Are check valves really reliable?
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Check valves belong to the category of automatic valves; they are primarily used in pipelines where fluid flow is unidirectional, allowing fluid to move in only one direction in order to prevent accidents. It is a common protective measure used in chemical plants to prevent the backflow of materials, but is this measure reliable? On January 25, 2005, at the Acetylene Service Company (ASCO) in New Jersey, USA, a failure of the check valve caused acetylene to flow back into the circulating water facility. It leaked through the drainage valves and spread throughout the facility; upon encountering an ignition source, this led to an explosion that resulted in the death of 3 employees and serious injuries to 1 other employee.
Sometimes check valves get clogged, and some media that tend to polymerize can also cause the valve core to stick
This post was last edited by ylb913 on 2015-11-21 07:36. I did come across a reliable one… In 2006, while we were transporting alkaline slag, the system got blocked after about 7 cubic meters had been delivered; using nitrogen at 0.7 MPa didn’t help to clear the blockage, and neither did using nitrogen at 2.4 MPa. This alkali slag line is not under our responsibility; it falls under the jurisdiction of the oil products workshop (which is responsible for the storage and transportation of oil products). However, the production department is unwilling to accept this, claiming that we have caused a blockage and asking us to investigate the cause along the line. Over a distance of about 1,400 meters along the way, we followed the standard procedure: ascending and descending the pipe racks, and choosing a point with valves for venting by removing the flange cover. Eventually, we found a one-way valve outside the wall of the tank area; we removed it as well – amazing! In a selectively operated check valve, when the valve disc falls off, it ends up lying vertically \"on top\" of the outlet – how is it possible for it to seal tightly in that position? ——I did some calculations back then: for a DN80 pipeline with a length of 1400 meters, the capacity is equal to 0.04*0.04*3.14*1400 = 7.03 cubic meters. Before sending in the alkali slag, we always clean the pipes to ensure they are unobstructed; therefore, the pipes are empty before sending in the alkali slag. What a coincidence? Were all the 7 cubic meters I sent out blocked in front of the check valve? ——Why calculate this? Since it was blocked after we sent out 7 cubic meters of material, it is believed that the pipeline was unobstructed at first; the blockage occurred during the process of sending in the alkali slag. Therefore, the production department claimed that it was our dirty alkali slag that caused the system to get blocked, thus shifting all the responsibility onto us.
I often say that one should not rely too much on the integrity of valves; they need to be checked regularly. An extra valve does provide an extra layer of safety, but valves can also fail.
It can be said that danger is everywhere
Over-reliance on check valves； One will suffer heavy losses ； I had already seen in the forum discussions that when starting the pump, it’s common to open the outlet valve first; or when stopping the pump, the outlet valve is not closed or is closed later ； This issue was discussed when addressing that problem ； Some experienced workers, when training apprentices, claim that it’s based on experience and that doing things this way makes it easier to open the valves ； There’s a check valve when spoken out loud ； The 90s ； There was a large chemical company (I won’t mention its name) that experienced a power outage ； The high-pressure fluid at the pump outlet flows back, causing the pump to reverse direction ； The pump coupling was shattered, and one of the fragments penetrated the head of an operator on site ； Causing its immediate death ； This is a real lesson written in blood ； I have experienced it myself as well ； Because of the emergency stop, the small number of personnel, and the pump outlet valve not being fully closed (note that it was not fully closed ； It’s not that the pump isn’t turned off) running at night ； A few cubic meters of liquid (each cubic meter worth 12,000 yuan) was sprayed out from the top of the liquid storage tank at the pump inlet; fortunately, it wasn’t completely closed ； Just a stream of liquid was poured ； (The pump is relatively large, it is a multi-stage pump with high resistance), but this did not cause any significant damage or losses ； I was the chief operator at that time ； I had a month’s worth of bonus deducted from me ； Both incidents involved check valves at the pump outlets ； That’s why ； Strictly follow the operating procedures ； Following the start-up and shutdown procedures is mandatory ； Under no circumstances should you resort to shortcuts or rely on luck ； This is what ensures the safety of our operators as well as the safety of the equipment ； Remember, remember ； This is the experience of an experienced chemical engineer ；
It is difficult to ensure the sealing performance of check valves; they can help mitigate water hammer, but they are not reliable for providing isolation. A shut-off valve should be used where one is necessary, and a blind flange should be used in those cases where it is required.
I’ve never really trusted check valves; it’s better to follow the operating procedures. What the old chemist on the 6th floor said makes perfect sense.
Check valves are generally reliable, but there’s no guarantee they won’t fail at any time. Last year, we had a situation where the valve disc of one check valve didn’t return to its original position; fortunately, no accident occurred
One more valve means one more potential point of leakage
Internal leakage in check valves is quite common; one cannot rely on the valve itself for sealing. Even a small amount of impurity or defect on the sealing surface can cause backflow. There should be manual valves installed before and after the check valve, so that leaks can be easily isolated and addressed