Compressed air piping system design field guide

What a compressed air system has to do

A compressed air system makes, treats, stores, and delivers air to tools and equipment at a pressure they can use. The goal is simple to say and easy to get wrong: clean, dry air at adequate pressure, with as little drop and as few leaks as you can manage. Air looks free because it comes out of the room. It is not. Compressing it is one of the most expensive ways to move energy in the building, and roughly seven to eight of every ten dollars you put into a compressor over its life is electricity, not the machine.

That cost is why this guide leans on two numbers all the way through: pressure drop and leakage. Every psi the piping eats is a psi the compressor has to make and never use. Every leak is air you paid to compress, hissing into the room around the clock. A system can pass a startup test, push tools fine on day one, and still bleed money for twenty years because nobody designed the piping to hold pressure or fixed the leaks once they started.

Two decisions sit underneath everything here and have their own guides. Which method joins the pipe is covered in the pipe joining methods guide, and where the shutoffs go is covered in the valve types guide. This one is the system: the parts in the chain, how big the pipe has to be, what it is made of, how the water comes out, and where the air finally meets the tool.

The parts of the system, in order

Air moves through the same chain in almost every shop, and each part has one job. Trace it from the wall to the tool and the design makes sense.

The compressor draws in room air and squeezes it. The receiver tank stores that air and smooths the pulses so the system sees steady pressure instead of the compressor's heartbeat. The dryer pulls the water back out, because compressing air wrings moisture into it. Filters catch the particulate, the condensate, and the oil carryover the dryer did not handle. The distribution piping, the main and the branches, carries the treated air across the building. The drops come down off that main to each work area. And at the tool, the FRL, the filter, regulator, and lubricator, sets the final pressure and conditions the air for that one point of use.

Skip a link and the system tells on you downstream. No dryer and the tools rust from the inside. No receiver and the compressor short-cycles and the pressure sags every time a tool fires. Undersized piping and the air arrives too soft to work. The chain is the design, and the rest of this guide is each link in turn.

The compressor and the receiver tank

The compressor makes the air and the receiver tank stores it, and the two work as a pair. Sizing the compressor is its own exercise tied to the connected tool load and the duty cycle, so treat it here as the source that feeds the piping rather than the subject of the design. What matters for the system is that it delivers the CFM the tools draw at the same time, with margin, and that it does not run flat out every minute, because a compressor that never unloads has no headroom and no life.

The receiver is the part people undersize or skip. It stores compressed air so short, heavy demands pull from the tank instead of forcing the compressor to chase every trigger pull. That stored air smooths the pressure the system sees, gives the controls time to react, and lets the compressor cycle on its own terms instead of hammering on and off. A blast cabinet, a large cylinder, or a line of impact tools all hit the system as a spike, and the tank is what absorbs the spike.

The receiver is a pressure vessel and it carries the code that goes with that. Tanks above the small-shop threshold are built and stamped to the ASME Boiler and Pressure Vessel Code, Section VIII, and they require a properly sized relief valve and a means to drain the condensate that collects at the bottom. More on the relief and the drain in the safety and condensate sections.

Why does pressure drop matter in a compressed air system?

Pressure drop is the pressure the air loses fighting its way through the pipe, the fittings, and the treatment between the compressor and the tool, and it is the enemy the whole design is built to beat. Every psi lost in the piping is a psi the compressor had to make and the tool never sees. The fix is not to crank the compressor up to cover it, because raising system pressure raises energy use and leak rate across the entire plant, not just the one starved drop.

The design target is to keep the total drop from the compressor to the most remote tool low. Many systems aim to hold it to about 10 percent of system pressure or less, and tight designs target only a few psi end to end. Treat those as planning figures, not law: the right number comes from the tools, the process, and what the equipment lists as its minimum operating pressure. The point is the same either way. You hold the drop by making the pipe bigger than the bare flow demands, not by feeding the system more pressure.

This is the single design driver behind the next few sections. Size the pipe to cut the drop, route a loop to cut it further, and keep the fittings and the treatment in the budget too, because a clogged filter or a string of tight elbows can eat as much pressure as a long run of undersized pipe.

How do you size compressed air pipe?

Size compressed air pipe for the CFM it carries and the pressure drop you will accept over its length, then go up from there, because with air, bigger pipe is cheaper to run. Unlike a water line, where you do not want to oversize, an oversized air main costs you nothing in operation. It lowers the velocity, lowers the drop, and gives the system a little extra storage in the bargain. The only penalty is material and labor up front, which is small next to twenty years of pumping against a pipe that is too small.

The two inputs are the flow and the length. Add up the CFM of every tool that can run at the same time, not the nameplate of each one in isolation, and add a margin for leaks and for the next machine the plant buys. Then take the real routed length of the run and add an allowance for the fittings, because every elbow, tee, and valve adds equivalent length the air has to fight through. A common screen is to keep velocity in the main under about 20 to 30 ft per second at peak flow, then confirm the pressure drop over the length lands inside the budget.

Undersized pipe is the quiet, permanent tax. It does not fail. It just drops pressure every hour the plant runs, so the compressor works at a higher setpoint to compensate and the energy bill carries it forever. When the sizing chart puts you between two pipe sizes on a main, take the larger one. The reel of bigger pipe is a one-time cost. The pressure drop is a bill that never stops.

Compressed air pipe materials

The pipe carries the air, and the material decides whether that air stays clean and whether the joints leak. Four metals do almost all the work in shop and plant air, plus one modern modular system that has taken over a lot of new installs. The one material that does not belong here at all is plastic pressure pipe, and that gets its own section next because it is a safety rule, not a preference.

Black iron and steel is the traditional choice, threaded or welded, strong and cheap and everywhere. The problem is rust. Moisture in the air corrodes the inside, and the scale flakes off into the airstream, narrows the bore over time, clogs filters, and contaminates tools and finishes. Galvanized has the same problem once the coating gives up at the threads. Copper is clean, corrosion-free, and lighter than steel, soldered or brazed or pressed the same way as plumbing copper, and its drawback is mostly cost. Stainless is the premium clean option, common on oil-free systems and processes that cannot tolerate any corrosion, and modern pressed stainless has cut what used to be slow, expensive welding.

Aluminum modular pipe is the popular modern answer. It is corrosion-free so the air stays clean, the bore is smooth so the drop is low, and the push-fit or press fittings go together fast, come apart to reconfigure, and seal without the leak paths that threaded steel joints open up. It costs more per foot than black iron but installs in a fraction of the labor and does not rust the system from the inside. How any of these actually get joined, sweat versus press versus thread versus grooved, is covered in the pipe joining methods guide.

Can you use PVC for compressed air?

No. Do not use PVC or CPVC pipe for compressed air. This is not a preference or a code technicality you can argue around. OSHA prohibits PVC for above-ground compressed air, and the reason is that PVC under air pressure does not split and leak the way a water line does. It shatters. When it lets go it throws plastic shrapnel across the room like a bomb, because compressed gas stores enormous energy and dumps all of it the instant the pipe fails.

The physics is the part to understand, because it is why air is different from water. A liquid barely compresses, so a water line that bursts loses its energy almost instantly and stops. Compressed air is a coiled spring. The whole system's worth of stored energy releases at once through the break, and it drives the fragments. There is a documented case of a PVC air line that burst 27 ft up in a warehouse and threw a fragment 60 ft into a roll of paper. That is the failure mode you are designing against.

It gets worse with time and temperature. PVC turns brittle as it ages, brittle below freezing, and its pressure rating roughly halves by the time the air around it reaches 110 degrees F, which is ordinary near a compressor. A PVC air line that holds today is a line that has been getting more dangerous every year it has been up. Run metal or run a piping system listed for compressed air. If someone before you ran PVC for air, it comes out. Treat that as the firmest rule in this guide.

Loop main versus dead-end branch

Two basic layouts move air around a building: a loop, also called a ring main, that ties the distribution piping back on itself, and a dead-end branch that runs out to its last drop and stops. The loop is the better design for most plants, and the reason is pressure. A loop feeds every drop from two directions, so the air splits and the flow in any one leg is lower, which cuts the velocity and the drop and gives the far corners of the shop pressure that holds up under load.

The dead-end branch is simpler and cheaper to install, and it works fine for a small shop with light, intermittent demand. Its weakness shows up at the end of the run, where the last tool is the worst served and the pressure sags hardest when something upstream is drawing. A long dead-end branch is also where condensate collects at the closed end with nowhere to go but into the last drop.

The loop's other advantage is operational. Because the air can reach any point two ways, you can isolate a section of the loop for service without killing the whole plant, as long as you put the isolation valves in to do it. A rough planning rule is that a looped layout carries noticeably more air than the same size pipe run as a straight line, on the order of half again as much, so the loop earns part of its cost back in the pipe size it lets you use.

Why does compressed air have water in it?

Compressed air carries water because room air is full of water vapor, and squeezing the air wrings that vapor toward its liquid point. Warm air holds a lot of moisture. When the compressor packs that air into a fraction of its volume and it then cools in the tank and the piping, the air can no longer hold all the water it started with, and the excess drops out as liquid condensate inside the system. A compressor is, among other things, a very effective machine for making water.

That water is the second enemy after pressure drop, and it does real damage. It rusts the inside of steel pipe and steel tools. It washes the oil out of air motors and bearings. It blows downstream into a paint gun and ruins the finish, into a sandblaster and clumps the media, into a pneumatic control and makes it act up in ways that get chased as a logic fault when it is really a slug of water. In freezing spaces it can ice up a line and block it.

You manage the water two ways, and a good system does both. You remove most of it with a dryer so the air leaves the equipment room dry, covered next. And you catch whatever still drops out in the piping with slope, drip legs, and drains, and you take the drops off the top of the main so the water cannot run down into the tool. Get the water out at the source and keep the rest from reaching the work.

The dryer and the dew point

The dryer is the part that pulls the water vapor out of the air, and it is rated by the dew point it can reach, the temperature at which the air would start to condense again. Drier air means a lower dew point. The right dryer for a system is set by how dry the process needs to be and how cold the air will get downstream, because air dried only to 50 degrees F dew point will condense again the moment it hits a 40 degree F outdoor run.

Two types cover most work. A refrigerated dryer cools the air to drop the water out and then reheats it, and it gets the pressure dew point down to roughly 35 to 40 degrees F. That is dry enough for general shop and tool air and it is the common, lower-cost choice for indoor systems. A desiccant dryer runs the air through a bed that adsorbs the moisture, and it reaches far lower dew points, commonly down to around minus 40 degrees F, which is what you need for outdoor lines that freeze, for instrument and control air, and for processes that cannot tolerate any moisture.

Match the dryer to the duty. Pay for a refrigerated unit on a heated indoor plant and you are done. Reach for desiccant where the air runs cold, where the spec calls a low dew point, or where the application is unforgiving. Either way the dryer has a condensate drain that has to actually work, because a dryer collecting water it never discharges is just an expensive piece of pipe.

Slope, drip legs, and taking the drop off the top

Even with a good dryer, some water drops out in the piping as the air cools across the building, so the distribution has to be built to collect it and get rid of it. Slope the main in the direction of flow, a slight pitch is enough, so the condensate runs downhill to a low point instead of pooling. At those low points and at the ends of runs, install drip legs: a short vertical extension of pipe below the main with a drain at the bottom that catches the water gravity pulls down and lets you blow it off, manually or with an automatic drain.

The rule that separates a system that works from one that floods tools is where you take the drop. Take every branch and drop off the top of the main, not the bottom. Air leaving the top of a horizontal pipe is the driest air in the line, because the water is running along the bottom. Run the take-off up and over from the top and the condensate stays in the main and heads for the next drip leg. Take the drop off the bottom and you have built a funnel that pours collected water straight down into the tool.

This is the moisture mistake that shows up in the field constantly. A plant complains of water at the bottling line or the paint booth, and the take-offs are off the bottom of the header, draining the whole main into the worst possible spot. Top take-offs and drip legs at the low points are cheap to build in and miserable to retrofit. Get them in on the drawing.

Filters and the FRL at the point of use

Filtration cleans the air the dryer could not finish, and most of it lives at or near the point of use as the FRL: the filter, regulator, and lubricator stacked together at the drop. The filter pulls out particulate and any condensate that made it this far, and a coalescing filter goes further and strips out oil aerosol and fine mist for applications that need oil-free air. The regulator sets the pressure for that one tool down to what it actually wants, which is usually lower than main pressure and is the cheapest way to cut both air use and wear. The lubricator, where the tool needs it, meters a little oil into the air to keep air motors and impacts alive.

Match the FRL to the tool. An impact wrench wants the lubricator. A paint gun or a plasma cutter wants the lubricator gone and a coalescing filter in front of it, because oil in the air wrecks the work. Sizing matters too, because an undersized filter or regulator is just another pressure drop sitting right at the tool, choking the air after you went to the trouble of sizing the main correctly.

Filters load up and that is the point, but a loaded filter is a pressure drop in disguise. Watch the differential across it, or at least change it on a schedule, because a plugged element can eat more pressure than a long run of pipe and nobody notices until the tools go soft.

The drops to the tools

A drop is the line that brings air down from the main to a work area, and how you build it decides whether that station gets dry air at full pressure. Take it off the top of the main, as covered above, run it down to working height, and land it on the FRL and a quick-connect coupler so a tool or hose snaps on and off without tools. The quick-connect is convenience, but it is also a small restriction, so on a heavy drop size it up to match the flow rather than necking the whole station down to a 1/4 in coupler.

Put a shutoff at the top of each drop so you can service the station, swap an FRL, or chase a leak without bleeding the whole plant. That valve plus the drip leg at the base of the drop is the standard detail: isolate above, drain below, condition through the FRL, connect at the coupler. It is a small amount of pipe and fittings per station and it is the difference between a clean work cell and a wet, soft one.

Leave a little slack in how you place drops, because work cells move. The strength of a loop main with top take-offs is that adding or relocating a drop is a tap into the loop, not a re-plumb of the building, especially with a modular system that comes apart and goes back together.

Leaks: the silent cost

Leaks are the largest, quietest waste in almost every compressed air system, and they run around the clock whether the plant is making parts or sitting empty on a Sunday. The U.S. Department of Energy puts the loss in a typical, unmanaged facility at 20 to 30 percent of the compressor's output, blowing out of fittings, couplers, hoses, and worn tools you walk past every day. That is not a rounding error. That is a fifth to a third of the most expensive utility in the building, paid for and thrown away.

The trouble is you cannot hear most of them. A leak on a running production floor makes its noise up in the ultrasonic band, around 20 to 40 kHz, well above what your ears catch over the machinery. That is why a real leak survey uses an ultrasonic detector that translates that hiss down into something you can hear and point at. Tag what you find, fix it, and log it, because leaks come back as fittings loosen and hoses age, so the survey is a routine, not a one-time event.

The payback is unusually fast for plant work. A facility that runs a steady find-and-fix program can pull leakage down to under 5 to 10 percent of capacity, and the recovered air often lets the compressor run at a lower setpoint or unload more, which compounds the savings. Of every efficiency move on a compressed air system, fixing leaks is usually the cheapest and the one that pays back first.

Isolation valves so one repair does not stop the plant

Isolation valves let you shut off a section of the system to service it without dumping the whole plant, and where you put them is a design decision, not an afterthought. Without sectioning valves, every leak repair, every FRL swap, every added drop means bleeding the entire system and shutting down everyone on it. With them, you close two valves, work on the dead section, and the rest of the shop keeps running.

Put a valve at each drop, valves that section a loop main so you can isolate one leg, and a main shutoff so the whole system can be locked out and bled for major work. On a loop, sectioning valves are what let you take half the ring down while the air still reaches every drop from the other direction. A full-bore ball valve is the usual pick for air isolation because it is open or closed with a quarter turn and adds almost no pressure drop when open, which matters on a system where you fought for every psi.

Which valve goes where, and why a ball beats a gate for this duty, is covered in the valve types guide. The design point here is to draw the isolation in from the start. Retrofitting shutoffs into a live system is far more work than welding or pressing them in while the pipe is open.

Air quality classes and ISO 8573

Not all compressed air has to be the same cleanliness, and ISO 8573 is the standard that lets you specify how clean. It rates the air on three contaminants, particulate, water, and oil, and assigns a class number to each, where a lower number is cleaner. So an application is not just dry or not dry. It is a set of three numbers covering solids, moisture, and oil, and the treatment train, the dryer and the filters, is built to hit those numbers.

Match the class to the work, because over-treating costs money and under-treating ruins product. General shop and tool air is forgiving and lives at a relaxed class on all three. Food and beverage contact, pharmaceutical, electronics, and medical air sit at the tight end, where particulate is measured in fractions of a micron and the water and oil limits are strict. The cleanest classes are where a desiccant dryer, coalescing filters, and sometimes oil-free compression all stack up to get there.

Treat ISO 8573 as a planning framework and confirm the exact class against the process spec, the equipment requirements, and the application, because the right answer is set by what the air touches at the end. A class that is fine for an impact wrench is nowhere near clean enough for a tablet press, and a class built for a clean room is money wasted on a tire shop.

Oil-free versus lubricated air

Compressors come in lubricated and oil-free designs, and the split decides whether any oil reaches the air. A lubricated compressor uses oil to seal and cool the compression, and a little of it carries over into the air as aerosol, which coalescing filters can then strip back out downstream. An oil-free compressor keeps oil out of the compression entirely, so there is no carryover to filter.

Pick by what the air touches. Lubricated compression with good filtration is the common, lower-cost choice for general shop air, impacts, and most plant work, and the carryover is a non-issue once the filters are right. Oil-free is the call where even a trace of oil is unacceptable: food and beverage contact, pharmaceutical, medical breathing air, electronics, and a lot of painting, where oil in the line fish-eyes the finish.

Going oil-free changes more than the compressor. Plants running oil-free often pair it with stainless or aluminum piping rather than steel, because the whole point of clean air is lost if it picks up rust on the way to the tool. The compression, the treatment, and the pipe material are one decision, not three.

Safety: stored energy is the hazard

A compressed air system stores a large amount of energy, and that stored energy is the hazard that runs under all of it. The whole reason PVC is banned is this energy: when a pressurized component fails, it does not leak quietly, it releases everything at once. Design and build the system so the energy stays contained and has a controlled way out when pressure climbs.

The non-negotiables are short. Every receiver and pressure vessel carries a properly sized relief valve set at or below the vessel rating, and that valve never gets plugged, painted over, or valved off. Receivers above the small-shop size are built and stamped to the ASME Boiler and Pressure Vessel Code, Section VIII. Air hoses under pressure whip viciously if a coupling lets go, so secure connections and use whip-check restraints or safety clips on the couplings that can come apart under load. Never aim a blow gun at skin or use one above the pressure its safety nozzle allows, because air driven into the body is a medical emergency, not a joke.

Lock out and bleed the section before you open it. The pipe can read zero at a gauge that is stuck or isolated from the part you are cutting into, so verify it is actually dead and drained before the wrench or the saw comes out. And keep PVC out of the system entirely. The pressure hazard and the no-PVC rule are the two safety lines on this job that do not bend.

Sizing the receiver and storage

The receiver tank gets sized for the demand swing it has to absorb, not just to have a tank in the room. A system with steady, even demand needs less storage. A system with big, short spikes, a blast cabinet, a bank of cylinders, a press that fires hard and then waits, needs more, because the tank is what feeds those spikes so the compressor does not have to chase them. Undersize it and the compressor short-cycles and the pressure dips on every spike. Size it right and the compressor runs longer, steadier cycles and lasts longer.

A common rule of thumb ties storage to compressor capacity, often in the range of several gallons of receiver per CFM, with more for systems that swing hard or that need the tank to ride through a brief peak. Take that as a starting point and let the demand profile and the compressor manufacturer's guidance set the real number, because a variable-speed compressor and a fixed-speed one want different amounts of storage. Some plants add a second receiver out near a heavy intermittent load so the storage sits where the spike is.

Bigger storage also buys a little pressure stability and a slightly lower compressor setpoint, which loops back to energy. The receiver is cheap next to the compressor and the energy bill, so erring larger on storage is the same kind of good bet as erring larger on pipe.

Energy efficiency: where the money actually goes

Compressed air is expensive to make, so the design choices that matter most are the ones that cut the energy it takes to run, and three levers do most of the work. Fix the leaks, hold the pressure drop low, and run the lowest system pressure the tools and the process will accept. The three compound: lower leakage and lower drop both let you lower the setpoint, and a lower setpoint cuts energy and shrinks the remaining leaks at the same time.

System pressure is the lever people overlook. Every increment you raise the setpoint to cover a soft tool or a sagging far corner raises the energy across the whole plant and increases the flow out of every leak, because leak rate climbs with pressure. A rough industry figure is that each couple of psi of unnecessary system pressure adds about one percent to the energy bill. So the cheaper move is almost always to find why that one drop is soft, undersized pipe, a plugged filter, a bottom take-off, than to lean on the regulator and pressurize the entire building to cover it.

This is why the piping design and the energy bill are the same conversation. Oversized pipe, a loop, top take-offs, clean filters, and a tight leak program all let the system run at a lower pressure and deliver full air at the tool. The system that was designed to hold pressure is the same system that is cheap to run.

Installing the piping: supports, thermal, and connections

A clean design fails if the install is sloppy, and air piping has a few details worth getting right. Support the pipe at the spacing the material and size call for so it does not sag, because a sag becomes a low spot where condensate pools between drip legs and undoes the slope you built in. Use hangers suited to the material, and isolate dissimilar metals where they meet so you do not set up galvanic corrosion at the joint.

Account for thermal movement. The pipe leaving a hot compressor and crossing a cold warehouse expands and contracts, and aluminum and copper move more than steel for the same temperature swing. Long straight runs need that movement absorbed in the layout or with the fittings, especially on modular systems where a hard-locked run can stress the joints as it grows and shrinks. Leave the compressor connection itself flexible so vibration does not telegraph into the hard piping and loosen joints.

Joint quality is where the leaks you spend years chasing are born. A pressed joint with a missed crimp, a threaded joint with thin or sloppy sealant, a solvent joint rushed before cure, each one becomes a leak the moment the system pressurizes. How each connection is actually made, and how to make it hold, is the pipe joining methods guide. Make the joints right on the first pass, because every one of them is a future leak if it is not.

What to document

A compressed air system that is not documented is a system the next person has to reverse-engineer with a flashlight. Record what was installed and why, so the people who service it, expand it, and audit it can do their work without guessing. The record is also what a leak survey and an energy audit start from, and it is what tells you whether the system still matches the load it was built for.

Capture the source and the treatment, the distribution, and the design intent that drove the sizing. The table below is the short version. Keep it with the as-builts and update it when the plant adds a machine or moves a cell, because a stale air drawing is how a system ends up undersized for a load that crept up on it one tool at a time.

Common mistakes

• Running PVC or CPVC for compressed air, which can shatter under pressure and is prohibited by OSHA above ground.
• Undersizing the pipe, so the system runs a permanent pressure drop and a higher compressor setpoint to cover it.
• Taking drops off the bottom of the main, which funnels collected condensate straight down into the tool.
• Leaving out drip legs and condensate drains at the low points, so water pools in the piping.
• Skipping the dryer, so moisture rusts the lines and tools and ruins finishes and process.
• Ignoring leaks, which commonly waste 20 to 30 percent of the compressor's output around the clock.
• Omitting isolation valves, so every small repair means shutting down the whole plant.
• Raising system pressure to cover a soft drop instead of fixing the undersized pipe or plugged filter behind it.

Field checklist

Standards and references

Several bodies govern different parts of a compressed air system, and naming the right one for the point keeps the work defensible. OSHA is the safety authority that prohibits PVC for above-ground compressed air and governs the pressure and blow-gun hazards, and its hazard bulletin on the use of PVC pipe is the document behind the no-plastic rule. Treat that prohibition as firm and verify the current OSHA requirements for the installation.

The receiver and any other pressure vessel fall under the ASME Boiler and Pressure Vessel Code, Section VIII, which is what the tank is built and stamped to, and the piping system design draws on ASME B31, the pressure piping code, for the piping itself. Air cleanliness is specified to ISO 8573, which sets the purity classes for particulate, water, and oil. These are the frameworks, and the exact editions, the local amendments, and the AHJ control how they apply to a given job.

Hedge the design numbers and lean hard on the safety rules. The pressure-drop targets, the velocity screens, the dew points, the receiver-per-CFM rule of thumb, and the air quality class are planning figures to confirm against the tools, the process, the equipment manufacturer, and the project spec. The no-PVC prohibition and the relief-and-bleed safety practices are not figures to hedge. They are the lines that keep someone from getting hurt.

Units and terms

Compressed air work mixes a few unit systems and a lot of shorthand, so the same idea reads differently across a tool sheet, a compressor nameplate, and a drawing set.

Flow is in CFM, cubic feet per minute, sometimes qualified as SCFM at standard conditions, while metric sources use cubic meters per minute or per hour and liters per second. Pressure is psi in the shop, often psig at the gauge, and bar or kPa on metric equipment, where about 14.5 psi makes one bar. Dew point, the dryness measure, is in degrees F or C. Air cleanliness is the three-number ISO 8573 class. The FRL is the filter, regulator, and lubricator at the drop, and a drip leg, also called a drop leg, is the dead-end vertical with a drain that catches condensate.

CFM / SCFM

Cubic feet per minute of air flow; SCFM is referenced to standard conditions

psig / bar

System pressure at the gauge; about 14.5 psi equals one bar

Pressure drop

Pressure lost to the pipe, fittings, and treatment between compressor and tool

Pressure dew point

Temperature at which the compressed air would start to condense; the dryness rating

FRL

Filter, regulator, and lubricator assembly at the point of use

Drip leg / drop leg

A vertical dead-end below the main with a drain to catch condensate

Receiver

The air storage tank that buffers demand and smooths pressure; an ASME pressure vessel

ISO 8573 class

Compressed air purity rating for particulate, water, and oil; lower is cleaner

Related tools

Calculators and readiness checks for this work

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