API 685

What is API 685 and Where is it Used?

API 685 covers sealless centrifugal pumps for petroleum, heavy-duty petrochemical and gas industry process services. It is mainly associated with magnetic drive pumps and canned motor pumps.

What are sealless pumps?

Sealless pumps do not use a traditional shaft seal exposed to the atmosphere. Instead, torque is transmitted through a containment shell or the motor rotor is integrated into the pumped liquid environment.

Main API 685 pump types

• Magnetic drive pumps — torque is transmitted by magnetic coupling.
• Canned motor pumps — motor and pump are integrated in a sealed arrangement.

Where API 685 is used

• toxic liquids,
• hazardous chemicals,
• flammable hydrocarbons,
• services where leakage must be minimized,
• environmentally sensitive applications.

Why use API 685?

The main reason is containment. If leakage to atmosphere is unacceptable or extremely costly, a sealless pump can be a better solution than a conventional sealed pump.

Engineering limitations

Sealless pumps require careful review of heat generation, minimum flow, bearing lubrication, solids content, dry running risk and containment shell losses. They are not universal replacements for all mechanically sealed pumps.

API 685 vs API 610

API 610 is for conventional centrifugal pumps with shaft sealing systems. API 685 is for sealless centrifugal pumps in similar heavy-duty industries where containment is the key issue.