compressed air challenge

1. Use soapy water; bubbling indicate leakage. Also check for unexplained pressure drops, excessively frequent compressor running, hissing noises etc. Proper maintenance will be able to detect minor leaks before they become major ones.

2. The client must specify required air flow, pressure, outlet points etc. You need to know both the pressure and flow requirements when sizing the compressor. To minimize pressure drop, use correct sized piping. http://en.wikipedia.org/wiki/Darcy-Weisbach_equation

3. Refer to the ideal gas law for more details. Basically, the cooler the air, the denser it is, so you can store more mass of air in a given size of receiver under the same pressure. http://en.wikipedia.org/wiki/Ideal_gas_law

4. Only if you have pneumatic equipment. Having more than one receiver enables you to shut one down for maintenance.

5. Depends upon the compressor design, obviously. It could mean nothing, or it could mean a defective unloader valve, depending upon the compressor design cycle.

1) Leaks are a common problem for any compressor or system, old or new.

A simple test is to see how long the compessor runs, and then how long it stops, when all your machines are switched off. The on/off ratio will give you some idea of how much air is being wasted. If a lot, then you need to isolate various sections of the system to pinpoint where the leaks are. Hopefully (with all machines switched off) you will hear the sub-sonic leaks. Then progressively you need to test the pipes and valves etc for super-sonic leaking joints and seals etc - soapy water or electronic testers. Fixing leaks in threaded pipes is not easy.

2) You need to know all three parameters, ie, the flow, pressure and temperature, to work out demand. Most machine suppliers will tell you this for each machine. Then you need to add them up for max demand, and apply a diversity factor to average out the supply.

You can then find out pressure drop etc, and if it matters you fix it.

3) Cooling the air intake is not a practical proposition in terms of efficiency. But taking air from a cold area (with ducting if necessay), in preference to a hot area (like an unventilated compressor room), is certainly worthwhile - if not essential.

4) and 5) Receivers at the compressor end are usually sized to give proper pressure/flow control for system - so that the compressor does not stop/start frequently.

Receivers could be larger or sited elsewhere provide some form of air pressure stabilisation to iron out local peak air demands. In terms of health and safety, if the air is used to provide respiratory protection to people wearing airline breathing apparatus, then the receiver must be sized to provide enough air and for a duration long enough for the workers to escape to a place of safety in the event of a compressor failure.

1. Hard work. If you can be in the plant when everything BUT the compressors are shut down you can hear it from the whistle and hiss. For larger equipment, air flow rate meters can be a help. Good record keeping is a must. The other posters also have good suggestions in this area.

2. As posted earlier, you need to know both flow rate and required pressure. Also, need to know what pressure loss is in the piping between compressor and point of use. If a new building and system I advise and try to design for a maximum pressure drop of 5% of total pressure. If you need 100 PSI design pipe sizes to limit pressure loss to 5PSI. It costs money to pressurize air, don't lose the money spent through too much pressure loss.

If the air system is kept well filtered and dry, there is no corrosion in the piping system. If you can't, add 10-20% in pipe pressure loss for oversizing the piping.

There are several piping layouts available, mainly variations on the loop system and the trunk and branch system. There are pros and cons to both. Each plant will have different points of use, so engineering judgment comes in play.

Cooling the intake will make the air more dense, so the compressor will move more MASS of air for a given CFM. It will probably pump up to full pressure faster. The increased mass will cause the air compressor to work harder and possible overload the motor. I had the experience with a 3000 cfm 100 psi centrifugal compressor, and the manufacturer ended up trimming the impellers due to overload trips in the winter time.

4. Air receivers for storage are only effective if the compressor operates at 50% or greater pressure than the point of use. Then you have the possibility of limiting the time of compressor run or using stored air to handle large peak demands.

In the old days, with older reciprocating piston compressors receivers were a point for moisture and dirt to drop out of the air and for pressure pulsations to be absorbed. Use of rotary screw or centrifugal compressors, use of good air dryers, and good filtration minimizes the need for receivers. I would also investigate possibly oversizing main pipe distribution to account for some of the receiver size and minimize the size of the storage tank by the compressor.

5. Sometimes. Older recips were operated in this fashion because there would be less wear and tear due to starting and stopping the compressor and due to less motor problems due to inrush current issues. If a compressor runs loaded for most of the time and infrequently unloads, it may barely be keeping up to production due to being worn (rings and valves), marginally sized, dirty filters, plant air leaks, or a combination of issues.

Air leakage should be avoided at all costs. Compressed air is extremely expensive to make and eveen a tiny hole will cause large pressure losses in the system. To measure your system you need to measure CFM at your required pressure. Because 10 CFM at 1 atmosphere is only 5 CFM at 2 atmospheres. Your compressor is moving molecules, same number each stroke - the difference is in the machines ability to squisch more molecules into the same space. cooling the compressed gas is good to a point. cooling takes the energy out, so Cooling AFTER compression will waste some of the energy youjust put in, however it also lowers the pressure ( allowing more air to be pumped in) so if your use is combustion it is good, very good. Cooling the inlet air is best as this keeps the exiting air at a low temperature without loosing pressure. You can use a radiator arrangement, like a car air to water intercooler or a heat pump like an air conditioner unit to chill the air below ambient, aiming for the compressor output to be at room temperature so as not to lose pressure when the gas cools to ambient. Finally, the pressure tank has an affect on both temperature and pressure. The gas in the compressor pipes is moving at high speed, when it hits the tank it stops moving, converting the energy to heat and pressure. consequently the tank gets hot, sometimes hotter than the gas inside. this process looses energy you just put in in the compressor. Consequently, in continuously used systems such as factories, pressure tanks should be used only for pulse reduction, there should be no provision for gas storage. if they are used they should be placed well away from the compressor on a dead end line.

Don't forget water condensation on the inside lines caused by the change in Vapour pressure. you will extract Gallons of water in the tropics and coastal areas. running the inlet through a dessicant can save considerable energy by removing liquids before yo compress the vabours.

PVc and Poly pipe are both good cheap options for factory air not above 200PSI.

A compressor will move a variable number of molecules depending on temperature and pressure of inlet air - cold air in a high atmospheric pressure area has more molecules per stroke than warm air in a low pressure zone.

Cooling compressed air will help remove water as a liquid before it condenses in the piping system, which is very helpful in preventing downstream problems.

I have heard you should NEVER use PVC for compressed air. When PVC fails, it can shatter catastrophically and send shards of broken PVC into the surrounding area. There are a few special plastic pipe systems approved for compressed air, but I am not certain if poly pipe is one of them. Be very careful specifying type of pipe for compressed air,