Rotor seals

Rotor Seals To balance the thrust on the rotor, usually there are one or two labyrinth-type seals on the rotor. These seals often are damaged if there is dust in the incoming fluid or gas, and wear on the backside seal causes serious upsets in thrust-bearing loads. Provisions are available for coUecting and disposing of the dust which tends to accumulate in the seal so as to protect the seal from serious erosion. 

Dust-laden streams can also cause operational problems. A turboexpander that can efficiently process condensing streams (gas with fog droplets suspended) can usually handle a stream with suspended solid particles, as long as the particle size does not exceed 2-3 p. The newer designs reduce erosion of expander back rotor seals by disposing of... 

The reaetion turbine avoids this U-turn and its effieieney penalty. In the reaetion turbine half of the pressure energy is spent aeross the rotor, so there must be a seal around the rotor. With the rotor inlet at its periphery, the diseharge from the rotor may now be ehosen at a redueed diameter radial, or quasi axial, shaft-eoneentrie position. Sinee the diseharge is obviously smaller in diameter, the rotor seal will also be smaller in diameter beeause it only needs to suiTound the diseharge portion of the rotor. As a eonsequenee, seal loss is redueed and shaft thrust deereases as well. Likewise, the diseharge or seeondary nozzle losses are redueed beeause the gas exits at lower veloeity. 

The basic difference between this type of valve and the normal external loop sample valve is the incorporation of an extra port at the front of the valve. This port allows the injection of a sample by a syringe directly into the front of the sample loop. Position (A) shows the load position. Injection in the front port causes the sample to flow into the sample loop. The tip of the needle passes through the rotor seal and, on... 

Screw compressors use two counterrotating screw-like shafts (Figure 13.11a). Lubricating oil is required in some designs to lubricate the rotors, seal the gaps... 

Autosampler or injector—replace rotor seal in injector valve or high-pressure needle seal pack, sampling needle, and sampling syringe. 

The injector s wetted surfaces are stainless steel and acid-washed tubing, except for the rotor seal. The seal is a block of beryl or carbon liber-impregnated Teflon , like the pump seal, drilled for the loop and bypass pathways. Movement from inject to load is sealed and lubricated by the Teflon face plate. The injector outlet is drilled to 0.01 in and equipped with a compression fitting carrying tubing of the same diameter. 

Injector rotor seal (tearing—sample carryover) and needle seal (scoring—leakage) ... 

Spare parts that are needed are compression fittings and ferrules, plunger and injector rotor seals, an extra plunger and seals, column filters, and injector needle port seals. If you do not use pacification, you might want to keep a set of check valves on hand. I always have one coil each of 0.01- and 0.02-in tubing in addition to my column blank. A replacement solvent inlet line with a porous stone is useful in case of corrosion. If you filter solvents, you need cellulose, nylon, and Teflon filters. You also need a back-up lamp for your detector. 

Rotor Seal—TcflonR surface that seals the injector and separates the flowing mobile phase from the sample loop until an injection is completed. 

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

Cause b Small rotor seal tear is trapping sample. 

Unswept dead volume. Minimize number of connections ensure injector rotor seal is tight ensure all compression fittings are correctly scaled. 

Rotor seal failure —> Replace rotor seal. 

Damaged rotor seal —> Rebuild or replace valve. Rotor too tight —> Adjust rotor tension. 

Highly concentrated salts (> 0.2 M) and caustic mobile phases can reduce pump seal efficiency. The lifetime of injector rotor seals also depends on mobile phase conditions, e.g., operation at high pH. In some cases, prolonged use of ion pair reagents has a lubricating effect on pump pistons that may produce small leaks at the piston seal. Some seals do not perform well with certain solvents. 

Rotor seal wear should not be over-tightened. 

Figure 4.5 shows clearly how a loop valve operates. The loop is filled with sample solution and the internal channelled rotor seal is then turned to bring the loop within the eluent flux. These valves are known as six-port valves as they have six connections. 

Figure 4.5 Loop valve. The hatched area is the rotor seal.

The rotor seal is usually made from vespel which has the best mechanical... 

Important features of all injection systems are their precision and carryover (the appearance of traces of the preceding sample in the chromatogram). They are determined following the routine described in Section 25.6. Precision should be better than 0.3% relative standard deviation. Carryover should be less than 0.05%. These low values are only possible with well maintained instruments where the rotor seal and needle are replaced in regular intervals in addition, the sample needs to have... 

Replace rotor seal and/or stator. If the surface of the stator is scratched it must be replaced in any case. Otherwise the new rotor seal will be ruined within a short time. Column too old or contaminated ... 

Replace worn parts of the autosampler, i.e. needle, capillary between needle and valve, rotor seal and/or stator. 

The main causes are worn rotor seals, poor capillary fittings and capillaries with too large an inner diameter. 

Every system runs as well as it is maintained. Some approximate figures which should not be exceeded The pump seals should be replaced after one or two years. The autosampler rotor seal should be replaced not later than after 7000 injections... 

If excessive carryover is encountered, explore the use of pre- or postinjection flush or an alternate rotor seal (e.g., PEEK vs. Vespel). 

Pump seals Column frits Rotor seal Lamp... 

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