Plunger sealing

Salmona et al. [66] used El and CIMS to identify benzothiazole derivatives leached into injections by rubber plunger seals from disposable syringes. One of the compounds was used as a rubber vulcanisation accelerator, and four others were formed during syringe sterilisation with ethylene oxide. Applications of hyphenated chemical impact mass-spectrometric techniques are described elsewhere GC-MS (Section 7.3.1.2), for polar and nonpolar volatile organics, SFC-MS (Section 13.2.2) and TLC-MS (Section 7.3.5.4). 

Capillary rheometers are used extensively to measure viscosity in the intermediate to high shear rate range. The rheometer has for all practical purposes a lower limit in viscosity measurement because of the plunger seals. These seals are shown on the bottom of the plunger in Fig. 3.16, and they induce a frictional resistance when they are pushed through the rheometer barrel. The piston force can be evaluated without polymer in the barrel, but it is always a source of error at low viscosities because of experimental variability. Moreover, barrel friction is one of the critical corrections that must be made when evaluating viscosity measurements... 

Crank drive (multiplex) 2, Plunger/seal 3, Liquid-end (monoblock). 

Fig. 4.1-18. Coaxial arrangement of pump valves (URACA). a, Plunger b, Plunger seal c, Suction valve d, Discharge valve 3, Components with pulsating internal pressure.

The problem- points in high-pressure machines are certainly the dynamic shaft- and piston-or plunger seals. Seals create special problems when they slide rapidly under high-pressure and if the fluid being sealed has no lubricating actions. Cyclic stress creates additionally fatigue problems in the seal. 

It should be noted that shaft- and plunger-seal problems can be avoided by using hermetic (seal-less) pump types. 

Fig. 4.1-53. Plunger seal of an ethylene hypercompressor 3000 bar (NUOVO PIGNONE). a, Plunger b, Seal housing c, Sealing rings d, Compressor cylinder e, Lubrication oil.

Plunger—A piston, usually of sapphire, driven by the pump motor into the pumping chamber to pressurize and displace solvent through the outlet check valve. The rear of the chamber is sealed by the plunger seal, made of hardened TeflonR that fits tightly around the plunger. 

Seal—Wear surface that both lubricates and separates moving parts in the HPLC. (See Plunger Seal, Rotor Seal, and Needle Port Seal.)... 

The tips used with the micropipette contribute greatly to the accuracy of the analysis and different types are better suited to certain uses and volumes. In general, the dead air space between the sample and the plunger seal should be kept to a minimum since this can seriously affect both accuracy and precision, due to the air expanding in response to even very small... 

Because of the high volume expansion ratios available across the leakage path with hydrogen and helium, use of labyrinths was considered for the high-pressure plunger seal. While theoretical analysis of an ideal labyrinth shows... 

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