How To View The Sealing Form Of Fire Pumps

Sep 29, 2025

How to view the sealing form of fire pumps? Sealing has become a common situation in mechanical equipment, and it has gradually become a form of use in equipment such as fire pumps. It can be said that fire pumps without good sealing cannot be used well.

When the fire pump is working, the secondary impeller rotates together with the pump spindle, and the liquid in the secondary impeller also rotates. The rotating liquid generates an outward centrifugal force, which not only resists the liquid flowing towards the mechanical seal, reducing the pressure at the mechanical seal, but also prevents solid particles in the medium from entering the friction pair of the mechanical seal, reducing the wear of the mechanical seal grinding block and extending its service life. In addition to sealing, the secondary impeller can also reduce axial force. In submersible sewage pumps, axial force is mainly composed of the pressure difference force of the liquid acting on the impeller and the gravity of the entire rotating part. The direction of these two forces is the same, and the resultant force is the sum of the two forces.

From this, it can be seen that under identical performance parameters, the axial force of a fire pump is greater than that of a typical horizontal pump, and the balancing difficulty is greater than that of a vertical pump. So in submersible sewage pumps, the reason why bearings are easily damaged is also closely related to the large axial force. If a secondary impeller is installed, the direction of the pressure difference force exerted by the liquid on the secondary impeller is opposite to the combined force of the two forces, which can offset some of the axial force and prolong the bearing life. However, using a secondary impeller sealing system also has a disadvantage, which is that a portion of energy is consumed on the secondary impeller, usually around 3%. However, as long as the design is reasonable, this loss can be completely reduced to a lower limit.

Generally speaking, in sealing situations with contaminated process fluids, ordinary contact type double end mechanical seals are commonly used. A blocking fluid auxiliary system is used to inject a blocking fluid with a pressure higher than that of the sealed medium between the two seals to prevent leakage of the sealed medium to the outside. However, in practice, there may be malfunctions due to various reasons that cannot effectively prevent the leakage of the sealed medium, especially for process pumps that transport media containing solid particles, frequently start and stop, and are easily evacuated. The reliability of the seal is far from satisfactory.

Whether the fire pump can be used well depends on whether the sealing effect we do is good or not. Sealing work is not for anything else, but to enable us to work better when using the pump.