The Role of Hydraulic Balance in Mechanical Pump Seals

Cartridge mechanical seals for pumps

The least reliable part of centrifugal pumps is the mechanical seal. Most seals prematurely fail even before the seal face wears away. One of the common reasons for premature failure is face instability as the geometric balance ratio of the seal is too low.

This guide will discuss the forces applied to the seal to understand the pressure gradient factor and seal balance ratio. Balanced seal faces are likely to separate before wearing out, while unbalanced seals are not prone to this kind of separation. The potential instability of the balanced seals is an essential factor in minimizing seal reliability.   

Packing – A Sealing Method

In most machines, a shaft enters the housing under pressure. The machine’s essential and desirable feature is minimum leakage in areas surrounding the shaft. The centrifugal pump is the most common example of this machine. The end face mechanical seal and packing are the most common elements for limiting leakage.

Packing uses resilient material that is arranged around the shaft to create a long axial seal. The packing rings are compressed inside a chamber by using an adjustable gland. A small amount of leakage is required to cool and lubricate the shaft-packing interface.

Mechanical Seal

The mechanical seal comprises less resilient materials than packing, and a spring is used to give automatic compensation for wear and resiliency. The rotating face and the spring are driven by a locking collar secured with the shaft.

The hydraulic forces and the spring maintain a small gap between the stationary and rotating faces – the primary path of leakage. These locations can also be referred to as secondary leakage paths. The heat between the faces is generated by viscous shear and rubbing between faces, so the seal plate comprises a port for liquid injection.       

Mechanical Seal Design

A mechanical seal is an intricate combination of a heat generator, thrust bearing, sealing device, and heat exchanger. It may be operated under cavitation, liquid-vapor conditions, and mixed or full film lubrication. The seal’s dimensions and the lubricating liquid are used to determine its success or failure.

Moreover, the hydraulic balance regulates fluid distribution throughout a mechanical pump system. This balancing supplies fluid to several channels according to the mechanical seal design. Balancing valves help distribute the system’s flow evenly.

Double-balanced mechanical seal for pumps

To choose the right mechanical sealing solutions for pumps, reach out to professionals at Robco of America. They also offer custom-designed seals to suit various industrial applications and a variety of mechanical seals for agitators, compressors, reactors, centrifugal pumps, and bead mil units.

If you’re looking for reliable mechanical seal repair services, call 1-800-662-0585 for technical support or email at To learn more, check out their website.

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