Dry piston pumps

Because of the problems that can potentially arise with oil-sealed pumps, there is an increasing trend to use dry pumps in many applications. Various types are available including Roots pumps backed with suitable pumps (see Section 3.2.3), multi-stage Roots pumps, screw-, hook-and-claw- and scroll pumps. Dry piston pumps and diaphragm pumps are also available but their pumping speed range is restricted. The... 

The pumping speed vs pressure curves for hook-and-claw pumps and a multi-stage dry piston pump are shown in Figures 3.3 and 3.4, respectively. 

Figure 3.4 Pumping speed characteristics of a four-stage dry piston pump (S0 max = 30 (60 Hz)-40 (50 Hz) m3 h l)...

A Roots pump (Sth = 150 m3 h1) is backed by a directly connected dry piston pump. Calculate the pumping speed of the combination given the data in Tables 3.5 and 3.6, provided by the manufacturer. 

Table 3.5 Pumping speed v.y pressure for the dry piston pump...

A clean and dry vacuum system (qpy = 0) with V = 2000 I (as in example 1) is to be pumped down to a pressure of Pend - 10 tAbar. Since this pressure is smaller than the ultimate pressure of the rotary piston pump (Sg max ... 

Aqueous hydrogen peroxide of a given concentration was poured into a vessel with a piston pump, which continuously injected it into the reactor. Methane was supplied from a gas cylinder with pressure sensors at the output. It was purified and dried, then heated and injected into the reactor. The reaction system is of a homogeneous (non-catalytic) flow type and operates in plug flow mode. 

Rotary vane/rotary piston pumps 1 -stage, p -10" mbar 2-stage, />ult - 10"3 mbar Dry pumps... 

A filter press (Figure 11.9) consists of a set of trays, generally made of polypropylene, set in a steel (or, preferably, stainless steel) frame, held tightly together by a hydraulic jack. These trays are covered with cloth and designed to form filtration chambers between the trays that receive the turbid liquid, thus making it possible to collect the filtered liquid. The filter is fed by a high-pressure piston pump. At the end of the operation, a compressed air circuit dries the filtration residues. 

Question by J. W. Hunt, Constock Ind. Methane. Ltd. What cleaning and drying-out procedures are used on the piston pump prior to use ... 

A pump which has been running without glycol for some time should be checked before returning to normal service. The pump will probably need at least new O rings. The cylinders and piston rods may also have been scored from the dry run. ... 

A few strokes of the piston in a dry liner may ruin the liner. When the pump does not fill by gravity or when the cylinders have been emptied by standing too long or by replacement of the piston and liner, it is essential to prime the pump through the suction valve cap openings. 

Modern pump designs also include a means for flushing the piston with solvent behind the pump seal (not shown in Figure 13.4). The solvent for this is drawn in from a separate reservoir and pumped back into this same reservoir. The purpose is to continuously rinse the piston free of mobile phase residue such that abrasive solute crystals resulting from a mobile phase that has dried out on the piston will not deposit there. These solutes, such as the salts dissolved in the buffered mobile phases used in ion exchange chromatography, may otherwise crystallize on the piston and then damage the piston or the pump seal when the piston moves back and forth. Mobile phases that contain such solutes must be flushed from the system after use so that there is also no crystallization on the front side of the seal. 

Like Roots pumps, claw pumps belong to the group of dry compressing rotary piston vacuum pumps (or rotary vacuum pumps). These pumps may have several stages their rotors have the shape of claws. 

Figure 34 Freeze-drying plant condenser and shelves cooled with LN2. Clean-in-place system in chamber and condenser. 1, LN2 inlet to condenser and heat exchanger 2, N2 outlet from the condenser and heat exchanger 3, heat exchanger for the brine in shelves 4, brine to and from shelves 5, pressure plate for stoppering of vials 6, piston rod with bellows 7, hydraulic piston for 5 and 6 8, hydraulically operated valve 9, hydraulic system 10 and 13, water and steam inlet 11, pumping system 12, water outlet. (AMSCO Finn-Aqua GmbH, D-50354 Hiirth, Germany.)...

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