High pressure seals

In high pressure sealing in the oil field service, it should be noted that hardness, modulus, extrusion resistance and resistance to blistering under rapid decompression can all be increased with an improvement in cross link density. However the elongation is reduced, the elasticity diminished and so the sealing potential is lessened. 

The employed seals are ring seals, cleat-section high-pressure seals or even an all-metal seal. 

Other problems with pneumatic intensifier pumps include the fact that access to the high pressure seals for inspection and maintenance is usually quite restricted, by nature of their design. Because of the way they operate, the flow they produce is inherently highly pulsatile in nature and they also tend to be extremely noisy in use. For these reasons, pumps of this type are not used in general analytical HPLC. However, pneumatic intensifier pumps have found a niche in the packing of HPLC columns, where the intermittent nature of the function and their ability to deliver very high pressures compensate somewhat for their shortcomings in the analytical field. 

With apparatus designed for maximum operating pressures of 200-350 atmospheres the reactor head is generally bolted to the tank with the high pressure seal made with a compressible gasket. Other versions of autoclaves have quick opening closures that can be used to pressure maxima around 100-125 atmospheres. 

Figure 4.6 Filling the loop by three different autosampler designs a, pull-loop b, push-loop c, integral-loop injection. 1 = sample vial, 2 = syringe with stepper motor, 3 —loop, 4 —from pump, 5 —to column, 6 = to waste, 7 = low-pressure seal, 8 = high-pressure seal, 9 = position of the movable loop when the valve is switched and the sample transferred to the column.

Figure 7.1 Various column terminators. (A) Union with male thread (B) union with female thread (C) cartridge system (simplified). 1—column 2 = sintered metal and Kel-F frit 3 = union 4= 1/16 in capillary 5 — casing 6 — high-pressure seal 7 = column seal with frit 8 — retaining nut.

Replace the frit. If black particles are visible on the frit (rather common) it is necessary to replace the high-pressure seal and perhaps also the piston. In addition, check if the seal is resistant to the solvent in use. (However, today s seal materials should be resistant to all common solvents, including water.)... 

Leak of the piston flushing seals or of the high pressure seals ... 

This is a definite sign that the high pressure seals must be replaced. 

High-pressure seal Extraction ring RF coil... 

Fig. 4.36 A low-temperature, high-pressure probe for solid-state NMR (a) an overall cross-sectional view and (b) details of the high-pressure seal and feedthrough. ...

Fig. 7.4 A piston-cylinder high-pressure apparatus (a) the pressure frame, (b) a 100 tonne hydraulic ram, (c) the piston, (d) the bottom plug, (e) high-pressure seals, (f) a double-walled pressure vessel, (g) the pressurizing fluid, (g) a 500 bar hydraulic fluid for pressurization, (i) hydraulic pressure used for piston extraction, (j) the sample. (Reproduced by permission from PSIKA Ltd).

Fig. 7.5 Details of piston seals (a) a piston honed to a mirror finish that is accurately cylindrical and machined to an interference fit to the cylinder, (b) a A ring of bronze or brass, fitting the chamfer of the piston and precisely fitting the diameter of the cylinder (this ring will deform somewhat to create the high-pressure seal above pressures of about 5 kbar), (c) a rubber O-ring which can seal pressures below 5 kbar (above this pressure elastomers tend to become brittle), (d) a backing ring of PTFE, (e) a circlip to prevent rings falling off when the piston is extracted, (f) an accurately machined 45° chamfer.

The optical path along the axis of the cell was 5.0 cm long x 1.9 cm in diameter with a sapphire window at each end of 2.5 cm in diameter X 1.3 cm thick. The high pressure seal between the stainless steel cell body and the sapphire windows was made using silver-coated, metal C-rings. The volume of the sample cell was "14.5 cm. ... 

Electrical connection through to high pressure seal and detection... 

Worn high pressure seals of the pump —> Replace the seals. 

Strong and clean structural, hermetic, and high-pressure seals can be obtained from this process. Important determinants of bond quality in induction welding are the joint design and induction coil design. With automatic equipment, welds can be made in less than 1 s. 

Provide high-pressure seal water for the RCP seals. 

Table 5.7 shows anticipated properties when high pressure sealing is required. 

High pressure sealing capability Poor fatigue life... 

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