Troubleshooting Pump Issues

In sequential injection, pump troubles are the most common issue. These issues can range from
poor precision or accuracy, pressure surges, aspiration air leaks and plunger repositioning errors. In
order to identify which facet of the pump is causing the problem, one must look at more than just the
pump itself. More often than not, exceeding the syringe pump’s physical/mechanical limitations is the
main cause.
First, lets examine the cases where the syringe pumps limitations are not breached. If an
operator is having trouble receiving robust reproducibility, there could be portions of the valve rotor
stuck within the rotor channel. This is the result of the valve actuating over a rotor that is not completely
flush with the valve head/stator. To identify this, unscrew the stator from the valve head (locating the 3
Allen screws on the valve head). Remove the stator and then the rotor. Take a close look at the rotor to
see if there is plastic shedding in the rotor channel. If there is, use a Kimwipe and your nail to smooth
out the rough area on the rotor. If the problem was the rotor, this would immediately improve
accuracy/precision results.
 
The next item to check is whether or not the system is over pressurized. An over pressurized
system will move fluid even after the syringes have stopped moving. One has to physically observe the
movement of fluid (either by watching the waste or reagent lines) to see if valve actuations cause fluid
to move instead of the pumps themselves. If a valve actuation is responsible for moving fluid out/into
waste/reagent containers, and an operator cannot seem to get accuracy or precision, the pressurized
system could be the problem.
 
Aspiration on the MicroSIA units is not as robust and powerful as dispensing. The act of
aspiration puts a lot of pressure strain on connections downstream of the pump. Once the pressure of
aspirating out of either long lengths of small ID tubing or through check valves and other pressuregenerating
components is too potent for the pump, air leaks occur. This will generate an army of
bubbles into your system, which will cause accuracy/precision problems. Also, the liquid becoming
aspirated will not fully enter the space desired.
 
Lastly, SIA systems that have exceeded the pressure capacity (~60-80PSI) can have pumps fail to
return to the home position (where the plunger is all the way up). This happens when the system is
running and the method causes fluid to dead-head on the syringe pump. Once the home position has
been forcefully changed by this, that syringe will no longer return to home until the system is depressurized
and communication is reset. Other ways to deal with this issue (if the method in use cannot
change much) is by commanding the syringe pump 3-way valve to the “Top” position while the system is
pressurized. Once the syringe needs to be utilized, the operator must have the system de-pressurize (by
commanding the valve to the waste position) letting the fluid exit the system. Once the pressure is
equilibrated, the syringe pump may be used to move fluid once more.