Hello,
Thank you all very much for your responses to my trivial question about the liquid valve, including Jerry Hirschinger, Kenneth Knott, Thomas Eubanks, Mark Swanson, Martha Morton, Ben Banks, Markus Voehler, Michael Strain, Johannes Leisen, Sheng Cai, Jeffrey Walton, Daniel Plant, Marcus Wright, Guy Bernard etc.
Two main reasons are 1, moisture such as tank has been sitting in the rain. and 2, liquid valve open all the way.
Other reasons include malfunctional valve, or inappropriate handling. To avoid this, make sure the cryogen liquid valve is dry before open it. and don't open all the way. Have a plastic strap wrench within reach just in case.
I copy the responses below. Hope it can help other less experienced lab managers.
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1, The valve should be the same effort to close that it was to open. It sounds like the valve was wet and the moisture froze in the open position so ice obstructed smooth operation. Never leave a rotary cryogen valve opened all the way against the stop. Any moisture can freeze the valve open. Always open it to the stop and then close it 1/4 to 1/2 turn so it cannot freeze the stop surfaces together.
Never open a wet cryogen valve. Dry it with a heat gun if necessary before you open it.
If there is a problem closing a cryogen valve, immediately open the dewar vent valve to relieve all pressure. With no internal tank pressure the flow will stop. Then you have no stress to go get a heat gun and thaw the valve.
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2, Was it a rainy day when you received it? This often happens when the tanks are delivered in wet conditions and water gets into the valve and freezes up making it very difficult to close...
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3, I have learned two things since I've been filling...The first is that if you open the valve all the way when filling it makes it much harder to close. I open the valve all the way and then turn it back a turn or so....The other is that as soon as the liquid runs out and you start to push just gas it freezes the valves worse than when you're pushing liquid...If you can... switch to ball valves..much easier to deal with than gate valves which seen to come standard
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4, That happens sometimes. You can call the vendor and report it and they *should* take it out of service and repair it. Also, we frequently get tanks that have a broken vacuum seal and they evaporate in just a few days. When that happens, the top of the tank usually gets an ice block.
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5, I have this problem on a regular basis, when my nitrogen vendor gets new employees. They tend to overtighten and begin to strip tank valves, especially cryogens. I use a channel lock to open and close these.
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6, That has happened to me in the past on numerous occasions. What I learned to do was #1 not to open the valve all the way and #2 while the fill was taking place, to periodically (every 1-2 min) to turn it back and forth a little to be sure it isn't freezing.
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7, I’ve seen it mostly when there was moisture on the valve (rain, excessive humidity), which froze up during the fill. When in question, I now always turn the valve open and close a bit while it is cooling down and filling.
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8, In my experience this is more of a problem if the liq N2 dewar has just been recently refilled... maybe it gets moisture condensed in the valve packing. When possible I try to avoid using the dewar until the next day, or at least a few hours, after refill.
I always keep a strap wrench (plastic) on hand in case the valve is hard to turn. These are very inexpensive and available from Grainger or McMaster Carr... or maybe local hardware store.
Also during the fill I "excerise" the valve by turning the knob back & forth a little to keep it from freezing up.
If the dewar is owned & supplied by vendor, you should complain... sometimes the valves get old and need to be replaced. I think loose valve packing may encourage moisture getting in. If you own the dewar... the same thing applies. Your machine shop may be able to service the valve.
The above precautions seem to completely eliminate panic stuck valve incidents at the end of the fill when N2 is splashing everywhere. I got the strap wrenches when I started having undergrad helpers doing the N2 fills.
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9, Have the tanks been sitting in the rain and getting wet prior to the liq. N2 fill? The valves may freeze up if they are just a little bit wet. This happened to us before and the only way to close the valves was by unthawing them using a strong heat gun
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10, It was due to high humidity in the air and ice was built up in the valve. Check your humidity before you turn it on.
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11, ...usually when that happens it’s because the valve was opened all the way against its stop and when it gets cold differential contraction tightens it. Thus, it is good practice to not open the valve all the way, or if you hit the stop, turn it in a half turn. Full flow is reached before the valve hits the stop.
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12, Yes, it's a bad valve. Make sure you tell the vendor. Try not to break it if you use a wrench to close it. It may help to use a heat gun on it. Seems like if it's going to do this you get an indication in that the valve doesn't open as easily as it should (it might make a scrunchy noise...)
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13, Happened to us as well. I ditched the company (National Welders now AirGas) after repeatedly asking them to fix the tanks. We lease tanks from AirProducts now. They come each week fill the tanks and we pay for what we use plus the lease. They cover all maintenance. It just works.
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14, I have found it convenient to install a lever valve between the transfer tube and the connection to the LN2 tank. There's always sufficient leverage with the lever valve to close it quickly, then, if the valve on the tank has frozen, I can resolve the problem at a more relaxed pace since LN2 is not spilling all over the place.
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Best regards,
Dejian
Received on Thu Oct 29 2015 - 07:04:47 MST