Which device functions similarly to packing in a pump?

The device that functions similarly to packing in a pump is a mechanical seal. Mechanical seals are used to prevent the leakage of fluids around the rotating shaft of a pump. They provide a tight seal that maintains the integrity of the fluids being pumped while allowing for rotation without friction, which is similar to how packing works.

Packing consists of various materials that are placed around the shaft to create a seal, preventing leakage. Both packing and mechanical seals aim to minimize fluid leakage while allowing the pump to function effectively without excessive wear or damage to the components.

The other options don't serve the same purpose in a pump's operation. O-rings and gaskets are primarily used in static applications to create seals between stationary surfaces. A capacitor, on the other hand, is an electrical component used to store and release electrical energy, which is unrelated to the sealing functions within a pump.