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The purpose of the compressed air piping system is to deliver compressed air to the points of usage. The compressed air needs to be delivered with enough volume, appropriate quality, and pressure to properly power the components that use the compressed air.

The air system piping is sized using velocities based on flow volumes at actual conditions (ACFM) rather than at standard conditions.

A poorly designed compressed air system can

• Increase energy costs

• Promote equipment failure

• Reduce production efficiencies and

• Increase maintenance requirements

It is generally considered true that any additional costs spent improving the compressed air piping system will pay by itself many times over the life of the system.

Compressor Discharge Piping

Discharge piping from a compressor without an integral aftercooler can have very high temperatures. The pipe that is installed here must be able to handle these temperatures. The high temperatures can also cause thermal expansion of the pipe, which can add stress to the pipe. Check the compressor manufacturer's recommendations on discharge piping. Install a liquid filled pressure gauge, a thermometer, and a thermo-well in the discharge airline before the aftercooler.

Pipe must be carefully sized and arranged to minimize pressure drop. A good rule of thumb that is commonly used is to limit pressure drop to less than 1 PSIG per 100 linear feet. This applies to the rate of flow through any particular section of piping, and has little to do with total compressor capacity. Certain point of use applications may take compressed air at a rate of flow greater than the capacity of available compressors for a short duration. If the piping is sized per the capacity of the available compressor(s) rather than the rate of flow, it might represent a restriction that causes pressure to drop system-wide.

Piping and Fitting Pressure Drop

Pressure drop in a compressed air system is a critical factor. Pressure drop is caused by friction of the compressed air flowing against the inside of the pipe and through valves, tees, elbows and other components that make up a complete compressed air piping system.

Pressure drop can be affected by pipe size, type of pipes used, the number and type of valves, couplings, and bends in the system.

The cost of piping pressure loss can be calculated in real dollars. For every 2 pounds per square inch gauge (psig) loss in pressure, 1 percent more total kilowatts (kW) are required to overcome the loss. For example, a 10-psig-pressure drop in a 200-kW system operating 4,000 hours per year at 8 cents per kilowatt-hours (kWh), will cost an additional $3,200 in energy annually.

When condensate traps are faulty, air quality suffers tremendously, potentially affecting product quality. Look for operational problems and leaks, and be aware of where the condensate is going. Consider upgrading electrically timed solenoid drains because they waste a considerable amount of energy. Demand-type drains are available to bleed condensate without wasting air.

To avoid carryover of condensed moisture to tools, outlets should be taken from the top of

the pipeline. Larger pipe sizes, shorter pipe and hose lengths, smooth wall pipe, long radius swept tees, and long radius elbows all help reduce pressure drop within a compressed air piping system.

The connection points on air-consuming machinery and air tools are always a potential air leak point. Make sure connections are tight and hoses are in good working condition.

Pressure loss can be costly if the piping is not designed properly. It is always better to oversize the compressed air piping system that pays by itself and allows for expansion of the system.

Air receivers also are collection points for contaminants and are used to mechanically separate condensed liquids. If the condensate traps are not working properly, air receivers can fill with condensate and contaminants, not compressed air. Make sure the drains work correctly and replace if necessary.

Point of use components

Air must be delivered to the point of use at the desired pressure and in the right condition.

• Too low a pressure will impair tool efficiencies and affect process time.

• Too high a pressure may damage equipment, and will promote leaks and increase operating costs.

It’s a balancing act, but getting it ‘just right’ delivers good savings for you.

Rate of flow considerations at the point of use is much more important than in sizing distribution piping. When end users complain of low pressure the first thing blamed is the piping because “the user is at the other end of the system” or “the piping system has been expanded haphazardly over the years” (or whatever the excuse), the real problem is not necessarily the piping. The real source of problems described as “low pressure” usually resides in the choice of installed point of use components. While some loss in pressure is to be expected, a properly designed system should have a pressure drop below 10% of the compressor’s discharge pressure.

Pipe drops, filters, regulators, lubricators, quick disconnects, and hose must all be sized for the rate of flow at the point of use. A common mistake is to buy a tool that uses 100 SCFM, apply a 10% utilization factor to it and size all of the in-line components for 10 SCFM. The components need to be sized for the 100 SCFM rate of flow, not some averaged demand level used to size compressors!

The incorrect sizing of pipes can result in excessive pressure drop. Air should travel at a velocity of approximately 6-10m/s– the higher the velocity the higher the pressure drop.

• Properly design the distribution system; for example, minimize bends in the piping;

reduce the distance the air travels

• Operate and maintain air filtering and drying equipment to reduce the effects of moisture, such as pipe corrosion

• Select aftercoolers, separators, dryers and filters that have the lowest possible pressure drop for the rated conditions

• Specify pressure regulators, lubricators, hoses, and connections that have the best performance at the lowest pressure

• When purchasing components work with suppliers to ensure that products most efficiently meet the desired specifications for the air pressure required taking into account all of the system characteristics.

Carefully consider the possibility of separate dedicated air systems where these vary

significantly. For example, shop air; tank agitation air, and instrument air should generally not be combined on the same distribution circuit.

It is always beneficial and efficient to seek ways to reduce pressure drop rather than increasing discharge pressure or adding additional compressor capacity.