Finding Leaks in Your Vacuum Furnace – Part VIII

In our previous post on inert gas leaks, we discussed how to bring the inert gas system back online after all leaks have been identified and corrected. Once you have brought the inert gas system back online and verified that there are no leaks, it is time to bring the pressure down to zero and begin final charging of the inert gas system.

There are two common methods for performing final charging of the inert gas system.

Method One – Manual Purging

This first method is generally considered the easier of the two methods; however, it usually costs more to perform and there’s less certainty that all of the air was fully purged from the system. If you have parts that are extremely sensitive to air, this might not be the method for you.

To manually purge the system, you would:

  1. Pressurize the buffer tank to full pressure
  2. Bring the pressure back down to atmosphere (i.e., manually purge all of the gas out)
  3. Repeat steps 1 and 2 approximately four to five times to purge the air out of the tank

In the end this method works, but it’s time-consuming, noisy and it can waste a lot of money – especially if you’re using argon gas – because you’re filling the tank and venting the pressure back down several times. As a result, you could use almost half a month’s worth of gas in an hour. In addition, you’re never 100 percent sure that all of the air is out of the tank, meaning you could get some discolored loads out of the furnace until the air eventually finds its way out of the system.

Method Two – Evacuation and Refilling of the System

While manual purging is usually the more popular method, evacuating and refilling the system provides complete certainty that all of the air was removed from the buffer tank.

To refill the system, you would:

  1. Vent the pressure in the buffer tank down to atmosphere
  2. Pump the furnace down
  3. Manually open the backfill valve
  4. Pump the vacuum chamber back down to a full vacuum and let it sit for one hour
  5. Once the hour is over, close the backfill valve, open the manual isolation valve and refill the system back to operating pressure with pure, air-free gas

When evacuating and refiling the inert gas system, users will close the red backfill valve (right) and open the yellow manual isolation valve (left) before refilling the system back to operating pressure.By using this method for final charging of the inert gas system, you now know beyond a shadow of a doubt that your gas storage tank system is 100 percent free from leaks and air.

However, people often make a common mistake when it comes to charging their inert gas system. This mistake involves them hooking the gas up to the buffer tank and pressurizing it to 200 pounds per square inch (PSI) – but, they forgot to evacuate the air out first. They will then see that the system is at operating pressure and run production; however, a significant percentage of that 200 PSI is still air, which ends up resulting in discolored parts and lost production.

In our next post in the series, Finding Leaks in Your Vacuum Furnace – Part IX, we will discuss the external and internal causes and effects of inert gas leaks in relation to the vacuum furnace.

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