Our lab is using SpectraSystem P1000 pump (from Thermo Separration products Inc)that is five years old. Recently its pressure kept jumping several hundred psi up and down and made the system couldn't work properly. What is strange is that it only behaved weird when pressure drop is over 1900 psi although before this is quite normal working pressure.

Does anyone here know what is wrong? We have tried different mobile phase and different columns and had excluded them from problem causing parts. If it is the pump, which part of the pump should be checked first? Thanks a lot.

I DONīT KNOW THIS KIND OF PUMP, BUT THE SAME HAPPEND TO ME WITH AN NORMAL HPLC PUMP , AND IT WAS CAUSED BY A BUBLE OF AIR INSIDE THE VALVES.
ALSO, MAY BE YOU ARE HAVENING PROBLENS WITH THE JOINT OF SEALS.

It could be air in the pump. This seems to be removed best while pumping pure methanol through the system while it is under load ie when a column is attached-an old one is best when you are trying repairs! However, if you have no problems until a certain pressure is reached, you could try replacing the transducer check valve. These cost about $250 so you should discuss this suggestion first with the TSP service engineers. Note many of TSP pump spares are interchangeable. If you have another TSP instrument, you might be able to swap the valves briefly to see if the problem goes away-but do verify that the part is the same with the service engineers before attempting this.

You need to order an inlet and transducer check valve for the pump. There is also a possibility that the coupling between the pump motor and the cam (which drives the piston followers) is failing. I worked on TSP equipment for years. This pump is about the right age foe the coupling to crack and fail. The way to check this is to pop the cover and inspect the mechanism with the system running...

Thank you very much. I'll check the valve and see what happens.

You may want to try sonicating the inlet and outlet check valves before you go and order whole new assemblies. Many times this will take care of the problem. You may have dirty check valves which the sonication would take care of. I haven't worked on TSP pumps, but I have been a FSE for about 15 years and this works in a large percentage of this type of problem.