How many types of self-flushing mechanical seals are there?

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There are two types of pressure cover mechanisms: one uses the pressure difference generated by the pump itself to achieve flushing (Figure 55); the other involves a pressure-raising device in the sealed chamber to circulate the sealing fluid. This method is often used in self-cleaning systems with cooling. The pressure-raising device can be a small impeller (Figure 56), a vortex impeller, and a pumping screw, etc. Based on the flow direction of the sealing fluid, it can be divided into forward flushing, reverse flushing, two-way flushing, and through-flushing. Positive flushing is from the pump outlet, through the flow control orifice plate, into the sealing chamber (Figure 55). Backwashing is from the sealed chamber through the flow control orifice plate to the pump inlet (Figure 57). For double-support pumps, two-way flushing can be employed (Figure 58). The pressure in the sealing chamber at the outlet side is higher than that at the inlet side; the two sealing chambers are connected by pipes, with reverse flushing occurring at the pump’s outlet and forward flushing at the inlet, which is why it is called two-way flushing. Through-flow flushing: The flushing fluid enters the sealing chamber from the pump outlet via an orifice plate, and after flushing, it flows back to the pump inlet (Figure 59). This method is often used for sealing low-boiling-point liquids. The clearance between the bottom sleeve and the seal, located between the impeller and the seal, is required to be small. The various self-cleaning methods mentioned above are used for sealing clean fluids at moderate temperatures. For cleaning fluids with higher temperatures, self-flushing with cooling is used. It involves using a pumping device to remove the fluid from the sealed chamber; after passing through a flow-limiting orifice plate and a cooler, the fluid has its temperature reduced before being sent back into the sealed chamber (Figure 60). If the fluid is not clean, a filter can be installed in the pipeline (Figure 61). Some people also refer to self-flushing as internal circulation.