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ORIFICE PLATES vs. STEAM TRAPS
In the very early days of steam engineering, steam traps were not available. To get rid of condensate, orifice plates, needle valves and petcocks were in common use. Since the amount of condensate varies from time to time, it is physically impossible to have an orifice or a valve without some steam loss. The amount of steam loss will naturally vary, but if we are going to be on the safe side, some steam loss must occur. Steam loss is money wasted and therefore, industry began to design steam traps which would accommodate varying loads with out steam loss. Now, all of a sudden, we are back to the possible use of orifice plates. Let us not forget that the orifice plate designed to take care of the maximum possible load does waste steam, whereas a properly designed quality steam trap, as long as it is functioning properly, does not waste steam. Therefore, it benefits the steam user to use good steam traps and to check them periodically to avoid steam loss.
It is very easy for someone to go into a plant where maintenance of steam traps is not as it should be or where inferior quality steam traps are used in an installation and replace them with orifice plates and show fantastic savings. However, orifice plates do waste steam, which could be avoided by utilizing good steam traps and maintaining them properly.
It is a proven fact that quality steam traps last a long time without wasting steam. This has been verified in our laboratory over and over again where traps more than five years old, and some ten and twelve years old, have been returned for steam loss tests and the results clearly show that, in spite of many years of service, the traps still do not lose steam.
In order to prevent an accumulation of condensate and the inherent danger of waterhammer, orifice manufacturers recommend a safety factor which varies from a low of 1.5 to probably 2 or more. This means that on a 100#/hr. load with a safety factor of 1.5 the orifice is designed to carry 150#/hr. load. This means that at a normal load, steam is being wasted and as the load decreases, more steam is wasted.
When the loads to be handled are too small, the diameter of the orifice is naturally small - in some cases as small as .020". Chances are, when installed in the average industrial steam system, the orifice will clog. If it does, waterhammer may result with a probable loss of property and possible injury (or worse) to personnel. It is all very well to say that these orifices are protected with a very fine mesh screen. What must be remembered is that the orifice in many cases may clog with an accumulation of iron oxides. These oxides are so fine that no screen, with possibly the exception of a filter, will arrest them. Using a filter to arrest these small particles would undoubtedly result in the filter clogging and again, waterhammer could result.
To show how costly steam loss can be using orifice plates, we cite a few examples. The calculations for these examples are based on Flexitallic's Bulletin 474 entitled, "Design Handbook." The data was taken from the curves for water flow and steam flow in this handbook. The data has been checked in our laboratory and found to be reasonably accurate.
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