User manual

60 Bio-inert Quaternary Pump User Manual

5 Optimizing Performance

Optimize the Compressibility Compensation Setting

The compressibility compensation default setting is 100 × 10

-6

/bar for the

pump. This setting represents an average value. Under normal conditions the

default setting typically reduces the pressure pulsation to values below 1 % of

system pressure that are sufficient for most applications and for all gradient

analyses. The compressibility settings can be optimized by using the values for

the various solvents described in Table 5 on page 61. If the solvent in use is not

listed in the compressibility tables, when using isocratic mixtures of solvents

and if the default settings are not sufficient for your application the following

procedure can be used to optimize the compressibility settings.

1 Start the pump with the required flow rate.

2 Before starting the optimization procedure, the flow must be stable. Check

the tightness of the system with the pressure test.

3 Your pump must be connected to a data system or Instant Pilot with which

the pressure and %-ripple can be monitored, or connect an external

measurement device to the analog pressure output (see “Electrical

Connections” on page 168)

4 Starting with a compressibility setting of 10 × 10

-6

/bar increase the value

in steps of 10. Re-zero the signal display as required. The compressibility

compensation setting that generates the smallest pressure ripple is the

optimum value for your solvent composition. If ChemStation (classic view)

is used and the ripple shown is positive, then the compressibility setting

should be decreased. If it is negative, it should be increased.

NOTE

When using mixtures of solvents it is not possible to calculate the compressibility of the

mixture by interpolating the compressibility values of the pure solvents used in that mixture

or by applying any other calculation. In these cases the following empirical procedure has

to be applied to optimize your compressibility setting.

Inappropriate settings would mainly affect retention times of peaks eluted at the beginning

of a gradient. Therefore optimize settings for the solvent at the beginning of the gradient.

For mixtures containing up to 50 % water, use compressibility settings of water.