Does Your Absorber Have a Leak?
So, you think you might have a leak, right? But what makes you think that? The following are some possible indications that you have a leak: (a.) You’re getting excessive purging. (b.) The mercury manometer has a high vacuum reading. (c.) The performance of the machine may be falling off, or it may not be meeting standards. You will not be making the proper tonnage, or temperature split—which, for example, should be 55 degrees return chilled water, and 45 degrees supply chilled water (or possibly 46 or 47 degrees). (d.) If you find yourself running the vacuum pump more often or longer to achieve the same performance results, that is another indication that you may have a leak. More than likely, you have already noticed one of these things. (e.) Finally, if the vacuum is too large because you have too big of a leak, the machine will not work at all, and you’ll start to get crystallization. The performance of the chiller will begin to suffer.
How to Check Your Absorber for a Leak
- If you think you have a leak, the first step is to completely evacuate the absorption chiller (i.e. absorber, vapor absorber, vapor absorption chiller, etc.), using the vacuum pump. You want to make sure you remove all of the non-condensables (a fancy word for air or gasses, sometimes hydrogen).
- The next step is to record the vacuum reading. Chilled water at 45 degrees, for example, the vacuum reading should be approximately 6mm.
- Next, stop the vacuum pump and record the time. Wait one hour and check the vacuum reading again. Note: If the vacuum rose to 26mm in one hour, then you have a leak. If you take the first reading (6mm) and subtract it from the second reading (26mm), which is 26mm – 6mm, you have a rise of non-condensables of 20mm in one hour. If your chiller is tight and chemical analysis is correct, it should rise 20mm in one week not one hour. Note: If it only rises 10 to 15mm in three hours, you still have a leak and it should be repaired. It should rise 10 to 15mm in a week. If you’re getting a rise of 20mm or more in an hour, this is a big leak. If it rises 30mm or more, this is a huge leak and it should be repaired as soon as possible. If you wait, you will just have to continue to purge with the vacuum pump more frequently in order to achieve performance.
- If you do have a leak (or you think you do), you will want to call an absorption chiller technician to check it and repair it as soon as possible.
The Consequences of Delay. An absorber does what it says: It absorbs water vapor in the chiller. The absorber is made of steel. The lithium bromide inside the absorber is a salt solution of 54 percent. When oxygen is exposed to the inside of the absorber along with the lithium bromide, corrosion takes place at a very fast rate. Inhibitors are added to the lithium bromide to stop the corrosion. Some of the inhibitors are chromates, molybdates, and nitrates. These are used to coat the inside of the steel to protect it from corrosion. Thus, non-condensables are not your friend. If the leak is too large it will deplete the inhibitor, quickly attack the shell of the chiller, and create hydrogen gas.