Ring friction during the reinstallation of centrifugal pumps
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I am a maintenance technician for low-temperature methanol washing systems. I work on centrifugal pumps that transport low-temperature methanol (around -40 degrees Celsius). There were two problematic situations during the maintenance and reinstallation of these pumps: when installing them back in place due to seal leaks, there was severe friction at the ring area. It’s important to note that we didn’t cause any damage to this ring during maintenance; in fact, no harm was inflicted on it. Yet, when the pump casing was tightened, the pump wouldn’t rotate. Even with great care and even force applied, it still didn’t work. When the pump was taken apart again, it was found that the ring had been scratched due to friction. We then had to grind the ring smooth, first using a file and then sandpaper. Even after doing this, it was necessary to apply even force when reinstalling the pump to avoid problems with its rotation. We wonder if it’s due to thermal expansion and contraction; otherwise, why does the mouth ring seem to get bigger, making it so difficult to put it back in?
It has little to do with thermal expansion and contraction; after all, the variation trends of the impeller ring and the casing ring are the same. It is recommended to manufacture two guide rods to be installed at the locations of the large cover bolts – with these guide rods for positioning, installation should be easier
Here are some personal opinions; they’re not necessarily correct, just for reference. Based on your description, I think the problem may lie in the incorrect fit between the upper cover and the mouth ring; the clearance between the pump’s upper cover and the mouth ring should be 0, or there should be a tightness of 0.01 mm. This way, during operation, neither will the mouth ring rotate together with the rotor nor will it deform. In your factory, there is a tendency for the mouth ring to deform under such conditions. You can use lead wires and by changing the gasket at the joint to conduct measurements and make adjustments.
Since there are many types of centrifugal pumps, if the pump in question is an IHF pump, the most likely cause is an excessive gap between the impeller and the rear cover (also known as the static ring seat). In such cases, it suffices to sand the cone at the connection point where the impeller is attached. For other types of pumps, such as canned pumps (and it should be noted that canned pumps don’t have mechanical seals), the principle is the same: find a way to reduce the distance between the impeller and the rear cover (it might be the distance to the graphite bearing seat; however, I recommend referring to the manufacturer’s instructions to ensure compliance with the standard requirements).
Reply to 2# 565026033: Since the bolts are installed on the pump casing, they also serve a positioning function; moreover, tightening them is done by two people working symmetrically, tightening them in half-turns at a time. Anyway, we dealt with the mouth ring twice, and it stopped getting stuck.
Reply to 3# Zhongzhaoxing: Hello. The tightness of 0 or 0.01 for the gap between the upper cover and the mouth rings is as expected. What I’m referring to is the gap between the mouth rings themselves. In our case, there is significant friction between those mouth rings; however, trying to address this friction issue results in an increase in the gap, which affects performance.
Reply to 4# qinkaimin: The distance between the impeller and the rear cover becoming smaller should not affect the gap between the collar rings; the collar rings are there merely to reduce losses in useful work.
LZ, you’re really skilled – I’ve learned a lot from you. It seems like one of the seals wasn’t polished with a file. .
Oh, this colleague is a joke; it’s because of the intense friction.
It’s best to measure the dimensions and base decisions on those figures; it’s also possible that alignment is not correct
It’s probably because the cold pump didn’t cool down sufficiently