• Pressure in the exhaust or low pressure manifold can be maintained with a regulator.
• Reduced pressure lowers the dew point so the low pressure air is dryer.
• The expanded, lower pressure air is cooler until heat is adsorbed.
• Air spring cylinders only require 3 way valves rather than 4 way valves.
• Standard cylinders are less expensive than spring return cylinders.
• An air spring never wears out or breaks.
• Large diameter air bags could provide great force with the lower pressure for less cost than conventional cylinders.

A question was presented approximately as follows:

"I would like to supply 200 psig to a 20 foot long, 1/4" tube (We will take that to be .25 I.D.) that has 1/8" holes every 3 inches".

We do not understand many facets of the existing situation. At the known risk of assumption we will divide the 20 foot length of tubing by .25 foot (3") to determine that the number of 1/8" holes is 80.

My friends I messed this up and need to start over right after good morning.

At 200 psig each 1/8" hole could flow as much as 48 SCFM and 80 of those critters could flow 3,891 SCFM to atmosphere. That would require a

The question may have been posted in jest or something is missing.

This one becomes a "NEVER MIND".

Some remedies might be:

1. Reduce the number of 1/8" diameter outlet holes.
2. Reduce the diameter of the outlet holes.
3. Increase the ID of the supply tube.
4. Increase the supply pressure.
5. Tell us what you wish to accomplish.

IF YOU WANT TO GET WATER FROM A WELL

Water level 73 feet below 1382 foot surface.

There are a few cute ways to get the water from your well even discounting a bucket brigade of Dallas Cheer Leaders.

The reason you have heard that you cannot siphon water over 35 feet is that (at sea level) the atmospheric pressure is approximately 14.7 PSIA (absolute). This would theoretically raise water 33.9 feet in a perfect vacuum. All that is required is to adjust the local pressure in the well above ambient enough to complete the lift.

#1 Put a cap on your 6" Dia well casing with a tube through it or (double sided pipe fittings, for bulk head effect).

Connect a tube or pipe that will extend 140 feet from the well cap to below where the surface of the water in the well will be after it is depressed by pressure. Flexible nylon with some weigh on the end would work. That is a long way for rigid pipe and definitely not rigid plastic.

Add a pressure port (eg. 1/4 NPT) to the well cap.

Connect compressed air to the cap pressure port. Pressure as low as 25 PSIG will provide enough lift once you prime and start a siphon but the flow will be unenthusiastic.

Since a cubic foot is equivalent to approx' 7.48 gallon you will displace 7,480 gallons of water with 1000 cubic feet of compressed air. At a dollar per 1000 SCF of compressed air you can water a lot of cows for a buck. If you are filling a pond that will be extra. You can pump much water with a bottle of nitrogen as well.

#2 Much less fun would be to trench and bore horizontally into the well casing about fifty feet below the top of the well and use a natural siphon.

If you decide to go with the Dallas Cheer Leaders give me a call.

Edited 3/23/07 with thanks to Kceum & GW

How many times have you been told that perpetual motion cannot be achieved?

This is strange when we live on a globe that is in perpetual motion or something darn near like it.

The rotation of our earth within an associated (but unattached) atmosphere causes winds by viscous drag. The air that is our atmosphere nominally weighs .075 pounds per cubic foot at sea level and lessens with altitude. As the surface of our earth turns against the atmosphere at least two really great things happen.

First would be prevailing winds which at the 45th parallel here in Oregon come off the Pacific Ocean traveling from West to East. With a viscous couple at the boundary layer someone with more time and shook-um might give us a SWAG number for that kinetic energy based upon the surface area of the earth, viscosity and weight of air, velocity of rotation and form factor. I am going to cop out and say it is a mega bunch.

The second wonderful event is created by the ability of air to adsorb water vapor. As the air comes ashore here in the NW after a long trip over the Pacific it carries considerable water vapor. The weight of the water vapor is a another great big number (GBN).

As the winds push moisture laden air up slope as they come ashore the temperature gradient, cooler temperature, at higher elevations reduces the amount of vapor the air can hold. It rains.

What does that mean to us? It means that we can count upon a continual force produced by the air mass moving across the earth and there is a gazillion gallons of water vapor much higher than the surface of the earth. The weight of this water vapor is another tremendous potential energy.

Every sailor and skier knows that the wind and gravity are our friends. They also offer perpetual potential energy. Add to these wave motion, tides, temperature and barometric pressure changes harvest-able force differential.

"I see a shining city~~" on the shore with rain (fresh water) captured in reservoirs above and the excess water run through turbines. Sea water lifted by a series of air foils and run through turbines etc. etc. Don't sell your home in Topeka or stock in fossil fuels yet but be watchful.