Teflon seats

A convenient laboratory-scale storage device consists of a Schlenk tube (about 100 raL) with a Teflon valve in the side arm and a socket joint on top of the body of the tube. The stopper is the corresponding Teflon-seated ball joint attached to a small Teflon valve (Fig. 2), which allows the air in the space above the socket to be purged with nitrogen prior to closing the tube. The ball and socket joint is preferable to the common cone and socket arrangement because the metal oxide crust that invariably forms in the joint is more easily broken. 

Containment of Materials. All experimental work with hexafluorides was carried out in a metal manifold constructed of nickel tubing and fittings which could be evacuated by both mechanical and diffusion pumps. The manifold incorporated Monel diaphragm valves and a number of 1 in. diameter valves with brass bodies. Monel bellows, and Teflon seats. The hexafluorides were transferred between vessels in the manifold by vacuum distillation at room temperature. 

Nickel-plated copper vessels were used in all radiolysis experiments. The vessels were made from copper tubing, 1.5 inches in diameter. The bottom was a 1-mm. thick copper sheet which was silver soldered to the approximately 10-cm. high vessel. A Hoke brass valve with Teflon seat and phosphorus bronze bellows was attached to the top of the vessel by a 1/4-inch Swagelock fitting. Each vessel and all parts of the valves were nickel plated. 

Tetrafluoroethylene gaskets are the most suitable for use in storage tanks, pumps, and valves. Stainless steel plug valves or ball valves should have Teflon seats. 

On installing Teflon packings, place and seat each ring ringer tight. Do not use wrenches or pliers. 

SEAT 81C-TEFLON, KEL-F, ORVESPEL 83C-BUNA-N 81S-TEFLON,KEL-F, OR VESPEL 83S-BUNA-N... 

VACUUM RELIEF TEFLON AIR-CUSHION PALLET SEAT... 

The Teflon and ion-exchange beds were eluted with the eluents as follows The addition funnels containing each bed were separated from the parfait column, and a separate, empty, addition funnel was loosely mounted on top to supply eluents. The bottom stopcock was closed, and the first eluent was slowly added until air escaped the bed and the bed was covered by 0.5 cm of liquid. The upper addition funnel was then firmly seated, and elution began by opening the bottom stopcock. Flow was adjusted to less than 3 mL/min with... 

The apparatus was constructed entirely of stainless steel. The pump packing, valve packing, O-rings and solenoid valve seats were all made of Teflon. 

Since the Teflon-to-glass seal at the seat of the valve is much more dependable than the O-ring-to-glass seal at the stem, the valve should be attached to a piece of apparatus in the orientation which best utilizes the seat seal. For example, if the valve shown in Fig. 8.10a is used on a portable gas bulb, the seat seal on the valve should be closest to the bulb. Any leakage into the bulb would then have to occur past the seat seal. If the bulb were attached to the other arm on the valve, the bulb would be exposed to the relatively poor stem seal. Any leakage past the stem seal would then contaminate the contents of the gas bulb. 

Ceramic materials, including sapphire, have been used extensively in HPLC pumps for more than 20 years as pistons and check valve components. These materials have also been used to construct heads because of their good chemical stability. The use of ceramics is limited, however, because of high cost and brittleness. Although many systems have one material as the primary construction material, the wetted surfaces of a pumping system can contain several other materials. Therefore, for material-sensitive applications, all the materials in the HPLC eluent flow path should be considered. Materials that may be encountered are polymeric materials for pump seals such as fluoropolymers, polypropylene, and Teflon sapphire pump pistons and check valve seats ruby check valve balls Kalrez, KelF, or ceramic washers and spacers polymer-based transducer components and in older systems connections and joints made with silver solder. 

Teflon tube that has a restricted outflow orifice. The dimensions of the tube are not critical and may vary from 10 to 40 mm in inside diameter and from 100 to 600 mm in length. For a given separation, greater efficiency may be obtained with a long narrow column, but the resultant flow rate will be lower. A fritted-glass disk may be seated in the end of the tube to act as a support for the packing material. The column is fitted at the end with a stopcock or other flow-restriction device to control the rate of delivery of the eluant. 

Metal tubing is often terminated in a pipe thread. This is an accurately tapered and threaded unit, and an assembly must be well tightened with a pair of wrenches in order to seat the joint. Small leaks can be sealed by wrapping the inner member with a thin film of Teflon tape, available as Teflon Tape (du Pont) or Tape Dope, before assembling the joint. 

Valves. Considerable difficulty was experienced with leaking valves on the ozone lines near the generators. Different types of packings were tested until a satisfactory material and shape solved the difficulty. Teflon valve seats and packings have since been used. 

Figure 36-2 is a schematic of a commercial microwave bomb designed to operate at 80 atm, or about 10 times the pressure that can be tolerated by the moderate-pressure vessels described in the previous section. The maximum recommended temperature with this device is 250°C. The heavy-wall bomb body is constructed of a polymeric material that is transparent to microwaves. The decomposition is carried out in a Teflon cup supported in the bomb body. The microwave bomb incorporates a Teflon 0-ring in the liner cap that seats against a narrow rim on the exterior of the liner and its cap when the retaining jacket is screwed into place. When overpressurization occurs, the 0-ring distorts, and the excess pressure then compresses the... 

Cover the gel strips with Teflon membranes, except the areas where the sample cups are going to be applied (see Note 14). Dab the gel area around the prospective sample cup location with a paper towel if there is liquid over it otherwise, leave it alone. After putting the cups on, lightly press on the cup to make sure it sits flatly on the gel. This is also a quite tricky step. Any misalignment of the cups will cause the sample to leak out. Observe the cups from several angles to make sure that they are seated correctly (see Note 16). Apply the sample, taking care not to disturb the sample cup. 

In practice, only the seat 0-ring of the "Flickit" valve is replaced with Kalrez. Other valves use Teflon plugs without a seat 0-ring and are backed by Viton 0-rings. Since Kalrez does not have the resiliency of Viton, the "Flickit" valve O-ring seat should be inspected periodically to ensure that its shape (and the seal) have been retained. 

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