Mechanical pumps piston pump

Mechanical pump (vacuum technology) A compression-type vacuum pump with moving parts. The term is generally applied to pumps used for roughing or backing (Example oil-sealed mechanical pump, piston pump, diaphragm pump, etc.) and not high vacuum pumps (Example turbomolecular pumps). See also Vacuum pump. 

Reciprocating pumps are those most commonly used in high performance Ic. The single-piston type usually has inlet and outlet check valves with some mechanism such as variable stroke frequency to minimize the effect of pump pulsations. Dual-piston pumps operate with the pistons 180° out of phase to minimize pulsations. For this system to work optimally, the piston units must be identical. 

Mechanical efficiencies of steam pumps vary with the types of pump, stroke and the pressure differential. Some representative values are 55 to 80 percent for piston pumps with strokes of 3 inches and 24 inches respeedvely, and pressure differential up to 300 psi. For the same strokes a plunger design varies from 50 to 78 percent, and at over 300 psi differendal the efficiencies are 41 to 67 percent [9]. Steam required is approximately 120 Ibs/hour per BHP. 

Huff [23] found that reciprocating and rotary piston pumps were the most economical mechanical systems for their range of application. Obviously, the economic discussions are dependent on the vacuum expected and the local utility costs, plus the cost of maintenance. 

The syringe type pump consists of mechanically driven piston emptying a large volume chamber 250 ml). In some... 

Propelling unit(s), aimed to move the samples. They are generally peristaltic pumps, although their function can also be served by piston pumps and the pressure exerted by a gas or gravitational force. They are intended to set and keep several streams in motion— the flow-rate of such streams should be regulatable and maintained as constant as possible (normally accomplished by using flexible tubes that withstand the mechanical pressure to which they are subjected). 

Several methods have been used to produce the pulse action required in these columns. A reciprocating, plunger pump, from which the valves have been removed, may be connected to the extractor as at (a), Fig. 12, with a direct liquid connection between the column and the pump piston. Such an arrangement is perhaps mechanically most reliable, al-... 

Air-pressure-driven active devices. Air-pressure-driven aerosolization is the concept employed in a number of devices currently in different stages of development with drugs for local or systemic action. These devices rely on a small patient-operated air pump. Air is compressed by mechanical means (piston or bellows) and is released on the external trigger given by the patient s inspiratory cycle. Because of the use of this air pump, these devices have an active aerosolization mechanism and are assumed to be less flow-rate-dependent than passive DPI devices. 

The third classification of pumps is according to the mechanism by which the liquid is forced through the chromatograph (Fig. 3.4). Although a wide variety of pump designs have been developed over the years, nearly all LC pumps since the 1980s are based on some variation of the reciprocat-ing-piston pump. 

Fig. 7.13 This series of drawings displays how gas is drawn into a piston mechanical pump, compressed, and expelled into the atmosphere.

In addition, mechanical pump oils can be specialized for use in specific environments such as those with high-oxygen contents. Some are blended for use in specific types of pumps such as direct-drive pumps, belt-driven pumps, and rotary-piston pumps. As with most things, no single product fits the bill for all circumstances. Thus, there are many varieties, grades, and types of mechanical pump oils. 

Positive-displacement pump—A pump that conveys fluid by directly moving it using a suitable mechanism such as a piston, plunger, or screw. 

A discernible trend in modem pump design is towards the use of very small pistons (stroke volume around 100 pi). These tiny pistons have to be operated at very high driving speeds, to provide the flow rates required in analytical HPLC. However, when they are used in combination with electronic feedback pulse control mechanisms, as described above, they can provide extremely stable solvent delivery characteristics. Such is the efficacy of this approach that single piston pumps designed in this way are able to easily out-perform older dual piston pumps, and are consequently beginning to account for a major part of the LC pump market. 

The mechanical vacuum pump consists of an eccentrically mounted rotor driven inside a cylindrical housing. Two types of mechanical pumps are constructed (a) the rotary piston type, where the rotor comes in close contact with the housing and thus makes the seal between intake and exhaust compartments, and (b) the vane type pump where two vanes, spring-mounted in the rotor, make contact with the walls of the housing and thereby divide the space between the rotor and the housing. Typical construction is shown in Figs. 2 and 3. 

Modern pumps have more features and better reliability and performance than earlier models because of better designs in seals, pistons, and check valves as well as innovations such as dual-piston in-series and piston seal wash.2 Performance at low rates can be improved by variable stroke mechanism, micro pistons, or active check valves. The fluidic components in more inert pumps for bio-purification or ion-chromatography are often constructed from titanium or polyetheretherketone (PEEK). Low-pressure mixing quaternary pumps have become standard equipment in research laboratories whereas high-pressure mixing pumps are popular for LC/MS, HTS, and micro LC applications. 

These pumps can be designed with or without a diaphragm. Their operation involves the same mechanism as a cam-drive piston pump, but the movements of the piston are achieved by passing (or not) an electric current through a coiled resistor around the piston [29]. As the solenoid-driven displacement is very abrupt, the pump delivers a pulsed flow [30]. 

One of the first prototypes involved the use of integrated microconduits [104]. The flow channels, the injection device and the outlet to the detector were mechanically engraved into a flat PVC block using channels with a cross sectional area of 0.8 mm2 and covered with a flat plate glued on top of the machined block. The system was operated with a conventional peristaltic pump. A similar system, but using a piston pump, was proposed in the 1990 s [105]. 

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