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along and deposited in your air tools or horns and whistles. You want water in your prized M5? I don’t think so!
     But a far more important consideration is internal receiver rusting, where you can’t even see it. No matter that the outside of the receiver sports a nice, shiny coat of paint. Who cares about that? You need to be interested in what’s happening inside the receiver. All air receivers have inspection ports big enough to let you at least look inside and see what’s going on. Bigger industrial receivers have manhole plates that you can remove so that you may actually climb inside the receiver to look around. Propane and refrigerant cylinders don’t have inspection ports. Propane and refrigerant gases have been dried and contain virtually no water vapor. But air tanks take hot, moist air from a compressor and store it, and moisture and internal corrosion are very important considerations. (Be sure that all pressure is relieved from a receiver before removing an inspection plug!)
     To be safe, you need to use a real air receiver for compressed air duty. It’s designed with all of these considerations in mind. To be really safe, it should have the ASME (American Society of Mechanical Engineers) seal. [Illustrated at the end of this article.] ed.
     This will be stamped into either the tank itself, or on the manufacturer’s label which typically is welded to the receiver, and also states the year it was made, what its maximum allowable working pressure is, the temperature rating, the maker’s name and location, and a serial number at the very least. If you don’t see these indications or the seal, you should not even consider using it.
     Another thing is presence of inspection ports on a typical 60, 80, 100, 120 gallon receiver or manhole(s) on a big industrial receiver. I have heard of manhole plates and inspection ports being welded in place to avoid leaks. This is extremely dangerous. If the manhole plate or plug is welded in place, how are you supposed to see what’s going on inside? They are there to help you. A good gasket for a manhole plate or pipe thread sealant around a plug is the way to take care of a minor leak, not welding them in place.
    This also brings up another crucial point. Welding on an air tank. Sometimes you need to add an extra fitting. This should be done by certified welders who are familiar with all of the considerations involved and who can do a hydrostatic test on the receiver after the welding has been completed. One of the most important considerations of welding on receivers is to inert them before welding. Welding heat can vaporize oil inside a receiver and make the atmosphere in the receiver potentially explosive. It’s pretty safe to say that most piston type (reciprocating) air compressors discharge a little of their lubricating oil along with the air and moisture that they send to the receiver.

     Welding on tanks involves evacuating the air and maintaining a flow of some inert gas such as CO2 or Nitrogen in the tank to prevent an explosion. Hydrostatic testing involves filling the receiver completely with liquid and then pressurizing it to (typically) double its design pressure. Since liquids are incompressible, if the tank should rupture or if a weld fails, there is no explosion, just a sudden leak and an instant drop of the pressure. Explosions result when compressible gasses are in the vessel because they expand rapidly upon a sudden release of pressure and turn a rupturing vessel into high-velocity shrapnel.
     Realize that if you have a pressure of 100 PSI in your air tank, then there is a pressure of 100 pounds on every square inch of surface of that tank. Add up all those hundreds of square inches of surface area that your receiver represents, and you’ll see that the force that is trying to rip that tank apart amounts to many tons altogether. This is why it’s so important to use the right kind of a tank and to check it regularly and carefully.
    Sometimes it’s a nuisance to get to a drain valve on the bottom of a receiver, but drain it at least once a day regardless. Put in an automatic drain valve if necessary and make sure that it always works. Drain even more than once per day if you use the compressor a lot or if the weather is damp and the air has high humidity to begin with. You’ll be amazed at how much water you’ll get.
     Another reason to drain the receiver regularly is that if you allow it to fill with water, you will reduce its air storage capacity. If you have a 60 gallon receiver that has 30 gallons of accumulated water stored in it, then you really only have a 30 gallon receiver. And, every time when you draw air from this receiver, you can be sure that you’ll be getting lots of water vapor carried along as well which will ruin your pneumatic tools and may also damage many different types of horns that are not rated for operation on steam as well as air.
     If you have access to the Internet, you can look up the ASME and find out exactly what their requirements are for certified air receivers. Be aware also that in many states, uncertified air receivers are illegal. We of Horn & Whistle hope that you will both read and heed this article. If you are using a non-certified vessel, or one in which you can’t remove the inspection plugs or manholes, stop using it and get the right type of vessel for the job you are doing. It will be a lot less expensive than a possible explosion. Air receivers when pressurized are potential bombs. A 60 gallon tank holding 150 PSI will cause major property damage to your home if it explodes and if you are standing or working near it, well, you won’t even know what happened. Save those propane and refrigerant cylinders for the applications for which they are made. Make sure you drain your air receiver regularly. Remove the inspection ports and look inside annually at least. Safety First!
ASME seal

At the right is a reproduction of the ASME seal. When obtaining a compressed air receiver, always make sure that you observe this seal on the tank.

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Horn & Whistle Magazine periodically includes articles such as this one that deal with enjoying our hobby safely. The Horn and Whistle hobby is loads of fun, but there are some safety considerations that you should be aware of so that you will maximize your enjoyment of our hobby.

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