Liquid Mixtures
Standard Cylinder with Dual-Port Valve and Precharged Pressure Pad
Liquid mixtures using a standard size cylinder with dual-port valve and constant pressure pad are blended gravimetrically with GRAVSTAT using balances calibrated with weights traceable to NIST. The head space above the liquid is initially pressurized (precharged) with an inert gas such as helium. The head space pressure should be constantly maintained through the dual-port valve using a high-pressure inert gas cylinder. Liquid is withdrawn from the bottom of the cylinder using the pressure in the head space.
Advantages
The head space pressure is held constant as the liquid is withdrawn from the bottom of the cylinder via a dip tube.
Disadvantages
More volatile components (i.e. those with a higher vapor pressure) tend to accumulate in the inert gas head space. Buildup of volatile components in the head space lowers the accuracy and consistency of the calibration standard.
Recommended Uses
Adequate for mixtures with components having low volatility and it provides a constant sample delivery pressure.