7
Troubleshooting
Pump Pulsation
Thermo Scientific
Accela Pump Hardware Manual
87
Pump Pulsation
Pump pulsation is the variation in pressure with time due to the motion of the pump pistons.
Pump pulsation can be divided into these categories:
•
Normal Pressure Pulsation
•
Abnormal Pressure Pulsation
Normal Pressure Pulsation
The pump continuously monitors the system pressure and bases its pressure readout on a
30 second interval. Under normal operating conditions, the Accela Pump shows very small
variation in pressure. At pressures greater than 100 bar (10 MPa, 1450 psi), the pump
pulsation should be less than 1 percent. For instructions on monitoring the backpressure of
your system from the data system, see
“Monitoring the Pump Pulsation”
on
page 43
.
The pressure status readback at the bottom of the Direct Control dialog box for the pump is
in units of standard deviation. At a backpressure of 100 bar, a standard deviation of less than
1 bar (0.1 MPa, 14.5 psi) is acceptable. The pressure status readback for the pump in the
Information view is in units of percentage standard deviation. At backpressures greater than
100 bar, a standard deviation value of 1.0 percent or less is acceptable.
Abnormal Pressure Pulsation
Abnormal pressure pulsations can normally be divided into two categories. Large pressure
pulsations are generally considered to be those with a standard deviation in pressure of greater
than 10 bar (1 MPa, 147 psi). Minor pressure pulsations are those with a standard deviation
in pressure of less than 10 bar.
Pressure Pulsations with SD over 10 Bar
Pressure pulsations with a standard deviation of the pressure greater than 10 bar are, in most
cases, caused by air bubbles trapped in one of the piston chambers. To clear trapped air
bubbles, run the pump at about 200
μ
L/min with methanol or acetonitrile for about
15 minutes. This flow rate is much more effective than purging at higher flow rates.
Insufficient flow to the pump can also cause strong pump pulsations. If the above procedure
does not reduce the pulsation, replace the solvent reservoir filters and thoroughly purge air
from the system.
If you determine that the abnormal pump pulsation is not related to trapped air, the cause
might be related to one or more damaged piston seals. Replace both piston seals as described
in
Chapter 6, “Maintenance.”
Note
Because the Accela Pump does not use electronic damping, its pressure fluctuation
often appears to be higher than that for conventional pumps.
