Diaphragm Piston Pumps

Diaphragm piston pumps use a sort of oil chamber between a reciprocating piston (operated by a crankshaft) and the diaphragm (Figure 9-10). Provided that no puncture occurs in the diaphragm, slurry does not come in contact with the piston. A special control system is installed to detect diaphragm rupture. 

Fig. 24.4 Flow sheet of the used SAS plant (SI solvent, 52 solution, FI filter, VI, V2 automatically driven needle valve, PI syringe pump, V3 hand valve, F2 filter, HPV high-pressure vessel, F3 particle filter (with sinter metal Mt), F5 three-way valve, V6 metering valve, DM demister, AS antisolvent stream, 5 solvent stream, P2 diaphragm piston pump, V4 three-way valve, CV check valve, PRV pressure relief valve) (from [1])...

Reciprocating Pumps There are three classes of reciprocating pumps piston pumps, plunger pumps, and diaphragm pumps. 

As the flow rate and quantity of liquor are the most important controllable variables in developing design data, a feed pump suitable for accurate and continuous flow is required. Depending on the size of the pilot column system, the use of peristaltic, diaphragm, piston-type or centrifugal pumps are recommended. The feed pump should be used in combination with a volumetric or gravimetric flow control... 

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... 

Reciprocating or positive-displacement pumps with valve action piston pumps, diaphragm pumps, plunger pumps... 

Spring-loaded bypass valves (with or without a diaphragm) open or close in response to changes in pressure, diverting more or less liquid back to the tank to keep pressure constant. These valves are used with roller, diaphragm, gear, and small piston pumps. 

Body feed pumps work best if run continuously, recirculating back to body feed tank only when the filter is off-stream for cleaning. Piston pumps should have ceramic pistons, and flush-out connections on packings may be desirable. Outlets on single outlet diaphragm pumps should be at the bottom of the diaphragm chamber to prevent accumulation of filter aid in the chamber. 

Pressure is commonly controlled in systems using diaphragm or piston pumps by adjusting the proportion of the output flow from the pump that is diverted into a return line back to tank. This can be actuated by a simple butterfly valve, an adjustable spring-loaded ball valve, or a valve based on the use of air pressure to control the line pressure. Measurements of the response characteristics of commercially available valve systems have shown that most are able to achieve within 10% of a set value in less than 10 s (Rietz el a/., 1997), and this then has formed the basis of environmental performance standards for agricultural crop sprayers that have recently been agreed within the European Community. 

The flow rate can be varied by modifying the cam rotation speed or the position of the piston/cam attachment and, hence, the pumped stroke. This kind of pump, especially the diaphragm-type pump, has often been used in microfluidic systems [27], The main drawbacks are the high purchase cost, flow rates typically in the nL min-1 range, the need for one pump per channel and the susceptibility to air locks and suspended particulate matter [15]. Flow reversal is not possible. 

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]. 

Fig. 4.6.5. Schematic representation of reciprocating pump. 1. motor driven piston (stroke height can be changed) 2, O-ring piston seal 3, diaphragm 4, pump head with back valves 5. eluent inlet 6. eluent outlet.

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