Reciprocating chemical pumps
Chemical pumps are disclosed in which all parts wetted by the fluid being pumped are made of fluoroplastic material, with the pumps having check valves that include floating ball members and O-rings positioned adjacent to the floating ball members. The retainer area in which the O-ring is received has a diameter that is at least about 0.01 inch larger that the diameter of the O-ring so as to allow the O-ring to move slightly. The intake and discharge ports of the pumps comprise a bore extending into the body of the pump, with a threaded counterbore formed concentric with the bore to form a flat, annular surface between the bore and the counterbore at the inner end of the counterbore. A threaded fitting is received in the counterbore, and a seal is formed by compressing an O-ring against the annular surface at the inner end of the counterbore. The head of the pump is secured to the body thereof using spring type means that either continuously applies a spring force against the head to force the head into sealing engagement with the body of the pump or forms an expanding spring seal between the head and the body of the pump. In the manufacturing of integrated circuit chips, it has been necessary because of cleanliness requirements and the corrosive nature of the chemicals used to employ chemical pumps that are formed from fluoroplastic materials such as polytetrafluoroethylene. All surfaces of the pumps that are wetted by the chemicals being pumped are formed from the fluoroplastic material. It is advantageous to form the body and heads of such pumps from the fluoroplastic material. The surfaces of all flow channels and pumping chambers which are formed in the body and heads will then, of course, be formed of the fluoroplastic material. However, three major problems as will be identified below have been encountered in making the chemical pumps from fluoroplastic material. The chemicals being pumped are usually maintained at elevated temperatures, and the three problems are all related to the fact that fluoroplastic materials are subject to plastic deformation and creep at elevated temperatures. The problems are caused because parts of the pump made of fluoroplastic material and which are subject to stress of pressure or other forces tend to distort and change slightly in their shape over time. The first problem involves leakage in check valve seals used in the pumps. When seal areas in the passages of the pumps distort even slightly, the check seals are likely to malfunction and leak. The second problem involves leakage at fittings on the suction and discharge ports of the pumps. Fittings on the suction and discharge ports, which have generally been threaded into corresponding threaded bores in the body of the pump, specifically tapered pipe threads, often fail or leak due to the distortion of the fluoroplastic material in the area of the threaded bores. The third problem involves leakage at the interface of the heads and bodies of such pumps. Seals around the head and body of the pumps tend to malfunction and leak due to the distortion of the fluoroplastic material due to elevated temperature, pressure and forces used in connecting the head of the pump securely to the body of the pump.
Shanghai Kaida Pump Mfg. Co., Ltd.