PM-90 TROUBLESHOOTING

This section contains troubleshooting tips specific to the PM-90 pump. For general troubleshooting see the main TROUBLESHOOTING page.

Continuous Buzzing Sound
- Grasp each pump head with your hands. Is the audible noise significantly reduced? If so, the noise is due to motor-generated vibration. At certain flow rates, the stepper motor excites the pump module to greater vibrations. This can cause the pump module to contact the adjacent pump module or the sheet metal front panel.. This is more likely to happen when there is no load (no high pressure) and at higher flow rates.
- Open the purge plug, reduce the flow rate to 50 µL/min. and observe the L and R indicator on the LCD screen. Does the pump make a continuous knocking sound the entire time while either L or R is displayed? If so, Contact BAS.
Intermittent Buzzing Sound
- Open the purge plug , reduce the flow rate to 50 µL/min. and observe the L or R indicator on the LCD screen to correlate the noise with Left or Right head. Does the buzzing resolve into a continuous knocking sound which only occurs with one head? Does the knocking sound occur only towards the end of stroke of one head? If so, the pump head is not engaged to the drive mechanism. Remove the head and reinstall it.

Check FLOW RATE setting. Is it set for a valid, non-zero range (1-1999 µL/min)?
Has the Run/Stop key been pressed to start the pump? The LCD will display pumPing or iniTing while the pump is operating.
Is the high- or low-pressure limit displayed on the LCD? If so, see below.
Is there an error message on the display? If so, contact BAS.
Check for loose connections on the inlet side of the pump. Purge with freshly degassed mobile phase.
Is the mobile phase reservoir empty. Purge with fresh mobile phase.
Is the solvent uptake frit clogged? Clean or replace.

Check for loose inlet connection to that head. Purge with freshly degassed mobile phase.
Head not engaged to drive mechanism. Remove head and reinstall.
Inlet check valve failure. Switch inlet check valves between the two heads. If the problem follows the check valve then clean or replace inlet check valve cartridge.
Check the irrigation port outlet behind and under the head. If wet or buffer salt deposits have accumulated, a seal may be leaking. See the section for seal replacement.

The mobile-phase reservoir is empty. Make fresh mobile phase and purge as described in the STARTUP section.
There's a leak in the system. Check all connections.
Inlet check valve failure. Switch inlet check valves between the two heads. If the problem follows the check valve then clean or replace inlet check valve cartridge.
Check the irrigation port outlet behind and under the head. If wet or buffer salt deposits have accumulated, a seal may be leaking. See the section on seal replacement.
The low pressure limit is set too high. Reset to a reasonable value for your conditions.

The high-pressure limit is set too low. Reset to 4000 PSI or a reasonable value (1000 PSI above your typical operating pressure) for your conditions.
The injection valve is not fully in the inject or load position. Rotate it to one side.
The injection valve is not rotated fast enough when switching from load to inject or inject to load. When making an injection the valve must be rotated quickly or pressure may exceed the high pressure limit.
There's a clog in the flow path. It could be anywhere between the pump outlet and the detector. It may be the in-line solvent filter. Start opening fittings at the detector and work towards the pump. At some point the pressure will drop, pinpointing the location of the clog. (NOTE: There will be a normal drop in pressure when the column is removed.)
Have you changed to a more viscous mobile phase (e.g., one with methanol)?

The most common cause of pressure fluctuations at microbore flow rates is the failure of check valves to seal. This can be caused by air bubbles or contaminants in the check valve. Purge the pump with freshly degassed mobile phase. If performance improves, air bubbles were in the check valves. If the problem returns, degas the mobile phase more frequently and check the connections to the inlet side of the pump where air can be sucked in. Note which head is compressing on the LCD display (L or R) when the pressure drops.
Switch the inlet check valves between the two heads. If the pressure drop now occurs on the opposite pump head, it is associated with the inlet check valve on the head showing the problem. Clean or replace as described in the CHECK VALVES section.
Switch the outlet check valves between the two heads. If the pressure drop now occurs on the opposite pump head, it is associated with the outlet check valve on the head that does not show a pressure drop. Clean or replace as described in the CHECK VALVES section.
One or both pump heads may need an overhaul. See the PUMP HEADS section.
One of the outlet lines from the pump to the pressure manifold may be clogged. Remove and examine. Replace as necessary.
Check the irrigation port outlet behind and under the head. If wet or buffer salt deposits have accumulated, a seal may be leaking. See the section on seal replacement.

Fluid leaks from (or salt accumulates around) fittings. Leaks indicate that FITTINGS need to be tightened or replaced.
Fluid leaks (or salt accumulates) around pump heads or from irrigation waste ports. This indicates that the plunger seals are worn and leaking. Replace the PLUNGER SEALS to prevent internal corrosion of the pump head.
Fluid leaks (or salt accumulates) around the junctions of the pressure transducers. Replace the PRESSURE TRANSDUCER O-RINGS.

If the pump heads or cabinet feel warm, clean the FAN FILTER and check that the fan is operating.