By Matt Clinite, Sales Director
Leak-up rates can be deceptive. You may see clean, bright parts coming out of your furnace even when the leak-up rate suggests a problem. Other times, you might notice part discoloration without any sign of an increased leak rate.
These are common situations that can lead to confusion and additional troubleshooting. Let’s take a closer look at both scenarios, and some practical ways to pinpoint the issue before spending hours diagnosing the wrong problem.
Clean Parts, Suspicious Leak-Up Rate
One of the most common reasons that you may be getting a clean part, despite a higher-than-expected leak-up rate, can be a worn seal in one of the backfill or partial-pressure valves.
These types of leaks allow inert gas to enter the chamber, so there may be no chemical interaction between the leaking gas and the parts. However, a slow inert gas leak can still cause issues during a recipe that requires a low vacuum. For example, a process gas leak may prevent the furnace from reaching the vacuum level needed to trigger the main valve to the diffusion pump.
The best way to test out this theory is to isolate the gas supply by using the manual valve to shut off the gas lines to the furnace, drawing the furnace into vacuum, and checking to see if there is still a leak rate anomaly.
If the leak rate returns to normal with all the manual valves closed, it likely means gas is leaking past either the backfill valve or the partial-pressure solenoid, indicating the valve should be replaced.
As always, follow the manufacturer’s instructions for replacing a valve. If you’re replacing a butterfly valve, take advantage of Ipsen’s Recommended Procedures for Installing a Butterfly Valve.
Remember that leak rates are cumulative. Many different sources may be contributing to a high leak rate, so don’t just stop once you have found one leaky valve – be thorough and make sure you catch all leaks as you test the whole system.
Discolored Parts, Consistent Leak-Up Rate
Discolored parts are a sign that unwanted gas, typically atmospheric air, has entered the furnace during processing. But how can this happen when there are no alerts to an increased leak rate?
The answer is frequently a leak or air incursion in your process gas tank or gas service lines.
Air can sometimes find its way into the tank or the lines during a refill, or as a result of the natural expansion and contraction of service lines due to changes in temperatures.
It may seem counterintuitive that gas lines under pressure could allow ambient air to enter, but a physics phenomenon called the Venturi effect can cause atmospheric air to be drawn into the line, displacing the process gas as it flows out.
Before assuming that air has gotten into the process gas reserve tank, make sure there are no leaks anywhere along the process gas lines with a bubble test. Be sure to pay close attention to every fitting and bend.
If you discover a leak of any amount, follow all process gas safety protocols, seal the leak (no matter how small), and report the leak to your safety point of contact.
After a thorough inspection, if no leaks are discovered in the process gas lines between your furnace and the reservoir, it may be advisable to have your process gas tested for dew point to detect any presence of moisture.
Tip: To avoid encountering air pockets in your process lines after a process gas tank refill or work on a gas line, backfill your furnace and pump it down once or twice to make sure any unwanted air is evacuated from the system and that all lines leading to your furnace are properly charged with nothing but process gas. If the process lines from your furnace to your reservoir are particularly long, you may need to repeat this cycle more than twice.
For more helpful tips, visit our Ask the Expert Page.