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Disc stack centrifuge bowl leaking is a common occurrence. This troubleshooting article will discuss the various reasons for the bowl leaking and how to fix it.
This article refers to some disc-stack centrifuge bowl parts which are unique to these types of machines. The reader can see a brief explanation of each of these parts in our disc centrifuge terms glossary.
A self-cleaning, disc-stack centrifuge has a split-bowl design. It means that the upper and lower parts of the bowl have a designed opening between them. The self-cleaning mechanism requires the two parts to separate, which allows the separated sludge to exit the bowl.
Under standard processing, the bowl needs to be closed to prevent the liquid from escaping the bowl through the sludge outlet. This requirement means that the two parts of the bowl need a tight seal when they are in a closed position.
The upper part of the bowl, known as the bowl hood, has a circular seal embedded around its periphery. This seal ring is a sacrificial part known as the Nylon Seal Ring.
The lower part of this sealing mechanism is the Sliding Piston. This part is the only independently moving member inside the bowl cavity. The sliding piston has a protruding lip around its outer edge.
The Sliding Piston lip butts up against this Nylon Seal Ring to form the seal. See the image below showing the bowl cross-section of this seal.
As mentioned earlier, a leaking bowl means that this seal is not functioning correctly. This malfunction allows the process liquid to escape through this seal.
The main sign of a leaking bowl is a continuous discharge of process fluid during the fluid process cycle. The operator can see this discharge coming out through the sludge discharge chute.
This leak diverts some or all of the process fluid resulting in reduced or no flow through the clean oil path. Most centrifuge control systems monitor the pressure in this pipe, and flow loss will trigger the no-flow alarm.
The leaking process fluid will also cause resistance to the bowl rotation due to the air friction experienced by the escaping fluid at high velocity. This drag on the bowl causes the motor to draw a higher current, which is also detected by an advanced control system.
As described above, a few reasons can cause the centrifuge bowl to leak. We will briefly discuss each of the causes and a suggested remedy to fix the issue.
As mentioned earlier, the Nylon Seal Ring is a sacrificial part. During the sludge discharge cycle, the accumulated sludge exits the bowl at a high velocity past this seal ring. The sludge particles cause wear on the seal ring surface as they pass the seal ring. Over time this repeated process causes wear on the Nylon Seal Ring.
Inspecting and replacing the Nylon Seal Ring is the immediate fix for this problem. That is assuming a worn-out seal ring is the cause of the leak.
Another important consideration here is the periodic replacement of the Nylon Seal Ring. Consider the centrifuge operation with a worn-out seal ring, which is leaking the sludge-laden process fluid. The sludge particles will also cause wear on the sliding piston lip. The sliding piston is an expensive part to replace. Therefore, it is better to routinely replace the inexpensive Nylon Seal Ring to protect the sliding piston from wear.
The photograph below shows an eroded sliding piston lip caused by a leaky bowl seal.
It is possible that the sliding piston does not form the complete seal against the seal ring in some cases. The piston can cause this improper seal if the piston seal is not functioning as intended.
The operator should investigate this possible cause if the seal ring and the lip on the sliding piston appear to be in good condition.
Often a couple of inert sludge discharge cycles that the operator manually initiates can fix this problem. However, if this quick remedy does not fix the bowl leak, it must be thoroughly inspected for any impediment that may cause the piston to move within the bowl.
In older centrifuges, the bowl closing water may leak out from the bowl closing chamber due to worn valve plugs or a bad gasket or o-ring.
During the process, a slow leak of the bowl closing water can gradually reduce the upward force on the sliding piston causing it to slip down, resulting in the bowl leaking.
One of the features of our automatic centrifuge control systems introduces fresh closing water into the bowl periodically. This feature can alleviate the cause of the bowl leak.
We have come across damaged sliding piston lips quite often. Improper handling of the sliding piston during servicing can cause indentations on the sliding piston lip. These tiny gauges do not allow the seal ring to contact the entire sliding piston lip surface fully. The highly pressurized process fluid in the bowl escapes through the tiniest gaps in this seal, causing the bowl to leak.
The OEM recommends using a fine-grade abrasive tool to gently blend the indentation to the rest of the lip surface. This repair of the sliding piston lip often fixes the leak.
Partial discharge centrifuges can open and close the bowl in a very short time span. This quick opening allows this type of centrifuge to discharge some portion of the separated sludge. A standard design partial discharge centrifuge discharges approximately 70% of the sludge space in the bowl.
If the process fluid is not pre-strained and contains large solid particles, these particles can get caught between the nylon seal ring and the rising piston lip. The particles can get embedded in the nylon seal ring, which causes the seal to be uneven and incomplete. These embedded particles are another possible cause of a leaking bowl.
Replacement of the damaged seal ring is the proper fix for this cause of bowl leakage.
Fluid draining through the sludge outlet does not always imply a leaky bowl. There are other possible reasons for fluid draining from the sludge outlet unexpectedly. This section discusses some causes of fluid leaking through the sludge outlet.
The small lock ring or paring chamber cover houses the paring disc pump in the upper part of the bowl hood. A loosely fitted small lock ring allows the process fluid to leak through it. The leaking process fluid then drains down the centrifuge frame’s inner side and out the sludge drain.
This leak appears as soon as the bowl is full of fluid and continues throughout the process. The simple fix for this leak is to stop the centrifuge and fully tighten the small lock ring.
The upper paring disc pumps out the heavy phase from the disc centrifuge. Sludge buildup can cause this impeller to be blocked. The heavy phase fluid now overflows from the centrifuge bowl top and down the frame into the sludge outlet.
This fluid draining is again a constant flow and appears to be a leaky bowl. The operator needs to stop the centrifuge and clean the paring disc pump to fix this condition.
Hopefully, this article has given the reader a clear understanding of the causes of disc centrifuge bowl leaking and relevant fixes.
Also, Dolphin Centrifuge customers can always call us to avail of our lifetime technical assistance.
by Sanjay Prabhu MSME
Engineering Manager, Dolphin Centrifuge