Leakage problem of the centrifugal pump seal
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My installation consists of around 300 horizontal single-stage centrifugal pumps, using methanol as the fluid. The operating temperature is 65–70 degrees, and the pressure is approximately 1.0 Mpa. Single-end face bellows are used for sealing (with some pumps employing single or multiple springs). During operation, all parameters of the pumps are normal and there is no leakage from the mechanical seals; however, when the pumps are shut down, leakage occurs to varying degrees. (It was normal before; this issue started last December.) Even the machine seal manufacturers who went to the site were unable to find the cause. I have also been engaged in equipment technology management for over 20 years, but I am utterly puzzled by this issue; the possibilities related to design, manufacturing, and material quality have already been ruled out. Going crazy! I am extremely grateful for seeking advice from all the experts and seniors!
The temperature drops when the pump is stopped, and the mechanical seal wears out
Is the poster from the north? Could it be that the raw materials used contained an excessive amount of water, which led to freezing after the pumps were stopped?
If more than 300 units are experiencing dripping to varying degrees, then factors such as alignment issues, clearance between the impeller and its ring, compression amount of the mechanical seal, and bearings can be ruled out, as it’s unlikely that all of them would fail at the same time. Could it be that there has been a change in the medium you use? Pressure? Purity? Then you mentioned the leaking mechanical seal; the manufacturer also came by. So what was found after it was taken apart? Are those leaking mechanical seals due to a broken rotating ring? Is the static ring broken again? Has the O-ring corroded again? Is it that the compression amount of the dynamic ring spring is gone again? If it’s completely intact, then there can be no dripping. What is the pressure to be maintained before installing the mechanical seal, in kilograms? Will there be leakage during pressure holding?
I think it’s because the machine seals have thinned to some extent due to prolonged operation; when there is a medium present, the temperature rises and causes thermal expansion. You can try adjusting the compression level of several of these machine seals
I think it’s a matter of compression volume; the pressure during operation is different from the spring compression force when the machine is stopped.
Take a close look to see where the leak is – is it between the mechanical seal end cover and the shaft sleeve, or between the shaft sleeve and the shaft? It’s best to have two pictures, one of a close shot and one of a distant shot!
Is it a problem with the sealing ring of the mechanical seal? Is it caused by the large temperature difference when starting and stopping in winter, as a result of the sealing ring material not being suitable?
Sealing leakage under static conditions can occur at either the dynamic or static sealing surfaces. One possible reason is that the compression amount is too low; another reason is that, after prolonged operation, gum or deposits may form on the dynamic ring seal, disrupting the perpendicularity between the end face of the dynamic ring and the shaft sleeve, which prevents tight fitting with the end face of the static ring and thus leads to static leakage.
Static leakage: Reason 1 – the compression amount may be too small； Secondly, long-term operation can cause changes in the structure of the moving ring seal or the accumulation of adhesive substances, which disrupts the perpendicularity between the end face of the moving ring and the shaft sleeve. This, in turn, affects the fit between the end faces of the moving and stationary rings, leading to static leakage.
1. After stopping, the motion path between the stationary ring and the moving ring becomes offset； 2. Methanol vaporizes easily; movement generates heat, which increases wear and results in a smaller compression volume ； 3. For subsequent purchases, high-quality domestic shielded pumps could be considered. 4. I’ve encountered this issue in other factories before; perhaps the material used in your pumps is not suitable for transporting methanol, and it might be worth trying another material.