Difference Between Plant Air and Instrument Air?

Instrument air is often specially dried to reduce the risk of condensation freezing-out in the small-bore piping. It would not be unusual in higher latitudes to find instrument air that is dried to a dewpoint of -40degC, for example.

Instrument air as said above is dry air, its also filtered for fewer particulates and oil is removed...

Normal plant air will be dirtier, contain oil and high humidity - remember a lot of pneumatic tools need the air to have oil in a mist form in the air to lubricate the tool.

Instrument quality air should have this oil removed as well as the water and particles...

John.

"Normal plant air will be dirtier, contain oil and high humidity"

Not where I worked. It was widely used in labs. for various and sundry purposes and we had filters to remove oil and drier beds to get the dew point well below 0 deg. F.

Shops and outdoors tools were equipped with oilers to lubricate the tools.

In that case Stan you were using Instrument grade air...

John.

Plant air is typically dirty with oil and often contains condensate. In any facility that I have dealt with, the instrument air is highly filtered with a dewpoint of -40 deg F or lower.

Hi Dear ..

Hell OH !! I see you have a problem (hic..) in seperating (or was it identifying ) plant and instrument air. I also see you have a few informed opinions in form of replies to your query. Well dear friend...if you have time here is one more..in lighter spirit (or air..if you may)

There are a few questions you have posed, I assume it is not compulsary to answer all.. or is it ? And I also assume that I can answer the later ones first..OK

1) So "can one system do the job of the other". I think this is the most important and intellegant question I have coem across in a loooong time.. The asnwer is YES adn NO. Yes if it is a system ful of hot air (like my reply here) and NO if the system youa re suing is qualified as 'sensative' by say NASA, DRDO, IFCT, etc

2) "what is the exact technical/application wise difference between plant air and instrument air" Stupid question... me thinks..you have answered your query

Plant air is the mixture od O2, N2, dust, dirt used in the plant

and instrument air is the mixture of dirt, dust, N2 and O2, used in the isntrument

3) "why are both forms of compressed air required"

on this one you better tell me when you get a good enough reply...BUT for starters...

I think (the whole idea about compressing AIR) it is a big cartel organised by the BIG companies like Dresser Rand, Chicago Pneumatics, Khosla and Kislorkars, Pigone, etc who make those BIG machines for compressing air and other things...they simply do not want us to use the air as is.. un compressed,,see we have plenty full

Most compressors that supply plant air requirements do so at pressures up to 150 psi or so and the compressors that do that require lubrication sort of like an oil system in your car. This air, being contaminated mainly with lubricants cannot be economically cleaned and dried to meet the requirements of clean air in instruments, where the oily air would gum up the workings in instrument controllers, and the high pressures of plant air are not required in instruments therefore it would be impracticle, and uneconomical to use high pressure oily air. It all boils down to cost and practicality.

One important thing however, a lot of plants use plant air for general use and some plants have it hooked up to emergency air for personnel use. This is a mistake since the oily air could be mistaken and used by people. Therefore you might check your plant and ensure that any air supply used for personnel is from a non-oil injected air supply. It should also not be instrument air since the dried instrument air can have adverse effects on breathing, especially for asthma sufferers.

thanks to all the contributors of this thread! from all the discussion, I undestand that Insrtu air is comp air of purest form .. free of oil/moisture as it is used to actuate instru while plant air need not be purified... as it is for general purpose.

Here I need ot know one more thing.... wat kind of genral purpose does'plant air' servE? where else will the plant need compressed air apart from pneumatic actuation??

General purpose plant air use is dependent on type of facility and what work/production is performed in it. It sounds like what you need is a plant survey as to what would be the best application of plant/instrumentation air.

Very good list of Service Air applications + pneumatic cylinders and motors, e.g. in robotics. Some old applications use it for Logic System Elements.

Plant/Utility or Service Air usually has much higher nominal pressure (80 to 150 psi rarely up to 300 psi) than instrument (2 to 15 psi for analog actions with supply usually over 20 psi). For European units: 14.7 (about 15) psi = 1 bar = 100kPa (approx.), where atmospheric normal is also 760 mm Hg = 1 Atm = 1000 hPa.

What is your blood pressure? ............/.......... in which units?

Analog transmitters P/I have: Input =0.2 to 1 atm // Output =4 to 20 mA

Power pneumatics use lower pressure/ lower forces and higher speed comparing to hydraulics where are slow motion under v. high pressure and high forces.

I must differ with you on using instrument air for utility air. Suppose that a crew is sent out to bust up a concrete pad and attaches 3 jack hammers to your 3/4" inst air header.

I am sure you can see the results in pressure control.

we always protected the inst air header with placards that were installed on any bleed or branch valve reading: "Do not operate" periodic inspections were made to ensure that no cross connections were made between the plant and inst. air systems or any other system. (once had a Dowtherm line connected, Much much difficulty with that)

So what`s the difference between IA and breathing air, or process air ?

They all do what it say`s on the can !

Instrument air must be dryed to remove any moisture and/or condensate for:

1. Protecting the instruments and controls from damage.

2. Obtaining exact readings through these instruments and controls.

,

Comment for Tcinc002 - post #5.

Good point. Under no circumstances should asthma sufferers be considered as suitable candidates for hooking up to general purpose air. The implication here is they are expected to wear breathing apparatus to provide respiratory protection against a toxic and hazardous environment - that they should not be exposed to in the first place.

There are strict safety standards for 'Breathing Air' (BA), and they all require the air to be very dry - similar to instrument air.

Hospital air is very dry, and it is used with beneficial effect to treat asthma sufferers. Thus there is no case to argue about dry air having 'adverse effects' on asthma sufferers.

Historically, the 'dry-air-is-harmful' argument was used to avoid spending money on filters, dryers and purifiers.

Comment for Guest - post #11.

The air treatment process to filter and dry IA is much the same as Breathing Air, but BA must additionally be free of toxic gases and vapours - ie. purified.

It comes down to cost and consequence.

Bad IA (or any process air come to that) leads to breakdowns, product spoilage and loss - with identifiable costs that have immediate effects on pockets of the company.

Bad BA leads to employee poor health (maybe death) and long delayed damage settlements from 'difficult-to-prove' drawn out court battles (previously thought to the 'cheaper' option) - but not so nowadays.

Whatever you ethics or motivation, it is absolutely false economy not the treat the air to the required standard at the outset.

Normally you 'treat' the air to ensure the standard required is achieved at the point of use. You might need a combination of various grades of air, but as a general rule-of-thumb, if the highest quality is applicable to 'half' the air - then you might as well treat the lot to the same standard.

The other rule-of-thumb is to find an economic solution to do the complete job properly, rather than try to save money by doing half a job.

Does this make sense.

Cliff.

Instrument air is usually at a lower psig than plant air ( 40 or 50 vs 100 or so for plant air). Instrument air also must be drier and cleaner than plant air. It should have a very low dew point -30 to -40F is typical in the NE USA where my power plant is located.This is to prevent freezeups if the plant gets cold or if some of your equipment is exposed to the weather. It should also be oil free to prevent any problems with small particles getting stuck in small orifices. Actually all compressed air should be oil free to minimize any possibility of an explosion. Explosions are a real possibility when oil is entrained in your air. Oil free compressors are expensive and many plant operators cut corners here. This IMO is not the way to go. You can use the same compressor for both. Split your supply into 2 receivers - run the instrument air supply thru a dessicant type dryer/filter setup and maintain that receiver at a lower pressure. You should also have some sort of a backup system to insure a safe and orderly plant shutdown if some unexpected failure occurs. One last thing - if your plant uses Scott or MSA type breathing equipment for any type of "fresh air" jobs be aware that instrument air is not a substitute for breathing air. Ed

Most of the differences have been covered by the preceding post, but if I may offer a couple more reasons to separate I/A and Plant air. Plant air can be used for most anything say pressuring out material from a tank. Say we used I/A for this, hook up a hose, connect it to the bottom of the tank, open a valve to pipe outlet to waste truck, turn on air, tank starts unloading into the waste truck, truck gets full, turns off valve to truck now pressure equalizes in tank and I/A liquid in tank moves into I/A system OH Crap my instruments are dissolving. IT has happened.

Next scene act II. Critical instrumentation on a furnace is keeping everything safe and orderly. workers move in and connect jackhammer to Instrument air line, jackhammer starts to work and large volume of I/A is draining header. Heater controls go berserk, Operators spot the problem and politely tell contractor to get the f outta the plant. (Operators can get like that)

Contractor is miffed and bangs around a lot and in his state of mind is not careful in removing I/A air connection and breaks valve off header. Oh Crap, Dangerous situation exists for a while but is beautifully controlled by interlock systems that shut the plant down, then lost production in operations and construction. I/A should be treated as a safety critical system.

As you may have noticed in the posts, there is no hard and fast division between plant air and instrument air. However OSHA has provided somwhat rigid guidelines for breathing air.

There are a wide range of air usages, and each user of using device will have requirements for the quality of air required for relatively trouble free operation. Air directly out of a compressor is hot, and relatively contaminated, and will begin to condense water slowly into the pipeline. There is a wide variety of equipment that could be used to condition, clean, and/or dry the air out of a compressor.

Usually, plants will condition all of the air to some minimum requirement and call it plant or shop air. For fine process instrumentation and controls that have a higher sensitivity to dirt, oil, crud, and dirt, a small volume of plant air (or a special compressor) will be setup and more finely conditioned to keep from fouling up the instrumentation.

Compressed air for construction usage has minimal treatment. Plant air in a pharmcutical of food production environment might be considered instrument air by other users.

Beauty is in the eye of the beholder. In this case, understand what the various air users require and add equipment to meet the requirements.

Hi.

I agree; difference is the conditioning of air. i.e. dew-point control of compressed air is important. refer to Parker Group - "Domnick Hunter"

In Food industry, you need to filter-out lubrication oil (even if you're using FDA oils like Shell cassida) from your plant air in places where aeration processes (marshmellow prod.) are employed. For sure, you don't want to add compressor oil to your product.

There are hundreds of suppliers of filters and dryers around the world, so why Domnick Hunter in particular - do you work for them?

I admit that I may have given the impression you've pointed out. Sorry for this misleading. But, Please Read carefully! I haven't suggested anyone to use a brand. My statement is a suggestion to check the web-site.

Atlas Copco, Ingersoll Rand web-sites are worthwile, again, searching for.

By the way, I'm the Improvements Manager of a Biscuit/cake/chocolate Producing Company (end user).

Hello guest - in reply to post#21

Thanks for the clarification.

Cliff.

Go out into a shop and pull the valve on the bottom of a drying unit ... or open the drain plug under the compressor. That mixture of water and oil is spread through out the system in small quantity's. Don't want that in your sensitives.

A number of good points about instrument air and plant air with it generally being agreed that IA has to be cleaner, dryer and free of oil. However, a few comments about breathing air. BA is quite different and you have to go by the rules for when workers health is at risk. Neither IA or PA are okay without adequate treatment. This can be to remove oil, particulates, to get the right humidity level and to control odors. In addition, just because a "food grade" lubricant was used in the compressor does not mean that it okay to breath or to even get in the product. Most food grade products are H1 for INCIDENTAL FOOD CONTACT. As far as I know none were tested for breathing and the MSDS's only give data on the effects of mists of new material. Once the oil has been used in a hot compressor it changes and often nasty compounds like PNA's and nitrosamines can form. See also the notes in http://www.osha.gov/dts/chemicalsampling/data/CH_275150.html.

If you do not have breathing air and need it consider getting a proper compressor or if trying to clean up existing air get the right equipment and test the air. Spare lungs are not a stock item.

Ken Brown

An air supply is required to drive pneumatic actuators in most facilities. Instrument air in pneumatic equipment must meet quality standards, the air must be dirt, oil, contaminant, and moisture free. Frozen moisture, dirt, and the like can fully or partially block narrowed sections and nozzles, giving false read- ings or complete equipment failure. Air compressors are fitted with air dryers and filters, and have a reservoir tank with a capacity large enough for several minutes' supply in case of system failure. Dry, clean air is supplied at a pres- sure of 90 psig (630 kPa⋅g) and with a dew point of 20°F (10°C) below the min- imum winter operating temperature at atmospheric pressure. Additional information on the quality of instrument air can be found in ANSI/ISA-7.0.01- 1996, Quality Standard for Instrument Air.

Instrument air is air which is totally free from moisture ,dust and oil particals.Instrument air having pressure in the range 3-15 psig.This used for pneumatic operated control valve.

Plant Air or Service air or utility air contain oil particals or moisture.Not cleaned/filtred as Instrumrnt air.This used for all common purpose.

An oil-lubricated compressor is certainly suitable for plant, shop, instrument control, AND breathing air. Hear me out.

Plant air may be well above 150 psig and at high flow-rates (cfm). The moisture SHOULD be removed with an absorbent filter or dryer to a dew point of -40deg or less. This makes sure the moisture doesn't freeze in the line at high flow-rates.

Shop air should also be dry, filtered, AND have oil mist or bubble style lubricators near the tool application. Pneumatic tools NEED lubrication to have a long life. I also recommend the operator add a small squirt of oil to the air inlet prior to the start of the shift AND at break times. This really improves tool life.

Instrument air should be dry & filtered, unless you have an actuator which needs lubrication.

Breathing air can be produced by an oil lubricated compressor as long as there is adequate filtration to remove the oil. It should be tested frequently.

At our site, we produce air at 2,800 psig and 1,700 scfm. It is dried to -60 deg C and the oil vapors are removed to<5 ppm. All air is regulated down in at least 2 stages. Shop air and air motors have oil added as needed. Breathing Air is sampled regularly and has additional filtration and a hydrating bath.

Hello coastalforu

Air at 2,800 psig and 1,700 scfm, is a lot of pressure and a lot of air.

what do you use it for ??

If all air is regulated down in 2 at least stages - why the high pressure to start with ?

Just curious.

Replying to HORACE:

We test rocket engines of various types at this location - originally the F1 & J2 for the Apollo Program, the the Space Shuttle Main Engines, now the J2x and some others for satellite launch & the Constellation Program to return us to the Moon. High-pressure air is stored in vessels in the Test Complex. Large amounts of dry air are used to dry the engines after test. Most engines burn Hydrogen & Oxygen, producing huge amounts of steam. There can't be any residual moisture in the engine prior to the next test as these propellants are stored in the liquid state (Cryogenics - very cold) and the water would freeze during engine chill-down. Solid particles (ice crystals) do tremendous damage when moving at sonic speeds.

It's all about cleanliness and dryness.

Go to the ISO 8573 series of standards.

The natural state of of untreated compressed air is dirty wet and oily.

Unless you have taken the trouble to dry and filter the air at source, then that is what you get.

There is a cost involved here. The capital cost of suitable treatment devices, power cost to run them, and on-going maintenance - which set against the 'cost' (labour, time and materials) of not treating the air (plant break-downs, rust, corrosion, blockages, stoppages and product spoilage) - puts the matter in perspective.

Instrument is traditionally ultra clean and dry.

Quite frankly in this day and age, since just about every air powered or air using device suffers from 'dirty' air, it thus makes sense to have a compressor system to deliver air of the best quality to all devices.

There is no good economic reason not to treat the air.

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