Practical Protein Chemistry - A. Darbre 1989

Current state of automated liquid-phase amino acid sequence analysis
Major problems encountered when using an automated sequencer
Vacuum line leaks in a single-pump system

In this configuration, the roughing pump is used solely to actuate the reagent supply Valves and to evacuate the manifold, meaning it requires very little maintenance. Our pump operated smoothly for over two years without even an oil change! However, based on our experience, the high-Vacuum system can be a source of elusive leaks—though these occur less frequently than in a dual-pump setup. By placing a stopcock upstream of the cold trap, it is easy to check for leaks both before and after the trap. This technique is particularly valuable because many complications seemingly caused by a vacuum leak in the instrument actually stem from issues with the trap itself.

After checking the vacuum with the stopcock closed, the outlet of the trap is sealed with a large rubber stopper coated with vacuum grease, and the stopcock is opened. Leaks in the trap typically occur either in the drain line or at poorly sealed trap lead-ins. Completely thawing the trap and resealing the exhaust line will usually resolve the issue (at least temporarily). The optimal solution, however, is to redesign the drain assembly. Lead-in leaks can be fixed by regreasing the O-rings or replacing them entirely.

In our experience, vacuum leaks between the cold trap and the Reactor are highly unlikely; neither the solenoid valves nor the air cylinder valve have ever been a source of major trouble.