Vapor Return Credit: Proposed formulas for computing amount to be allowed purchaser when a vapor return line is used without the meter being set to compensate for same: Formula 1: Gallons delivered to vehicle tank X (vehicle-tank pressure+14.7) 7.0X (vehicle-tank temperature+460) =gallons. P1 Pressure on vehicle tank at start of loading, P=Pressure on vehicle tank at finish of loading, T1=Temperature of vapor in vehicle tank at start of loading, Outage Volume of that portion of vehicle tank above the liquid, after loading, expressed in gallons, 14.7 Atmospheric pressure (sea level), 460 Number of degrees Fahrenheit from "absolute zero" to 0° F. DISCUSSION OF FOREGOING PAPER THE CHAIRMAN. Mr. Fuller, when transporting the equipment is the load removed from the knife-edges of the scale? MR. FULLER. By means of the drop lever, all weight is removed from the knife-edges of the scale during transportation of the equipment. MR. WITT. After the liquefied gas is dispensed from the meter system into the supply tank of a truck, must this be kept under pressure, and are special tanks required? MR. FULLER. These tanks must be of very heavy construction so that they will withstand the pressure necessary to keep the liquid from vaporizing. About 250 pounds pressure is required. I may add that in California, liquefied petroleum gas is used to a tremendous extent on freight transports and passenger busses and is being used on some passenger cars. One man is even using liquefied petroleum gas as fuel for an airplane and is getting splendid results. THE CHAIRMAN. The use in the East is largely as fuel for heat, is it not? MR. FULLER. I believe that is so at the present time, but I think, from what I hear about the numerous advantages of using it as motor fuel, that the use of liquefied petroleum gas will undoubtedly spread, so that many officials will be called upon to test liquefied-gas dispensing systems just as we are in California. Of course, if one tries to test such a system with an ordinary 5-gallon field standard, the hose many be inserted in the standard and the valve opened, but not a drop of liquid will reach the bottom of the bucket. AIR ELIMINATION FOR LARGE-CAPACITY METERS By C. P. GRIFFITH, Vice President in Charge of Engineering, S. F. Bowser & Co., (Inc.) The problems involved in air eliminators for use with large-capacity meters vary a great deal for different types of installations, and I have concluded that consideration of types of installations might be the most helpful thing we could do in the short time we have for this subject today. I first want to offer a few general comments in regard to the subject, and then we will have some lantern slides showing some equipment and some installations and endeavor to point out the problems involved. I realize that this presentation will be elementary to some weights and measures officials and to meter men present, but it is my hope that I can make it helpful to those weights and measures men who have not had an opportunity to become familiar with the problems involved. This subject has been given very careful_consideration on the part of meter manufacturers for many years. I remember, away back in 1913, on the first day of my employment with the company with which I am still associated, the chief engineer of the company invited me to make a trip through the factory with him, and one piece of equipment that was in production in one department was new to me. I asked about it and was told that it was an air eliminator for use with meters in the petroleum industry. This was my first contact with air eliminators, and I mention it only to show that these devices are as old as meters themselves. The air eliminators are to a very large extent manufactured by the meter manufacturers, and this is as it should be, as it tends to make the meter manufacturers completely responsible for the satisfactory operation of a particular installation. It is, of course, well recognized that modern meters will measure and indicate any air or gas passing through them exactly the same as they do for the liquid passing through them, and in view of this, suitable air eliminators must be provided to ensure accurate meter performance. The most difficult problems for air eliminators are the installations that include power pumps, and for this reason I will confine my remarks to installations that include pumps. The development of air eliminators has always been an interesting research problem. In our own laboratory we have made models of glass, or if this is impractical because of the size of the unit, we use steel containers having a number of glass windows so that we may observe exactly what is taking place inside the unit while under actual operation. We have found in this manner that with some air eliminators we did actually separate the air from the liquid, but due to a turbulent flow inside the unit, this air was again mixed with the liquid and passed on out with the liquid and on through the meter. Constructing the units of glass enables us to correct such conditions. The size of an air eliminator for a particular installation is in some cases all out of proportion to the size of the meter it is to protect. In other words, you may find it necessary to provide a 6- or 8-inch air eliminator to protect a small meter because of the particular installation conditions. This situation makes it necessary to carefully analyze each installation to determine exactly what is required to ensure accurate meter operation. Meter manufacturers have found it necessary to manufacture a number of types of air eliminators, as well as a number of sizes of each type, in order to handle the great variety of installation conditions that are encountered. There are, of course, many installations that will operate highly satisfactorily with an air eliminator of the most simple type, but there are others requiring a much more elaborate device and one much more expensive. This brings in the question of economics, so about the only practical plan to follow is to analyze the particular installation and furnish the equipment that will ensure accurate meter performance. Meter manufacturers recognize the necessity of adequate air eliminators, as satisfactory meter performance on many installations is impossible without the proper air eliminator. We have learned the hard way that air-eliminator performance is as important as the meters themselves in securing accurate meter operation. Notwithstanding the progress that has been made in this direction, if we get a report of inaccurate meter performance today, the first thing we do is to carefully analyze the installation from the standpoint of air elimination, and many times faulty air eliminators are found to be responsible for the trouble. I don't want to leave the impression that the problems are insurmountable by any means, but I do want to emphasize the fact that different installations present a variety of problems. The air that must be separated from the liquid is in some cases very intimately mixed with the liquid and this entrained air is difficult to separate from the liquid. We have also the problem of free air to contend with. This is easier to handle than entrained air, but with some types of installations, some of which will be illustrated later, the large volume of free air becomes exceedingly difficult to handle. Figure 7 is an air eliminator in about its most simple form. It consists of a pressure receptacle having inlet and outlet connections; a simple baffle is interposed between the inlet and outlet. Air is separated in this particular air eliminator by gravity only. The size of the receptacle must be such as to slow up the velocity of the liquid to such an extent that the air has a chance to separate from the liquid. The simple baffle shown here is omitted in other types of air eliminators and much more elaborate baffles substituted for it. In some cases the interior construction is so arranged that a centrifugal motion of the liquid is set up as an aid to gravity separation. The internal construction of these units is highly important from the standpoint of air separation. The air, after being separated from the liquid, rises to the top of the receptacle, and all air eliminators are provided with some means of exhausting this accumulated air. On this drawing we show a simple float-operated vent valve; in fact, most air eliminators employ some type of float-operated air-vent valve. The design of this valve is important. It must be of ample size to exhaust all the air that the pump, or pumps, will deliver when the source of liquid supply is exhausted, and do so without creating any pressure at the outlet of this receptacle. It is obvious that pressure in these receptacles must be reduced to zero gage pressure when only air is entering; if not, the meter will continue to run and air will then pass through the meter, resulting in a false indication of delivery. Another important feature in the design of such float-operated vent valves is the pressure at which they will open. This drawing shows a lever of the first class. You probably will not find an air eliminator on the market having the simple construction shown. These float levers are compounded, usually so that a float, while weighing only a few ounces, will open a valve poppet of about 1-inch diameter under a pressure of from 50 to 75 pounds per square inch in the receptacle. The disposition of a vent line from the air exhaust of these air eliminators is a matter of some interest to weights and measures officials. Perhaps the best solution of this problem is to run this vent line back to the top of the tank that is the source of supply; however, in many cases this is impractical because of the distance involved. On some installations the vent line is connected to the meter discharge line. This is satisfactory only if the discharge line is very short, such as in A B A, Float-operated vent valve; B, outlet; C, inlet. FIGURE 7.-Simple form of air eliminator. the case of a gravity meter on a truck tank. It is obvious that with a long meter discharge line having this vent line connected into it, accurate meter operation is impossible. I saw installations some years ago having this vent line connected into the pump suction line. This is definitely bad practice and should not be tolerated. When this is done you cannot exhaust the air and, in fact, you have no air eliminator at all. In many installations this vent line exhausts to the atmosphere adjacent to the air eliminator. This is entirely satisfactory from a weights and measures standpoint, but it must be recognized as a fire hazard. Figure 8 illustrates another type of air-vent valve which I will call a "power-operated vent valve." The float as shown operates a small pilot vent valve. The air exhausted through this pilot valve acts on a plunger which opens the large poppet. This construction makes it possible to open the large poppet with a small, light float. Poweroperated vent valves of this, or a modified design, will be encountered on large air eliminators in some cases. FIGURE 8.-"Power-operated" vent valve on air eliminator. In this connection, I can say without fear of contradiction that inadequate air eliminators are usually found to be inadequate from the standpoint of air separation and not because of their inability to exhaust the air that has been separated from the liquid. FIGURE 9.-Pump-operated meter installation-supply from above-ground tank. Figure 9 illustrates perhaps the most simple of pump-operated meter installations. It will be observed that the pump suction comes 423341-42-4 |