Diaphragm pumps, check-valve

The use of PPy-Nafion-PPy trilayers has enabled a low-power pump to be constructed at Dublin in which two trilayers act as tweezers in compressing the fluid inside a flexible polyurethane tube. Through the choice of conical inlets and outlets to create unidirectional fluid movement, flow rates of up to 1.6 pi s were achieved [96]. A further pmnp design involving a polypyrrole-polydimethylsiloxane diaphragm with check valves has been developed, with a pumping rate of 52 pi min [97],... 

The pump check valves for reciprocating pumps (whether diaphragm or plunger) should be designed with care. They should have a low NPSH requirement, have a good kinematic performance and should be subject to as little wear as possible. The last-named condition implies that hard and corrosion resistant materials should be used for the valve cone or plate as well as for the seat. A typical valve and pump head design is shown in Figure 9.27. 

Fig. 4.1-35. Diaphragm compressor (HOFER). a, Diaphragm b, Gas space c, Discharge valve d, Suction valve e, Diaphragm cover f, Perforated plate g, Hydraulic cylinder h, Oil overflow valve i, Oil return j, Cylinder cooling k, Check valve 1, Crank drive m, Cooling-water in/out n, Oil-cooling coil o, Oil chamber p, Oil injection (leakage compensation) q, Compensation pump r, Check valve s, Oil supply.

Pump. Solution is pumped at low flow rate through the cell by means of a Lapp Pulsafeeder pump Model LS-10. Difficulty in maintaining constant flow at slow flow rates was traced to small air pockets in the diaphragm pump head that would not spontaneously pass the exit check valve. This difficulty was remedied by the aspiration of the feed solution to remove dissolved gases. To minimize the hazard of implosion of the feed reservoir, a cage was made from 1/4-inch hardware cloth to fit the 20-liter reservoir. 

A piezoelectric pump is constructed with two glass plates and a silicon wafer [22]. A pressure chamber and a raised flat surface suspended with a thin diaphragm are formed on the upper glass plate (Fig. 3). The piezoelectric actuator is placed on the raised flat surface. In order to guide the flow of the pumped liquid, two check valves made of poly-silicon are fabricated on the silicon wafer... 

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. 

Another strategy for exploiting piston movements in flow systems involves the attachment of the piston to a diaphragm. The moving piston then acts as a pivot and its movements press and release the diaphragm. The wetted surface of the pump is normally made of PEEK or Viton [28]. One-way directional check valves (usually ball-style valves) are required. 

Fig. 7. Diagram of a simple diaphragm reciprocating pump, a = motor, b = drive mechanism, c = plunger piston, d = piston seal, e = low-pressure hydraulic chamber, f = safety device, g = high-pressure hydraulic chamber, h = diaphragm, i = solvent chamber, j = column check valve, k = to column, 1 = reservoir check valve, m = reservoir.

The precision of both piston and diaphragm reciprocating pumps depends greatly on the efficient functioning of the reservoir and column ball check valves, which must be perfectly designed. They are made of stainless steel or, for miniTHal wear, sapphire. Sometimes the seats of the check valves are in sapphire and the balls in ruby. The pistons can be made of stainless steel, glass or sapphire. 

A second topic paralleling microvalves is the development of micro dosing elements and micropumps. The developments are concentrated primarily on the miniaturized diaphragm pump. These micropumps normally consist of a displacement diaphragm driven periodically using piezoelectric, thermal or electrostatic principles, and two passive check valves that direct the flow of liquid from the inlet to the outlet. 

Figure 3 shows a micropump fabricated by thermoplastic molding and diaphragm transfer. The overall dimensions are 7 10 2 mm The 1 pm thin polyimide serves as diaphragms for pumping and for the check valves. A resistive copper heater is periodically powered to drive the pump, 1.7 ms short current pulses of 100 mA, frequency 30 Hz, were used to deliver unfiitered air at rates of up to 220 pl/min, and a maximum pressure of 130 hPa was generated. A micropump did not fidl in a continuous run of 50 hours at 30 Hz,... 

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