3.4.8

1. 3.4.8 Examining & Maintaining Platform Scales & Liquid Meters Keeping the bulk plant safe and productive means plant operating personnel must understand the operating characteristics of platform scales and liquid meters. • In this module you will learn to identify: • Operating characteristics and maintenance procedures for platform scales • Operating characteristics of liquid meters and metering systems • Procedures for maintenance of liquid meters

2. Characteristics & Maintenance of Platform Scales Platform Balance Beam Scales In most states and jurisdictions scales must bear certification decals from weights and measures officials, and be periodically inspected and calibrated for accuracy. Figure 1. Diagram of a Single Beam Scale

3. Characteristics & Maintenance of Platform Scales Platform Balance Beam Scales Figure 2. Single Beam and Double Beam Scales

4. Characteristics & Maintenance of Platform Scales Platform Balance Beam Scales Double beam scales incorporate two balance beams into one assembly. One scale is set for the cylinder tare weight, while the second scale is set for propane weight and dispenser hose weight. Platform scales require periodic maintenance and daily checks for accuracy. They must be level and protected from weather, especially accumulation of water, snow or ice. Each day before cylinder filling operations are started, the scale(s) should be checked for proper registration at “zero” (no weight on the platform) and with a known weight.

5. Maintenance of Platform Scales Maintenance procedures should include: • If the scales are equipped with a charging manifold and automatic shutoff devices, inspect them for proper operation. • An accumulation of leaves, snow, ice and other debris can frequently cause the platform to bind and produce an inaccurate scale reading. Check and clean these recessed areas frequently. • The platform is removable on some scales by prying off the retaining clips. Occasionally, the edges can be bent outward during inspection so that when the platform is replaced, these pried-out edges scrape against the side of the pit. If necessary, straighten bent edges. • Clean and periodically lubricate loops, pivots and bearings. Do not use oil on scale parts unless instructed to do so by the scale manufacturer. • All scales should be checked periodically using standard dead weights that approximately total the combined tare weight of the various cylinders filled and their propane contents.

6. Characteristics of Liquid Meters Figure 3. Propane Liquid Meter

7. Characteristics of Liquid Meters Measuring Chamber a. b. Figure 4. Rotary Piston Meter

8. Characteristics of Liquid Meters Measuring Chamber Courtesy of Schlumberger Measurement Division c. d. Figure 4. Rotary Piston Meter

9. Characteristics of Liquid Meters Measuring Chamber Courtesy of Liquid Controls Corp. Figure 5. Measuring Chamber, Transmission and Seal

10. Courtesy of Liquid Controls Corp. Figure 5. Measuring Chamber, Transmission and Seal Characteristics of Liquid Meters Measuring Chamber

11. Characteristics of Liquid Meters Measuring Chamber

12. Characteristics of Liquid Meters Gear Train—All meters have some type of provision for changing the ratio between the final output of the gear train and the gears in the register by small amounts. Such devices are often referred to as "gear shifters" or "adjusters" and are used to compensate for errors in meter readings of less than .30% caused by wear to internal parts or slight differences in the method of delivery.

13. Characteristics of Liquid Meters Courtesy of Neptune Meter Co. Figure 6. Change Gear Arrangement

14. Characteristics of Liquid Meters Register Head Change Gears & Drive Measuring Chamber & Drive Gear (Temperature Compensator in Front)

15. Characteristics of Liquid Meters There is usually a seal either on the input or the output shaft of the gear train to prevent the propane from leaking out of the meter body and entering the register. The seal is usually a U-shaped packing or O-ring that fits around the drive shaft and is designed to be replaceable in case it begins to leak. Measuring Chamber & Drive Gear (Temperature Compensator in Front)

16. Characteristics of Liquid Meters Temperature Compensators—Since propane liquid changes volume significantly even with relatively small changes in temperature, most propane meters are equipped with devices that sense the temperature of the product and automatically correct the volume measured by the meter to the equivalent volume at 60° F. Cut-away View of Temperature Compensator (This picture is not in your book.)

17. Characteristics of Liquid Meters The Register Courtesy of Schlumberger Measurement Division Figure 7. Meter Registers

18. Characteristics of Liquid Meters The Register— Computer registers are typically used on propane cargo vehicles where the driver must leave a printed record of the delivery and a bill for the customer. Other similar registers print only the start and finish readings on the meter or the total volume delivered. Courtesy Midwest Computer Register Corp. Figure 8. Computer Meter

19. Characteristics of Liquid Meters Meter Calibration — Because even the smallest deviations from the correct tolerances inside the measuring chamber are enough to affect a meter's accuracy, many state and local regulations require dealers to have their meters recalibrated or "proved" on a regular basis. This is generally done with a volumetric prover (tank of certified capacity), which is filled through the meter being tested. Meters with temperature compensators are usually tested three times. They are tested twice with the compensator disconnected and then a third time with it engaged. NOTE: In most states, meter proving is under the authority of the Bureau of Weights and Measures or the Weights and Measures division of the Department of Agriculture. In either case, the responsible agency usually places a seal on the meter when it has been proved and found accurate. If the seal is broken for any reason, the meter must be proved again and resealed before it is placed back into service.

20. Characteristics of Liquid Meters Meter Maintenance — As meter parts wear, the tolerances inside the measuring chamber increase so that the meter actually "gives more" than is shown on the register. Propane cargo vehicle drivers and other personnel should be alert at all times for signs of developing meter trouble. These include erratic meter operation, obvious over or under registration, increasingly noisy operation, and excessively slow delivery rates. Repairs to the gear train and/or register are too complicated for the average dealership and are usually left to specialized repair stations. The damaged register or gear train is usually exchanged for one that has been completely rebuilt.

21. Metering System Components Vapor Eliminator — Most metering systems also include a vapor eliminator with an integral strainer and back check valve. Strainer— Meters are highly sensitive to dirt and debris which can scratch the lining of the measuring chamber and, in extreme cases, jam the meter. All metering systems should include a strainer to trap and filter foreign matter in the propane line and prevent damage to the meter.

22. Metering System Components Liquid Transfer SystemStrainer Figure 9. Strainer (Transfer System)

23. Metering System Components Vapor Eliminator —Strainer Vapor Eliminator Strainer (Picture is not in your book.)

24. Metering System Components Preventing Vapor from Entering the System— Propane meters must be kept liquid full for several reasons. They depend on propane liquid for lubrication of all close fitting parts inside the measuring chamber. Since propane vapor occupies a far greater volume than the equivalent amount of liquid, the meter will over-register any time there is vapor in a measuring chamber. Most state and local codes require meters to be equipped with some type of a device to prevent vapor from entering the meter before or during delivery. This function is usually performed by a vapor eliminator and differential valve.

25. Metering System Components Preventing Vapor from Entering the System Figure 10. Vapor Eliminator

26. Metering System Components Differential Valves Courtesy of Fisher Controls Co. Courtesy of Neptune Meter Co. Figure 10. Vapor Eliminator

27. Metering System Components Preventing Vapor from Entering the System Neither vapor eliminators nor differential valves require significant maintenance under normal conditions. If either should fail, it is usually the result of a collapsed float or worn release valve or, in the case of the differential valve, a torn diaphragm or damaged valve seat. Damage to any of these parts will cause the meter to behave erratically or stop the flow of liquid altogether. If repair parts are needed, they are readily available from the manufacturer and are easily installed.

28. Procedures for Maintenance of Liquid Meters Meter Calibration Many state and local codes require companies to recalibrate meters on a regular basis. Generally, this is accomplished by filling a volumetric prover (a tank of certified capacity) through the meter being tested. Meters with temperature compensators are usually tested three times, twice with the compensator disconnected and once with it connected. After the third test, the volume of propane in the prover is corrected to 60° F and compared to the meter reading. The temperature compensator is then adjusted accordingly. The responsible agency usually places a lead seal on the meter when it has been proved accurate.

29. Procedures for Maintenance of Liquid Meters Meter Strainers • Like pump strainers, meter strainers seriously restrict the flow of liquid through the delivery system if they become clogged or excessively dirty. For this reason, strainers should be checked and cleaned on a regular basis. • Never attempt to bleed down a meter [solely] by opening the hose end valve on the delivery hose. Doing so reduces the pressure only in the hose, not in the meter. [Trapped liquid between the vapor eliminator check valve and the differential valve must be vented as well.] • Strainers installed in a new system or new strainers in an existing system should be cleaned after the first two weeks of operation and then monthly or periodically as the requirement develops through experience; thereafter, follow company procedures.

30. Time to See If You Got the Key Points of This Module… • Complete the Review on pages 15 & 16. • See if you are ready for the Certification Exam by checking off the performance criteria on pages 17 & 18.