Solenoid pumps

There are, of course, noncontact printing devices useful for the construction of microarrays (see Figure 4.2). These are microdispensers that eject droplets by several different mechanisms (solenoid, piezoelectric, heated jet, acoustical wave). Perhaps the best-known commercial dispensers are the syringe driven-solenoid pump (e.g., Cartesian BioDot) and piezo systems (e.g., Packard Biosciences). 

FIGURE 6.4 Schematic representation of the operation of a solenoid pump. The figure refers to a pump without a diaphragm. 1 — spring 2 — piston around which the solenoid is wound 3 — pump chamber. Left and right portions — full and empty chamber (stroke volume). The check valves are not shown. 

D.A. Weeks, K.S. Johnson, Solenoid pumps for flow injection analysis, Anal. Chem. 68 (1996) 2717. 

The flow analyzer involves simple apparatus such as samplers, liquid drivers (peristaltic pumps, piston pumps, solenoid pumps), injection devices (rotary valves, injector-commutators), reactors and flow lines (usually narrow bore tubing), mixing chambers, and flow-through detectors. As a rule, these devices are readily available in most laboratories devoted to chemical analysis. Regarding detection, almost all analytical techniques have been used in flow analysis a small flow cell volume and a short response time that is compatible with system dynamics are important detector parameters. 

The propelling systems normally used in FI are peristaltic, piston, syringe, and solenoid pumps, gravity-driven sources, electro-osmotic flow (EOF) devices, and osmotic pumps. 

Figure 2.18 shows an MPFS system capable of performing the speciation of Fe(II) and Fe(III) with and without preconcentration depending on the results successively obtained [21]. The system uses five micro-solenoid pumps (MPs) and a solenoid valve (V). Micropumps are used to insert the sample, carrier, eluent (HCl), oxidant (hydrogen peroxide), and chromogenic reagent (ammonium... 

M.E. Carrasco, J.A.G. Bautista, M.J.V. Garcia, Automated sequential monitoring of ammonium, phosphate and nitrite in wastewater by multi-commutated peristaltic and solenoid pumped flow system - a comparative study, Chem. Anal. 52 (2007) 757-770. 

Titrations may be automated using a pump to deliver the titrant at a constant flow rate, and a solenoid valve to control the flow (Figure 9.5). The volume of titrant delivered is determined by multiplying the flow rate by the elapsed time. Automated titrations offer the additional advantage of using a microcomputer for data storage and analysis. 

A low-pressure switch can also be used in conjunction with a thermostat and a solenoid valve in the pump-down circuit. In this method of control, the thermostat does not stop the compressor but de-energizes the liquid line solenoid valve to stop the supply of refrigerant to the evaporator. The compressor continues to run and pumps down the evaporator until stopped by the low-pressure switch. When the thermostat again calls for cooling, it opens the solenoid valve, liquid enters the evaporator and the low-pressure switch will close again to restart the compressor. This method is used to ensure that the evaporator is kept clear of liquid when the plant is off. If there is any leak at the solenoid valve, it will cause the... 

Solenoid valves are used in refrigeration and air-conditioning systems for refrigerant lines, oil pressure pipes (to control oil return and capacity reducers), and water and compressed air lines. Four-port changeover valves (Figure 9Ab) are used to reverse flow in defrosting and heat pump circuits. A de-energized expansion valve will act as a solenoid valve. 

The test pressure is released and a vacuum pump connected to draw from all parts of the circuit. This may require two connections, to bypass restrictions such as expansion valves, and all valves must be opened within the circuit, requiring electrical supplies to solenoid valves and the operation of jacking screws, where these are fitted. 

Day-to-day variations in flow rate, check valve efficiency, or mixing solenoid performance (in binary, ternary, or quaternary pumping systems) can also contribute to retenbon shifts. Therefore, compound identification should be performed only by spiking with a known standard or by direct identification with, for example, mass spectral analysis. 

For batch operations, introducing solenoid valves in water scrubbers, direct contact condensation and the flushes used to protect pump and agitator seals, such that if the operation is not in use, the flow of water is stopped. 

Four different types of tasks are performed by automation. Two involve the sequencing of valves and pumps Involved 1n the setup and completion of the designed experiment through the operation of the test and hydraulic fluid systems. The other tasks involve the control of the temperature bath and data collection. To perform these tasks, a1r-actuated solenoids and optically coupled sol Id-state relays are used. These devices are controlled by an electrical circuit consisting of the device connected 1n series with a power supply and a channel on the actuator card In the HP 3497. The power supply 1s either 24 VDC for use with the solenoids or 5 VDC for the solid-state relays. The actuator output channel acts as a simple on/off switch which allows power to be supplied to the solenoid or relay when closed. The logic of the circuit 1s controlled by application programs running on the local HP 1000. 

All mechanical and electrical components should be examined and verified that they are functioning properly. These components include the solenoid valves for water cooling systems, cooling water pumps, cooling fans, electrical heaters, thermocouples and other temperature sensors, pressure sensors, and gear pump operations. 

The burner in the test facility, shown in Fig. 18.1, is an axisymmetric nozzle, which is concentrically placed into the circular suction collar. To achieve a top-hat velocity profile with laminar boundary layer at the nozzle exit, a fourth order polynomial with a large contraction ratio of 31.6 1 and an exit diameter of D = 10.16 mm is used in the design. The suction collar assembly is connected to a vacuum pump through a series of solenoid valves so that a counterflow, which is in the opposite direction of the fuel-air mixture flow, can be established... 

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

Reciprocating positive displacement pumps may have adjustment of the length or frequency of the stroke as another control feature. These may be solenoid or pneumatic devices that can be operated off a flow controller, as shown on Figure 3.21(d). 

Solvents from reservoirs are mixed prior to entering the single reciprocating pump. Compositional accuracy is achieved through solenoid valves that operate on a time cycle. To prevent a nonuniform aspiration cycle or siphoning, optical or electrical encoders can make the proper adjustment of solvent composition. A very short aperture time of the solenoid valve is required. 

The ChromSpher Lipids column (250 mm X 4.6-mm ID stainless steel 5 /Am) was purchased from Chrompack (Middelburg, Netherlands) and used as received. Solvent flow was standardized at 1.0 ml/min and run temperatures at 22-23°C. A small cooling fan was used to minimize temperature fluctuations and bubble formation at the solvent pump mixing solenoid. 

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