Mechanical seal flushing oil pressure
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The seal flushing oil used for the hydrogenation feed pump in my company is diesel supplied from the plant; the medium pumped by the pump is wax oil, at a temperature of around 100 degrees. The temperature of the diesel is less than 30 degrees, the outlet pressure of the pump is over 170 kilograms, while the pressure of the flushing diesel is 4 kilograms. How can flushing be achieved with such a low pressure? With such a large pressure difference, wouldn’t the flushing oil fail to enter the pump? I’m not quite sure about this
Based on your description, I guess your machine seal should be a pressure-sealed seal. Regarding pressure: The discharge pressure is 170 bar. Is it a multi-stage centrifugal pump? If so, the pressure acting on the mechanical seal is not the outlet pressure, but rather the pressure in the pump chamber. The pressure in the pump chamber of a multi-stage centrifugal pump is generally slightly higher than the inlet pressure of the pump; in other words, the pressure in the pump chamber is low, while the sealing fluid pressure of 4 bar is higher than that pressure. The leakage direction of the internal seal is such that the sealing fluid leaks into the pump chamber. Regarding the leakage amount: The normal leakage rate of the seal is very low, and the amount of sealing fluid that leaks into the pump chamber can be disregarded. Massive leakage occurs only when the seal fails; typically, there is an alarm in the sealing system that allows for the detection of abnormal leaks.
The flushing oil pressure just needs to be higher than the pressure in the machine pump’s sealing chamber； The pump outlet pressure is high, but the pressure in the pump’s seal chamber is not necessarily high ； Since it’s already set, the pump factory must have done the calculations properly; there’s no problem.
It’s a multi-stage centrifugal pump. The mechanical seal is located at the end near the outlet; shouldn’t it be in a position closer to the outlet pressure?
The pump should have structures such as balance pipes to ensure that the pressure in the pump chamber does not become too high. I’m not in the pump business, so I’m not very familiar with the details. You can ask the pump manufacturer. It is also possible to use an upstream pumping seal, with pressure-raising grooves on the sealing surface. Further analysis requires more detailed information.
Is the pressure in the sealing chamber of a single-stage centrifugal pump much lower than that at the outlet, and slightly higher than the pressure at the inlet?
Pressure estimation for the seal chamber of a single-stage centrifugal pump: inlet pressure + 1/3x(Outlet – Inlet)
This post was last edited by space ★ Xuan on 2016-5-7 at 11:04. The feed pump for the paraffin hydrogenation unit is of the BB5 type as per API standards (a multi-stage centrifugal pump). The high-pressure pump is equipped with balance pipes and balance devices; the pressure in the sealing chambers, whether for the inlet or outlet seals, is the same as the pump’s inlet pressure. Generally, the pressure in the feed tank for high-pressure hydrogenation is designed to be between 0.3 and 0.35 MPa. Regardless of the outlet pressure, as long as the pressure of the flushing oil is 0.4 MPa, there should be no problems. Note: Just to clarify, such a mechanical seal should be based on API specification 32 combined with specification 53
You’re right; could you share any materials on mechanical seal solutions?