Several issues with the pump

What kind of pump are you talking about? I’m not very knowledgeable; I’ve really never heard of it

I suggest: 1. Install the seals first, then fill the pump. 2. Generally, for pumps, seals are installed at both the inlet and the outlet. 3. If the pressure of the liquid inside the pump is 2.8 MPa and the outlet pressure is 4.0 MPa, then the pressure of the sealing fluid should be 3.0 MPa. 4. If the pump is shut down for a short period of time, there is no need to drain all the liquid from the pump; however, if it is shut down for an extended period, it is necessary to drain all the liquid from it. If it is not drained completely, the seal does not need to be closed.

1. Sealing should be carried out first before filling the pump with liquid; this is especially true for double-seal pumps, while it’s less important for single-seal pumps. 2. The seal of the pump is the shaft seal. 3. The pressure of the sealing fluid should be 3–5 kilograms higher than the pressure inside the pump. 4. In the case of a short-term shutdown, it’s not necessary to drain all the liquid; if the seal is closed without draining the fluid, it has little effect on single-seal pumps, but it can cause damage to the seal in double-seal pumps

My answer is the opposite of yours: fill the pump first, then start the sealing process. A sealing fluid pressure of 3.0, slightly higher, is appropriate; the specific pump manufacturer will provide you with the correct value.

The mechanical seal cannot withstand reverse pressure; generally, the pressure in these liquid seal tubes is higher than the flushing pressure, which in turn is higher than the pressure inside the pump casing. If there is a pressure gauge on the pump casing, you can read that value; if not, it can be assumed that the pressure lies between the inlet and outlet pressures. As long as the flow rate for flushing is appropriate, there’s no need to worry about the pressure – it will already be at the appropriate level. It is advisable to keep the pressure in the liquid seal tube at a slightly higher level; we have 2 kilograms at the inlet and 6 kilograms at the outlet, so the pressure inside the pump casing must be between these two values, with the pressure in the liquid seal tube being just over 7 kilograms. I mean, most of the pumps in our factory are like this.

As long as there is no back pressure, a difference of two or three kilograms in pressure will not cause damage to the mechanical seal; however, if there is back pressure of two or three kilograms, the mechanical seal will be damaged. If you don’t have any reference data, then design a slightly higher pressure difference, such as three to four kilograms; under normal conditions this will not cause backpressure, so there should be no problems. There’s a formula I’ve forgotten how to use in order to estimate the pressure inside the pump based on the inlet and outlet pressures; in your case, it’s probably around 3 kilograms inside the pump. For that liquid seal tube, 100 psi of nitrogen is sufficient

Well, the previous entry wasn’t written properly; the pressure inside the pump should be greater than 3 kilograms, maybe around 3.5 kilograms. An additional 2.8 kilograms of back pressure can damage the mechanical seal; even if it doesn’t get damaged, it’s still not good for it, so don’t do that. If the slurry pump requires flushing or discharge, and in the case of solvents, there is no need for discharge if the pump is stopped for a short period of time.

Seal it first, and get the filling pump ready for use. An excessive pressure difference may damage the pump. There is no need to drain the fluid when the pump is stopped temporarily; however, drainage is necessary if the pump is stopped for an extended period or needs repair