ge ejector system, but a multistage ejector system must be evaluated by checking the last stage first.
Multistage, No-Load Vacuum: Â Typically, a multistage ejector system is started up backwards from the last (Z) stage to the first. The Y stage cannot operate properly until the Z stage is working, the X stage will not work unless the Y and Z are operating, and so on.
Troubleshooting a multistage ejector system should also proceed in this back-to-front order. Check the vacuum of each stage during process load conditions, and compare it to its design value. When the measured vacuum of a stage is worse than its design, the cause of the problem at that stage must be found and corrected before proceeding any further.
The next step is to performance-test the stage in question by checking its no-load vacuum. For example, if the stage being checked is the Y stage of a three-stage ejector system, a blank should be installed on the Y suction flange. Since the Y stage is designed to discharge to a vacuum created by the Z stage, the Z stage, and intercondenser if present, must operate simultaneously during this test.
With the Y stage steam valved off, first check and record the Z stage no-load vacuum to be sure it is meeting the manufacturer’s tested value. Then, with the vacuum gage still connected to the Z stage, turn the Y stage steam on. If the Z stage vacuum steadily falls off, the intercondenser is most likely the cause of trouble and should be inspected.
As mentioned in the preliminary checklist, a condenser temperature rise much greater or less than design may be an indication of a water-flow problem. A water-flow problem can result in a higher condenser temperature and an overloading of the following stage with uncondensed vapor. In this case, as the Z stage falls off, the Y stage vacuum would follow.
Examples of direct-contact condenser problems include: a blocked tailpipe, air leakage into tailpipe, damaged water distributor, or a plugged water nozzle. Surface condenser problems include: a blocked drain, air leakage into tailpipe, or split or fouled tubes.
If the Z stage vacuum is within specifications, move the vacuum gage to the Y stage. If the Y stage vacuum measures exactly the same as that of the Z stage, a blocked Y stage nozzle may be the cause. However, at this point, if the Y stage vacuum does not measure reasonably close to the manufacturer’s tested no-load value, the stage should be disassembled for internal inspection.
Finding the Y and Z stage vacuums within specifications, remove the blind flange from the Y stage suction and repeat the procedure at the X stage. It is important to remember that each stage must meet its design vacuum before continuing the testing.
At times it may be impractical to make and install a blind flange on the suction connection of an ejector due to the size of the unit. In most cases, however, these larger stages will be the W or X. If the no-load testing has ruled out the Y and Z stages and the condensers ass possible causes of the vacuum problem, and internal inspection of these larger stages may be the more practical step to follow.
Internal Inspection: There are several things to look for when performing internal inspection of an ejector. Usually any kind of corrosion or erosion that is obvious to the eye and touch will affect the performance of an ejector. An indication of wet steam will show as lines (“wiredrawing”) etched up and down the inside of the steam nozzle. The point along the diameter where the steam contacts the venturi is another location that may be gouged due to wet steam.
Steam leaking around the nozzle puts an artificial load on that stage, resulting in poor vacuum. Leakage of this sort should be noticeable as a discoloration where the nozzle seats on the steam chest, or as erosion of the nozzle threads. A process that causes corrosion or buildup of material on the internals of an ejector will also effect the performance of that unit.
Critical dimensions such as the nozzle orifice or venturi bore diameter, obtained from the manufacturer, will enable a measureme