To permit pumping of corrosive fluids such as high-temperature acids and the like, particularly in the semiconductor industry, positive displacement pumps have been developed which utilize a plastic bellows as a pumping member. Such bellows is typically constructed of Teflon and has a plurality of coils flexibly joined together to define an extendable and contractible sleeve, one end of which is closed, and the other end of which has a movable piston rod extending therethrough. This bellows is movably disposed within a pumping chamber in which the pumped fluid is alternately supplied and discharged. The bellows, in the interior thereof, is attached to the piston rod, and is alternatively extended and contracted to effect a pumping operation by reciprocating movement of the piston rod.
With this known pump, which is typically a double acting arrangement having a pair of bellows connected to opposite ends of and simultaneously driven by a common driver, it has been conventional to provide an interior support ring within each coil of the bellows to prevent inward collapse of the bellows during the pressurizing and pumping operation (that is, during the axial extension of the bellows). Such support ring typically comprises an elongate rod of spring material which is rolled to form a loop of a diameter slightly smaller than the interior diameter of the bellows coil. This loop is inserted into the bellows and then radially expanded so as to fill out and radially support the bellows coil. The ends of the split loop, which ends are flat, are disposed in abutting engagement with one another to hold the loop expanded and to form a substantially continuous ring for radially outwardly supporting the bellows coil. However, with this arrangement, it has been observed that the abutting ends of the support loop can become dislodged from one another. Thus, the loop tends to radially contract and the ends create edges which can effect undesired wear and possible puncturing of the thin plastic bellows.
This known pump is also extremely limited in its service application in that, due to the fragility of the plastic bellows, only about a 30 to 35 psi pumping pressure can be tolerated when a high temperature fluid, such as an acid at about 180.degree. C., is being pumped, even when support rings are provided in the bellows. Since the capacity of this bellows-type pump is directly proportioned to its pumping pressure, its capacity and range of service in the pumping of high temperature fluids is extremely limited.
Accordingly, this invention relates to an improved bellows-type pump which overcomes the aforementioned disadvantages. More specifically, the improved bellows-type pump of this invention incorporates a means for internally pressurizing the interior of the pump bellows so that the discharge pressure of the pump, and its pumping capacity, can be greatly increased. In the preferred embodiment, the pump has a pair of bellows which operate out of phase, and the pressure in each bellows is maintained substantially constant, and the pressure in the pair of bellows is equalized.
In another embodiment of the present invention, the bellows does not contain a support ring and is internally supported only by the means for pressurizing the interior of the bellows thereby eliminating wear points in the bellows.
In a still further embodiment of the present invention, the means for internally pressurizing the bellows additionally comprises a leak detector means for determining the leakage of process fluid into the bellows and shutting down the pump if necessary, thereby eliminating the danger of process fluid leakage into the environment.
Other objects and purposes of the invention will be apparent to persons familiar with pumps of this general type upon reading the following specification and inspecting the accompanying drawings.