When is a mechanical seal typically used instead of packing in pumps?

A mechanical seal is typically used instead of packing in pumps when the pump suction pressure is equal to or greater than 60 psi due to several reasons related to performance and reliability.

Mechanical seals are designed to handle higher pressures and provide a more effective sealing solution than packing. When the pressure in the system is higher, the mechanical seal can maintain its integrity and prevent the leakage of fluids more effectively than packing materials, which may wear down or fail under increased pressure conditions.

Also, mechanical seals tend to have better alignment and a lower friction coefficient than packing, which can improve the efficiency of the pump operation at higher pressures. They also require less maintenance and are less prone to failure compared to packing, especially in high-pressure situations.

In contrast, the other options present conditions that may not justify the use of mechanical seals. Low temperatures, low suction pressures, or the use of only non-corrosive fluids do not inherently call for mechanical seals, as these factors may still allow for the effective use of packing or other sealing methods. Hence, the application of mechanical seals is optimally suited for scenarios involving higher pressures.