I have a question regarding machine seals that has been bothering me for a long time; I hope some expert can help answer it
Thread Content
Generally, for single-stage pumps, the seal water pressure should be about 1–2 kilograms higher than the inlet pressure; too high a pressure is also not desirable. If the normal pump inlet is connected to a horizontal, atmospheric-pressure tank with a pressure of about 1 kilogram, then the seal water pressure can be 2 kilograms higher than the inlet pressure; in other words, a pressure of 3 kilograms for the seal water will suffice. However, there is one problem that has been bothering me for a long time. Before starting the pump, the outlet valve is closed first, and at that point the pressure inside the volute should be equal to the pump’s outlet pressure. If the pressure at the pump outlet is 6 kilograms, the spring force of the mechanical seal is 2 kilograms, and the pressure of the seal water is 3 kilograms, then when the pump is started and the outlet valve is closed, causing pressure to build up in the volute, the spring force of the mechanical seal, which is 2 kilograms, plus the pressure of the seal water, which is 3 kilograms, amounts to only 5 kilograms. Since the pressure in the volute is 6 kilograms, this could push the mechanical seal aside, allowing material to enter the seal chamber. In that case, the statement that the pressure of the seal water should be about 2 kilograms higher than the inlet pressure is incorrect; it should be higher than the normal outlet pressure of the pump. It should be 6 + 2 = 8 kilograms. I must have misunderstood something here – please, someone with more expertise can explain this to me.
How does a spring force of 2 kilograms come about?
There is a problem: the water pump should have a balance pipe; it’s not clear whether it does exist, and this should be given attention.
It should normally be 1-2 kilograms higher than the pressure in the sealing chamber, not the inlet pressure
Pump manufacturers or sealing manufacturers will choose between balanced and unbalanced seals depending on the operating pressure. Why does the pressure in the sealed chamber have to be the same as the outlet pressure when the valve is closed? For a single-stage cantilever pump, the impeller usually has balance holes, and the pressure in the sealing chamber is slightly higher than that at the inlet. First, close the outlet valve; at this point, the pressure inside the volute should be equal to the outlet pressure of the pump. ”Is the inlet pressure equal to the outlet pressure?
I agree with you; it should be higher than the pressure of the sealing gas.
The sealed chamber is equipped with a throttle ring; the pressure there is lower than that in the volute but higher than the inlet pressure；
Balance tubes are not present in all pumps; some single-stage centrifugal pumps with external flushing use balance holes on the impeller to counteract axial forces, while multi-stage pumps make more use of balance tubes.
The mechanical seal generally only experiences higher pressure. . The tighter it is pressed. . It won’t be pushed away