Time-pressure pump method

Time-pressure pump method. Time-pressure, the simplest and oldest of the methods, is still in use today. According to this method, pulsating high-pressure air actuates a plunger that forces the adhesive through a syringe. 

Time-pressure pump dispensing is a method to deposit adhesive or solder paste by applying a pressure pulse for a specific time duration on a reservoir of material (see Rg. 40.17). A precisely controlled quantity of adhesive or solder paste emerges from the selected orifice size, which is deposited on the circuit board. Often, the material comes prepackaged in a syringe that is inserted into the machine. 

The spectroscopic methods are based on time-resolved pump-probe schemes where the collision-free regime is usually attained by using low pressure conditions. Application of various linear and non-linear laser techniques, such as LIF (laser-induced fluorescence), REMPI (resonant-enhanced multiphoton ionization) and CARS (coherent antistokes Raman spectroscopy) have provided detailed information on the internal states of nascent reaction products [58]. Obviously, an essential prerequisite for the application of these techniques is the knowledge of the spectroscopic properties of the products. 

Although time-pressure, auger, and piston systems are the most commonly used methods of needle dispensing, some other pump designs exist. For the purposes of fuel cell stack assembly, however, the considerations listed above apply to most technologies. 

The vacuum chamber (Fig. 2) is a 20 x 39-in. stainless steel cylinder of all heliarc-welded construction. The chamber is suspended in an insulated aluminum tank. The chamber volume after correction for the pump lines and cryosphere was calculated to be 202 liters. This chamber size makes possible the use of commercially available standard leaks, without introducing significant errors in the time measurement when calibrating the gas analyzer by the rate of pressure rise method. The 7-in.-diameter cryosphere has a calculated surface area of 995 cm . The coolant transfer lines to the cryosurface are vacuum-jacketed to prevent possible condensation. 

The third type of pump used in dispensers, linear piston, is a true positive-displacement pump. This pump uses a piston to change the volume of a reservoir that is fed from the main syringe. The displacement of the piston produces an equivalent positive displacement of fluid through the pump. Changes in viscosity have litfle or no effect on the repeatability of dispensed mass. Of the three methods, the repeatability of the linear-piston type is the best ( 1%, except for very small dispense volumes of less than 20 pl). " Repeatability of the time-pressure method is 10% and for the auger method is 4% (short term less than 30 min). 

Of these, because method i) requires a great deal of space and many days for drying, it is seldom used. Soil paste is not fluid enough to use pressurized pump transport or filtering and the mechanical dehydration remains rare. The use of additives is easy to use, needs little spaee, and continuous treatment is possible. Thus, it is more often used. The additives used for this purpose are cement, calcium carbonate, and polymers. Polymers do not require ineubation time and are effeetive nearly instantaneously. The soil ean be treated eontinuously. Henee, this method ean be a part of the soil pressure sealed method. In the ease of polymers, ehanging the soil to basic pH can be avoided. Table 4 shows the experimental results of soil improvement following inelusion of polymerie materials. In this table slump or flow values are used to evaluate the fluidity of eonciete or mortar. 

The power consumed to operate a wet electrostatic precipitator is much less than that required by most other methods of control. There are four areas in which power is consumed (1) electrostatic power, (2) fan power, (3) insulator heating power, and (4) pump power. The total electrostatic power input required for operation is 0.8 to 1.0 kW/1,000 ft of collection area. A comparable piece of equipment is a venturi scrubber with 50-in.wg pressure drop. The power required for this installation would be 6 to 7 kW/1,000 cfm. This would mean that approximately seven times the power would be needed to achieve the same amount of cleaning with a venturi scrubber as opposed to using a precipitator. 

The sampling of a suction lysimeter is initiated by applying a vacuum (approximately 40-50 cm of mercury) through the vacuum/pressure line with a hand pump or electric pump. The valve on the sampling line must be closed. A constant vacuum may be maintained on the lysimeter using an electric pump. The time required before collecting a sample from a lysimeter will depend on the method of vacuum application, the moisture content of the soil, and the soil type. 

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