These pumps are a special type of reciprocating pump that utilize the action of a diaphragm moving back and forth within a fixed chamber. Sometimes the diaphragm is used to power a reciprocating pump with air or natural gas. Figure 10-9 shows a typical diaphragm pump where flexure of the diaphragm creates the pumping action. When gas pressure is applied against either diaphragm it forces liquid out. When the gas is relieved the diaphragm flexes under the pressure in the suction line and allows liquid to enter.
The advantages of a diaphragm pump are that it can handle large amounts of suspended solids, is inexpensive to repair, can handle low flow rates inexpensively, and can run periodically without any liquid. However, diaphragm pumps require frequent maintenance because they are reciprocating pumps and because the diaphragm has a tendency to fatigue with time. They generally cannot handle very high flow rates, or discharge pressures. A patent-pending high-pressure diaphragm pump is currently being offered by a leading diaphragm pump manufacturer.Claims of discharge pressures of up to 250 psig (with 80 psig air/gas supply) have been advertised, and flow rates of up to 96 gpm are reported. High-pressure output is obtained through the use of a surface area differential to intensify pressure output. When a diaphragm action is used to power a reciprocating plunger pump it is possible to handle large discharge pressures, but only if the flow rate is very small. Be careful that any mixing of power gas and pumped fluid does not create a hazard in case there is leakage through the diaphragm.