Volume And Helium Consumption - Assuming the test method to be the conventional design (pressure on tire side and vacuum on inside), the helium shroud must be large enough to accommodate the largest wheel size. This results in considerable excess volume when testing the smaller wheels on the same machine.
One of the design consequences of accommodating the largest wheel is a substantial increase in the cost of helium unless the helium can be recovered or other options are considered.
When testing a 15" wheel in the same shroud designed to accommodate an 18"x10" wheel, the empty shroud volume is approximately fifty-one (51) liters. This translates into an estimated usage of over 51 liters of helium gas during each test.
Helium Recovery - Even if helium recovery is used, the impact on the equipment cost and cycle times are listed as follows:
A. A helium recovery system must be capable of evacuating the shroud at the end containing fifty-one (51) liters of air before filling helium. This results in longer cycle time.
B. Fifty-one (51) liters of helium must be evacuated from the shroud at the end of each cycle to accomplish a 76%-80% recovery rate.
C. The above recovery process will have a net effect on extending the cycle time by an estimated six (6) to eight (8) seconds.
D. Because of the large compressors and pumps required to accomplish this task, an expensive recovery system requiring approximately 120 amps at 480 VAC of energy usage is needed.
Other options - Another consideration is to test the 18" or larger wheel sizes on a separate machine. The vision system would identify these wheels and divert them to a specific machine when required.
Using gas mixes other than 100% helium it is possible to reduce helium consumption by using concentrations of helium as low as 10%. Using mixed gas, with lower helium concentrations has a direct effect on sensitivity.
LDS recommends for the helium to air concentration to be no lower than twenty-five (25) percent. The following issues should be addressed prior to selecting a gas mixture:
A. The gas mixing system and compressor must have the appropriate capacity to handle the gas requirements and fill time needed to meet production goals.
B. If house air is used as a source gas to be mixed with helium, the air must be dry and clean because dirt and water vapor present in the air can be forced into small leaks. During the evacuation process, moisture will freeze disguising actual leaks.
The quality of the air should meet dry nitrogen standards.
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There is a global helium shortage. Each time an MRI is performed, helium is used. Please rethink your helium balloon purchase.